 Analyzing the entirety of the atmosphere is vital in studying weather, understanding synoptic systems, and ultimately, providing forecasts. However, when studying smaller mesoscale phenomena, the atmospheric boundary layer (ABL) is the way to go. The ABL is the layer of the atmosphere which is directly influenced by the surface of the earth through exchanges in energy, moisture, and turbulence. To give an idea of its size, the troposphere (where almost all weather occurs) in mid-latitude regions is on average 12 miles high, but the ABL is only about a tenth of that. Two subsets of the ABL, each with their own distinct processes and functions, will be investigated in depth to understand its importance in the weather world. The Land Boundary Layer The boundary layer over land, also known as the land boundary layer (LBL) is one that almost everyone sees and interacts with every day. This boundary layer forms by growth with the diurnal cycle. The sun heats up the ground which in turn destabilizes the lower part of the atmosphere, generating dry convection. This convection mixes the air vertically elevating the boundary layer as it does so. In addition to heightening the LBL, this creates low level turbulence. The height of the boundary layer depends on many different weather processes that occur daily, not just convection on a sunny day. For example, fronts, deep moist convection, precipitation, temperature and moisture advection, amongst others can significantly impact the height of the LBL. For a typical summer sunny day, with no significant weather features in the area, heights of the LBL extend up about 1-2 km with extreme cases such as in desert environments up to 4-5 km. How do we know where to spot the boundary layer on a typical day? There are a few ways to go about this. One visual way is to look at the sky. Fair weather cumulus clouds, if present, will typically give an estimate of the LBL’s elevation. Below these clouds lies the mixing of the air from convection and hence a turbulent environment of varying intensities. Above these clouds exists an inversion, essentially the best way to pick out the LBL depth. Another method utilizes a vertical profile of the atmosphere. In the sounding below from North Platte Regional Airport on the 27th of June 2018 at 00Z, the boundary layer is shown to be around 1.2 km above ground level (AGL) (the surface elevation is about 850 m, meaning the boundary layer is from the surface to 1.2 km above this). The temperature around this height shows a distinct increase for the next few hundred meters while the moisture significantly drops off above this increase in temperature. What this physically signifies is the almost uniform air below the inversion because of the mixing from thermals, shown by the unvarying moisture throughout the LBL. The widely varying moisture above this level is a testament to the mixing not being present and hence the boundary layer ceasing to exist at and above, in this case, 1.2 km AGL.  The LBL and its processes are very important to the Plains and Midwest United States, especially during the nighttime hours. Essentially a nocturnal increase in winds develops around 850mb after the sun goes down and lasts into much of the overnight providing moisture, instability, and wind shear to support thunderstorms during the nighttime hours. More on this process and the physics behind it will be provided in a future article to further explain the LBL’s importance in the weather world. The Marine Boundary Layer Switching gears, the marine boundary layer (MBL) chiefly differs that of the land boundary layer in that it has direct contact with the ocean instead of the land, allowing for large amounts of heat and moisture to be exchanged. However, the MBL is harder to study than the LBL for a few reasons. First off, there is a lack of observations due to the difficulty of studying the atmosphere over the ocean. Even on an island, local influences from the land can affect soundings. Consequently, little is known about the MBL. Whereas cumulus clouds can usually be seen above the LBL, stratocumulus clouds are more likely to be seen over the MBL. These flat, low-lying clouds are very important to the earth’s radiation budget, since these clouds essentially act as a white blanket over large swaths of the ocean. This large blanket has a very high albedo (high reflectivity), meaning that these clouds will globally cool the earth’s surface. See below for a satellite image of a swath of these clouds.  The stratocumulus clouds in this layer are formed top-down. An air parcel on the top of the cloud will become negatively buoyant and stable by the cooling of the stratocumulus cloud. This will cause the parcel to sink; therefore causing surrounding parcels to rise (imagine dropping a rock in a cup of water, the water level will rise to make room for the rock as it sinks to the bottom). This process in the MBL creates a well-mixed layer with lots of turbulent air (see here for a great article on turbulence). This turbulent air allows water vapor and heat to be transported up to the cloud, which the cloud needs to stay alive. Note the difference in boundary layer formation from the LBL. To recap, the MBL develops via stability and sinking air (top-down process) whereas the LBL develops in pretty much the exact opposite way; destabilization and convection (bottom-up process) matures the LBL. Another important phenomenon that occurs in the MBL is decoupling. Essentially, decoupling occurs when the air that sinks below the cloud base does not reach the ocean surface; this is usually due to intense sunlight. The warming of the sun allows the stable air to retain some buoyancy, and therefore does not completely sink to the bottom of the ocean surface. This will cease the turbulence halfway up the cloud layer, meaning there is little to no air movement. As a result, this disallows the warm water vapor at the ocean surface to reach the cloud surface. Due to this lack of water vapor reaching the cloud, the cloud therefore thins and evaporates. Therefore, this diurnal process of decoupling essentially dissipates the cloud. See below for a comparison of a well-mixed and decoupled MBL.  As a whole, the planetary boundary layer is one of the most important aspects of the climate system. It is in direct contact with either the land or ocean surface, making boundary layer research essential to more accurate forecasting. Many important processes occur in the boundary layer, such as convection, turbulence, and decoupling, making it a vital part of our atmosphere to study and understand.
