Sleet vs. Freezing Rain

A common wonder to many people is the difference between sleet and freezing rain. The two are formed very similarly, however I hope to clear up any overlap of the two you might have now. Thanks to my Aunt Kim for submitting this great question! (You may also submit a question of your own simply by scrolling to the bottom of the page and clicking on 'Leave a Response'.)

Sleet
Sleet has many different meanings around the world. For example, in Australia and the UK they refer to sleet as partially melted snow that falls from the sky. Their name for the precipitation we in the United States call sleet is put in a much simpler version, ice pellets. So how does sleet form? Well way up in the atmosphere a snowflake begins to fall from a cloud. On it's way down it may hit a layer of air that happens to be above freezing, causing the snowflake to become a partially melted snowflake or a cold raindrop. As this partially melted snowflake or cold raindrop keeps falling, it may encounter a deep layer of air next to the ground that happens to be below freezing (32 degrees Fahrenheit, 0 degrees Celsius). This causes it to turn back into ice in the shape of a tiny pellet. Hence, sleet is formed. Sleet is typically transparent and only has a diameter of about 1/5 of an inch or less.


Sleet.
Photo Courtesy: http://upload.wikimedia.org/wikipedia/commons/9/9f/Sleet_on_the_ground.jpg

A common characteristic that most people notice is its tendency to bounce when it strikes the ground. Or perhaps your more familiar with the tapping sound it makes when it comes in contact with glass or metal. If it helps you remember better, think of sleet as "frozen" rain.

Freezing Rain
The same process occurs during the formation of freezing rain as that of sleet; however, the layer of freezing air closest to the ground may be too shallow, prohibiting the raindrops to refreeze before they hit the ground. So freezing rain hits the ground as a supercooled water droplet. Supercooled essentially just means that a water droplet exists at below freezing temperatures. These supercooled liquid droplets will spread out and freeze almost immediately when it hits a cold object. This forms a thin layer of ice, which can be dangerous on roadways. Ice storms that occur are the result of freezing rain accumulating. Below are a couple of pictures I managed to snap of a tree branch and a lock during the January 2007 ice storm that struck the Houston area.




When freezing rain hits a ground that is below zero, it will freeze immediately forming something we call rime. Rime traps air between the droplets once on the ground, which helps explain why rime is white in appearance.


Rime.
Photo Courtesy: http://upload.wikimedia.org/wikipedia/commons/8/8b/Rime_ice.jpg

Airplanes can accumulate rime ice on the wing as it flies through a cloud with tiny supercooled liquid droplets, causing a redistribution of air flow. Luckily, rime is lighter in weight when compared to clear ice, making it easier to remove with de-icers. Icing is heaviest and most severe in temperatures between 14 - 32 degrees Fahrenheit, mostly because the concentration of liquid water is higher in warmer air. Airports generally prepare planes if this kind of weather is expected during the flight by spraying the planes down with antifreeze before take-off. On a side note, a substantial buildup of ice on the masts of sailing boats at sea can cause the vessel to capsize.


Sources:
Ahrens, C. Donald. "Precipitation." Meteorology Today: an Introduction to Weather, Climate, and the Environment. Belmont, CA: Brooks/Cole, CengageLearning, 2009. 180-183. Print.
Burroughs, William James., and Richard Whitaker. Weather. San Francisco, CA: Fog City, 2007. 222-223. Print.

Derechos

Many people have never even heard of a derecho (pronounced day-ray-sho) before. A derecho causes an enormous amount of damage with straight-line winds that extend for several hundred kilometers along a squall line's path. The word derecho was coined by Dr. Gustavus Hinrichs, a physics professor at the University of Iowa, in a paper he published in the American Meteorological Journal in 1888. Derecho is the spanish for "straight ahead" or "direct". On a side note, many believe the word tornado originated from the spanish verb tornar which means "to turn".

IN DEPTH: What is a Derecho?
I gave a one sentence definition of a derecho in the opening paragraph. Put into different words, it is a widespread and long-lived windstorm associated with a band of rapidly moving showers and thunderstorms. The winds are sometimes so strong that they will push the squall line outward. This forms a shape on RADAR that meteorologists call a 'bow echo'. Below are a couple of examples of a bow echo on RADAR that produced a derecho windstorm. Notice that the stronger precipitation (red) is occurring in a bow-like shape.


