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Rochester, NY
19 May 2013
 

    About Benjamin Ayres

    Articles by: Benjamin Ayres

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    Last week we discussed the role jet streams have on temperature. Northward movement of the jet allows for warmer air from the south to penetrate into the higher latitudes. Conversely, as the jet moves south toward the equator, chilly air from our Canadian friends permeates southward into the heart of the U.S. These drastic temperature variations can happen quickly and become quite an annoyance. However, the jet is associated with much more than temperature differences, as any area in the path of a strong jet stream can be subject to severe weather and significant precipitation.

    Pressure systems and the Jet

    Regardless if you’re a weather novice or expert, most people have heard the terminology “low and high pressure systems”. Discussing the development and formation of pressure systems is a looooong conversation for another day, but there is an obvious correlation between these pressure systems and the mid-latitude jet.

    As cold air pushes southward, the jet is thus forced in the same direction and a trough in the upper atmosphere (5–8 miles above the surface) digs southward. In the opposite direction, warm air forces the jet northward, resulting in a bump in the jet also known as a ridge.

    Large surface low-pressure systems form immediately to the east of an upper-level jet in the trough. Most lows have fronts attached known as warm and cold fronts, and these fronts give us much of our severe and rainy weather. Often, the most intense weather is associated with cold fronts as cold air violently lifts warmer air upwards, triggering precipitation. The greater the temperature difference, the stronger the cold front which is then able to produce more lifting. The stronger the jet is aloft, the greater the temperature difference at the surface, which can result in more precipitation.

    Streaking in the Jet

    Although a jet stream is defined as a thin current of rapidly moving air, flowing west to east in the upper part of the Earth’s atmosphere, there are sections within the jet that are faster than its surroundings. These sections are known as jet streaks and are usually located between the trough and ridge in a jet. Since jet streaks are faster than their surroundings, the air aloft diverges faster, which creates lower pressure at the surface and consequently enhances the amount of precipitation.

    Think of a jet streak as a bottle of soda. The regular jet stream is a gently shaken bottle of soda and when opened the soda might fizz to the top or barely fizz over, removing only a little soda from the bottle (creating a weak low pressure in the atmosphere). On the other hand a jet streak is like a violently shaken bottle of soda, when it’s opened the soda explodes out of it (creating a strong low pressure in the atmosphere).

    The evolution of the jet stream is one of if not the most important weather phenomena to understand. If stormy weather is coming your way, the amplified jet is probably to blame.

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    Since April fools day is just around the corner, many Rochesterians might be thinking the local meteorologists are playing some joke by forecasting highs that will barely reach the 40 degree mark along with a high possibility of a mix of rain and snow for Monday, April 1st. Unfortunately, that seven-day forecast graphic couldn’t be more accurate.

    Although spring technically began March 20th, there has been little to no evidence of “spring” along the eastern seaboard so far this year. Rochester has been averaging about 4°F below the March average of 43°F. This is a far cry from a year ago as the average temp over the course of the month soared to 57°F. Without a doubt it is human nature to want to blame something for this awful spring.

    So what do I blame?  I blame the jet stream.

    What is a jet stream?

    A jet stream is a thin current of rapidly moving air, flowing west to east, that is usually several thousand miles long and located in the upper part of the Earth’s atmosphere (~6–7 miles above the Earth’s surface). There are two main jet streams in each hemisphere, a weaker one in the subtropics, often crossing the southern portion of the U.S. and a more active jet in the mid-latitudes near the Canada/U.S. border..

    This jet in the mid-latitudes is very active because of the collision of arctic and tropical air masses. The rapid change of temperature between these air masses near the surface, also known as the temperature gradient, creates a stronger jet aloft. Temperature differences create pressure differences, which leads to wind. Consequently, the greater temperature differences at the surface, the stronger and more active the jet aloft.

    Because a jet stream is contingent on temperature differences, jets are most active during the winter over the mid-latitudes. As the northern hemisphere mid-latitudes begin to warm up into the spring and summer the jet stream moves north.

