Hobie Science :: Why is The Sky Blue “RePost”

School is almost out for the summer, and you are waaaaaaay behind on your papers!!! Have no fear, Gary Larson is here to hook you up with all the research you need to answer the question “Why is the Sky Blue??”

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For this weeks science blog we will leave the oceans and look at what makes the sky appear blue. And no, it is not because the ocean is reflecting the color of the water into the sky. (Ed Note: Full disclosure, I have always thought this to be true before Gary explained it to me)

In order to understand what makes the sky blue we must first understand the basics of sunlight and color. I recently read a fascinating article about a young Isaac Newton’s early experiments with light waves. The year was 1665 and a 23 year-old Newton was home from school due to the plague. Newton confined himself to his room and began experimenting with a prism. He closed his blinds and cut a small hole allowing a small stream of light to pass through. Newton then held a prism into the beam of light causing the light to scatter, ultimately casting a rainbow upon his wall.

Prior to this experiment it was widely believed that sunlight was white in color and therefore could not be muddied or changed. What Newton proved was that sunlight actually consisted of all the colors in the visible light spectrum together. There were many people who criticized this experiment, mostly due to religious credence, claiming that white light was holy in nature and could not possibly be made up of colors, and that the prism itself contained the colors of the rainbow.

Subsequently Newton devised a second experiment consisting of a second prism. Remember, this was in 1665 and a prism was not easy to come by. So, Newton held the second prism into the blue portion of the rainbow allowing only blue light to pass through and just as he had presumed, only blue light was cast against the wall.

Visible light is part of the electromagnetic spectrum consisting of the electromagnetic wavelengths between about 400 and 800 nanometer. For reference, one-nanometer is one-billionth of a meter.

As we can see from the electromagnetic spectrum above, the colors containing the highest amounts of energy, thus the shorter wavelengths, are violet and blue. When sunlight passes through the atmosphere these higher energy wavelengths scatter, being absorbed and reflected off the molecules that makeup our atmosphere causing the sky to appear blue. In space, where there is no atmosphere, the light is not being scattered off of molecules therefore appearing black.

Why, then, does the sky not appear violet? This has to do with how our eyes work. We have three different light receptors in our eyes called cones. They respond most strongly to the colors blue, red, and green. Therefore, although violet and blue wavelengths are being scattered in the atmosphere our sensory system, using the blue cones in our eyes, tell our brain that the sky  is blue as it is the strongest wavelength stimulating the blue cones.

So this week when you are at the beach, looking up at the blue sky, you will have a basic understanding of why you see blue, but stick around until sunset and the orange and red sky will open up a whole new set of questions. This will be discussed next week.

-Gary Larson

Hobie Science :: The Fallacy of Cleaning the Gyres | The Surfer’s Journal

The sad reality of what is a drift at Sea….

 

The topic of cleaning, or the ability to clean, plastics from our Oceans is obviously a touchy subject. It drifts on and off the front pages of our news. In our continued effort here at Hobie Surf Shop Blog to bring you “Surf Science” education, we felt the need to share some enlightened thoughts on the cleaning of the five ocean gyres, also known as swirling “Garbage Patches”. We hope to get our resident Surf Scientist, Gary Larson’s, thoughts on the subject soon…..

 

 

Boyan Slat’s “Ocean Cleanup Array”

 

The Surfers Journal recently ran an article called “Trash Pick Up” touting 19 year old engineering student, Boylan Slat’s, “Ocean Cleanup Array” (see photo interpretation above) as our catch all solution to the problem of plastics in our Seas. The idea behind the Array, is a simple yet complexly designed machine that is anchored in the Ocean and it just sits and waits for the currents to bring the plastics to its outstretched funnels. The plastics are then separated from the plankton and such, stored, collected, then recycled into new plastic products… simple, right?? Not a chance says Stiv Wilson….

 

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Stiv Wilson’s words in response to “Trash Pick Up.” (Keep reading Wilson’s take at Inhabitat.com, the man knows his stuff.)

As the policy director of the ocean conservation nonprofit 5Gyres.org, I can tell you that the problem of ocean plastic pollution is massive. In case you didn’t know, an ocean gyre is a rotating current that circulates within one of the world’s oceans – and recent research has found that these massive systems are filled with plastic waste. There are no great estimates (at least scientific) on how much plastic is in the ocean, but I can say from firsthand knowledge (after sailing to four of the world’s five gyres) that it’s so pervasive it confounds the senses. Gyre cleanup has often been floated as a solution in the past, and recently Boyan Slat’s proposed ‘Ocean Cleanup Array’ went viral in a big way. The nineteen-year-old claims that the system can clean a gyre in 5 years with ‘unprecedented efficiency’ and then recycle the trash collected. The problem is that the barriers to gyre cleanup are so massive that the vast majority of the scientific and advocacy community believe it’s a fool’s errand – the ocean is big, the plastic harvested is near worthless, and sea life would be harmed. The solutions starts on land.

