Friday, July 11, 2014

What is El Niño, and How Does it Affect Hawai'i?

If you ever pay attention to the weather forecast, you’ve probably heard about a phenomenon called El Niño.  However, if you’re like most people, you probably don’t have a clue as to what El Niño refers to or what it means.  You may have the vague notion that it causes changes in the weather, but you might be unsure at to the nature of those changes.  For example, does it make it rain more?  Less?  Does it make it hotter or cooler?  This confusion is understandable, because the effects of El Niño vary depending on where you are!  In this post we’re going to dispel some of the mystery and confusion surrounding El Niño in general and explain how this phenomenon affects Hawai’i.  Looking at El Niño gives us the chance to examine a number of other aspects of the oceanic-atmospheric relationship, and helps us to think about oceans and the atmosphere as a big system.  You may find this information useful, since many climatologists are predicting unusually strong El Niño conditions for 2014.

Explaining ENSO

Map from Wikipedia.
El Niño, which means “the (male) child” in Spanish, is actually part of a larger periodic cycle that affects ocean currents around the equator in the Pacific Ocean.  This cycle is called the El Niño Southern Oscillation, or ENSO for short.  Before explaining ENSO, though, let’s look at how the equatorial Pacific Ocean usually works.  A good place to start is the trade winds.  In Hawai’i we know that the trade winds generally blow from the northeast, and are generally very reliable in the summer.  These winds provide a nice breeze and keep the weather pleasant most of the time.  The trade winds are part of a pattern of atmospheric circulation called the Hadley Cell circulation, which we’ve explained elsewhere.  These winds flow across the Pacific towards the equator, and because of the Coriolis effect (from the rotation of the earth), they also blow towards the west.  Related to this is another pattern called the Walker circulation, which causes the prevailing winds to blow towards the west along the equator.  This is because the air pressure is normally high around Tahiti due to sinking air.  The wind always blows out of high pressure areas.  In contrast, by Australia and Indonesia the air pressure is low, which means that air is rising up through the troposphere.  Wind always blows into low pressure areas.  The wind pushes the water towards the west, and so the warm equatorial water tends to pool in the western Pacific around Southeast Asia and Australia.  These are the normal conditions, as you can see in the diagram.  There are some interesting aspects to this circulation pattern.  For example, it causes the thermocline to be deeper in the western Pacific.  It also makes sea level slightly higher in the western Pacific.  When this pattern is particularly strong we call it “La Niña”, which in Spanish means “the (girl) child”.  La Niña conditions tend to decrease rainfall in the eastern Pacific in places like southern California.

As you can see from the maps in the above paragraph, this means that the water temperature is higher in the western Pacific.  This means that there is a lot of evaporation, which provides moisture to the equatorial regions of South and Southeast Asia.  At the same time, the water is much cooler off the coast of South America.  Since the wind normally blows to the west, this draws water away from South America, which in turn pulls up cold water from the depths below.  This nutrient-rich water creates the richest fishing area on the planet.

Graphic from Windows to the Universe.

Reversing the Walker Circulation

Every now again, however, the westward flow of the Walker Circulation weakens or even shuts down all together.  On average, this happens about every 2-8 years.  When the winds weaken, the warm water that has pooled in the western Pacific starts to move back towards the east (1), since the wind is no longer pushing it.  The difference in air pressure between Tahiti and Indonesia is much less in this case, and in some instances the trade winds will actually blow in the opposite direction.  The term “El Niño” refers to these conditions.  El Niño has significant effects not only on ocean temperatures, but wind and weather throughout the Pacific and beyond.  Areas in the eastern Pacific get abnormally wet, whereas the western Pacific is drier.  For example, the strong El Niño in 1998 caused widespread storms across the western part of the United States.

This has indirect effects on humans, as it can lead to droughts in India, China, and other places in Asia.  Historically El Niño conditions have contributed to some of the most devastating famines in history (2).  There are economic effects as well.  For example, when El Niño occurs it shuts down the cold water upwelling off the coast of Peru that plays such a large role in the fisheries there.  The fisheries industry is extremely hard hit when this happens, which in turn affects the entire economy of Peru.  At the same time, the Polynesian wayfinders that initially discovered and settled in Hawai’i and other islands in the Pacific had a keen understanding of El Niño.  The periodic reversal of the trade winds allowed them to expand to islands and archipelagoes that would have been much more difficult to reach under normal conditions.

El Niño’s Impacts on Hawai’i

Now that we understand the basics of El Niño, we can begin to look at how this curious phenomenon affects the weather here in Hawai’i.  Both La Niña and El Niño seem to affect our rainfall patterns.  As you know, Hawai’i has two seasons: the dry Kau season, which runs from about May to September or October, and the wetter Ho’oilo season, which lasts from October to May.  When there is a particularly strong La Niña, the Kau season tends to be significantly wetter, whereas the El Niño phase generally correlates with much lower rainfall totals (and even drought) during the Ho’oilo season.  In addition, during La Niña the normal wet season is often abnormally wet.  For example, in early 2006 Hawai’i experienced 40 straight days of rain during the La Niña wet season.  You can see the pattern illustrated in the rainfall maps of Maui and Kahoolawe.  Since this year is an El Niño year, many experts are expecting drier than average conditions starting in around October.  However, as we were writing this blog it was still uncertain as to how strong the 2014 El Niño would turn out to be.

Climatologists and other researchers at the University of Hawai’i are currently carrying out work to deepen our understanding of ENSO’s effects on the archipelago.  For example, one research project is focusing on how microclimatic variables such as solar radiation, relative humidity, temperature and potential evapotrasporation respond to ENSO phase changes in different seasons here.  Other work focuses on quantifying the effects of ENSO on the dry season, since the dry season is often downplayed as ENSO is generally discussed as a wet season phenomenon in the context of Hawai’i.

Although we understand the basics of ENSO, looking into the future there is still a lot of uncertainty surrounding the phenomenon.  One big unknown is how the ENSO cycle will be affected by climate change.  It is likely that one or more of the physical processes that are responsible for determining the characteristics of ENSO will be modified by climate change, but it isn’t yet possible to reliable speculate as to whether ENSO activity will be enhanced or dampened, or if the frequency of events will change.  Thus there are exciting frontiers of climate research that you might someday contribute to as you continue your studies of geography and atmospheric processes.


(1)  This reverse flow is called a “Kelvin wave”.

