 (Diagram showing each stage of twilight with the suns degree below the horizon) Twilight is defined by a period of time after sunset or before sunrise that the sky remains illuminated enough to still be able to carry on outdoor activities without the help of artificial light. It is caused by the refraction of light through the densities of our atmosphere from transmission of sunlight. Dawn is the term for twilight that occurs before the sun rises in the morning and dusk is the term for after sunset. Depending on the season or latitude, twilight can last anywhere from 70 to 100 minutes. In the mid latitudes, twilight tends to be longer during the summer and shorter in the winter months. It isn’t common knowledge, but there are three different stages of twilight. The National Weather Service (NWS) defines these stages as civil, nautical and astronomical twilight. Each stage is determined by the sun’s solar angle when it’s below the horizon. Civil twilight occurs from the time the sun sets or rises and when the sun’s geometric center is at a six-degree angle below the horizon. During this time, twilight is characterized by the appearance of larger bright planets and stars in the sky. Some left over pinks and oranges displayed from the sunset can still paint the sky. Artificial lighting isn’t needed to see your way around outside. The horizon is still able to be seen.  (Civil twilight: March 27, 2020 7:30 PM CDT Louisiana) Nautical twilight is when the sun’s angle is between six and twelve degrees below the horizon. During this time, you will be able to see more light from stars and planets through the naked eye. Most, if not all the displays of color from the sunset have disappeared. The horizon is still visible but artificial lighting may be needed to continue activities. The ability to start seeing stars during this stage of twilight is helpful to sailors who start setting course by the position of the stars. This is how nautical twilight gets its name.  (Nautical twilight: March 27, 2020 7:50 PM CDT Louisiana) Astronomical twilight is the last stage of twilight before it gets completely dark. Here, the sun's angle is between twelve and eighteen degrees below the horizon. Most celestial stars and objects can be seen in the sky at this point. During this final stage, it is hard to distinguish a horizon and artificial light pollution in populated areas tends to block on the remaining light of the day. This stage gets its name from astronomers observing objects in the sky. Brighter objects, such as stars and planets, can begin to be viewed by astronomers at this time. Other objects, such as nebula and galaxies, are easier to see during complete nighttime when the sun goes further below 18 degrees.  (Astronomical twilight: March 27, 2020 8:10 PM CDT Louisiana) There is so much to know about twilight and why it exists. It’s interesting to know there are three stages of twilight that are defined by different sun angles that demonstrate different characteristics before it becomes full night. Next time you find yourself driving to work in the morning or calling the kids inside for the night, reflect on the stage of twilight you are experiencing. It’s good to take a breath and reflect on our surroundings every once in a while.
To continue reading about twilight in part two and for more weather education, click here. © 2020 Meteorologist Alexandria Maynard Sources: Ahrens, C. Donald. Workbook/Study Guide to Accompany Meteorology Today: an Introduction to Weather, Climate, and the Environment. Brooks/Cole, CengageLearning, 2009. US Department of Commerce, and Noaa. “Definitions of Twilight.” National Weather Service, NOAA's National Weather Service, 16 Mar. 2015, www.weather.gov/fsd/twilight. “What Is Astronomical Twilight?” Timeanddate.com, www.timeanddate.com/astronomy/astronomical-twilight.html. “What Is Civil Twilight?” Timeanddate.com, www.timeanddate.com/astronomy/civil-twilight.html. “What Is Nautical Twilight?” Timeanddate.com, www.timeanddate.com/astronomy/nautical-twilight.html. “What Is Refraction of Light?” Timeanddate.com, www.timeanddate.com/astronomy/refraction.html.
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 (The angle of the sun below the horizon and the direction of light as it is refracted through layers of the atmosphere) When the sun is just below the horizon, we often find ourselves immersed in a state of illuminated darkness. It's a part of our day where we can still see our way outside. Many people drive to work in the early morning or come home in the nighttime and children playing outside are called in to dinner or woken up for school the next morning. It’s a part of the day we all find as a comforting end or beginning. A passage from one day to a new day. During the twilight hours, we all go about our business without a single thought of how and why this occurs. Unaware, that if we didn’t have an atmosphere, twilight wouldn’t exist.