Continue Reading at the link…

The Fallacy of Cleaning the Gyres | The Surfer’s Journal.

 

-Tracey Engelking

Hobie Science: Gary Larson Explains Hurricanes and Hurricane Swell

There is most definitely something special about the transition from the summer into autumn.  The months of September and October seem to always correlate with the best waves of the year, it happens to be in the middle of hurricane season and this year has been quite exceptional. Typically, hurricane seasons starts in early June, when the northern hemisphere begins to receive longer periods of sunlight resulting in warmer temperatures, and ends around the beginning of November when temperatures begin to cool. This year, as of September 24^th 2012, the east Pacific basin has produced 13 tropical storms/hurricanes. This is about average in quantity for the year but what is interesting is that 4 of the 13 hurricanes occurred in September, and this month isn’t over yet! Below is a map showing the hurricanes and their paths for the year so far.

Before we go further into the discussion about the most recent hurricane, Miriam, that began forming off the coast of Mexico on September 22^nd, it would be helpful if we went over how hurricanes work.

First of all, there are many synonyms for a hurricane. In the Indian and South Pacific oceans they are called tropical cyclones and in the northern hemisphere they are called Typhoons in the west Pacific basin and Hurricanes in the east Pacific basin and Atlantic ocean.

Another common curiosity is how hurricanes are named. Many decades ago the World Meteorological Organization comprised 6 lists of names, both feminine and masculine, and each list contained one name per letter of the alphabet except for the letters Q, U, X, Y, and Z. Only one list is used per year so at the beginning of a new year the next list is used. After the sixth list is used the cycle starts over.  Most recently we observed hurricane Miriam, M, the 13^th letter in the alphabet, the 13^th hurricane for 2012.

Hurricanes tend to always form between 5˚ and 20˚ north or south latitude. The Coriolis effect is what causes the distinctive spiral of clouds characteristic of hurricanes. At the equator there is no Coriolis effect, therefore hurricanes will never form at the equator nor will they ever cross the equator. Due to the Coriolis effect hurricanes will spin in a counter-clockwise direction in the northern hemisphere and clockwise in the southern hemisphere.

Because hurricane Miriam was recently spinning off the Mexican coast, and moved into the southern California swell window, I find it relevant to use as a reference of how hurricanes form and develop. Looking at the snapshot below, Miriam is easily identifiable just south of Cabo San Lucas. Another feature that is easily seen is the band of clouds that essentially split the northern and southern hemispheres. This band is the inter-tropical convergence zone (ITCZ) and it is where surface winds converge and thunderstorms are the result as the warm humid air rises, up to about 50,000 ft. above the ocean surface. It is along the ITCZ where many, if not most, hurricanes begin to develop.

Surface and atmospheric conditions must be just right in order for a hurricane to form. The ocean temperature needs to be about 80˚F to a depth of about 65ft., winds must be light and humidity must be high and extend up into the troposphere, about 30,000ft. It is only when these conditions are met and upper-level wind conditions are not too strong, a small cluster of clouds and thunderstorms will form. From this localized area of low pressure, the warm, moist air from the ocean surface rises high into the atmosphere where it cools and condenses. As air and moisture rise through convection, the relatively cooler surrounding surface air as well as the descending drier air from the tops of the thunderstorms moves in to fill the void. As this cycle continues, wind speeds will increase and the cluster of thunderstorms (tropical depression) will begin to organize, expand, and spiral into a massive vortex.

Technically, a hurricane can only be identified as a “hurricane” when surface level wind speeds reach 74mph, resulting in a Category 1 hurricane. It isn’t until wind speeds exceed 155mph that a hurricane reaches the highest Category 5.

Hurricanes usually dissipate when one of the fundamental conditions are disrupted. When the storm moves into colder water convection will cease thus stopping the movement of air. Upper atmospheric winds can also increase in speed causing wind sheer resulting in the disorganization of the hurricane. And also common is when the hurricane moves overland, the warm water source is eliminated and the storm quickly breaks down.

So, will hurricane Miriam send us some waves? Well, the answer to this can be fairly complicated. Let’s look at a snapshot of how Miriam was looking about two days after forming.