(2)  For an outstanding account of how El Niño, coupled with colonial administrative policies, contributed to famines in 19th century, see Mike Davis’s Late Victorian

Monday, May 26, 2014

A "New" Hawaiian Volcano!

Image from Sinton et al 2014 (see references).
Virtually everyone living in Hawai'i knows that the islands are volcanic in origin; if you live in Honolulu it's hard to miss obviously volcanic features such as Lē'ahi (Diamondhead), Kohelepelepe (Koko crater), and Puowaina (Punchbowl).  And nearly everyone has seen striking pictures and videos of the ongoing eruptions at Pu'u 'Ō'ō on the Big Island.  However, most people are probably not aware of the details of the lifecycle of our islands; they are born and eventually, just like all of us, they fade away into the sunset.  What's even more interesting is that our understanding of these events is constantly evolving and being refined by scientists, many of whom work at the University of Hawai'i.

In fact, our knowledge of the island of Oahu was recently enhanced by an exciting discovery revealed by a research team led by geologists at the University of Hawai'i.  Previously the conventional thinking was that Oahu was formed by two shield volcanoes: the Ko'olau volcano and the Wai'anae volcano.  However, the recently announced discovery indicates that there is in fact a third shield volcano which makes up part of the island of Oahu.  The newly-discovered volcano has been called Ka'ena by its discoverers, and is located approximately 20 kilometers off the coast of Ka'ena point.  In this post we'll tell you about the "new" volcano, but first we describe the context with a sort of "primer" as to how the island of Oahu formed in the first place.

Hot Spot Volcanism

The first thing to understand is that our volcanoes are special and differ from other volcanoes you might be familiar with, like Mt. Fuji, Mt. Pinatubo, and Mt. Saint Helen's.  This is because they form above a hot spot, which is an upwelling of mantle from deep within the earth.  The composition of the magma that flows out of our volcanoes is different from most other volcanoes found on continents or island arcs in that it flows much more freely and has a lower solidification point.  Practically speaking this means that the lava(1) can flow further away from the vent, and also that it doesn't plug up the vent, and so instead of a "classic" cinder cone volcano (like Mt. Fuji), our volcanoes grow much bigger and have gently sloping sides.  Indeed, our volcanoes are called "shield" volcanoes because they resemble a warrior's shield that has been laid upon the ground.

Relative size of cinder and shield volcanoes.  Graphic from US Geological Survey.

Another important thing to understand about our volcanoes is that while the hot spot doesn't move, the islands themselves do!  This is because the earth's surface is made up of a number of tectonic plates that move around due to convection currents within the mantle of the earth.  While a full description of plate tectonics will have to wait until a later post, we can understand that the tectonic plate upon which are islands sit (the Pacific plate) is moving in a northwesterly direction at about the same speed at which your fingernails grow.  This is why we have a chain of volcanic islands and not just one big island.

Diagram from Wikipedia.  

Stages in the Lifecycle of a Hawaiian Island Volcano

Now that we understand the fundamental difference between Hawaiian shield volcanoes and cinder cones, we can understand the various stages in the lifecycle of the Hawaiian Islands.  You might have noticed that the Big Island, which is currently still experiencing volcanic activity and is still growing, is far larger than the other islands in the archipelago, and that as you move towards the northwest the islands seem to get smaller and smaller, until finally you find very small atolls of Kure and Midway.  This is no coincidence.  This section will help you understand why this is the case.

1.  Preshield Stage.  This first stage happens deep in the depths of the ocean', several kilometers beneath the surface where there intense pressure due to the weight of the water above.  The preshield stage is characterized by infrequent, small-volume eruptions which produce pillow lava.  As the volcano grows the composition of the lava changes.  The volcano erupts more often, and produces more and more lava. When this happens the new undersea volcano enters the second stages.  It is very hard to observe the preshield stage due to the extreme depths and the fact that these vents are so hard to locate.

2.  Submarine Shield Stage.  This stage features continued effusive eruptions of pillow lava deep
Lō'ihi image from Wikipedia.
beneath the surface of the ocean.  The undersea volcano grows into a huge mountain.  Here in the Hawaiian islands the Lō'ihi volcano, which is located approximately 1000 meters beneath the surface of the ocean about 35 kilometers southeast of the Big Island, is in the submarine shield stage.  Volcanologists expect Lō'ihi to breach the surface and become our newest island within the next 100,000 years.  

3.  Explosive Stage.  The shield volcano enters this stage when the top of the erupting volcano begins to approach the surface of the ocean and the lava and ocean water mix to produce explosive eruptions.  Think about squirting a water gun at a campfire.  It sizzles, right?  Well, the explosive stage in the volcano's life cycle is based on the same principle, only a bazillion times bigger.  Currently there are no volcanoes in Hawaii in this stage, but Hunga Ha'apai island in Tonga is.  

4.  Subaerial Shield Stage.  After enough ash, debris, and other volcanic matter accumulates such that the volcano is no longer erupting into the sea but rather upon its own flanks it is said to have entered the subaerial shield stage.  Since the lava is no loner in direct contact with water when it is extruded the eruptions are much calmer.  Currently Kilauea on the Big Island is in this stage.  During this stage eruption rates increase and the island grows rapidly over a period of approximately half a million years.

Kilauea is currently in the subaerial shield forming stage.  Map from here.

5.  Capping (postshield) stage.  For some of the volcanoes, once they get to be high enough the composition of the lava they produce changes.  This different lava produces steep peaks on the top of the volcano that look like pointy hats.  If you've ever been up top he top of Mauna Kea you've probably noticed the steep landforms; these are the products of the capping stage.  However, it seems that not all of the volcanoes experience this stage; Ko'olau and Lana'i are notable exceptions.  Eruption rates slow significantly during this stage until the volcano stops erupting all together.  

6.  Erosional Stage.  Though this stage is usually presented as the 6th of 9 stages, it really begins as soon as the volcano breaches the surface of the ocean, as mother nature's erosive forces in the form of wind, waves, and rain immediately set to work tearing the new island apart.  However, the effects of these destructive forces are most apparent after the volcano has stopped erupting, and the island continues to be dissected.  You can really see the effects of erosion when you look at the elevation model maps of Oahu, which stopped erupting more than a million years ago, and the Big Island, which is still erupting today.  Note how rough the terrain of Oahu is compared to the Big Island; this is due to erosion.

This image of Hawai'i island and the below image of Oahu are digital elevation models (DEM) showing the topography of the islands.  Remember that these are not to scale; the Big Island is far larger than Oahu.  However, can you make any general observations about the topography of these islands?  What do you think explains these observations?  Images from SOEST UH.  