    Why so cold, Rochester?

    But so far this year, the jet hasn’t budged one bit. Unpleasant cold air has continually made its way into the Northeast from Canada due to a persistent pattern of surface lows, keeping the jet located to our south. Since the bitter air from Canada has been constant, the jet has not yet been able to begin its seasonal shift northward.

    There is always hope though as the ground continues to warm throughout the spring. Eventually, the jet will start to push its way northward. And once Rochester is on the south side of the jet, say hello to swim trunks and tank tops.

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    It’s okay to go outside now spring is finally here! Although it may still feel like January, it’s only a matter of time before snow banks and L.L. Bean Boots are replaced with chirping birds and flip-flops. Deciduous trees will soon become covered with leaves and springtime flowers like daffodils will make up flowerbeds across the northeast. But such change in scenery can surprisingly bring a change in weather, specifically an overabundance of precipitation resulting in flooding and even severe weather throughout the spring.

    Each day during the winter, we pass trees that sit stripped of their leaves and plants that have little to no life. We never really think about what effect the lack of agriculture in the winter has on our weather. It’s common sense that an abundance of leaves can form a canopy or that all living vegetation consists of water, but why are these factors important in terms of how we will be affected in a weather sense?

    The onset of spring means more daylight, which consequently means warmer temperatures. As the ground warms and habitual springtime rain falls, the mild spring atmosphere is able to evaporate more water from the surface and cause vegetation to transpire more water into the atmosphere. This means that anything that relies on water to flourish such as plants, crops, trees or even soil loses water to the atmosphere due to the mixture of evaporation and transpiration, this process is known as evapotranspiration.

    The more vegetated a region is, regardless if it’s a thick wooded area or a vast corn field, the more evapotranspiration will take place. Since this water is evapotranspirated into the atmosphere it takes on the form of water vapor or moisture. Severe weather enthusiasts know that during the spring, the more moisture that is present in the atmosphere, the greater possibility for the development and maturation severe weather or heavy precipitation. Therefore, it can be inferred that more evapotranspiration can equate to severe weather or local flooding.

    Locally, Upstate New York has a variety of vegetation that allows for large amounts of evapotranspiration. For example, the world-renowned Finger Lakes wine region is an ideal area for high amounts of moisture in the atmosphere. Since wine grapes feed off water from the soil and use a canopy of leaves and plants to protect themselves from incoming solar radiation, there is plenty of water for evapotranspiration of moisture into the atmosphere. And with hundred of wineries in the Finger Lakes region, there is no shortage of water in the grape vines, soil and canopy, therefore no shortage of evapotranspiration into moisture.

    As the days continue to grow longer, we will not only benefit from the warm weather but also from the springtime scenery. But be aware, as vegetation continues to grow in the spring, so does the possibility of a severe thunderstorm or even a tornado.

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    It’s amazing to think about how far the field of meteorology has come in the past 50 years or so. Atmospheric science has evolved from a minor concern among the public to a media cash cow. A primary reason of the growing interest in meteorology directly stems from great technological advancements in the 20th and 21st centuries. It seems like everyday there is a cutting-edge tool that will help meteorologists in their quest for the perfect forecast. Recently, this revolutionary invention is a portable doppler radar, known as the Doppler on Wheels (DOW).

    Implemented in the 1940’s, radar was initially used to detect enemy aircraft during World War II. These radar sent out microwave signals towards a desired target and listened for its reflection, allowing the U.S. Navy to successfully decipher the enemy and their whereabouts.

    When military radar operators noticed strange features on the radar, they reasoned that the radar must have picked up precipitation. Not too long after this, the first radar primarily used for weather was developed, commencing the need for weather instruments.

    Due to its accuracy in pinpointing the location and evolution of precipitation, radar has been one of the most important tools used in meteorology. About twenty years ago, all weather radar was updated to Doppler radar, a feature allowing for the detection of wind flow within regions of precipitation. This upgrade allowed meteorologists to identify areas of rotation in regions of precipitation, a telltale sign for tornadoes.