At this point in time Miriam was a category-3 hurricane with wind speeds around 120mph, and projected to send some significant swell towards southern California. Unfortunately, due to geographic constraints, southern California has a very defined hurricane swell window. Storms that occur off the coast of Mexico must move west to about 118˚W longitude for any of the swell to reach our beaches. So Miriam was looking pretty good at holding a high wind speed and movement.

The above image shows Miriam’s status as of Thursday, September 27^th. As can be seen, Miriam kind of stalled out at about 22˚N latitude and wind speeds decreased significantly to about 30mph. The result will be pretty fun, shoulder high waves along the south facing beaches and Friday and Saturday. On the upside, there was a very powerful south Pacific storm earlier this week that will send us some pretty significant swell, head-high plus, for Sunday and Monday.

So, for everyone participating in the Battle of the Paddle this weekend, there will be some surf to contend with; and let’s face it, board carnage is what the spectators are really wanting to witness!

-Gary Larson

Hobie Science: Why are the Oceans Salty?

Why are the oceans salty?

 

This weeks I thought it would be interesting to discuss what makes the oceans salty. First-off, let’s look at how the oceans were formed. As the young earth was cooling, about 3.5 billion years ago, many gasses were being emitted from the earth’s core, including water vapor.

As the earth further cooled, the water vapor reached a temperature where condensation occurred resulting in rain that continued to fall until, as we know today, water covers about 70% of the earth’s surface.

So what makes the oceans salty? Well, the ocean basins are the lowest portions of the earth where the vast majority of fresh water flowing down steams and rivers will eventually terminate. As streams and rivers flow over the surface they slowly erode the rock carrying away dissolved salts and minerals to the seas. Salt also comes from tectonic boundaries on the bottom of the oceans and also hydrothermal vents along divergent plate boundaries that release large amounts of salts and minerals.

There are also basins of water that are land locked by mountainous boundaries that are known as terminal lakes. In the western U.S. there are a few notable terminal lakes that have high salt contents. There is Mono Lake in Central California, the Great Salt Lake in Utah and Owens Lake, that is actually just a salt bed as all the water has evaporated from this lake and the rivers that once fed this lake have been diverted to supply Southern California with fresh water.

Back to the oceans. The average salinity (the amount of dissolved salt in water) of the oceans is about 35 parts per thousand (PPT) or 3.5%. That means that one gallon of seawater contains about eight tablespoons of salt and a cubic mile of seawater contains about 120million tons of salt!

Salinity is not constant at all parts of the ocean.

The areas in red show the the parts of the ocean where salinity is above average. You’ll notice that the areas of higher than average salinity are in the areas where the Trade winds blow. These are some of the most consistent winds in the world and are in parts of the world where the air and sea temperature are relatively warm. This combination of warm temperatures and high wind speeds result in high evaporation rates resulting in higher salinity.

So the next time you take that trip to Hawaii and your eyes are stinging a little more than normal after duck-diving through a set it’s only because the water is a little saltier than at home in California.

 

-Gary Larson

Hobie Science: Why is the Sky Red?

Red sky night, sailors delight… There may be some truth to this, but why does the sky appear red at dawn and dusk?

From last week’s blog it is understood that sunlight is the visible part of the electromagnetic spectrum and the sky is blue because the high energy blue wavelengths are being scattered and reflected while passing through our atmosphere.

What is happening during sunrise and sunset is that sunlight is passing through a much longer portion of the Earth’s atmosphere.

As can be seen in the image above, lightwaves from the sun are interacting with the atmosphere in a much more tangential manner. This means that lightwaves are not directly hitting the Earth’s surface, rather, they are passing through the atmosphere overhead more parallel to the Earth’s surface. It is only then we can see the red lightwaves being scattered in the sky.

The Earth’s lower atmosphere is much more dense than the air in the upper atmosphere. It is in the lower, dense portion of the atmosphere where most of the aerosols are found. Our atmosphere is mostly made-up of nitrogen and oxygen molecules. There are many other gases, e.g. argon, carbon dioxide, helium, neon, and methane, that vary in quantity depending on location. Many industrial cities have large quantities of manmade aerosols that hover in the lower atmosphere, often gaseous pollutants emitted from all sorts of factories. These areas often have brilliant, deep-red sunrises and sunsets as the lightwaves interact with particulate matter in the air. For us living in Southern California we are familiar with the amazing sunsets during fire season as forest fires pollute the sky with huge volumes of carbon (soot). Coastal cities are also well known for having beautiful sunsets, not due to pollution but because of the amount of salt that is in the lower atmosphere.

So the next time you catch an awe-inspiring sunset, enjoy! And revel in the fact that you now know why you’re seeing red.