7.  Renewed volcanism (rejuvenated) stage.  The seventh stage is one of the most fascinating and least understood stages.  It is clear that at some point long after (in some cases millions of years) the shield volcano stops erupting, new lava flows and hydromagmatic eruptions occur, which seem to be much more violent but much smaller than the shield volcano eruptions.  Virtually all of the craters on Oahu are examples of this stage, as are Kūpikipiki'ō (Black Point) and the Sugarloaf flow out of Mānoa valley.  There are a number of hypotheses to explain renewed volcanism and a full discussion is beyond the scope of this blog post.  This stage seems to continue for a long period of time, and some geologists date some of the volcanic activity over on the Waimanalo side as recently as 4,000 years ago, so it seems to me that Oahu is probably still in this stage!

8.  Atoll stage.  After the rejuvenated period ends, the islands continue to erode and erode for millions
Kure atoll image from here.  The Hawaiian name for Kure
atoll is Moku Pāpapa.  
of years, until there is nothing left.  However, since the Hawaiian islands are in warm tropical water, the growth of the island during the earlier stages provides an ideal habitat for corals, which over thousands and millions of years build reef structures which fringe the islands.  And although the island itself has eroded away because there are no more eruptions, the development of the coral reef is a biological activity that is only indirectly linked to the volcanoes, and so it continues as long as the water around the islands is warm enough for corals to grow.  Hence what remains when the island erodes away is an atoll, or coral island.  Midway and Kure islands are good examples of Hawaiian islands in the atoll stage.

9.  Guyot (seamount stage).  The last stage begins when the islands are pulled by the tectonic drifting of the Pacific plate out of water warm enough to support coral.  When this happens the reefs stop growing and eventually sink back into the sea, and so all that is left is a high spot on the ocean floor, known as a "seamount" or a "guyot".  Since these are beneath the surface of the water you can't see these, but they are very clear from sonar imagery.  There is a long chain of seamounts extending to the north all the way up to the Aleutian trench, where the seamounts are being subducted back into the earth's bowels by the slow grind of tectonic forces.  This is where the Hawaiian islands finally pass into oblivion.  We have no idea how many islands there have been in the past, but we do know that the oldest seamount is approximately 81 million years old.  The seamounts are called the "Emperor Seamounts" and are named for Japanese emperors.

The Hawaiian Islands and Emperor Seamounts.  Note the "bend" in the line of volcanoes, which indicates a shift
in the motion of the tectonic plates.  "My" means "million years" and indicates the age of the volcano.

The Ka'ena Volcano

Dr. John Sinton of the Department of Geology at the University of Hawai'i conducted the research that confirmed the existence of the Ka'ena volcano.  Based on maps of the sea floor, scientists had long suspected that there was third volcano, but until Dr. Sinton's research, no one could say for sure.  The way that Dr. Sinton and his team made the distinction was by collecting rock samples from beneath the ocean's surface off the coast of Ka'ena point using remotely-operated undersea vehicles (robots).  They compared the chemical composition of these rocks with other rocks taken from the Wai'anae volcano.  Geologists are able to look at the chemical building blocks of rocks, the actual minerals that make up the rock, for clues as to where the rock came from and how it was formed.  Each rock has its own chemical fingerprint.  This analysis confirmed that the lava that produced each of the rocks is chemically distinct.

According to Dr. Sinton's research, the Ka'ena volcano erupted before the Wai'anae and Ko'olau volcanoes, approximately 5 million years ago.  Thus the Ka'ena volcano had to grow from the bottom of the sea, and eventually reached a height of about 3,000 feet above sea level.  The Wai'anae volcano was eventually much higher, but it didn't have to grow from the very bottom of the sea and was instead able to use the Ka'ena volcano as a sort of stepping stone.  The discovery is really important because it addresses some questions geologists and geographers had about the hot-spot explanation for the Hawaiian volcanoes.  Most of the volcanoes are between 20 and 40 kilometers apart, but there is a gap of about 90 kilometers between the Wai'anae volcano on Oahu and the volcano that formed the island of Kaua'i.  Before the recent discovery no one could figure out why there was such a big gap between these two volcanoes.  Now we understand that there isn't really that big a gap since the Ka'ena volcano is approximately 20-30 kilometers off the coast of Oahu, which is very consistent with the spacing between all of the other volcanoes.  

So from all of this we can see what makes geography such an exciting field.  It's always changing and constantly being updated.  Even as we write this blog post research teams from UH and elsewhere are investigated the Ka'ena volcano cite to learn more about the genesis of the islands we call home.  Next time your out at Ka'ena Point, you can gaze out across the sea and think about how Oahu must have looked 3-4 million years ago! 


(1)  We use the term magma to refer to molten (melted, liquid) rock when it is beneath the earth's surface.  The term lava is used when it has been extruded onto the earth's surface.

References and For Further Reading

Sinton, John M., Deborah E. Eason, Mary Tardona, Douglas Pyle, Iris van der Zander, Herve Guillou, David A. Clague and John J. Mahoney.  2014.  Ka'eana Volcano--A Precursor Volcano of the Island of O'ahu, Hawai'i.  Geological Society of America Bulletin.  

UH News story on Dr. Sinton's research:

Tuesday, January 21, 2014

A Storm is Coming: Winter Weather Patterns In Hawaii

Pacific Surface Analysis showing approaching cold front
One of the main reasons that millions of tourists flock to Hawai'i each year is because the weather year round is fairly pleasant and predictable, and not as subject to the seasonal shifts that characterize the climate at higher latitudes.  But if you've spent any time in Hawai'i you've likely noticed that there are indeed seasonal shifts.  In the "summer" it's usually a little bit warmer, but the refreshing tradewinds blow a good bit more regularly, which helps to cool us off and brings rain to windward and mauka areas.  In the "winter" the trades aren't as reliable, and we have more frequent kona winds.  The Hawaiians, being excellent geographers, have names for these two seasons.  The warmer season is called Kau and generally lasts from approximately mid to late April until October, whereas the cooler season is called Ho'oilo and lasts from mid to late October until April.  The changes that come with Ho'oilo are the subject of this blog post.

The Big Picture...

