Mississippi State University Weather

Meteorological vs. Astronomical Winter

Astronomical winter starts on December 21st, but for meteorologists, it started on December 1st. Seasons for meteorologists and climatologists are grouped into time periods of three months. This is based on the annual temperature cycle as well as the calendar. For example, meteorological winter lasts from the beginning of December through the end of February. Seasons are grouped this way because it would be more accurate for weather observations, forecasting purposes, and recording climatological data (NCDC, 2013). Meteorological seasons also have a more consistent length. During a non-leap year, fall and winter are approximately 90 days, whereas spring and summer are about 92 days. The consistency of the climatological records since meteorological seasons first started taking place in the mid-1900s have helped with many industries across the United States, such as agriculture and commerce. According to the National Climatic Data Center, the natural rotation of the Earth revolving around the Sun forms the astronomical calendar and its seasons (2013). The seasons can last anywhere from 89-93 days, depending on the Earth’s rotation. The astronomical calendar has two solstices and two equinoxes. The solstices, which occur in winter and summer, note when the Earth’s equator is farthest from the Sun. The equinoxes, which occur in spring and autumn, note when the Sun is directly over the Earth’s equator. For example, the winter solstice in the Northern Hemisphere is when the Sun’s path is the farthest North it can be from the Earth’s equator (NCDC, 2013). However, the astronomical seasons are opposite in the Southern Hemisphere. When it is winter in the United States, it is summer in Australia. The astronomical seasons also determine the length of day. For example, because the Northern Hemisphere and the Sun are so far apart during the Winter Solstice, the length of days near the middle of December are much shorter. In addition, the annual temperature cycle is based off of the astronomical seasons; because of this, meteorological winter and astronomical winter are usually separated by about three weeks.  ~ Scott Sincoff _________________________________________________________________ Works Cited: National Climatic Data Center, 2013: Meteorological Versus Astronomical Summer—What’s       the Difference?. National Climatic Data Center. National Oceanic and Atmospheric       Administration. Web. https://www.ncdc.noaa.gov/news/meteorological-versus-      astronomical- ...

Weather Radar: How Does It Work?

Doppler radar is one of the most important tools a meteorologist uses to determine what is happening in real-time where he or she is forecasting. Most people are familiar with the green, yellow, and red pictures that radar generates because they see them on TV, but radar actually gives a meteorologist more information about the atmosphere than a simple image of rain. Image Credit: Hong Kong Observatory http://www.hko.gov.hk/wservice/tsheet/radmet1.jpg   A radar sends out a beam of radiation into the atmosphere. If there is rain falling, the radiation hits that rain and bounces back to the radar. Depending on how much energy is reflected back to the radar and how fast that radiation is bounced back, we can determine where and how heavy the rain is. Image Created Using Gibson Ridge Software The radar then sends this information through a computer that gives us the pretty green, yellow and red maps you see on TV when we are tracking storms and rain. Typically, the heavier the rain, the warmer the color. So, green usually means light rain, yellow means moderate rain, and red means heavy rain or hail. Radars can also measure winds, but that is a bit more difficult to interpret. A radar uses the same physical principles that explain why an ambulance siren sounds higher pitched as it is moving towards you and lower pitched as it moves away to measure winds inside of thunderstorms. By determining the frequency of the radiation reflected back to the radar site, the radar can determine whether the rain is moving towards or away from the radar, and how fast. From this information, a meteorologist can infer wind speed and direction inside a storm. Image Created Using Gibson Ridge Software This is the image a meteorologist would look at to determine wind speed and direction inside a thunderstorm. The green colors indicate winds moving towards the radar, and the red colors indicate winds moving away from the radar. The brighter the color is, the faster the winds are. That yellow box is a Severe Thunderstorm Warning that was issued because meteorologists used this image to estimate the storm was producing winds of 60 miles per hour. One...

A Crash Course in El Niño

1. Introduction Perhaps you have recently heard about the climate teleconnection referred to as “El Niño”. It has been making headlines throughout the course of 2015. According to the Australian Bureau of Meteorology (ENSO Tracker), El Niño conditions have been present since May 12th, 2015.   Since being declared, it seems at times as if El Niño could be responsible for or linked in some way to any number of observed weather events. Why did it rain so much in South Carolina? El Niño. Why was there flooding earlier this year in Texas & Oklahoma? El Niño. Can you explain how the drought developed in Mississippi and Alabama late this summer? Sure, El Niño. Why are the tropics so quiet? El Niño. Joaquín? El Niño. Perhaps you would like to know more about what El Niño is and gain better understanding of how it can impact our everyday lives. You are in good luck, because I hope to answer those questions in this post. Before delving straight into the impacts of El Niño, we need to make sure that we are aware of and understand a few things first. 2.The Southern Oscillation Index (SOI) In order to more fully understand El Niño, you have to first grasp the fact that it is just one of many climate patterns embedded within other more encompassing climate patterns. In the case of El Niño, the larger more encompassing pattern is known as the Southern Oscillation Index (SOI).  The SOI in simplest terms is the measure of the pressure differences between the Island nation of Tahiti and Darwin, Australia. Now why would anyone care about these pressures differences? They serve as a general measure for the intensity of the Walker Circulation which I will discuss more momentarily. The SOI consists of three distinguishable phases: La Niña, Neutral and El Niño. For the purposes of this post, I will only cover the latter two. 3.The “Neutral Phase” Before you run, you walk, before you walk you crawl. It also true that before you can fully understand something that is abnormal (El Niño), you must understand the “normal” relationship between the atmosphere and ocean. In the neutral state (neither El Niño...