Derecho moving through the mid-west.
Photo Courtesy: http://i.imwx.com/web/multimedia/images/blog/MCV8May_regrad12z.jpg


Derecho moving through Texas.
Photo Courtesy: http://www.srh.noaa.gov/images/fwd/highwind07/web_radar_0057Z_metar_01Z_may307.PNG

Don't be deceived by these images; not all bow echos produce a derecho, so don't always assume if you see this on RADAR that the strong windstorm is heading your way. By definition a derecho must be at least 240 miles in length, and its winds must meet the National Weather Service (NWS) criterion for severe wind gusts, greater than 57 mph, at most points along its path. A stronger derecho event can have winds in excess of 100 mph. On May 31, 1998 a derecho plowed thru Wisconsin and lower Michigan with wind gusts measured up to 130 mph. Bow echoes can vary in scale and have even been known to die out and redevelop during the course of a derecho formation. It is important to realize winds are not constant across the stretch of a derecho and they can vary considerably. A derecho is composed of several patches of stronger winds embedded in a general derecho path, called downbursts. In addition to the winds, another dangerous aspect of a derecho is the speed at which it moves. A typical bow echo system can move at speeds of 50 mph or greater, giving those caught up in an outdoor activity very little time to take shelter in a safe place.

THE THREE KINDS OF DERECHOS
Serial: Serial derechos are produced by multiple bow echoes embedded in a very long squall line (approximately 100 miles). They sweep across a very large area and are developed from a strong, migrating low pressure system. Tornadoes are also common to occur within a serial derecho.

Progressive: Progressive derechos are produced by a fairly short line of thunderstorms (40 - 250 miles in length) and they often take the shape of single bow echo. Unlike serial derechos, progressive derechos normally spawn off a weak low pressure system. This type of derecho is narrower than the serial derecho during the early stages of its existence, but as it advances it continually grows until it becomes almost as large as a serial derecho. Tornadoes are possible with progressive derechos; however, they are not common.

Hybrid: Hybrid derechos come from a strong low pressure system like serial derechos, but its other characteristics resemble those more like the progressive derechos.

WHEN AND WHERE THEY OCCUR
The most common target of these windstorms is right here in North America, mainly the United States and Canada. Approximately 20 derechos will occur in the United States every year. Derechos can however form anywhere in the world where conditions are favorable: where moist air masses, heat, and a large fairly level terrain exist (a non-level terrain could attribute to breaking up the winds as they sweep across the land). Prior to 2004, the only other recorded derecho event around the world occurred over eastern Germany in 2002. A similar storm, called a "Nor'wester", exists in Bangladesh and adjacent portions of India. From the descriptions of the events that occur, they seem to resemble a progressive derecho; however, this is not yet confirmed.

The most common time for derechos to occur is late spring thru summer, from May to August. July is the most dangerous month due to the warm and muggy afternoon conditions that can easily trigger these violent thunderstorms. In the United States, they occur along two axes: one which runs along the "corn belt" from the Upper Mississippi Valley into the Ohio Valley, and another which starts in the mid-Mississipppi Valley and ends in the Southern Plains. During the cool season from September to April they are not as frequent, but mostly occur in the region from eastern Texas into the southeastern states. Any derecho event west of the Great Plains is extremely rare. In the United States, derechos have occurred as far west as Texas, as far east as Maine, as far north as Michigan, and as far south as Florida.

DAMAGE ASSESSMENT
So what is this windstorm capable of doing? Well, for one, it can knock over trees and power lines fairly easily. On July 15, 1995 a powerful derecho went through New York State during the early morning and blew down several trees in Adirondack State Park. The winds are also strong enough to take down fences and roofs, collapse barns, overturn mobile homes, and cause high waves on lakes. With all this, it is very common to see many killed and injured from this natural disaster. I'll end with a picture of a shelf cloud, a characteristic commonly associated with bow echos. You can definitely see the strong winds from this derecho pushing out ahead.