-Gary Larson

Hobie Science: Surf Science 101: Why is the Sky Blue?

For this weeks science blog we will leave the oceans and look at what makes the sky appear blue. And no, it is not because the ocean is reflecting the color of the water into the sky. (Ed Note: Full disclosure, I have always thought this to be true before Gary explained it to me)

In order to understand what makes the sky blue we must first understand the basics of sunlight and color. I recently read a fascinating article about a young Isaac Newton’s early experiments with light waves. The year was 1665 and a 23 year-old Newton was home from school due to the plague. Newton confined himself to his room and began experimenting with a prism. He closed his blinds and cut a small hole allowing a small stream of light to pass through. Newton then held a prism into the beam of light causing the light to scatter, ultimately casting a rainbow upon his wall.

“Spectrum of Time” by Peter Erskine

Hobie Surf: Surf Science 101: Reading Buoy Data

For this week’s science blog, I thought it would be useful to take what we have learned in the past two blogs, about wave height and period, and apply that to how we read buoy observations, in-turn allowing us to do our own wave forecasting. Realtime buoy data is abundantly available via the internet through many sites. I find that the National Data Buoy Center (NDBC) online database offers the most helpful wave-data sets. Their database can be found at;  The National Data Buoy Center.

When you are at the NDBC site you will want to choose relevant buoy data that correlates to the location of the beach you plan on surfing at. I will be looking at the Dana Point buoy (#46223) for the following examples because this buoy is close in proximity to my local beaches and it is well exposed to swell from all directions. Some hints when choosing a buoy to use for forecasting; make sure it is not located on the leeward side of an island or tucked in too close to shore where points along the coastline might block swell from the buoy.

The Dana Point buoy collects wave and temperature data and records them every ten minutes.

Hobie Surf: Surf Science 101: Wave Speed

Last week’s blog focused on the genesis of ocean waves. This weeks I will attempt to breakdown the often lengthy journey open ocean waves take on before reaching the coastline. We know that from low-pressure storm activity, strong winds can create waves that can exceed 50-feet in height. Waves of these immense heights are common within the fetch and just outside the area of storm activity but decay rapidly during the initial distance traveled. kind of like how a brand-new car driven off the car lot instantly loses value, waves generally lose between 80 – 90 per cent of their energy in the first 100 miles traveled away from the area of storm activity. So, an initial wave height of 30-feet will be reduced to 6-feet, soon after traveling away from the area of propagation.

Once waves travel out of the fetch, or area where the wind is the generating force, they are no longer wind waves and in-turn identified as free waves, or what we understand as ground swell.

Wave Speed

For me, the most intriguing characteristic of waves is wave speed. As waves travel away from the storm’s influence they begin to organize into groups of waves with similar period and wave length called wave trains or wave groups.

Hobie Surf: Surf Science 101: Genesis of Waves

Welcome to a new feature on our blog, think of it as your Sunday morning read. A chance to get up, sip your coffee and learn something new, or enrich your knowledge on something you already know a lot about. Gary Larson, will take you through the science behind the things we all enjoy, but aren’t really sure exactly why/how they happen in his course  Surf Science 101. Enjoy!!

Waves

Ladies and gentleman summer is upon us and that means south-swells are aplenty. You’re excited for the 18-20 second, New Zealand ground-swell from about 200° but not exactly sure why? Well, feel free to saddle-up for the inaugural weekly installment of Surf Science 101, where I will attempt to enlighten you on some of the perplexing phenomenon we, as surfers, often encounter in the ocean. This week I will be exploring the formation of ocean waves, the variables involved and how they can travel for thousands of miles before breaking along the coastline.

Contrary to the explanations I have heard, from middle America folk to the well seasoned Southern California surfer, waves that we surf on a daily basis are not caused by the moon, tides or the large freighters criss-crossing the ocean. The only variable that is absolutely essential for wave propagation is wind. That’s it. If the planet Earth ditched its moon, ceased all tidal fluctuations and sank every boat in all seven-seas, but wind still blew over the surface of the ocean, we would still have waves.

That being said, there are three important factors that govern wave heights; wind speed, wind duration and fetch. Fetch is understood as the distance over water that wind blows in approximately the same direction. If there is an increase or decrease in any of these three variables the wave height will either increase or decrease, respectively. For example, if a 40-knot wind blew for 24 hours over a 100 mile fetch the wave heights would be larger than if the wind speed was 30-knots and the fetch was 50 miles.

Wave Propagation Chart. Wave heights increase when the wind speed and/or fetch length increases.