To learn more about the boundary layer, both over land or water, stay tuned in to GWCC and be sure to click here! ©2018 Meteorologist Joseph DeLizio(Land Boundary Layer) ©2018 Meteorologist Joseph Fogarty (Marine Boundary Layer)
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 For every summer that I can remember, I remember going outside and catching fireflies in the backyard. These cold-blooded bugs are bioluminescence, which means there is a chemical reaction between luciferin and luciferase. Luciferin is an enzyme which brings oxygen and luciferin together. This creates a lot of energy; to which they emit 100% of its energy by giving off light.
During the winter, fireflies are usually in the larval stage and hibernate by burrowing underground until they emerge in the spring. Larvae live underground in the winter, mature during the spring and emerge in the early summer. When they emerge, it ranges from the third week of May to the third week of June. In years when summer-like weather arrives before June, they tend to appear earlier than usual – like late spring. The air temperature and rainfall play a huge role in when they emerge. Since they feed on snails, slugs, and pill bugs, which are brought out by the rain and moist environment, fireflies like the muggy weather. Cold-blooded bugs like fireflies slow down when it gets cold. As the weather gets colder, the flash in the fireflies will flash at a slower rate. But once the air temperature reaches 50 degrees Fahrenheit and lower, that’s when they will stop flashing and flying around. An Ideal night for these insects is when it’s warm and muggy. If it rained during the day, an ideal environment would be present during the nighttime hours for their prey. If it is a cloudy night, the clouds act as a “blanket” over the surface, keeping the warm air from the day close to the surface. Since the moon doesn’t give off any radiation/heat, the clouds have stored energy from the day that they give off to the Earth’s surface during the night. This acts as a “blanket” to the surface keeping it warm throughout the night and not letting the heat escape. So, if you are trying to look for fireflies, then your best bet would be to do so on a warm and muggy night. To learn more about other interesting educational stories in atmospheric, oceanic, or climate science from around the world, be sure to click on the following link: www.globalweatherclimatecenter.com/education. © 2018 Weather Forecaster Allison Finch  Microbursts, coined by Dr. Testsuya “Ted” Fujita, are immensely powerful, localized columns of wind that occur when cooled air falls from the base of a thunderstorm at exceptional speeds – upwards of 60 MPH – and subsequently hit the ground, sprawling out in all directions. Upon the column of air reaching the ground and expanding outwards, it produces straight-line winds, which are capable of reaching speeds up to 100 mph – the equivalent of an EF 1 tornado on the Enhanced Fujita Scale, according to the National Oceanic and Atmospheric Administration (NOAA). Microbursts are more than capable of wreaking havoc by demolishing trees and powerlines, as well as causing extensive damage to buildings.