    Across the U.S., there are 155 Doppler radar that meteorologists use on a daily basis.  However, there will always be one major downfall with stationary radar: they can only “see” so far away. Essentially that means the further away an object is, the less accurate the radar is.

    That’s why atmospheric scientist Joshua Wurman created a fleet of three trucks known as the Doppler on Wheels. The concept behind the DOW is the closer it is to the weather phenomenon, the better data the radar will receive. This allows the DOW to be a pioneer in severe weather research.  Over the past 15 years, the DOW has collected data within a mile of a numerous tornadoes and within the eye wall of multiple land falling hurricanes.

    The DOW even measured the fastest wind speed ever recorded on earth, a 318 mph wind gust from a tornado outside of Oklahoma City in 1999.

    Although the DOW operators pride themselves on being trailblazers for tornado and hurricane research, the DOW has also recently studied other weather phenomena like lake effect snow. In fact, this February the DOW made a two-week trip to work with students at Hobart & William Smith Colleges to study how lake effect bands behave. During this visit, students were given the opportunity to operate the DOW and decipher the movement and precipitation type of lake effect off Lake Ontario. This is the same work done by real meteorologists in the field.

    Despite the fact that the DOW has departed HWS, students will have the chance to work with it once more, as it will make an extended two-month visit next December when all three DOW’s will travel to upstate New York to further study lake effect precipitation.

     

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    The conflict between good and evil is a concept that stems from an ancient myth thousands of years ago. However, long before this idea was conceptualized, the battle between good and evil existed on a planetary scale.

    In our galaxy (the Milky Way), all eight planets have unique size, characteristics and appearance. However, even though these eight planets have such distinct features, there are two planets known as twins. With luscious vegetation and more than half of the planet covered with water, Earth is the ideal planet for all living organisms. On the other hand, the planet that is strikingly similar to Earth in size, mass and composition, Venus, has temperatures upwards of 1000°F and an atmosphere 100 times thicker than Earth’s. Therefore, it’s no surprise that the planet known as the “Morning Star” is commonly referred to as Earth’s evil twin.

    The Amazon in Space?

    Venus’ composition and weather is a fairly new understanding though, as many scientists actually believed Earth’s evil twin possibly could have similar weather and surface features to our planet. This idea stemmed from the fact that Venus is essentially covered in clouds. Since clouds on Earth are composed of water vapor, researchers believed that there must be some sort of tropical “paradise” like lush rainforests or jungles encompassing Venus. However, this ideology came to an abrupt end when scientists learned of the hellish-hot temperatures on Venus.   To accompany these temperatures, the clouds on Venus are composed of drops of sulfuric acid.

    Composition of Venus’s Bizarre Clouds

    Scientists believe there are a couple of ways these sulfuric acid clouds formed. One is that these clouds were actually formed by early volcanic activity that released sulfur into the atmosphere and trapped it in the clouds. The sulfur was able to melt in the atmosphere since the melting point of sulfur is 386K and the surface temperature on Venus is about 750K. The other way is through photo dissociation (breakup) of carbon dioxide into carbon monoxide and atomic oxygen. Since atomic oxygen is highly reactive, when it reacts with sulfur dioxide, it results in sulfur trioxide, which can combine with water vapor to create sulfuric acid.

    Although these clouds have a much different composition than water vapor clouds on Earth, the sulfuric acid clouds surrounding Venus do precipitate. Sulfuric rain falls from the atmosphere of Venus, however does not reach the surface due to the extreme heat that evaporates the rain and forms clouds again. This sulfuric rain is much different from acidic rain on Earth since Earth’s acid rain is water with small amounts of sulfuric and nitric acid and Venus’s acidic rain is composed entirely of sulfuric acid.

    Due to its extremely close proximity to the sun and interesting atmospheric features, Venus’s weather has been long debated among scientists. But since we now know Earth has an evil sibling, it’s fair to say we lucked out.

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