Posted on by Tega Jessa

What is a Warm Front?

Warm Front
What is a Warm Front

[/caption]A warm front is the transition zone that marks where a warm air mass starts replacing a cold air mass. Warm fronts tend to move from southwest to southeast. Normally the air behind a warm front is warmer than the air in front of it. Normally when a warm front passes through an area the air will get warmer and more humid. Warm fronts signal significant changes in the weather. Here are some of the weather signs that appear as a warm front passes over a region.

First before the warm front arrives the pressure in area start to steadily decrease and temperatures remain cool. The winds tend to blow south to southeast in the northern hemisphere and north to northeast in the southern hemisphere. The precipitation is normally rain, sleet, or snow. Common cloud types that appear would various types of stratus, cumulus, and nimbus clouds. The dew point also rises steadily

While the front is passing through a region temperatures start to warm rapidly. The atmospheric pressure in the area that was dropping starts to level off. The winds become variable and precipitation turns into a light drizzle. Clouds are mostly stratus type clouds formations. The dew point then starts to level off.

After the warm front passes conditions completely reverse. The atmospheric pressure rises slightly before falling. The temperatures are warmer then they level off. The winds in the northern hemisphere blow south-southwest in the northern hemisphere and north-northwest in the southern hemisphere. Cloudy conditions start to clear with only cumulonimbus and stratus clouds. The dew point rises then levels off.

Knowing about how warm fronts work gives a better understanding of how pressure systems interact with geography to create weather. Looking at warm fronts we learn that they are the transition zone between warm humid air masses and cool, dry air masses. We know that these masses interact in a cycle of rising and falling air that alters the pressure of atmosphere causing changes in weather.

We have written many articles about warm front for Universe Today. Here’s an article about cyclones, and here’s an article about cloud formations.

If you’d like more info on warm front, check out NOAA National Weather Service. And here’s a link to NASA’s Earth Observatory.

We’ve also recorded an episode of Astronomy Cast all about planet Earth. Listen here, Episode 51: Earth.

Reference:
http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/af/frnts/wfrnt/def.rxml

Posted on by Tega Jessa

How Does Fog Form?

How Does Fog Form
San Francisco Fog. Image Credit: Wikimedia User, Mila Zinkova

Fog is a natural weather conditions that can cause visibility to become zero. It can cause accidents on normally safe roads and is such a serious weather condition that schools delay the start of the day until the sun burns it off. So how does fog form? First it is important to understand that fog is basically a cloud on the ground. This means like clouds it is a collection of tiny water droplets formed when evaporated water is cooled. The way it is cooled determines how fog is formed.

The first way that fog is formed is by infrared cooling. Infrared cooling happens due to the change of seasons from summer to fall and winter. During the summer the ground absorbs solar radiation. As air passes over it is made warm and moist. When the seasons change this mass of warm moist air collides with the cooler that is now prevalent. This cause is the water vapor in the air mass to condense quickly and fog is formed. This fog is often called radiation fog due to the way it forms. This kind is the most common type of fog. It also happens when an unseasonable day of warm weather combined with high humidity is followed by dropping temperatures

The next way that fog forms is through advection. Advection is wind driven fog formation. In this case warm air is pushed by winds across a cool surface where it condenses into fog. There are also other kinds of fog like hail fog or freezing fog. Each of these conditions is where condensed water droplets are cooled to the point of freezing. There is also fog formed over bodies of water. One type is sea smoke. This is a type of fog that forms when cool air passes over a warm body of water or moist land.

In general we see that fog is formed whenever there is a temperature difference between the ground and the air. When the humidity is high enough and there is enough water vapor or moisture fog is sure to form. However the kind of fog and how long is last and its effects will depends on the different conditions mentioned. One interesting kind of fog actually helps to make snow melt faster.

We have written many related articles for Universe Today. Here’s an article about stratus clouds, and here’s an article about acid rain.

If you’d like more info on fog, check out NOAA National Weather Service website. And here’s a link to NASA’s Earth Observatory.

We’ve also recorded an episode of Astronomy Cast all about planet Earth. Listen here, Episode 51: Earth.

Reference:
http://www.crh.noaa.gov/jkl/?n=fog_types

Posted on by Jerry Coffey

What Causes Wind?