Photo Courtesy: http://www.adjusterpro.com/insurance-adjuster-blog/wp-content/uploads/2009/05/storm81.jpg



Sources:
Ahrens, C. Donald. "Thunderstorms and Tornadoes." Meteorology Today: an Introduction to Weather, Climate, and the Environment. Belmont, CA: Brooks/Cole, CengageLearning, 2009. 380. Print.
"Derecho." Learn Weather Phenomenons. Web. 26 Aug. 2010. http://weatherfreaks.net/derecho.
"Derecho -- Meteorologists Describe Little-Known Giant Windstorms." Science Daily: News & Articles in Science, Health, Environment & Technology. 1 June 2006. Web. 26 Aug. 2010. http://www.sciencedaily.com/videos/2006/0602-derecho.htm.
Johns, Robert H., Jeffry S. Evans, and Stephen F. Corfidi. "About Derechos." Storm Prediction Center. 22 July 2010. Web. 26 Aug. 2010. http://www.spc.noaa.gov/misc/AbtDerechos/derechofacts.htm.
Whitt, Kelly. "Understanding Derecho Storms: The Frightening Power of Strong, Long-Lasting Straight Line Winds." Meteorology & Climatology. 7 Jan. 2008. Web. 26 Aug. 2010. http://meteorologyclimatology.suite101.com/article.cfm/understanding_derechos.

Fire Whirls

In conjunction with the release of the 'fire tornado' video out of Brazil today (you may have seen the video on Yahoo's home page), I have decided to discuss the nature behind this rare phenomenon. The first video below, courtesy of the Associated Press, is the video made famous today on the web. The second video is from the 2006 Shekell Fire in Moorpark, California. After viewing both videos, you should have a pretty good idea of what a fire whirl looks like.





While the more technical name for this is a fire whirl, it is also commonly referred to as a fire tornado or fire devil. I first became aware of fire whirls when I began my internship at The Weather Museum in Houston, Texas. I never knew something so monstrous could happen within a fire, and I finally understood why battling a wildfire can prove to be a tough task.

I'll start off by discussing some basics first. A whirlwind is just a vortex of wind, or more simply put, a vertically rotating column of air. There are many different types of whirlwinds, including tornadoes, waterspouts, land spouts, fire whirls, dust devils, and snow devils. We can break whirlwinds down into two categories: Major Whirlwinds and Minor Whirlwinds. Major whirlwinds are produced from powerful storms that interact with other high altitude winds to create a funnel. Tornadoes, waterspouts, and land spouts fall into this category. Fire whirls, along with dust and snow devils, belong to what we refer to as minor whirlwinds. This category produces a funnel from local winds spinning on the ground, as opposed to higher in the sky. I will focus on fire whirls today and discuss some of the other whirlwinds in future posts.

Fire whirls are usually caused by forest fires, wildfires, and post harvest stubble burning; however, they can also form as a result of bonfires, oil fires, volcanic eruptions, or nuclear explosions. Most large fire whirls are typically associated with a wildfire. They can occur under many weather conditions, but are most common in calm or light winds because it allows the heat to build up more rapidly. The two main requirements for a fire whirl to occur are warm updraft and convergence. Some organized source of angular momentum must exist, whether it be from wind shear (an abrupt change in wind speed or direction) or the fire's convective column. This creates large swirl velocities as air is carried along into the fire plume. Fire whirls carry smoke, debris, and flames aloft, which can very easily increase the rate of fire spread.

Most fire whirls are approximately 30-200 feet tall, 1-2 feet in diameter, and last only a few minutes. There are some that can climb more than 3/5 of a mile high and carry winds over 100 miles per hour; these typically can last for twenty minutes or so. Even though a fire whirl is classified as a minor whirlwind, it is capable of causing quite a bit of damage as it can uproot trees that are nearly 50 feet tall. So where are fire whirls most likely to occur? The most common occurrence is on the lee side of a ridge where the heated air from the fire is sheltered from the general winds. Mechanical eddies (a current of air moving in a circular motion different from that of the main current) are produced when wind blows across the ridge, which in turn can trigger a fire whirl. If you're located on a flat terrain, the lee side of the fire near the outside edges of the front are where fire whirls will be most likely.

An extreme example of a fire whirl in history happened back in 1923 with the Great Kanto Earthquake that struck a region of Tokyo, Japan. Approximately 38,000 people were killed after a fire whirl roared over Rikugun Honjo Hifukusho, a Former Army Clothing Depot that they all packed inside for shelter. The fire whirl was a part of a firestorm that spawned as a result of the earthquake. It is believed that high winds from a nearby typhoon (another name for a hurricane) attributed to the fire whirl's creation. The cause of the fire whirl shown in the first video out of Brazil was due to strong dry winds impacting a brush fire.