One major feature of Ho'oilo is the periodic occurrence of thunderstorms, which in general are relatively rare in Hawai'i due to the tradewind temperature inversion.   However, in the winter months, cold air and low pressure systems sweep down from the north, bringing occasionally severe weather along with the massive swells that the North Shore is so famous for.  But did you know that these storms are a part of the global system of atmospheric circulation?  It all begins with the earth-sun relationship, which you can read about in a previous post.  Since the earth is tilted, the point on the earth's surface that receives the sun's energy directly shifts over the course of the year, which basically means that the latitude that receives the most energy migrates over the course of the year.  This spot, called the subsolar point, is loosely tied to the Inter-Tropical Convergence Zone (ITCZ), an area of convection (rising air) and thunderstorms that helps to drive the entire global atmospheric circulation system!  You've probably learned in geography class about the ITCZ, which is part of the three cell model of circulation (1).

As with most everything in life, whatever goes up must come down.  This is true for air that rises in coriolis effect (to be discussed in a future post), which twists the path of the air (to the right in the northern hemisphere, to the left in the southern hemisphere.  This part of the global atmospheric circulation is referred to as the Hadley Cell, and there are two of them, one to the north of the ITCZ and one to the south.  You can see the general pattern in the figure below, which shows the circulation when it is summer in the northern hemisphere.
Three Cell Model diagram from here.
the ITCZ.  Once it reaches the top of the troposphere (the lowest layer of the atmosphere where virtually all weather happens), it diverges and circulates to the north and the south, sinking at approximately 30 degrees north and south of the equator, but the latitude at which the air sinks shifts along with the ITCZ and the subsolar point over the course of the year.  The places where this air sinks are high pressure areas, because the sinking air is exerting force on anything below it.  The ITCZ, conversely, is a low pressure area because the air is rising there.  Because of the rotation of the earth, the sinking air is subject to the

How this Affects Hawai'i...

As you can see, a major area of sinking air is usually located to the northeast of Hawaii.  Here in Hawaii we call this high pressure area the "Hawaiian High", but in general it referred to as the Northern Pacific Subtropical Anticyclone.  Anticyclones are areas of sinking air where the wind circulates outward from the high in a clockwise direction.  Note from the graphic the direction that the wind blows coming out of the high.  You should notice that our islands are right in the path of the wind!  This is the source of the tradewinds, which blow about 80% of the time in the Kau season.

July patterns.  Approximately location of Hawai'i denoted with red circle.  Map from here.
When it is winter in the northern hemisphere it is summer in the southern hemisphere, since the subsolar point and ITCZ shift to the south.  Along with this travels the Hadley cells.  Another characteristic of the northern hemisphere winter months is that the Hawaiian High tends to weaken, and so the tradewinds are less consistent.  At the same time, the storm-producing polar front (another part of the global atmospheric circulation), moves to the south.  One major characteristic of the polar front is that it produces low pressure systems that drive cold fronts and produce heavy rainfall and severe weather.  These are the same types of systems that generally bring high snowfall totals to the continent in the winter months.  Hawaii is much further south (and surrounded by the ocean), so with the exceptions of Mauna Kea, Mauna Loa, and Haleakala we don't get any snow.  But a few times a year the cold fronts do sweep down and roll over Kaua'i, Oahu, and the other islands, moving from west to east.

January patterns.  Red circle approximates Hawai'i's location.  Map from here.
When this happens there is a fairly noticeable sequence of atmospheric events that will, if you know what to look for, help you to predict the weather over the next couple of days and amaze your friends.  The first thing that will happen is that the wind will start blowing from the south (Kona).  This happens because the wind blows roughly parallel to an approaching cold front, heading in the direction of the low pressure area that is at the center of the storm system.  The wind will gradually strengthen.  You may also notice a very characteristic cloud progression.  The first clouds you notice will arrive a day or two ahead of the front (depending on how fast the front is moving).  These clouds will be very high (cirrus) clouds and will cover much of the sky.  Then as the front continues to move towards your island, you'll see lower and lower (and thicker, more ominous) clouds appear, until finally the sky is socked in by low cumulus clouds.  The reason that this happens is that the cold air that is approaching is abruptly pushing up the warmer, moist air in front of it.  This causes the air to cool, which leads to cloud formation.

When the front arrives it will bring with it significant rainfall and pretty heavy winds in some cases.  Sometimes the fronts pass quickly, but sometimes they may stick around for a couple of days.  After the front passes, you should notice clear skies, and the direction of the wind will shift; instead of coming from the south it will be coming from the west or northwest.  Then after a day or two if high pressure conditions return to the north of the islands, the trade winds will return.

The entire north Pacific at the time this post was written.  The symbols point in the direction the wind is blowing.  From National Weather Service.
That pretty much sums up winter cold fronts in Hawai'i.  These don't happen in the summer time because the polar front, which is the source of the disturbances, moves northward in the summer time.  So the next time the wind starts to blow from the south, keep your eyes on the sky, and you may be able to apply what you've learned here and in class.  And when you do, you can remember the kilo lani, or "sky watchers", who were special kahunas in Old Hawai'i that had a tremendous amount of knowledge about their natural environment, including the atmospheric conditions and signs that helped them to predict the weather.



(1)  To be discussed in a future post

Saturday, January 11, 2014

How to Outline a Textbook Chapter...

Photo by John Delay
School is starting up, and that means there's a fresh new crop of young, budding geographers eager to begin learning about way the world works.  But besides learning about the way the world works, students should also be working to develop study skills, which will help us not only to do well in class and retain the material that has been covered, but also to organize information and be more effective problem solvers in life in general.  One important skill that all students should master is how to outline a textbook chapter.

Outlining a textbook chapter helps you to distill out the most important concepts and material while organizing it in a way that makes it easy to review.  Many students are reluctant to outline chapters because it takes some time, but I promise that in the long run it really pays off, because you won't have to read the chapter again when it is time for an exam, and it will help you to remember the most important and useful points of the chapter.  For a standard textbook chapter, it generally takes me between 2-3 hours, but this includes a careful reading of the chapter.  It may take you a little longer, or you migth do it a little more quickly than me, but by the end you will have a great understanding of the chapter and you will also know what points are less clear to you so you can ask questions in class.

The steps to outlining a chapter are pretty simple.  Some guides say to read the chapter first, but I always do my outlines while I am reading through the chapter.  I think this is a much more efficient and effective method.  Some things to remember:

1.  Make a separate heading for each section in the chapter, and pay attention to the nested headings (sub-headings) within the chapter, and follow this pattern of organization in your outline.  This helps you keep track of the relationship of the concepts to one another and their relative importance.

