From newspapers to news programs, talk shows to magazines, facebook to twitter comments, it isn’t at all a rarity to find talking points regarding the latest, most destructive storm and its relation to the current climate. Often, these same discussions and commentaries go so far as to state that the weather phenomena at hand is a product of climate change. Though, this statement in nearly all cases is not true. Though why? Shouldn’t two things, both largely dictated by the atmosphere and surrounding environment directly correlate to strengthen or influence one another? The most simple answer is no. Weather and climate, as alike as they may seem, play vastly different roles, though they do intertwine and relate at many intersections. One may even note that they are of such a nature like that of fraternal twins: related, but not identical, and with great differences that differentiate and make them each their own being.
What sets these fraternal twins apart is primarily the time scales at which they occur. Weather refers to atmospheric events that occur over short time scales, such as days or weeks. In contrast, climate refers to atmospheric and environmental conditions occurring over long time scales such as decades and centuries. The weekly forecast your local TV weather person delivers is an example of weather: atmospheric conditions that can be observed within a small time frame no more than about a week in advance. Such weather events may be a simple rainstorm or sunny day, blizzard or thunderstorm. Even more destructive events, those that headline the news for days or even weeks at a time with their monstrosity and destruction, fall within the classification of weather, be it a tornado, a hurricane, or a severe thunderstorm.
Climate, as noted above, takes place over decades and centuries. Such events that are directly related to climate are things such as the average temperature for a city, province, or geographical region on a certain day, month, or season. Another example of climate may be the average amount of precipitation Buenos Aires, Argentina receives in the month of December. In short, climate is related to weather in that it is the long-term patterns of weather, usually thirty years or more, for a given area. Weather is heavily influenced by climate which may dictate when the rainy season occurs versus when the dry season takes over. Different areas within the world hold different climates, all of which contribute to the overall climate of the Earth. Even small ranges within forests or mountains may contain their own microclimates! In all, these many subsets of climate construct what is the global climate, that then in turn works to influence weather throughout different parts of the globe, creating unique atmospheric environments on which they fall.
Although seemingly similar at first glance, both climate and weather have very different and unique roles within Earth’s atmosphere. Though they are intertwined in many aspects, each has its own niche behaviors and defining characteristics that sets it apart from the other. Though certainly, these unique roles shape our environments to be what they are today.
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© 2019 Weather Forecaster Alexis Clouser
Transient Luminous Events: The Electrifying Phenomenon Illuminating our Skies (Credit: NASA)
Upper atmospheric lightning, also known as a transient luminous event, is an electrifying phenomenon that is not easily studied in the same way as “normal” tropospheric lightning that occurs in a typical thunderstorm. The European Space Agency Atmosphere-Space Interactions Monitor (ASIM) aboard the International Space Station is a collection of optical cameras and photometers along with a x and gamma ray detector that is used to detect the electrical discharges from upper atmospheric thunderstorms that make up transient luminous events. But what exactly are the different types of transient luminous events?
What is Corn Sweat?
Have you ever wondered why Iowa has some of the highest humidity and heat index values in the nation? You may be wondering how that can be since they are so far away from a water source, such as an ocean. The answer may lie in corn and a phenomenon which is known as “corn sweat.”
Corn sweat is a term used to describe the moisture that is released from the corn, causing more water vapor to be released to the atmosphere. The corn is able to draw moisture from the soil and into its leaves. At this point, the leaves “sweat,” meaning water is being released from the plant. This mechanism is also known as transpiration, when combined with evaporation, it is called evapotranspiration. This process has more of an effect the hotter it gets. This is because more water can be absorbed through the leaves of corn as the temperature of the surrounding air increases. Evapotranspiration is the main process that causes high humidity and heat index values for Iowa and even parts of Minnesota.
During the year 2011, people started looking at corn as a reason why some areas, such as Iowa and Minnesota, were suffering from extreme heat. On July 18th of that year, Knoxville, Iowa reached an astonishing heat index of 131°F. What might be just as impressive is the dewpoint that Minneapolis received that same day. The dewpoint reached a sweltering 81°F. That set a record for the highest dewpoint that the city has ever received up to that point. The following graphic is taken from July 18th, 2011. The dark green color on the image on the left is where most of the corn is located. The image on the right shows where the greatest heat was occurring. The pink areas are where excessive heat warnings were in effect and the orange areas are where heat advisories were issued. According to National Oceanic and Atmospheric Administration (NOAA), an excessive heat warning is issued when the heat index is at least 105°F for more than 3 hours per day for 2 consecutive days, or the heat index is more than 115°F for any period of time. A heat advisory is issued when the heat index is at least 105°F but less than 115°F for a 3-hour period. As you can see, the areas of large corn production coincide with the areas of the greatest heat.