The most common weather event leading up to the formation of a microburst is dry air entrainment, which occurs when dry air mixes with precipitation inside of the storm cloud. The dry air then causes the droplets to evaporate, resulting in a rapid decline of air temperature at the top of the thunderhead. This patch of cooled air then begins to sink, gaining ample momentum as it falls, essentially turning into a speeding column of air. When this cool, dry air is pulled further down by the weight of precipitation, it becomes “water loaded”and falls to the surface rapidly. Microbursts can be divided into two classes: wet and dry. Where you reside throughout the country will determine as to which class you’re most likely to experience. For example, if you reside in the Southeastern United States where conditions are primed for thunderstorms, you’re more prone to experiencing a wet microburst. Wet microbursts are typically fueled by both water loading and dry air entrainment. Dry microbursts normally begin with dry air entrainment from moisture within the upper levels, eventually turning into wind-driven weather events with minimal surface precipitation. These typically occur when the relative humidity within the upper atmosphere is moist yet drier beneath the surface. When this occurs, a storm can feed off of moisture high within the storm. As it produces precipitation, the precipitation falls into the dry air, evaporating and cooling the air around it. The Southwestern United States is more likely to experience this phenomenon. There are microbursts that share both the wet and dry characteristics and are referred to as “hybrids”. Hybrids are fueled by multiple influences such as water loading, dry air entrainment, cooling beneath the base of the cloud and/or sublimation – ice crystals forming directly into vapor. Though they’re far more common than tornadoes, microbursts are not as well-known. The National Weather Service estimates that for every single tornado, there are roughly ten microbursts reported. While there is not a specified study on how many microbursts occur on average, it is accepted that most wind damage occurring within thunderstorms is likely due to microbursts. The damages caused by microbursts can lead one to believe at first that they’ve been struck by a tornado. The sure-fire way of knowing whether a tornado struck is to study the damage pattern. Tornadoes tend to leave behind a more circular trail of destruction, while microburst winds create straight-line wind damage that typically have a central point of impact. In terms of age, the study of microbursts is still relatively new within the atmospheric science world. Despite overwhelming advances in technology, it’s still difficult to detect and forecast microbursts. Meteorologists are able to predict an environment that may favor microbursts, but it’s not possible to predict an exact location or a specific storm that may produce a microburst. When forecasting for prime conditions, radar is by far the most helpful tool. Radars show air colliding above the Earth’s surface, which commonly means some of that air is being forcefully pushed downward. Radar technology also has the capability of showing air diverging or spreading outwards in the lower atmosphere right above the Earth’s surface, giving strong indication that a microburst is occurring. As with any form of technology, radar does have its limitations. For example, if a microburst forms on the outer rim of the radar’s scanning circumference, it may appear as a small blip that the meteorologist misses. It also doesn’t help that microbursts can form so rapidly that one could crash into the surface before a warning can be issued. While there is no guaranteed way to predict microbursts, the best thing one can do to protect themselves is to stay weather aware. This can best be accomplished by paying attention to any severe thunderstorm alerts issued by your local National Weather Service.  There is no question that as we get deeper into the 2018 Atlantic hurricane season, many people around the country and the world have many questions about the likelihood of getting hit by a hurricane either indirectly or directly. More specifically, directly being an all-out head-on landfall in the context of a direct strike and then indirectly being a glancing blow where the eye does not officially make landfall but rather a region being impacted by spiral rain bands at a distance from the center of the tropical cyclone’s circulation core. Hence, as the National Hurricane Center often emphasizes to the general public, even though a hurricane may not be heading directly for your particular location, following the exact center track of a particular tropical cyclone is not what one should be concerned about. Rather, people should always be conscientious about the overall direction of a storm since regardless of the exact landfall location, you are likely to experience some degree of impact from the tropical cyclone if you are within 100 to 200 nautical miles from the center of the storm.
Looking at the graphic attached above (courtesy of Meteorologist Michael Lowry from the National Center for Atmospheric Research or NCAR), it is fairly clear that Florida is undoubtedly the national state leader in terms of historic tropical cyclone landfall occurrences. Based on the statistics from 1851 or 2017 across the tropical Atlantic basin, the state of Florida has accumulated a total of 229 tropical cyclone landfalls which is not even close to the second most landfalls held by Texas at 112 during that time. Hence, there is no question whatsoever that Florida “takes the cake” on historic tropical cyclone landfall likelihood potential. Therefore, if you are reading this and have any friends and/or family which live and/or plan to visit the state of Florida during this 2018 Atlantic hurricane season or any future years, be sure that they are always logistically and mentally prepared to do what may be necessary. That way, they would be able to more effectively avoid any substantial problems if a tropical cyclone landfall threat were to present itself. As the old phrase goes, always “be prepared” and be proactive rather than reactive. To learn more about other interesting educational stories in atmospheric, oceanic, or climate science from around the world, be sure to click on the following link: www.globalweatherclimatecenter.com/education. © 2018 Meteorologist Jordan Rabinowitz |
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