What’s that term, Virga?

Have you ever read or hear the term “Virga”? Maybe you have looked at radar seeing shades of light green, but there is no rain? “Virga” meaning “branch” or “twig” in Latin is precipitation falling from clouds and evaporating before it hits the surface. Cool right? Virga often looks like streaks in the sky or shafts under a cloud base. Virga can happen when low humidity and high temperatures make precipitation evaporate before it hits the surface. This process mainly takes place in Canada, the Middle East, Australia, at high altitudes, and in desert areas around the globe. You can also catch a glimpse of virga in western parts of the United States where clouds produce lightning, thunder, and no measurable rainfall at the surface. In the winter, virga can happen when rain or light snow is spotted in the sky and the surface is drier than aloft. It can also happen before a microburst thunderstorm.  Virga is pretty rare in the southeast so if you happen to catch a glimpse of the awesome streaks in the sky – make sure to take a photo. ~Meagan Massey       Photo 1 Citation: Jensen, Susan. Virga in Washington. 2015. EarthSky. Web. <http://earthsky.org/earth/virga-is-rain-that-doesnt-reach-the-ground>. Photo 2 Citation: Ratliff, Ron. Virga in Utah. 2015. Mexican Hat. EarthSky. Web. <http://earthsky.org/earth/virga-is-rain-that-doesnt-reach-the-ground>....

Painting the Sky: The Northern Lights

The Northern Lights are a natural phenomenon that occurs at high latitudes around the Earth’s poles, however earlier this week the beautiful light show was on display in parts of the United States. This is an extremely rare occurrence for us in the continental United States, but portions of the Northeast and Midwest were able to experience this magnificent event Monday and Tuesday nights. The lights were driven south to lower latitudes all due to mass solar eruptions that triggered a geomagnetic storm. With the timeliness of this spectacular event, what better topic to explore in this week’s blog than the Northern Lights!  What are the Northern Lights? This mystifying natural phenomenon is also known as Aurora Borealis. The Northern Lights mainly occurs at the poles in both the Northern and Southern hemispheres. Collisions between electrically charged particles cause the sky to illuminate in an array of colors. The lights can extend 50 to 400 miles above the surface and take many forms, such as scattered clouds of light, arcs, or shooting rays. Image Credit: NASA Aurora Image Gallery https://www.nasa.gov/mission_pages/sunearth/aurora-image-gallery/index.html What Causes this Phenomenon? The basic explanation for the Northern Lights is the collision between particles in the atmosphere and particles from the sun, but lets dive into a little more detail. This process originates 93 million miles away, when storms on the sun cause gusts of charged solar particles to be released into space. These particles are blown towards Earth by the solar winds and are mainly deflected by the Earth’s magnetic field. Keep in mind, the magnetic field is weaker at the poles, so at this location some particles are able to enter the Earth’s atmosphere. The positive charged particles (electrons) from the sun collide with gaseous particles within the upper level of the atmosphere, causing the particles to become ‘excited’.  Finally, as the molecules return to their original state, they emit photons, or small bursts of energy in the form of light. Image Credit: EarthSky via NASA What Causes Different Colors? Variations in color are due to the type of gas particles, Oxygen or Nitrogen, that collide with the particles from the sun as well as the altitude at which they collide....

Scattering 101

The Colorful Atmosphere As a lover of all things weather, one weather phenomenon in particular (that I love) are the clouds and beautiful blue skies that we see here in Mississippi on clear, calm days. Many people may wonder why the sky is blue. Why not, red, or green? It is a simple, yet complex idea dealing with a term called scattering. Keep in mind that the human eye can only see a small portion of what the sun is giving off from the electromagnetic spectrum. Our eyes can only see the visual part of that spectrum and with that comes different wavelengths represented by a multitude of colors. When the sun comes up every morning, the incoming solar radiation is in reach with Earth’s atmosphere, it is scattered in all different directions. Blue wavelengths are scattered much more efficiently and they are shorter which is why the sky looks blue. Science Made Simple. Digital image. N.p., n.d. Web. 29 Oct. 2015. <Http://www.sciencemadesimple.com/img_sky/horiz.jpg>. Now there are two terms to define more specifically that help to explain why the sky is blue and why the clouds are white; Rayleigh scattering and Mie scattering. As discussed earlier, the sky appears blue because of the sunlight that is reflected off of different molecules. Rayleigh scattering better defines this idea because the scattering of light off of the molecules of the air gives us the blue sky. For Mie scattering, it does not necessarily depend upon the wavelength but it gives off the white glare that we see around the sun when a lot of particles are in the air. Rayleigh scattering is the more dominant of the two because of its favor towards shorter wavelengths. The water droplets that make up the cloud are much larger than the parcels in the air and they do not depend on wavelength, so they are overshadowed by the blue wavelength leaving them with a white-grayish tint. The Natural Environment. Digital image. N.p., n.d. Web. 29 Oct. 2015. <https://laulima.hawaii.edu/access/content/group/2c084cc1-8f08-442b-80e8-ed89faa22c33/book/chapter_2/scatter.htm>. Sunrise & Sunset For sunrises and sunsets, this concept is a little different. Starkville is known for its beautiful sunsets and sunrises, almost everyone has either put a picture on Twitter or...