2016 was another year which brought a lot of attention to the idea of corn sweat. The image below shows the maximum temperatures. It’s interesting to note how much cooler the temperatures are in Iowa and Minnesota. This once again is due to the transpiration of the corn. The water vapor in the atmosphere will actually suppress the temperatures. The downside to this is that the humidity is much higher, so although the temperatures are cooler, the heat index will be greater. This can be seen in the second image which shows the heat index values. There is a noticeable 110-115°F swath of heat index values from Iowa into southern Minnesota. Once again, this is right where most of the corn production is located. As summer is quickly approaching, the term “corn sweat” will be used more frequently in much of the upper Midwest.
Credit: UCAR, Washington Post
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@2019 Meteorologist Corey Clay
With their Latin route aspero roughly translating to “make rough or uneven”, these distinctive but rare clouds appear to be rippling waves in the skies above. With Asperitas being the first new cloud type in over 50 years, how exactly do these particular clouds form and what exactly are their origins?
Since its cloud classification being accepted in 2015, research has been conducted to pinpoint the exact origin of these clouds, along with trying to understand how these cloud types form. The height of the base of these clouds are anywhere from 4,000 feet to 10,000 feet and they are classified as undulating waves. In fact, these wave-like structures form on the underside of established clouds and make the overall cloud look like a rough sea surface when they are viewed from below. Atmospheric dynamics are definitely in play during the formation and lifespan of these clouds. Like mentioned in a previous article on Kelvin-Helmholtz Instability, atmospheric and fluid dynamics play a role in the origins of these clouds. Shifting wind directions and velocities appear to cause Asperitas’ wave-like structure, much like how velocity and current direction influences a fluid. Winds shifting in the horizontal and vertical direction is thought to help create the structure of these clouds.
How exactly these clouds form is still somewhat of a mystery with much debate on how these wave-like clouds originate. It is hypothesized that they come into existence from the aftermath of convective thunderstorms, although Asperitas clouds have been sighted in calm atmospheric environments. Another theory suggests that these wave-like structures form from descending Mammatus clouds. When wind direction changes with height as Mammatus clouds descend, the clouds seem to present a wave-like structure like ones that can be seen on a sea surface. Regardless of hypotheses of how these clouds form, it is known that atmospheric conditions must be unstable to form a wavy cloud base. This is why convective thunderstorms are favored for the development of these clouds due to the atmospheric instability that is present during thunderstorms.
Like said above, Asperitas clouds are associated with Mammatus clouds and could possibly be associated with rainfall. As also stated, thunderstorms have occurred before and after the formation of Asperitas, but there are cases where an unstable atmosphere has occurred with these formations and no precipitation occurred. Truly, more research needs to be done in order to completely understand this newly classified cloud formation. With their menacing look which mimics rough seas, they are undeniably extravagant in their shape and formation as they traverse across the sky.
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©2019 Weather Forecaster Alec Kownacki
Sometimes, fog can seem like it appears out of nowhere. It is not unusual for someone to be driving and have fog suddenly roll in, completely obscuring the driver’s vision. Thankfully, there are ways to predict where and when fog might show up. There are generally four types of fog that all have their own ways of forming. By knowing these mechanisms of fog formation, one can much more easily predict where fog might form. The types of fog are as follows:
1. Radiation Fog
This type of fog is the most common in many areas of the United States. All fog occurs as a result of air becoming saturated, which is a fancy word for saying it can’t hold any more water. Generally speaking, the cooler air is, the less water it can hold, so the easier it is to become saturated. Radiation fog happens at night when the air cools down because there is no direct radiation from the sun. When the air cools, it can hold less water, so if there’s already enough air for the water to become saturated, then it’s likely that radiation fog will form.