Sources:
"1923 Great Kanto Earthquake: Facts, Discussion Forum, and Encyclopedia Article." AbsoluteAstronomy.com. Web. 26 Aug. 2010. http://www.absoluteastronomy.com/topics/1923_Great_Kanto_earthquake.
"Fire Whirl." Wikipedia, the Free Encyclopedia. Web. 26 Aug. 2010. http://en.wikipedia.org/wiki/Fire_whirl.
"Fire Whirls." Forest Encyclopedia Network. Web. 26 Aug. 2010. http://www.forestencyclopedia.net/p/p4/p140/p354/p450/p471.
"TORRO - Tornado FAQ's." TORRO. Web. 26 Aug. 2010. http://www.torro.org.uk/site/tfaq.php#whirlwind.
"Whirlwind (atmospheric Phenomenon)." Wikipedia, the Free Encyclopedia. Web. 26 Aug. 2010. http://en.wikipedia.org/wiki/Whirlwind_(atmospheric_phenomenon).

Rainbows

Many of us have heard Judy Garland singing "Somewhere Over the Rainbow" in the classic movie The Wizard of Oz. A rainbow is such a beautiful sight that everyone is sure to experience it several times throughout their life. While the science behind it isn't as complex as some of the previous posts, I will try to explain everything as clearly as I can. In addition, I will include some history of the discovery of the rainbow along with common myths different groups of people held about its presence. As usual, I will begin by showing some personal photographs I captured of rainbows.








THE SCIENCE BEHIND RAINBOWS:
A rainbow cannot occur just anywhere in the sky. We have to be positioned just right, with our back to the sun and our front towards the rain in order to observe a rainbow. The sun has to be fairly low in the sky for the phenomena to occur. In fact, once the sun is 42 degrees above the horizon, all rainbows will disappear. There's an old saying that goes something like this,

"Red sky in morning, sailors take warning,
Red sky at night, a sailor's delight."

We can replace the words 'red sky' in this saying with 'rainbow' and still maintain the same meaning. Typically, rain moves from the west to the east in the middle-latitudes (that's where we are!). Since the sun rises in the east, using the logic presented earlier, a rainbow in the morning would mean rain lies to the west and is heading towards the observer. With the sun setting in the west, a rainbow at night would be to the observer's east and foreshadow a rain free night.

Simply put, we see rainbows due to the reflection and refraction of light in a raindrop. There is some mathematical complexities tied along with it, though. Using the picture below as a reference, if the angle between the refracted light and the normal to the drops surface is greater than the critical angle, the light reflects off the back of the raindrop. The critical angle for water happens to be 48 degrees. Therefore, if light strikes the back of the raindrop at an angle greater than 48 degrees, it is reflected back and refracted as it exits the raindrop. An angle less than 48 degrees would indicate that light passes through the drop without being reflected (no rainbow).


Photo Courtesy: http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/opt/wtr/rnbw/frm.rxml

At some point in our lifetime, we are taught the acronym ROY G BIV to remember the order of colors in the rainbow. For those who don't already know, that stands for Red, Orange, Yellow, Green, Blue, Indigo, and Violet. On a primary rainbow, red will appear on the top and violet on the bottom. The reason for this order can be explained with a little bit of math. Violet light bends the most and will emerge from the raindrop refracted at an angle of 40 degrees relative to the incoming sunlight. Red light bends the least, emerging at a mere 42 degrees. All the other colors emerge somewhere between 40-42 degrees. Now wait a minute, you might be scratching your head realizing that based on those numbers, red would appear on the bottom and violet would appear on the top. While this might not make a whole lot of sense, we actually view red light coming from drops higher in the sky, and violet light from the drops that are lower. For every raindrop, only one color of light can be observed from it. That means it takes millions of raindrops acting like tiny prisms to make up a rainbow. No one person view the same rainbow as you do, in the sense that what light you see refracting towards you comes from different raindrops than the person who's standing next to you. So now that we understand why we see the spectrum in the sky, what determines the brightness or dullness of the light in a rainbow? It has to do with the size of the raindrops the sunlight is being reflected on. Larger raindrops will typically produce a brighter rainbow.

It is not uncommon to sometimes see what some people call a double rainbow. The technical name for this is actually a secondary rainbow; and while it's similar to the primary rainbow, it carries with it some key differences. Let's first observe a picture of a real life primary and secondary rainbow.