Oxygen is a valuable biosignature because Earth is oxygen-rich, and because life made all that oxygen. But if we find oxygen in an exoplanet atmosphere does that mean life made it? Or is there an abiotic source of oxygen? Image Credit: NASA

It was not until recent memory that what causes wind was understood. Wind is caused by air flowing from high pressure to low pressure. The Earth’s rotation prevents that flow from being direct, but deflects it side to side(right in the Northern Hemisphere and left in the Southern), so wind flows around the high and low pressure areas. This movement around is important for very large and long-lived pressure systems. For small, short-lived systems (outflow of a thunderstorm) the wind will flow directly from high pressure to low pressure.

The closer the high and low pressure areas are together, the stronger the pressure gradient, so the winds are stronger. On weather maps, lines of constant pressure are drawn(isobars). These isobars are usually labeled with their pressure value in millibars (mb). The closer these lines are together, the stronger the wind. The curvature of the isobars is also important to the wind speed. Given the same pressure gradient (isobar spacing), if the isobars are curved anticyclonically (around the high pressure ) the wind will be stronger. If the isobars are curved cyclonically (around the low pressure) the wind will be weaker.

Friction from the ground slows the wind down. During the day convective mixing minimizes this effect, but at night(when convective mixing has stopped) the surface wind can slow considerably, or even stop altogether.

Wind is one way that the atmosphere moves excess heat around. Directly and indirectly, wind forms for the primary purpose of helping to transport excess heat in one of two ways: away from the surface of the Earth or from warm regions(tropics) to cooler regions. This is done by extratropical cyclones, monsoons, trade winds, and hurricanes. Now, you have the answer to what causes wind and its primary function on our planet.

We have written many articles about the wind for Universe Today. Here’s an article about wind energy, and here’s an article about how wind power works.

If you’d like more info on wind, check out Visible Earth Homepage. And here’s a link to NASA’s Earth Observatory.

We’ve also recorded an episode of Astronomy Cast all about planet Earth. Listen here, Episode 51: Earth.

Posted on by Tega Jessa

Where is the Ozone Layer Located

Ozone layer hole. Image credit: NASA
Ozone layer hole. Image credit: NASA

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The Ozone Layer is the portion of the atmosphere that contains high levels of the oxygen molecule ozone. This molecule plays an important role acting as a natural UV shield for the Earth. You may wonder where is the ozone layer located to play such a vital role so effectively. The Ozone layer is actually located in the stratosphere in a region that is 10 to 50 km above the Earth.

So why is the Ozone layer so important? As mention before the secret lies in oxygen molecules. Normal oxygen in its natural molecular state is made up of only two atoms. However this changes when oxygen in the thermosphere is exposed the Sun’s ultraviolet rays. The rays separate oxygen molecules the free oxygen joins with the remaining two atom oxygen molecules to create ozone. This process might seem simple but it helps to screen out 99.5 percent of the ultraviolet radiation that the Sun sends towards earth. The times that the ozone layer didn’t screen out this type of radiation at such levels life was almost wiped out according to the geologic record.

You might think that this is an exaggeration until you observe the biological damage UV rays can do. We have already seen the harm caused when people don’t take the proper precautions when going to the beach. The least harm comes in the form of sun burn. People overexposed to the UV rays that do make it to earth have their skin damaged by the UV energy that penetrates their skin. However it gets more serious the longer a person is exposed to UV rays. The reason is because the damage gets to the cellular level causing cancers and genetic damage. Essentially it’s like being exposed to a nuclear reactor in melt down. The high energy radiation over time would accumulate harm in living tissue until it killed the organism exposed to it.

Despite its importance industry produced and released chemicals into the air that interfered with the ozone cycle. The main problem chemical CFC’s prevented oxygen molecules from complete the bonding process that is important for the completion of the ozone cycle this caused a major depletion of ozone in key areas of the Earth’s atmosphere. This is huge when the natural concentration of ozone was already quite low. This just goes to show the delicate balance that was upset. Fortunately nations upon hearing the harm caused started bans on CFC’s while industry tried to find alternatives to use in products. The result started to show with ozone depletion actually slowing down and reversing with scientist predicting recovery within the next century.

We have written many articles about the ozone layer for Universe Today. Here’s an article about the depletion of the ozone layer, and here’s an article about the ozone layer.

If you’d like more info on Earth, check out NASA’s Solar System Exploration Guide on Earth. And here’s a link to NASA’s Earth Observatory.

We’ve also recorded an episode of Astronomy Cast all about planet Earth. Listen here, Episode 51: Earth.

Posted on by Tega Jessa

What Color is the Sky

Space Travel
Atlantis Breaks Through the Clouds

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If you are a parent or are old enough to babysit younger relatives there is one question children ask that stumps most adults. It’s what color is the sky or why is the sky blue. This article will tell you why and do it in as simple a way as possible so that the next time a kids ask the question you have a good answer.