2.  Look for the main idea in each section and subsection and include that in your outline.  Then add in the facts and details that seem most relevant to you.  Sometimes this takes some getting used to, but it is useful to omit trivial points.  Always pay attention to the words in bold.  I usually define these under separate sub-headings.

3.  Repeat these steps for each chapter in the paragraph.

Soon you'll have a great, detailed chapter outline that will help you remember what you've read, and you will be able to go over it in a fraction of the time it takes to read the entire chapter.  And if you keep your outlines you'll probably find they are useful in other classes, or if you ever have to prepare a literature review or take comprehensive exams.

Below I've included a sample outline I made of the first chapter of McKnight's Physical Geography, the textbook we use for 101 at Leeward.  Use this as an example.  Your outlining style may be a little different from mine, but this will give you the basic idea.

Good luck, and have a great semester!


This outline took me approximately 2.5 hours for a 30 page chapter.

McKnight Chapter 1: Introduction To the Earth

I.  Introduction
A.  What do geographers study?
1.  Tangible things....rainfall, mountains, trees
2.  Less tangible things...language, migration, voting patterns
B.  What is this book about
1.  Fundamental processes in the natural world
C. This chapter sets the stage for the study of physical geography
1.  Important stuff in the chapter
a.  using science to explain natural environment
b.  the "spheres of the earth"
c.  Earth's place in the Solar System
d.  Latitude and Longitude
e.  What causes the seasons
f.  Time do they work?

II.  Geography and Science
A.  Intro to section
1.  Geography from Greek meaning Earth Description
a.  used to be purely descriptive discipline
B.  Studying the World Geographically
1.  Two basic branches
a.  Physical geography (Environmental)
b.  Cultural Geography (Human)
2.  Fundamental question: "Why what is where and so what?" (4)
3.  Also interested in interrelationships
4.  Global Environmental Change....a broad theme of the book
a.  both human and natural changes
b.  long and short temporal scales
5.  Globalization...another theme running through the book
a.  processes and consequences of an increasingly interconnected world
C.  The Process of Science
1.  Scientific method
a.  Observe phenomena that stimulate a question or problem
b.  Offer an educated guess about the answer (hypothesis)
c.  Design an experiment to test the hypothesis
d.  predict the outcome of the experiment if the hypothesis is supported and if it is not supported
e.  Conduct the experiment and see what happens
f.  Draw a conclusion or formulate a simple generalized rule based ont eh results of the experiment.
2.  Science best though of as a process or even an attitude for gaining knowledge
3.  New observations and new evidence often cause scientists to revise their conclusions and theories or those of others
D.  Numbers and Measurement systems
1.  Two different systems in use
a.  English System (US)...miles, pounds, etc
b.  International System (pretty much everywhere else).

III.  Environmental Spheres and Earth Systems
A.  Earth's Environmental Spheres
1. of Earth's crust as well as unconsolidated mineral matter...
2.  Atmosphere...gaseous envelope of air surrounding the Earth
3.  Hydrosphere....comprises water is all its forms....
a.  Cryosphere, or ice and snow, is part of this
4.  Biosphere....all parts where living organisms can exists.
B.  Earth Systems
1.  Definition: a system is a collection of things and processes connected together and operating as a whole (8).
2.  Closed systems....self contained and isolated from outside inclfluences
a.  Earth with respect to matter
b.  Not many other examples
3.  Open Systems....inputs and outputs
a.  most systems are like this.
4.  Equilibrium...when inputs and outputs are in balance over time
a.  If balance changes, equilibrium will be disrupted until a new equilibrium is reached...
5.  Interconnected Systems...most systems are connected with other systems
6.  Feedback Loops....some systems produce outputs that feedback into the system, reinforcing change
a.  Positive feedback loops change the system in one direction
b.  Negative feedback loops inhibit a system from changing
c.  tipping points (thresholds) beyond which the system becomes unstable and changes abruptly until it reaches a new equilibrium.

IV.  Earth and the Solar System
A.  The Solar System
1.  Earth one of 8 planets
2.  lots of other things in the solar system as well
3.  Origins....most think the big bang 13.7 billion years ago
a.  Our solar system 4.5-6 billion years ago from a nebula
4.  Planets
a.  Terrestrial...mercury, venus, earth, mars
i.  smaller, denser, less oblate
b.  Jovian....Saturn, Uranus, Jupiter, Neptune
i.  Larger, more massive, more oblate
B.  The Size and Shape of Earth
1.  The Size of Earth
a.  topographical maps are usually very exaggerated
b.  Relief of the earth isn't very great compared to total size.
2.  The Shape of Earth
a.  Almost, but not quite spherical
b.  Bigger around at equator than through the poles (flattened)
c.  An "oblate spheroid" (12)

V.  The Geographic Grid--Latitude and Longitude
A.  The Geographic Grid
1.  Equator, North Pole, South Pole
2.  Great circles....any plane that passes though the center of the sphere and divides it into two equal halves
a.  this is the largest circle that can be drawn on the sphere
i.  Creates hemispheres
b.  The path between two points on a great circle is always the shortest route (the "great circle route")
3.  Small circles are created by planes crossing through other parts of the sphere
4.  Grid system based on small and great circles.
B.  Latitude: description of location expressed as an angle north or south of the equator
1.  Expressed in degrees, minutes, seconds
2.  Goes from 0-90, N and S
3.  Lines connecting all points of same latitude are called parallels.
a.  these never cross
4.  Descriptive zones of latitudes
a.  low, midlatitude, high, equatorial, tropical, subtropical, polar
5.  Nautical miles...the distance covered by one minute of latitude: 1.15 miles.
C.  Longitude: an angular description of location in the east-west direction.
1.  A line connecting all points of the same longitude is a meridian
2.  Only parallel to one another when they cross the equator
a.  distance between them is not constant.
3.  Establishing the Prime Meridian
a.  problem is that there is no natural baseline for measuring longitude
b.  Prime Meridian through Greenwich England established by international agreement in 1883.
4.  Measuring Longitude
a.  Maximum of 180 degrees
b.  Also uses minutes and seconds
c.  halfway around the world from the PM is the international datae line.
D.  Locating Points on the Geographic Grid
1.  Latitude and longitude together can be used to find an exact location