Photo Courtesy: http://www.trekearth.com/gallery/North_America/United_States/West/Wyoming/douglas/photo19837.htm

You will notice in the picture that the secondary rainbow occurs above the primary rainbow. The colors on the secondary rainbow are the reverse of the primary, with red being on the bottom and violet being on top. You will also notice that the coloring on the second rainbow is much fainter than the first. The level or brightness and color reversion can be attributed to the simple science that two internal reflections are occurring instead of just one. Also take notice of the darker band in between the two bows. This is called Alexander's band, named after Alexander of Aphrodisias, who was the first to describe this phenomena back in 200 AD. Now I want you to take a look at the picture below. It is a snapshot from one of my favorite movies, A Perfect Getaway. Whoever was in charge of this scene obviously did not brush up on their science beforehand. The secondary rainbow is not reversed as it should be, and the primary rainbow is not the brighter of the two. Just a little flick flub I thought I'd throw in here for you, keep your eye out for another mishap like this when a film decides to display a double rainbow!


Incorrect display of primary and secondary rainbow in the 2009 film A Perfect Getaway.


THE DISCOVERY OF RAINBOWS, a brief history:
Aristotle is believed to be the first to try to describe a rainbow. He presumed that a rainbow was caused by the reflection of sunlight in clouds, which turned out to be incorrect. But he was able to explain the circular shape and say that a rainbow is not located in a definite place in the sky. In 1266, Roger Bacon mathematically measured the angle of a rainbow cone to be 42 degrees, with the secondary bow occurring 8 degrees higher. It wasn't until 1304 that a German monk, Theodoric of Freiberg, proposed that each raindrop in a cloud makes its own rainbow. He verified this with the diffraction of sunlight in a circular bottle, but his results were unknown until Rene Descartes rediscovered diffraction of a drop in 1656. Both of these men were aware that two bows existed, and that the reflection happened once in the primary bow and twice in the secondary bow.


A RAINBOW OF MYTHS:
I came across a site that listed several different myths that people from around the world believed at one point or another. I'll present them in a list so that they are easier to comprehend.

Christians: believe the rainbow was put in the sky by God as a covenant with Noah that He'd never destroy the earth by flood again
Mayans: belief similar to the Christians, however their world was destroyed by fire rain and those who escaped saw the rainbow as a symbol that the anger of the gods had ended
Norse & Navajo: the rainbow represented the distance between heaven and earth; it was the gateway or bridge to heaven that occurred when St. Peters opens the pearly gates. The Norse believed the bridge could only be used by gods or those who were killed in a just battle.
Buddhists: related the 7 colors of the rainbow to the 7 regions of earth. They viewed the rainbow as the next highest state achievable before Nirvana.
Islam: only had four colors in their rainbow (blue, green, red, yellow) and related them to the four elements of earth, water, wind, and fire
Hindu: believed a rainbow represented the archer's bow of their god of war and that he used the bow to shoot arrows of lightning to kill demons that threatened their land and people
Germanic mythology: the rainbow is the bowl that God used during creation to color the world
Incas: gift from the sun god
Arabians: a rainbow was tapestry woven by the south wind
Irish: believed leprechauns held a pot of gold at the end of the rainbow
Polish: similar to the Irish, but believed the gold was a gift by angels for the person who found it
Cherokees: believed it to be the hem of their sun god's coat
Aborigines: represented the Rainbow Serpent Mother, who was their goddess of creation
Greece: a rainbow is the symbol of the goddess Iris, who is also the goddess of healing
Roman mythology: the rainbow was the pathway used by the messenger god, Mercury
Honduras/Nicaragua: viewed the rainbow as a symbol of the devil and hid in their homes till it passed; believed looking at it put a curse on them
Japan: at some point in the past, the presence of a rainbow was a bad luck omen because it reminded them of snakes (which they considered evil)
Slavic mythology: a mortal touched the rainbow and was turned into a demonic-creature by the god of lightning and thunder

And finally.... WELCOME TO AGGIELAND!


Sources:
Ahrens, C. Donald. "Light, Color, and Atmospheric Optics." Meteorology Today: an Introduction to Weather, Climate, and the Environment. Belmont, CA: Brooks/Cole, CengageLearning, 2009. 542-544. Print.
Burroughs, William James., and Richard Whitaker. Weather. San Francisco, CA: Fog City, 2007. 256-257. Print.
"The History of the Rainbow." Carl Hemmingsens Software. Web. 24 Aug. 2010. http://www.datalyse.dk/Rainbow/history.htm.
Kuchinsky, Charlotte. "The Rainbow & the Various Myths Surrounding It, Page 3 of 3." Associated Content - Associatedcontent.com. 7 Dec. 2007. Web. 24 Aug. 2010. http://www.associatedcontent.com/article/466052/the_rainbow_the_various_myths_surrounding_pg3.html?cat=34.
Morgan, Sally, and David Ellyard. "Weather Wonders." Weather. [Alexandria, Va.]: Time-Life, 1996. 28-29. Print.
"Rainbows: an Arc of Concentric Colored Bands." WW2010 (the Weather World 2010 Project):. Web. 24 Aug. 2010. http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/opt/wtr/rnbw/frm.rxml.