A beam of light passing through a substance is called transmitted light. When that light is transmitted through varying densities, it either speeds up or slows down. When light hits a dense substance at an angle, it bends. The bending of light is called refraction. Because our atmosphere is so thick with varying densities, the light that is transmitted by our sun bends, slows down and speeds up as the sun carries out its rotation across the sky. When the sun is at different angles in the sky, it can change in light intensity or directness. At twilight, the sun sinks below the horizon. At this particular angle, the light is no longer being directly transmitted because it is blocked by the horizon. So, how is it we can still see light at this time of day? Due to refraction - the bending of light through our dense atmosphere - the light transmitted from the sun can still reach that part of the world. The more atmosphere the light has to penetrate through, the more it gets refracted. When the sun is below the horizon, light has to penetrate through the atmosphere at it thickest. Therefore by the time the light reaches your area before or after sunset, it has been bent around the circumference of the sun and angled toward you. This is how it still seems like it's partially light out after the sun dips below the horizon. When light travels through space, it is travelling through a vacuum. Space is a vacuum because it is lacking in matter, density, and pressure. When light travels through a vacuum it has nothing to slow it down or bend it. If our atmosphere didn’t exist, it would just be replaced with outer space. There would be no bending of light through different densities. Therefore, once the sun sets behind the horizon, it becomes completely dark. Twilight would not exist. To continue reading about twilight in part two and for more weather education, click here. © 2020 Meteorologist Alexandria Maynard Sources: Ahrens, C. Donald. Workbook/Study Guide to Accompany Meteorology Today: an Introduction to Weather, Climate, and the Environment. Brooks/Cole, CengageLearning, 2009. US Department of Commerce, and Noaa. “Definitions of Twilight.” National Weather Service, NOAA's National Weather Service, 16 Mar. 2015, www.weather.gov/fsd/twilight. “What Is Astronomical Twilight?” Timeanddate.com, www.timeanddate.com/astronomy/astronomical-twilight.html. “What Is Civil Twilight?” Timeanddate.com, www.timeanddate.com/astronomy/civil-twilight.html. “What Is Nautical Twilight?” Timeanddate.com, www.timeanddate.com/astronomy/nautical-twilight.html. “What Is Refraction of Light?” Timeanddate.com, www.timeanddate.com/astronomy/refraction.html.  What is a Cloud?
Fluffy and buoyant, wispy and moody, clouds arise in billions of different forms, each one unique in their characteristics and presence. Though, as beautiful and charismatic as each one is, what exactly is a cloud, and how do they come to be? At its most basic definition, a cloud is a mass collection of water droplets that form from the cooling of water vapor in the atmosphere. Depending on the altitude in the atmosphere, these water droplets cool either into water droplets or ice crystals. The higher in the atmosphere these droplets cool, the more likely they are to form ice crystals. These millions of tiny ice crystals then come together to form various sorts of cirrus clouds, thousands of feet in the air. Though, there is plenty of water vapor in the atmosphere just drifting about, so why is it that only some of this comes together to form a cloud? The answer to this question is CCN, or Cloud Condensation Nuclei. These miniscule particles in the atmosphere, on average only about 2 micrometers in diameter, are the surfaces on which water vapor may condense and become liquid. CCN can be a variety of particles, such as dust, salt, or other atmospheric aerosols. When water vapor collides with these particles, it condenses to form cloud droplets. These cloud droplets then accumulate to form what we know as clouds, be they composed of ice or liquid droplets. From cumulus, to stratus, cirrus and even the most abstract and rare forms of clouds, all undergo some form of this general process. Despite variations in some of the processes for different cloud types, all come to be those beautiful, powerful, and lovely formations that dot our skies. To read more about weather and atmospheric phenomena, click here! https://www.globalweatherclimatecenter.com/weather-education © 2020 Weather Forecaster Alexis Clouser  If you live in the United States, you’ve probably noticed that this winter has been unseasonably warm, and that the East Coast hasn’t seen much as much snow as it usually gets this time of the year. According to the National Weather Service (NWS), the overall snowfall for Baltimore, Maryland has been decreasing over the years. The normal snowfall for the area is around 20 inches, but in the past few years there hasn’t been much snowfall. The average high temperature for January 2020 was 48.5°F, and on the 11th and 12th the daily high even reached 70°F! The lowest daily high for the month was only 34°F on the 20th. Most of the month saw a high in the 40s, which is much higher than is the norm for the month.