VI.  Earth-Sun Relations and the Seasons
A.  Earth Movements
1.  Rotation on the access
a.  Takes 24 hours (one day) in counterclockwise (from N pole) direction
b.  The speed of rotation varies depending on latitude
c.  Rotation has several important effects
i.  Coriolis effect: deflection of winds and ocean currents
ii.  Brings all points through increasing then decreasing gravity of the moon, causing tides
iii.  Diurnal (daily) alternation of daylight and darkness
2.  Revolution around the sun
a.  365 days, 5 hours, 48 minutes, and 46 seconds
b.  Orbit is elliptical and so distance between earth and sun varies
i.  Perihelion is when we are closest to the sun (January 3)
ii.  Aphelion is when we are farthest away (July 4)
3.  Inclination of the Earth's axis
a.  imaginary plane of orbit is called the plane of the ecliptic
b.  Earth is tilted at 23.5 degrees off a line perpendicular to this plane
c.  the tilt is always in the same direction throughout the year.
4.  Polarity of the Earth's Axis
a.  Tilt is always in the same direction (axial parallelism).
b.  Combined effects of rotation, revolution, inclination and polarity result in seasonal patterns.
B.  The Annual March of Seasons
1.  Seasonal variation increases in general as you move away from the equator.
2.  Three things really important
a.  Latitude receiving sun from DIRECTION OVER HEAD (declination of the sun)
b.  Solar Altitude (height o the sun above the horizone)
c.  The lengtu of the day.
3.  June Solstice: About June 21
a.  the point in orbit where the north pole is maximum tilted towards sun
b.  Tropic of Cancer (23.5 N latitude) has sun directly overhead.
c.  Longest day in the northern hemisphere, shortest in southern
d.  24 hours of day north of Arctic circle, 24 hours of night south of Antarctic circle
4.  September Equinox: September 22
a.  All locations on earth experience 12 hours of day, 12 hours of night
5.  December Solstice: Around December 21:
a.  The opposite of the June Soltice...
b.  Sun directly overhead at Tropic of Capricorn (23.5 South)
6.  March Equinox: March 20
a.  Same as the September Equinox
C.  Seasonal Transitions
1.  Latitude Receiving the Vertical Rays of the Sun...
a.  Sun rays only strike vertically between Tropic of Cancer and Tropicc of Capricorn, depending on the time of year
b.  analemma is a diagram showingthe latitude of the vertical rays of the sun.
2.  Day Length
a.  At the equator day length is constant...12 hours
b.  Day length changes more seasonally the further you get from the equator
c.  Overall, the annual variation in day length is the least in the tropics and greatest in the high latitudes
3.  Day length in Arctic and Antarctic
a.  these regions experience 24 hours of daylight and 24 hours of darkness over the course of the year.
D.  Significance of Seasonal patterns
1.  Both day length and the angle at which the Sun's rays strike Earth determine the amount of solar energy received at any particular latitude
2.  The higher the sun is in the sky, the more effective is the warming.
3.  Seasons are basically determined by the amount of sunlight a place gets.

VII.  Telling Time
A.  Standard Time
1.  Telegraph and railroad and other technologies increase connectivity creating a need for standard time....
2.  24 time zones of 15 degrees longitude agreed to in 1884.
B.  International Dateline
1.  180th meridian is the international dateline
a.  opposite from the prime meridian.
C.  Daylight Savings Time
1.  Created to conserve energy during WWI in Germany
a.  US begins the policy in 1918.

Sunday, June 30, 2013

Things to Know About Albedo...

Which side of the T&C logo is hotter: the white side or the black?  Does
it matter?  For the answer see the end of this blog post.  
Have you ever heard that it is cooler to wear lighter clothes on a hot, sunny day?  How could this be?  How could the color of your clothes make a difference in temperature?  This couldn't possibly be true, could it?  Well, it is true, and the difference in temperature is explained by albedoAlbedo refers to the proportion of the sun's energy (insolation) that is reflected by a surface.  Albedo is generally expressed as a percentage, and so if it is high (say, 90%), then more of the sun's energy is being reflected by a surface.  The 90% figure means that 90% of the sun's energy is reflected off the surface.  If albedo is low (10% for example) then more of the sun's energy is absorbed.  In this case, only 10% of the sun's energy is reflected whereas the balance is absorbed.  If a surface absorbs more energy, it heats up more.  We can change the albedo of a surface simply by changing its color; light colored surfaces tend to have higher albedo than darker surfaces.  One very good example of this is clothing; on a sunny day here in Hawai'i white shirts can be as much as 30 degrees cooler than dark shirts.  In this post we'll be looking at another practical example of the difference that albedo can make.

A White Roof?

One of the neat things about studying physical geography is that we can see practical applications of what we learn everywhere.  A couple of years ago the property managers of the apartment complex that houses one of this blog's authors installed a "white roof", coating the roof of the building with a white polymer that significantly increased the roof's albedo.  In other words, the white roof reflected a great deal more energy than the old tar roof.  Immediately after the white roof was installed we noticed a big change in the temperature of the was a lot cooler!  Even on the hottest days of the year at the peak of the afternoon sun we no longer needed to run the air conditioner to stay comfortable.  The new roof made a big difference and has saved us money on our electric bill, which in turn leads to decreased greenhouse gas emissions.  In short, everyone wins.  

More recently the management company had the entire building repainted, which was long overdue.  The old color was pale pink, a very light color.  The new color is dark gray.  Based on our experience with the white roof, I was perplexed as to why the management company would go with a dark color, because I reasoned that the darker color would absorb more of the sun's energy, thus making the interior of the building slightly warmer.  I was also curious how much a difference the darker color made to the surface temperature of the building.  So we here at TWITB decided to do an informal investigation: we would measure the temperature using an ExTech infrared thermometer, a handy little tool which uses a laser to measure surface temperatures.    We measured the temperature at approximately 3:20pm, which is approximately the hottest time during the day in Honolulu (why this is the case will be covered in a future post).  Since the painters didn't quite finish the job on the first day there was still some of the old pink surface (see the photo to the left), and so we could compare the results.  We measured the pink surface, the grey surface, and the dark gray doors.  We measured them in the sun and in the shade as well.  Which one do you think we found to be the hottest?

We were really amazed with what we found.  First the pink paint in the shade was 98 degrees whereas in the sun it was 110.  The concrete bricks that had been painted gray were 103 degrees in the shade and 130 in the sun.  The door was most surprising; in the shade it measured 111 degrees, whereas in the sun it measured 148 degrees.  So as you can see the paint really makes a big difference!  Whether this affects the interior temperature is a more complex problem to solve; this depends on the specific heat and conductive properties of the bricks and the door.  