Lightning & Thunder

Both lightning and thunder are an aspect of meteorology that even young children are aware of. Almost everyone knows lightning is a discharge of electricity, thanks to Benjamin Franklin, who back in 1752 flew a kite attached to a wire and a key to prove this hypothesis. But there's a lot more to know about lightning and thunder, and I hope to expand the current knowledge you have with some information about the science behind it all. I'll begin with a picture of lightning I happened to capture in the middle of summer in 2008. It took a lot of time and patience, but I can finally say I have photographed lightning.



Lightning
Most of the lightning we are familiar with occurs within a mature thunderstorm, which is composed of cumulonimbus clouds. Cumulonimbus clouds are the big, towering clouds that grow in size vertically rather than horizontal. However, many people are unaware of other places lightning can occur. Volcanic eruptions, intense forest fires, nuclear detonations, heavy snowstorms, and some dust storms are also capable of displaying this phenomena. Below is a picture of lightning occurring in conjunction with the eruption of Eyjafjallajokul, the volcano that spewed lava in Iceland in the Spring of 2010.


Photo Courtesy: http://www.boston.com/bigpicture/2010/04/more_from_eyjafjallajokull.html

So we've all heard the saying "opposites attract", and this is in fact the main reason lightning forms. But how do the particles obtain a positive and negative charge? There are several theories that answer this question. One of them claims that when the tiny, colder ice crystals in a cloud come in contact with the larger, warmer hailstones that the ice crystals gain a positive charge and the hailstone a negative one. In other words, there is a net transfer of positive ions from the warmer object to the cooler object. The updrafts within in a thunderstorm could be responsible for carrying the tiny ice crystals to the top of the cloud and allowing the heavier hailstones to fall to the lower region of the cloud. Now we have a complete picture of the typical charges present within the cloud. Positive charges exist near the top, and negative charges are present near the bottom. A positive charge forms near the ground under the cloud, and this region of electrification actually moves along with the cloud. The most common type of lightning is cloud-to-cloud lightning. Only 20% is actual cloud-to-ground lightning.


Photo Courtesy: http://severe-wx.pbworks.com/f/charge%20separation.gif

Cloud-to-ground lightning starts off with a stepped leader that approaches the ground from the cloud base. The stepped leader is very faint and not visible to the human eye. At the same time, a current of positive charges flows upward from the ground. When the two meet, a return stroke travels upward to the cloud along the stepped leader's path at nearly 60,000 miles per second! This process can be repeated rapidly in the same lightning bolt creating a flickering effect we're all familiar with. There are two different cloud-to-ground lightning variants. Negative cloud-to-ground lightning is the more common of the two, occurring 90% of the time. This type is experienced when the negative cloud base is attracted toward the positive ground. The situation is reversed for positive cloud-to-ground lightning, as the positive charges present in the top of cloud reach negative charges on the ground. This creates a higher current level and can cause more damage. The average lightning bolt is 6-8 miles long and can travel 25-40 miles horizontally before turning down toward the ground. In October 2001, a visual lightning detection system measured a single bolt that traveled from Waco to Forth Worth to Dallas; that's around 110 miles!

The color of the flash of lightning can indicate different conditions. If a flash appears red, that typically means rain is present in the cloud. A blue flash indicates hail, and a yellow flash means there is a lot of dust in the atmosphere. White lightning conveys low humidity, which is a bad thing because fires are more likely to begin in these conditions. The lightning process continues in a cloud until all the charges in the cloud have dissipated.

There are 100 lightning strikes a second around the earth, that's nearly 8.64 million times a day that lightning strikes. The Empire State Building in New York City alone is struck about 500 times each year. So we always hear reports of fatalities, fires, and other bad situations arising from a lightning strike. However, few people realize the benefits lightning provides us. Lightning ionizes the air and produces nitrogen oxide. Studies suggest that this process could generate more than 50% of usable nitrogen in the atmosphere and soil, and nitrogen just happens to be an essential plant fertilizer. Lightning also plays a critical role in the natural cycle of forests by helping generate new growth. Areas burned by lightning triggered fires clear land of dead trees so that seedlings have space and soil to take root.