To understand why the sky is blue you need to remember how color works. Color is largely caused by how well an object absorbs the light spectrum. When you see a blue sky you only see blue because all the other colors were absorbed in the air. Any object with color works that way. For example a red ball is read because all the colors of light are absorbed by the ball except for red. This reflected light is what gives the object color.

This is what happens with the sky. The atmosphere is denser than we imagine and the different gases give the atmosphere unique properties in how it absorbs, diffuses, and reflects light. When sunlight passes through our atmosphere a portion of it is scattered and absorbed. The remainder either reaches the surface or is reflected back. The portion that makes it to us observers is 75 percent.

This process is called diffused sky radiation. So to review, we color because objects due to texture of dyes and surfaces absorb all light wavelengths and reflect back one or more. The reason we see the sky as blue is because the molecules in the air scatter the light absorbing most wavelengths of light except for blue.

In addition to this the sky is gray and overcast because of the water droplets in the atmosphere in the forms of clouds and humidity. water refracts light equally unlike air molecules in the atmosphere. This means we get the entirety of white light only it is dimmer just like when you shine a light through a white sheet.

The fact we see a blue sky is good thing because its shows that are atmosphere is at work shielding us from the full energy of the sun’s rays. While the sun is the largest source of energy to our planet, a lot of its high energy radiation that is deadly for living things. Our atmosphere plays it part by shielding us from that. So when you see a blue sky with your kid you can tell them it means the sky is acting like a huge shade blocking out the bad parts of the sun.

We have written many articles about the earth’s sky for Universe Today. Here’s an article about why the sky is blue, and here’s an article about how to find Venus in the sky.

If you’d like more info on the earth’s sky, check out an article about Strange Clouds. And here’s a link to NASA Space Place Article on Blue Sky.

We’ve also recorded an episode of Astronomy Cast all about Sky Survey. Listen here, Episode 118: Sky Surveys.

Posted on by Jerry Coffey

What Is Atmospheric Pressure

Thermosphere
The Moon viewed from Earth's thermosphere. Credit: NASA

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Just answering the question ‘what is atmospheric pressure?’ is not enough to give a full understanding of its importance. By definition atmospheric pressure is ‘force per unit area exerted against a surface by the weight of air above that surface’. Atmospheric pressure is closely related to the hydrostatic pressure caused by the weight of air above the measurement point. The term standard atmosphere is used to express the pressure in a system(hydraulics and pneumatics) and is equal to 101.325 kPa. Other equivalent units are 760 mmHg and 1013.25 millibars.

Mean sea level pressure (MSLP) is the pressure at sea level. This is the pressure normally given in weather reports. When home barometers are set to match local weather reports, they will measure pressure reduced to sea level, not your local atmospheric pressure. The reduction to sea level means that the normal range of fluctuations in pressure are the same for everyone.

Atmospheric pressure is important in altimeter settings for flight. A altimeter can be set for QNH or QFE. Both are a method of reducing atmospheric pressure to sea level, but they differ slightly. QNH will get the altimeter to show elevation at the airfield and altitude above the air field. QFE will set the altimeter to read zero for reference when at a particular airfield. QNH is transmitted around the world in millibars, except in the United States and Canada . These two countries use inches (or hundredths of an inch) of mercury.

Atmospheric pressure is often measured with a mercury barometer; however, since mercury is not a substance that humans commonly come in contact with, water often provides a more intuitive way to visualize the pressure of one atmosphere. One atmosphere is the amount of pressure that can lift water approximately 10.3m. A diver who is 10.3m underwater experiences a pressure of about 2 atmospheres (1of air plus 1of water). Low pressures like natural gas lines can be expressed in inches of water(w.c). A typical home gas appliance is rated for a maximum of 14 w.c.(about 0.034 atmosphere).

You can see that understanding ‘what is atmospheric pressure’ is just the tip of the iceberg. Once you have the definition in mind, it really comes together when you see the wide variety of applications.

We have written many articles about atmospheric pressure for Universe Today. Here’s an article about atmospheric pressure, and here’s an article about air pressure.

If you’d like more info on the Atmospheric Pressure, check out NASA’s Discussion Video on Atmospheric Pressure, and here’s a link to How Atmospheric Pressure Affects the Weather?

We’ve also recorded an entire episode of Astronomy Cast all about the Atmospheric Pressure. Listen here, Episode 151: Atmospheres.