So as you can see the color of a surface definitely does make a difference in surface temperature.  Let's look at some more examples.  In the picture below you will see some cars in a parking lot.  We've placed letters over a few surfaces.  This picture was taken at 3:30pm on a day when the official airport temperature was measured at 88 degrees.  "A" is exposed blacktop.  "B" is a white car in full sun.  "C" is a white parking space marker painted on the exposed blacktop.  "D" is shaded leaves.  "E" is a black car in full exposure to the sun, and "F" is a green car in full exposure.  "G" is blacktop in the shade.  For reference, we also measured a grass patch (not pictured) in the sun; its temperature was 110 degrees.  Match the letters from the picture with the numbers below the picture that correspond to the temperatures of each surface. 

1.  164 degrees.
2.  91 degrees.
3.  143 degrees.
4.  117 degrees.  
5.  114 degrees.
6.  151 degrees.
7.  138 degrees.

You can do similar tests yourself just by touching various surfaces on a hot day.  You'll also notice a big difference between the shade and exposed temperatures for the same surface.  In a future post we'll explain more in depth why color makes a big difference, but for now it's enough to know that darker things are hotter and lighter things are cooler.  As for the T&C logo, check out the pictures below.

White side.
Black side.
Answers: 1. E  2. D  3. F  4. B  5. G  6. A  7.  C  

Friday, June 21, 2013

The Solstice is Upon Us!

Photo from here.
Today is June 21st, the longest day of the year in Hawai'i.  Today the sun came up at 5.50am and will set at 7.16pm, for a total day length of 13 hours, 25 minutes, and 54 seconds.  We call this day the June (or Summer) Solstice.  After today the days will continue to get shorter until December 21st, with a day length of 10 hours, 50 minutes, and 12 seconds.  December 21st is the December (or Winter) Solstice.  In this post we will describe why there is variation in day length over the course of the year.

The Earth-Sun Relationship...

As we all know, the Earth revolves around the sun, a journey that takes approximately 365.22 days.  We also know that the earth is tilted on its axis at an angle of approximately 23.5 degrees.  This is why virtually every globe you ever see is tilted; it is demonstrating the earth's true orientation towards the sun.  But did you know that the tilt is always in the same direction?  This characteristic of the earth's orbit is called axial parallelism, and it is why days are shorter in the winter and longer in the summer.  This in turn is one of the biggest factors in seasonal variability; it is why the continental United States experiences winter, spring, summer, and fall.

Diagram from here.  

Have a look at the model we've provided.  As you can see, no matter what time of year it is, the earth's tilt is in the same direction.  If it is December, then more of the southern hemisphere is exposed to the sun at any given time, and less of the northern is bathed in glory of the sun's warming touch.  It follows then that in December it is summer in the southern hemisphere, and winter in the northern hemisphere.  If you imagine with your mind's eye that the earth is spinning around its axis (remember, one rotation equals one day), you can see that since more of the southern hemisphere is in the sun, the days are longer.  The opposite is true with the northern hemisphere.  Now look at the earth when it is June and the planet's northern hemisphere is at its maximum tilt towards the sun.  Can you see that more of the northern hemisphere is exposed to the sun, whereas less of the hemisphere is?  Thus the days are no longer in the northern hemisphere than in the southern.  Now look at the north pole.  Again, imagine with your mind's eye that the earth is spinning on its axis.  Look at the places close to the north pole.  Is there ever a point during a day (one complete rotation) that these points enter the darkness?  If you answered "no" you are correct!  These areas experience 24 hour days at this point, whereas at the south pole and near it there are 24 hour nights!

So at this point it should make sense to you that there is one day during the year when the northern hemisphere is at its maximum tilt towards the sun (whereas the southern hemisphere is a it maximum point away from the sun), and another point, roughly half a year later where the northern hemisphere is at its maximum tilt away from the sun (whereas at this point the southern hemisphere would be pointed towards the sun).  These two days are called the solstices, and they are the longest and shortest days of the year respectively in the northern hemisphere (and the opposite in the southern hemisphere).  

Now look back at the diagram.  There are two days of the year, one in March and the other in September, where the earth is pointed neither towards nor away from the sun; rather the tilt of the earth is perpendicular to a line drawn from the sun to the earth.  On these days every part of the earth receives 12 hours of daylight and 12 hours of night.  These days are called equinoxes.

So What Are the Tropics?

We've all heard the term "tropics", as in tropical storm, tropical paradise, and tropical fish.  But what does this really mean?  The "tropics" describes a very specific area on the earth's surface: all latitudes where the sun passes directly overhead at some point during the year.  Let's go back to our diagram of the earth-sun relationship.  Since the earth is rounded, there is a point on the earth's surface that is closer to the sun than all other points.  If you were standing on that point, the sun would be directly overhead.  Now since the earth is tilted, the spot on the earth where the sun is directly overhead changes over the course of the year.  The spot where the sun is currently overhead is called the subsolar point, and the latitude where the sun is directly overhead is called the solar declination.  Since the earth is tilted at an angle of 23.5 degrees, the subsolar point is found between 23.5 north latitude (the Tropic of Cancer) and 23.5 south latitude (the Tropic of Capricorn).  The area between these two lines of latitude is the tropics, and as we all know, Hawai'i is in the tropics.  This means that the sun will be directly overhead at solar noon in Hawai'i on two days during the year, one in May, and one in July.  Any place outside the tropics never ever experiences the sun directly overhead!  This is one more aspect of Hawai'i's geography that makes it special.  

Lahaina Noon?

Honolulu SkyGate at Lahaina Noon.  Photo from here.  
If you've ever been to Maui (or if you live there!) you may have visited Lahaina.  Lahaina is a major tourist attraction and is known as an old capital of the Hawaiian kingdom.  But Lahaina also gives its name to the day when the sun is directly overhead at solar noon in Hawai'i.  We call this "Lahaina Noon".  This name was immortalized in a contest sponsored by the Bishop Museum.  "Lahaina Noon" was chosen for these two days when the sun is at its greatest intensity because La Haina means "cruel sun" in Hawaiian.  On this day at solar noon you can witness something that no one on the continent ever sees (at least on clear days): a complete lack of shadows.  Since the Hawaiian Islands run to the northwest, Lahaina Noon happens on different days at different places.  In the table below you can see the dates for this year (2013); the Bishop Museum normally provides the dates on their website as well.

Information from the Bishop Museum.