Thunder
In Norse mythology, the god Thor was said to have carried a hammer around, and every time he was angered he would make thunder and lightning strike. Ask many children today what thunder is and chances are you will hear a response similar to this.


The Norse God, Thor.
Photo Courtesy: http://www.theepochtimes.com/n2/images/stories/large/2008/10/21/thor_web.jpg

The true scientific answer behind it all has to do with the heat generated by the lightning strike. A single lightning bolt can heat the surrounding air up to 50,000 degrees Fahrenheit; that's five times hotter than the surface of the sun. The heat causes the rapid expansion and contraction of the air surrounding the bolt, and consequently results in a shock wave we hear as a rumble or a boom. The reason we see the lightning bolt before we hear the thunder has to do with the speeds at which each travel. The speed of light travels at 186,282 miles per second, but the speed of sounds only travels at about .211 miles per second. A common method for judging how far away a lightning bolt is counting the number of seconds between the flash and the boom. For every five seconds, the strike is a mile away. So if you counted to 20, the lightning strike is 4 miles from where you are located. Thunder is inaudible farther than 20 miles away, so no need to count past 100 seconds.


Sources:
Ahrens, C. Donald. "Thunderstorms and Tornadoes." Meteorology Today: an Introduction to Weather, Climate, and the Environment. Belmont, CA: Brooks/Cole, CengageLearning, 2009. 389-95. Print.
Burroughs, William James., and Richard Whitaker. Weather. San Francisco, CA: Fog City, 2007. 50-51+. Print.
"Facts About Thunder - Weather Imagery." Weather Imagery - A Little Mix of Everything. Web. 23 Aug. 2010. http://www.weatherimagery.com/blog/facts-about-thunder/.
"Flash Facts About Lightning." Daily Nature and Science News and Headlines | National Geographic News. Web. 24 Aug. 2010. http://news.nationalgeographic.com/news/2004/06/0623_040623_lightningfacts.html.
"Lightning Facts and Myths." Lightning Safety from LightningTalks.com. Web. 23 Aug. 2010. http://www.lightningtalks.com/lightningfacts.htm.
Morgan, Sally, and David Ellyard. "Weather Myths." Weather. [Alexandria, Va.]: Time-Life, 1996. 32. Print.
"StrikeAlert: Lightning Facts." Outdoors Technologies: Strike Alert Personal Lightning Detector. Web. 24 Aug. 2010. http://www.strikealert.com/LightningFacts.htm.

Red Sprites and Blue Jets

Red sprites and blue jets are optical phenomena that occur above the cloud tops in intense thunderstorms. The following YouTube Video shows red sprites and blue jets in real time, courtesy of The Sprites Campaign conducted by the Geophysical Institute of the University of Alaska Fairbanks. Following the video, I will go into the details about what these are, how they form, and when then form.



RED SPRITES
Red sprites are generally associated with cloud-to-ground or cloud-to-cloud lightning. It is estimated that they begin above the cloud tops and extend up to a 95 kilometer (~60 miles) altitude. The bulk of the red sprites occur in the mesosphere, the 3rd layer of our atmosphere. The sprites are usually red at the top and blue tinted near the bottom tendrils where they shoot up from. So what gives them the red color? Current thinking is that sprites result when free electrons are accelerated by the sudden charge in electric field strength caused by the parent lightning discharge below in the storm. The electrons slam into molecules of nitrogen causing the nitrogen to glow. The massive, dim light flashes usually last about a few thousandths of a second. Research suggests this phenomena occurs nearly simultaneously with positive cloud-to-ground lightning strokes and they typically form in clusters stretching 50 miles or more across the sky. It is believed that they for from the disruption of the atmosphere's electrical field in such a way that charged particles in the upper atmosphere are accelerated downward toward the thunderstorm and upward to higher levels within the atmosphere. It is believed that scientists knew of the phenomena as early at 1886; however, their knowledge was not extensive and they merely reported in their journals to have seen something high above the thunderstorm that they did not understand. It wasn't until 1989 that a professor and his graduate students from the University of Minnesota accidentally captured video of this event while testing a low-light video camera for an upcoming research rocket flight. They received the name 'sprites' after being suggested by Professor David Sentman of the University of Alaska-Fairbanks in 1994. 'Sprites' are mythical, fleeting, and playful creatures that appear in mythology and Shakespeare's plays.