So, why is this happening? The answer is global warming, the long-term rise in the average temperature of the earth, along with climate change, a change in global or local climate patterns. These changes can be attributed to the increase in fossil fuel burning, which leads to carbon monoxide being released into the atmosphere. Carbon dioxide creates what is known as the greenhouse effect, when heat is prevented from escaping out into space and simply circulates within the atmosphere. Many laws have been put into place within the past few decades to help reduce the effects of climate change, including the Paris Agreement, a regulation in which many countries agreed to reduce carbon monoxide emissions, and the Clean Air Act, an act put into place in 1963 in the United States to reduce air pollution from factories. You, too, can help reduce air pollution that contributes to climate change. Many people have been driving electric or hybrid vehicles, which don’t emit as much carbon monoxide as other cars. Another way to reduce air pollution is to carpool with other people, take public transportation, ride a bike, or simply walk to your destination. This helps reduce the number of vehicles on the road emitting carbon monoxide from the exhaust. ©2020 Weather Forecaster Sarah Cobern To learn more interesting facts about the weather, visit https://www.globalweatherclimatecenter.com/weather-education  The term “bombogenesis” (also referred to as “bomb cyclone”) is a term that many people outside of the meteorology community have seldom heard. The most common time that it will be used is typically during strong Nor’easter events, which are storms that have a strong northeasterly flow that bring large amounts of snow, rain, and damaging wind up the eastern coast. Bombogenesis does not occur very often, but when it does, it’s nerve wracking to forecast for due to the potential damage it can cause. So what is it?
In order to explain what this phenomenon is, there is a need to explain what a mid-latitude cyclone is first. A mid-latitude cyclone is a low pressure system that has a counterclockwise flow (“cyclonic”) in the middle latitudes. They typically form along a polar front and will have a warm front on the eastern side with a cold front on the western side. These typically occur during the cooler months of the year between October and March. With that being said, bombogenesis is when a mid-latitude cyclone drops 24 or more millibars in surface barometric pressure in 24 hours. Basically, bombogenesis is the rapid intensification of a mid-latitude cyclone in a small period of time. When this happens, it can cause the storms that form along the cold front to become increasingly more intense than before, such as raging snow storms in the Northeast, as well as severe thunderstorms on a strong squall line (line of rapidly moving storms along a cold front that result in damaging winds, tornadoes, and heavy rain) to form along the front in the South. These can cause embedded tornadoes within the line itself, which is particularly more dangerous as these types of tornadoes are more likely to be rain-wrapped (where the rain will form a wall around the tornado causing it to be hidden and undetected without radar). Bombogenesis does not happen that frequently during the year, but when it does, it can get dangerous quick for the population that lies ahead of intense cyclone. More often than not, these systems typically become Nor’easters, and cause several inches to even feet of snow to fall over portions of the Northeast over a period of days as it pushes through. On the meteorological aspect of it, bombogenesis is a phenomenon that is exciting to see, but nerve wracking to forecast as some models struggle to agree on timing and severity. As instruments and models advance, these will be better forecasted in the future. For more topics in weather education, be sure to click here! ©2020 Meteorologist Ashley Lennard The main goal of weather forecasting is to provide information to the public so informed life or business decisions can be made. This could range from using sunscreen when going out or getting prepared for severe weather entering the area. To provide this support, forecasters have to look through a myriad of different maps and charts all providing different information to create an effective forecast. Maps can range from satellite imagery, surface pressure maps, or numerical modeling. Forecasters must choose which information is best applicable to the situation involved. For example, an area under a high-pressure system could expect calmer conditions, so looking at an Energy Helicity Index map wouldn't be applicable. To do this, forecasters can use a concept called a forecast tunnel to create a forecast. This process describes how meteorologists can start from the top of the atmosphere to the surface to develop a succinct forecast.