Posted on by Nancy Atkinson

Man-Made Aurora Will Help to Better Predict Space Weather

Northern Lights
The Aurora Borealis seen in Alaska.

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New experiments that create a man-made aurora are helping researchers better understand how nitrogen in our atmosphere reacts when it is bombarded by the solar wind. Scientists from the Jet Propulsion Laboratory fired electrons of differing energies through a cloud of nitrogen gas to measure the ultraviolet light emitted by this collision, and the findings show our previous understanding of the processes that create the aurorae – which can also adversely affect orbiting satellites– may have been in error.

For more than 25 years, our understanding of terrestrial space weather has been partly based on incorrect assumptions about how nitrogen — the most abundant gas in our atmosphere –reacts when it collides with electrons produced by energetic ultraviolet sunlight and solar wind.

The new research has found that well-trusted measurements published in a 1985 journal paper by researchers Ajello and Shemansky contain a significant experimental error, putting decades of space weather findings dependent on this work on unstable ground.

New technology has allowed the researchers to better create and control the collisions and avoid the analytical pitfalls that plagued the 1985 findings.

The new results from the team at JPL suggest that the intensity of a broad band of ultraviolet light emitted from the collision changes significantly less with bombarding electron energies than previously thought.

The researchers studied ultraviolet light within the so called ‘Lyman-Birge-Hopfield’ (LBH) band to better understand the physical and chemical processes occurring in our upper atmosphere and in near-Earth space.

“Our measurement of LBH energy-dependence differs significantly from widely accepted results published 25 years ago,” said Dr. Charles Patrick Malone from JPL. “Aeronomers can now turn the experiment around and apply it to atmospheric studies and determine what kind of collisions produce the observed light.”

In addition to helping researchers to better understand space weather, which can help protecting the ever-growing population of satellites in Earth orbit, the new findings will also help further our understanding of phenomena like Aurora Borealis (the Northern Lights) and similarly the Aurora Australis (Southern Lights), which are caused by collisional processes involving solar wind particles exciting terrestrial oxygen and nitrogen particles at the North and South Pole.

The researchers are hopeful that their findings will also assist the Cassini project understand happenings on Saturn’s largest moon, Titan, as LBH emissions have been detected by the orbiting robotic spacecraft.

The research was published in IOP Publishing’s Journal of Physics B: Atomic, Molecular and Optical Physics.

Posted on by Tega Jessa

What was the Largest Tornado Ever Recorded?

Determining the biggest tornado can be a tricky endeavor. First of all, there is no direct absolute way to measure the width of a tornado. There is also the fact that a tornado can be ranked by many factors such as wind speed, level of destruction caused, drop in barometric pressure, or the length of travel path. Each of these play a role in determining the overall power of a tornado.

Another problem is that in many cases like in the Tornado Alley of the Midwestern United States, a storm system often produces multiple tornadoes. This can make it difficult to measure an individual tornado since it destructive force is combined with that of other tornadoes spawned by the same storm system.

While there is no definitive method there are some records that can give us a general idea about some of the greatest tornadoes in recorded history. The most powerful tornadoes tend to be in the United States, but there are others that can compete in other parts of the world.

The title of most devastating tornado goes to the Tri-State tornado of 1925. The twister traveled through three states and killed 698 people. This makes it the deadliest tornado in US history. It also had the longest track and duration traveling a distance of over 200 miles and lasting 3.5 hours. Even then this is just for the United States. The deadliest tornado in the world occurred in 1989 in Bangladesh taking over 1300 lives.

The closest measure to the Biggest tornado would be the widest damage path. This the with of the destruction a tornado causes not it actual size. This measure is a good estimate for the actual width of the tornado’s funnel cloud. The storm that holds the record occurred in Wilber-Halland Nebraska. The tornado had a destruction path with a width of over two miles. The tornado destroyed most of the buildings in the area.

As you can see you define the largest tornado by many factors. This just shows the various ways in which we as casual observers can measure and determine the power of a tornado. This provides an interesting insight into what makes a tornado so destructive and hard to predict. It is also important to remember once again that tornadoes rarely occur as singular phenomenons. A group of smaller tornadoes in an outbreak can be as effectively powerful and destructive as one major tornado.

If you enjoyed this article there are other pieces on Universe Today that you will loved to read. There is an interesting article about the winds on Venus. There is also another interesting article on Global warming.

You can also check out resources online. There is a great article about Tornadoes on National Oceanic and Atmospheric Administration website There is another interesting piece on tornadoes on the University Corporation for Atmospheric Research website.

You can also check out Astronomy Cast. Episode 151 talks about atmospheres.