2. Advection Fog
This type of fog happens when warm, moist air rolls over a relatively cool surface. A good example of this type of fog is the fog that occurs under the Golden Gate Bridge. The water under the Bridge is usually cool, while the air the moves over it is typically warmer. The air that moves over the cool water cools down as a result, meaning it can’t hold as much water like in radiation fog. Then, the warm moist air becomes saturated from cooling, which forms the fog. One can expect advection fog near cool water bodies during warm months. Of course, this isn’t the only way advection fog can form, but this is the most common way by which this happens.
3. Upslope Fog
This type of fog happens when moist air moves up mountains and cools down. Since it gets colder and colder as you move up mountains, moist air that moves up mountains will cool down. So, like in radiation and advection fog, the air cools down, and it can’t hold as much water. When the air becomes saturated, it’s likely that fog will form. That is why it’s so common to see fog on mountains, especially at night. At night, there can be a combination of radiation and upslope fog, creating much more fog than elsewhere.
4. Evaporation Fog
Evaporation fog is unique to the other types of fog in that, instead of lowering the temperature of the air to create fog, it adds moisture to the air. This type of fog occurs when water vapor is added to an air mass that is already close to being full of water. That extra bit of water vapor is enough to push the air to become saturated, forming fog. This type of fog most often comes from cool air moving over a warm body of water, and is often mistaken for steam. One can expect this type of fog most often during autumn, because the water is still warm from the summer, but the air is getting cooler.
These are all the major types of fog that form. To help increase understanding of where fog most often forms, and what type of fogs form where, a map showing the average number of days with fog in the United States has been added below (credit: Mike Marston).
Meteorologists use these different classifications of fog and their causes when determining when and where fog might form. They utilize this information to create fog warnings that can help drivers prepare for dense fog. This information is available on the National Weather Service website, and on most weather apps. It’s always important to be wary of fog, especially when driving. By knowing how fog forms, one can be ready for it when it arrives.
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© 2019 Weather Forecaster Cole Bristow
Commonly located in the Great Plains of the United States is a phenomenon known as the Nocturnal Low-Level Jet, or sometimes referred to as the nocturnal low-level wind maximum. It is known to be one of the primary causes for convective initiation during the warm season that occurs during calm, quiescent conditions.
The Nocturnal Low-Level Jet is defined by the American Meteorological Society as a jet stream located within the lower 2-3 kilometers of the troposphere that occurs during the night. This jet is a fast-moving stream of air that rapidly transports warm, moist air from the Gulf of Mexico northward at speeds ranging anywhere from 25 to over 70 knots! This low-level jet forms as a result of the diurnal temperature change and the resulting interaction between the surface layer and boundary layer of the atmosphere. During the day the forces resulting from a southerly geostrophic wind that include friction, Coriolis, and pressure gradient forces are in balance. However, the frictional component goes away during the nighttime as the daytime vertical mixing ceases to be distributed throughout the boundary layer. This imbalance of forces results in winds becoming supergeostrophic and in the overall net acceleration of the wind creating this nocturnal jet.
The warm, moist air that’s transported ahead of approaching synoptic and mesoscale disturbances as a result of this jet can generate large amounts of convective available potential energy (CAPE) and increase low-level vertical wind shear. These ingredients all help in the initiation of severe weather. Also, as this low-level jet often intersects with frontal or outflow boundaries, it can trigger longer-lived mesoscale convective complexes (MCC’s) that can produce heavy rain, winds, and sometimes more severe convective storms that can form tornadoes.
This nocturnal wind maximum is often enhanced by the natural, downward sloping of terrain that occurs from West to East by the diurnal oscillation of the thermal wind. This is shown by the figure below.
As shown in (a) during the day the surface can quickly heat up, but the sloping terrain causes the air towards the West to be warmer than the air to the East at the same height. The warmer air to the West results in a higher pressure than the relatively cooler air to the East causing surface pressure to rapidly decrease with height. The Coriolis force then kicks in and deflects the air to the right (southward) creating this Northerly daytime low level jet. (Remember that the thermal wind always blows with colder air to the left.)
As shown in (b) during the night the process is reversed. Since the ground towards the West cools off more quickly due to radiational cooling, it is relatively colder than the air to the East at the same height. This causes the thermal wind to reverse and a southerly low-level jet will develop and known as the nocturnal low-level jet.
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© 2019 Weather Forecaster Christine Gregory