Planetary and Hemispheric scales start this process and this could involve parameters like Rossby Waves. They are on the scale of tens of thousands of kilometers, in respect of size of the system. Afterward, you move to the synoptic-scale which is on the scale of several hundred to several thousand kilometers. This would typically involve features like high and low-pressure systems. Lastly, the smallest scale for the forecast tunnel is mesoscale. These are smaller-scale features on the order of a few to several hundred kilometers. An example of these features would be sea breeze and squall lines. These scales are interconnected and using the forecast tunnel helps forecasters see these features and how they relate dynamically.
Furthermore, it is imperative that meteorologists make forecasts promptly so that the forecast remains relevant to the public. Traditionally, the larger the scale, the fewer time forecasters will spend working on the specific features within that time scale. Planetary scale features are on such a large magnitude that they shouldn’t experience significant changes during a traditional forecast period, so monitoring it should take the least amount of time. Conversely, mesoscale features require more time because the nature of the size scale is smaller. These features are harder to examine if they are going to impact the forecast area and how they will evolve with time. Photo Creds: The Comet Program To learn more about this and other weather educational topics, be sure to click here! ©2020 Weather Forecaster Dakari Anderson  Photo Credit: New York Times
It’s well known that acid rain causes damage to plant and animal life. When acid rain flows through an environment, it can break down aluminum from its surroundings in the soil and carry the metal with it, consequentially, lowering the pH of the water nearby and underground. Both effects can cause a great deal of damage to plant and animal life by making the water intolerable to certain species. Since plants and animals are interconnected by food chains, animals resistant to pH changes are adversely affected when their food supply consumes their own tainted food supply. For example, many plants may die in an area due to acid rain, causing an herbivore that can withstand the pH changes to die as well because its source of food is gone. What’s not as well known is how exactly acid rain originates. Most of it comes from harmful pollutants made by humans, especially those from burning fuel in factories or cars. When fuel is burned, it releases energy as well as byproducts including carbon dioxide (CO2), sulfur dioxide (SO2), and nitrogen oxides (NOx). By observation, one can tell that water mixes well with a lot of compounds. The water in the atmosphere is no exception. When water in the atmosphere meets these byproducts, they can mix and create potentially hazardous compounds such as carbonic acid (H2CO3), sulfuric acid (H2SO4), or even nitric acid (HNO3). While these compounds are greatly distilled by the water, they are still harmful to plant and animal life. Additionally, gases from burning fuels don’t even have to mix with rain to reach the ground. They can sink into the ground in their original forms and stick to objects near the surface, adding to the adverse effects from gas pollutants. Since carbon dioxide is a relatively abundant trace gas in the atmosphere, virtually all rainwater is at least slightly acidic because of the presence of carbonic acid. Thankfully, carbonic acid is a weak acid that doesn’t affect the pH of rainwater to the point of making it harmful. The same could not be said for sulfuric acid or nitric acid. These acids are quite powerful in comparison to carbonic acid. They can cause the pH of water to swing down and create acid rain, which has an average pH of 4.3. For comparison, the pH of pure water is 7 and the pH of regular rain is 5.6. It’s important to note that the pH scale is not linear, but logarithmic. That is, it doesn’t increase and decrease at a constant rate. Instead, it increases and decreases exponentially the farther it gets from the neutral pH of 7. As a result, acid rain is over 10 times more acidic than regular rain on average! What can be done to prevent acid rain or decrease its impact? The primary answer is to decrease the number of harmful byproducts coming from factories, since it’s not possible to get the gases out of the atmosphere once