Kau Ka La I Ka Lolo

Map from NOAA.  
The old Hawaiians were very attuned to the movement of celestial bodies (the sun, stars, and the moon) and referred to the day when the sun was directly overhead as kau ka la i ka lolo.  This expression can be translated as "the sun rests on the brains".  We understand now that these days had special significance to the old Hawaiians as well.  Based on research by University of Hawai'i Department of Anthropology graduate Dr. Kekuewa Kikiloi we have learned that many of the archaeological remains on Mokumanamana Island (generally known as Necker Island, one of the Northwest Hawaiian Islands) are tied to rituals associated with the passing of the sun directly overhead.  Mokumanamana happens to be right on the Tropic of Cancer, and so the sun is directly overhead here.  The Old Hawaiians were keenly aware of this fact, and so the island had a priestly significance to them; high-ranking priests would make periodic journeys to Mokumanamana to calibrate their calendars and for other ceremonies.

Necker island landsat image from Papahanaumokuakea National Monument website.  


Will the islands receive more energy from the sun on there respective Lahaina days or on the June Solstice? 

What compass direction will the Sun be oriented at solar noon on the days following the first Lahaina noon day? 

Why are there two Lahaina noon days for all of the Islands South of Mokumanamana (Necker) island?

Have the islands located north of Mokumanamana ever experienced the Lahaina noon sun?

Saturday, June 8, 2013

A Trip up Ka'ala 2: Climate and Altitude in Hawai'i

In our last post we described a recent trip we took up to the top of Mt. Ka'ala, the highest mountain on the island of Oahu, topping out at just over 4000 feet.  We described how the temperature changes with the altitude, decreasing the higher you get.  We discussed the rate at which this happens, which is described as the adiabatic lapse rate.  We also discussed humidity and how atmospheric moisture content affects this cooling rate.  All of this helped us understand the basic pattern of rainfall on the Hawaiian islands.  In this post one of the geography crew will describe how climate, which is determined by temperature and moisture, changes with altitude here in Hawai'i.  He'll also tell us about how these different zones are associated with vegetation.

Climate Zones

Have you ever wondered why clouds
Koppen chart from here.  
form high on the mountain slopes and not at the mountain base, or why there is a dramatic change in plant species as you move upslope?  A lot of this has to do with the distinct climate characteristics found in the islands.  Four of the five major climate zones described in the Köppen climate classification system can be found in the Hawaiian Islands and within these zones there exists a host of distinct microclimatic sub-zones determined by temperature and precipitation characteristics.  The differences in microclimates and the associated vegetation that can be found within these microclimates can be attributed to the vertical profile of the atmosphere.  As you increase in elevation you decrease in temperature at a specific lapse rate depending on your environment and this temperature profile dictates the phase change of water in the atmosphere.

Diagram from here.
Climatic zones on mountain slopes in Hawai‘i  can be characterized with reference to 4 atmospheric layers described by Riehl et al., (1951).  These 4 climate zones with the corresponding atmospheric layers in parentheses are: 1) marine (subcloud), 2) fog (cloud), 3) transitional (inversion), and 4) arid (free atmosphere).  The sub cloud layer extends from sea level to the lifting condensation level ( LCL, 600 - 800 m) at which point clouds begin to develop.   In a simpler explanation the LCL is the point at which a warm moist air mass needs to be lifted so it sufficiently cools to the point at which water makes the phase change from a gas to a liquid (condensation).  The cloud layer exists from the LCL to the base of the Trade Wind Inversion (TWI) which can lie anywhere between 1000 and 4000 m (Cao et al., 2007).   The TWI is a synoptic subsidence of warm air that was originally uplifted at the equator by convective and convergent processes.   The TWI, which is present 80-90% of the year (Cao et al., 2007), has a profound impact on the climate at high elevations  The thickness of the inversion layer is about ~300 m and above this point the stable dry air of the free atmosphere layer can be found.  The height and thickness of each of these atmospheric layers vary in space and time in response to large-scale circulation features and surface heating (Giambelluca and Nullet, 1991).  This layered system exists only in the presence of the trade winds and disappears when cyclonic systems interrupt them.

The vegetation characteristics across elevation gradients in Hawai‘i are dependent on several factors, including, substrate, topography, precipitation, available genotypes and the fragmentation and severe modification of native vegetation, especially at lower elevations (Mederios, 1986).  On hike up the mountain we were able to experience lower two climate zones mentioned above  and the distinct vegetation associated with these zones.  Three basic ecosystem types occur between the leeward coast and the summit of Mt. Ka‘ala. These can be distinguished by rainfall, elevation, and vegetation type. Lowland dry shrubland and grassland occurs at the lowest elevations although introduced trees are also present. Lowland dry and mesic forest, woodland and shrubland occurs further inland. At higher elevations wet forest and woodland can be found. A special type of ecosystem called tropical montane cloud forest (TMCF) occurs in the summit region and harbors many rare natives species. The ecosystems at lower elevations are dominated by introduced vegetation as a result of disturbance. Native vegetation becomes more dominant the farther one moves up the mountain. The vegetation at lower elevations in the Waianae range area of Mt Kaala is dominated by introduced tree species. Near the coast kiawe (Prosopis pallida) is frequent. Moving inland, koa haole (Leuceana leucocephala) becomes a dominant species. Along the first part of the trail to Mt Kaala itself both species can be seen. Larger silk oak trees (Grevillia robusta) can also be seen. Coffee trees (Cofea Arabica) can also be seen. Moving up the steep slope rainfall increases and disturbance decreases. Native tree species like koa (Acacia koa) and ohia (Metrosideros polymorpha) become common. The last leg of the trail moves into the cloud zone and ohia becomes the dominant tree. Olapa or lapalapa Cheirodendendron trigynum or platyphyllum) becomes more frequent. Olomea (perrotetia sanwicense) is also present. These are the dominant trees in the mosaic and bog at the  summit. Also very frequent shrubs include pukiawe (Leptocophylla tameiameia). Rare plants like kolii (tremotlobelia macrostachyus are also present.


Cao, G. G., T. W. Giambelluca, D. E. Stevens, and T. A. Schroeder (2007), Inversion Variability in the Hawaiian Trade Wind Regime. J. Climate, 20, 1145–1160, doi: 10.1175/JCLI4033.1

Giambelluca, T.W. and Nullet, D. (1991) Influence of the trade-wind inversion on the climate of a leewared mountain slope in Hawai‘i , Clim Res., 1, 207-216