BLUE JETS
Blue jets dart upward in a cone-like shape from the tops of thunderstorms that experience vigorous lightning activity. The narrow cones propagate upward in narrow cones of ~15 degrees full width at vertical speeds of roughly 100 kilometers/s (approximately 50-100 miles per second). The reach a height of about 25-50 miles before they begin to fade out. Unlike red sprites, they do not appear to be correlated to specific cloud-to-ground lightning discharges, and to this day they continue to not be well understood. They are more likely to occur at the highest portion of an intense thunderstorm cell, such as ones that produce tornadoes and severe weather. It is possible to see blue jets with the naked eye because they are brighter than sprites.


Photo Courtesy of http://www.electricyouniverse.com

Sources:
Ahrens, C. Donald. "ELVES in the Atmosphere." Meteorology Today: an Introduction to Weather, Climate, and the Environment. Belmont, CA: Brooks/Cole, CengageLearning, 2009. 390. Print
Heavner, Matt. Red Sprites and Blue Jets. Geophysical Institute of the University of Alaska Fairbanks. Web. 22 Aug. 2010. http://elf.gi.alaska.edu/.
"Lightning." Wikipedia, the Free Encyclopedia. Web. 22 Aug. 2010. http://en.wikipedia.org/wiki/Lightning#Blue_jets.
"Sprites, Blue Jets and Elves." Sky-Fire.tv. Sky-Fire Productions, Inc. Web. 22 Aug. 2010. http://www.sky-fire.tv/index.cgi/spritesbluejetselves.html#19.

Sundogs

A sundog is an atmospheric optical phenomena that is incredible to see first hand. The first time I saw them for myself was December 28, 2009 on my way home in the early evening. I spent an hour or so outside photographing nature's beauty, and calling others to have them take a look also. I first learned about this phenomena while taking an introductory Atmospheric Science class at Texas A&M University. I must say, I never expected to see it first hand. At first glance at the photos, it appears as if a little dot of a rainbow appears on either side of the sun; however, I will go into the science behind it all in the following paragraph. (Side note: Chief Meteorologist Tim Heller posted the second photo pictured above on the air of ABC-13 News in Houston, TX on 12/28/09)




THE SCIENCE BEHIND SUNDOGS:

Sundogs, also called parhelia ("with the sun") or mock suns, appear as brightly colored spots on either side of the sun. William Shakespeare appears to have mentioned this phenomena in Henry VI, Part 3 (1590) when he has Edward, the Prince of Wales, says, "Dazzle my eyes, or do I see three suns?" Sundogs will appear in a 22 degree halo. In simpler terms, if a human being were to stand facing the sun, they will appear 22 degrees to the right and left of the observer. Hexagonal plate-like ice crystals with a diameter larger than approximately 30 micrometers (1 micrometer = 1 millionth of a meter) that are present in the air tend to fall slowly and orient themselves in a horizontal manner. It is from this position that the large number of ice crystals act as a prism, refracting and dispersing the sunlight that passes through them, creating brightly colored spots we know as sundogs. A well developed sundog will display red on the inside and blue on the outside. This is because red light is least bent, and blue light is more bent. Sundogs can climb up to an angle of about 45 degrees above the horizon, so in order of this optical effect to occur, the sun must be fairly low in the sky. Since ice crystals are needed for sundogs to occur, it is normally associated with the presence of cirrus cloud, or high clouds that form 20,000 feet above the earth's surface. In the troposphere (the lowest level of our atmosphere - where all our weather occurs), the temperature decreases with height, so cirrus clouds are composed exclusively of ice crystals. This type of cloud is one of the easiest to identify, as it appears thin and wispy in appearance. Although not always a reliable assumption, some believe the presence of sun dogs in cirrus clouds indicate an approaching frontal system or developing low-pressure.


Sources:
Burroughs, William James., and Richard Whitaker. Weather. San Francisco, CA: Fog City, 2007. Print.
Ahrens, C. Donald. "Light, Color, and Atmospheric Optics." Meteorology Today: an Introduction to Weather, Climate, and the Environment. Belmont, CA: Brooks/Cole, CengageLearning, 2009. 540-41. Print.
"Sun Dog." Wikipedia, the Free Encyclopedia. Web. 22 Aug. 2010. http://en.wikipedia.org/wiki/Sun_dog.