they’re up there. Many factories have methods of extracting harmful products out of their emissions and international treaties exist to limit certain types of emissions from factories. It’s essential for those who wish to decrease the prevalence of acid rain to understand where it comes from so the sources of these pollutants can be targeted and limited. By having a full comprehension of how acid rain is formed people can work towards limiting their harmful impacts. © 2020 Weather Forecaster Cole Bristow  Altocumulous clouds forming a mackerel sky (first photo) and swift cirrus clouds resembling mares tails (second photo) Another beautiful sight for the eyes, Mackerel Skies and Mares Tails are cloud formations that have distinctive patterns and displays of beauty in our atmosphere. These cloud formations are rather common and can hint at inclement weather as they are often seen during specific weather patterns. So, if you see these beautiful cloud formations you will be aware of the weather that is expected to precede.
Characterized by rows of clouds arranged in a pattern of ripples or waves often resembling fish scales, a mackerel sky is quite a crowd pleaser of beautiful sky displays. This type of cloud formation is created by two different types of cloud formations: altocumulus and cirrocumulus clouds. Altocumulus are mid level clouds that are made up of mostly water droplets that form at elevations around 2000 meters to 7000 meters. These clouds are puffy and can be dense at times, blocking out most of the sunlight making the day look almost overcast. Cirrocumulus clouds are higher level clouds. They are mostly made up of ice crystals and take the form of small puffy white tufts. These are not likely to block out most of the sun like altocumulus can. They are rather thin in nature and more scattered. Although these clouds are fair weather clouds, meaning they are often seen during times of calm weather, these clouds most often prelude to unsettled weather. Altocumulus and cirrocumulus clouds are usually an indication of rising air and are seen ahead of a warm front. When warm air rises you can expect moisture to condense into rain. Most of the time when altocumulus clouds are spotted in the morning during a humid summer, pop-up thunderstorms can be expected by late afternoon that same day. Mares tails are characterized by clouds that are long, thin and wispy. They are called mares tails because they resemble the long flowing tails of horses. Cirrus clouds form like this.They are thin, high-level clouds solely made up of ice crystals. They are so high in the atmosphere they are influenced by strong upper level winds called prevailing winds that flow in a specific direction depending on the region. You can also spot these clouds on a clear fair weather day out ahead of a warm front. Sailors used to use clouds as weather predictors during their trips across seas when technology and weather predictions were not as advanced as they are today. Whenever a combination of mackerel skies and mares tails was spotted, it meant that the weather was deteriorating and a low pressure system was on its way. This was typical of these clouds, being ahead of a warm front meant a cold front was to follow. Both warm and cold fronts are associated with low pressure systems that can produce wind, heavy rain and unsettled seas. © 2020 Meteorologist Alex Maynard For more education on the atmosphere click here. Sources: Ahrens, C. Donald., and Robert Henson. Meteorology Today: an Introduction to Weather, Climate, and the Environment. Cengage, 2019. “Cirrocumulus Clouds.” Met Office, www.metoffice.gov.uk/weather/learn-about/weather/types-of-weather/clouds/high-clouds/cirrocumulus. “Clouds Form Due to Weather Fronts.” UCAR Center for Science Education, scied.ucar.edu/cloud-form-weather-fronts. “Weather Lore That's A Bit Fishy.” Farmers' Almanac, 5 Jan. 2020, www.farmersalmanac.com/what-is-a-mackerel-sky-26275.  Crepuscular rays spreading out from behind a cloud One of the most beautiful additions to a sunset, Jacob’s Ladder, also known as crepuscular rays, sunbeams, light shafts or God’s fingers can be seen quite often in the sky. Usually on a cloudy day when the sun peeks through, near twilight, beams of light will flow from the clouds to the ground or spread out into the sky. It delivers a dramatic experience to the onlooker as they gaze at the display of light. Many describe this scene as something out of a bible, as if angels were ascending to heaven from earth on beams of light or that the sun was drawing up water from the ocean. Jacob's Ladder is an optical phenomenon made by sunlight that is scattered by particles of haze or dust in the sky. The dust, tiny water droplets or haze scatters the light making a certain area of the sky appear brighter. Light scattering is when a beam of light hits an object of imperfect shape and gets redirected or reflected back in many different directions. Most of the time, the beams of light scattered from the cloud are a blue or yellow tint. This is due to the type of particle that is scattering the light. Some particles are selective scatterers, meaning that when a beam of light hits them, they tend to absorb certain wavelengths of that light and scatter the other wavelengths. Different colors of light have different wavelengths. For example, reds, yellows and oranges have larger waves then blues, purples and greens. So, if you spot Jacob's ladder, and the beams of light are yellow, you can tell that the particles scattering them are absorbing shorter wavelengths and scattering longer wavelengths of light. The name Jacobs ladder originates from a biblical story about a patriarch that had a dream about a stairway to heaven. Although it has many versions, the story is simplified. During a quarrel with his brother over their birthright to the family inheritance Jacob fled from his brothers rage. During his escape, he stopped for the night and slept on a rock. When he slept he had a dream about a ladder or stairway to heaven shrouded in golden light where he saw God at the top and angels ascending it from earth. It's easy to see where this optical phenomenon may resemble the description in Jacobs dream. Most of the time, crepuscular rays that shine down and touch the earth are so golden and breathtaking that they look as if they are coming from the open doors of heaven. © 2020 Meteorologist Alex Maynard For more information about the atmosphere, click here. Sources: Ahrens, C. Donald., and Robert Henson. Meteorology Today: an Introduction to Weather, Climate, and the Environment. Cengage, 2019. Ancient-Origins. “Stairway to Heaven: The Story of Jacob's Ladder.” Ancient Origins, Ancient Origins, www.ancient-origins.net/myths-legends-europe/stairway-heaven-story-jacobs-ladder-006173. Baker, Jess. “Science Behind the Optical Illusion of Crepuscular Rays (PHOTOS).” The Weather Channel, The Weather Channel, 4 Aug. 2015, weather.com/news/news/fingers-of-god-crepuscular-rays-20130220.  Many of us see weather forecasts and hear the terms “European models” and “American models” within them. But do we know what the difference is between these models and what they both mean? The main differences between the two models involve accuracy and time frame of predictions; however, both are global models.
The American model, also known as the Global Forecast System model (GFS), is operated by the National Weather Service (NWS). Forecasts are produced four 4 times a day, and can predict up to 16 days in advance. The computing power used to create these models can process eight 8 quadrillion calculations every second. According to the National Oceanic and Atmospheric Association (NOAA), the computer that runs these calculations is in the top 30 fastest computers in the world. The European model, known as the European Center for Medium-Range Weather Forecasts (ECMWF), is more powerful than the American model, and generally a better model. The main reasoning for this is the organization and processing of the data, as well as the power of the supercomputer itself. In fact, the European model was able to accurately predict when Hurricane Sandy would turn into the northeastern section of the United States before the American model could. While the American model can predict up to 16 days in advance, the European model can only predict up to 10 days in advance. Although the time frame is shorter, 10 days is typically seen as the “practical limit” of forecasting, and thus is more accurate than the American model. Forecasts are only so reliable, and the farther in advance one wants to forecast, the less accurate a forecast becomes. ©2020 Weather Forecaster Sarah Cobern To learn more about weather forecasting, visit https://www.globalweatherclimatecenter.com/weather-education |
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