Posted on by John Carl Villanueva

Gases In The Atmosphere

Atmosphere layers. Image credit: NASA
Atmosphere layers. Image credit: NASA

[/caption]There are different gases in the atmosphere. There’s nitrogen (the most abundant of them all), oxygen, and argon. There are of course a lot more but they’re no more than 1% of the entire atmosphere.

Among the minority are the greenhouse gases, carbon dioxide being the most prominent of them all. These gases are presently cast as harmful to the planet, being the primary cause of global warming. Of course, they’re only harmful because they’ve exceeded their ideal levels. Anything that comes in excess is not good, right?

At ideal levels, greenhouse gases play an important role in keeping our planet warm enough for us and other organisms to live comfortably. Unfortunately, the rapid rate of industrialization has caused greenhouse gases to accumulate, forming a layer too thick for infrared radiation (which originally came in from the Sun as solar radiation) to escape.

The different gases in the atmosphere actually make up five principal layers. Starting from the lowest layer, there’s the Troposphere, followed by Stratosphere, then the Mesosphere, then Thermosphere, and finally the Exosphere.

The peak of Mount Everest, high as it is, is still part of the Troposphere. The Stratosphere is the layer at which most weather balloons fly. The Mesosphere is where meteors mostly ignite. The Thermosphere is where the International Space Station orbits.

Since the Karman line (which serves as the boundary between the Earth’s immediate atmosphere and outer space) is found in the lower region of the Thermosphere, much of this layer of gases in the atmosphere is considered outer space. Finally, the exosphere, being the outermost layer, is where you can find the lightest gases: hydrogen and helium.

Many properties of the gases in the atmosphere are dependent on the altitude at which they are found. For instance, average density of these gases generally decrease as one rises to higher altitudes. As a result, the pressure (being due to the collisions of the particles that make up the gas) also decreases in the same manner.

Since the force of gravity pulls down on the masses of these gases, the heavier gases are typically found near the surface of the Earth while the lightest ones (e.g. hydrogen and helium) are found in higher altitudes. All these properties are just generalizations though. Temperature and fluid dynamics also influence these properties.

Want to learn more about the atmosphere and air pressure? You can read about both here in Universe Today.

Of course, you can find more info at NASA too. Follow these links:
Earth’s Atmosphere
Earth

Tired eyes? We recommend you let your ears do the work for a change. Here are some episodes from Astronomy Cast:
Atmospheres
Plate Tectonics

Posted on by Nancy Atkinson

Earth’s Upper Atmosphere is Cooling

New measurements from a NASA satellite show a dramatic cooling in the upper atmosphere that correlates with the declining activity of the current solar cycle. For the first time, researchers can show a timely link between the Sun and the climate of Earth’s thermosphere, the region above 100 km, an essential step in making accurate predictions of climate change in the high atmosphere. This finding also correlates with a fundamental prediction of climate change theory that says the upper atmosphere will cool in response to increasing carbon dioxide.

Earth’s thermosphere and mesosphere have been the least explored regions of the atmosphere, in fact some have called it the “ignorosphere.” The NASA Thermosphere-Ionosphere-Mesosphere Energetics and Dynamics (TIMED) mission was developed to explore the Earth’s atmosphere above 60 km altitude and was launched in December 2001. One of four instruments on the TIMED mission, the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument, was specifically designed to measure the energy budget of the mesosphere and lower thermosphere. The SABER dataset now covers eight years of data and has already provided some basic insight into the heat budget of the thermosphere on a variety of timescales.

The extent of current solar minimum conditions has created a unique situation for recent SABER datasets. The end of solar cycle 23 has offered an opportunity to study the radiative cooling in the thermosphere under exceptionally quiescent conditions.

“The Sun is in a very unusual period,” said Marty Mlynczak, SABER associate principal investigator and senior research scientist at NASA Langley. “The Earth’s thermosphere is responding remarkably — up to an order of magnitude decrease in infrared emission/radiative cooling by some molecules.”

The TIMED measurements show a decrease in the amount of ultraviolet radiation emitted by the Sun. In addition, the amount of infrared radiation emitted from the upper atmosphere by nitric oxide molecules has decreased by nearly a factor of 10 since early 2002. These observations imply that the upper atmosphere has cooled substantially since then. The research team expects the atmosphere to heat up again as solar activity starts to pick up in the next year.

While this warming has no implications for climate change in the troposphere, a fundamental prediction of climate change theory is that the upper atmosphere will cool in response to increasing carbon dioxide. Emissions of carbon dioxide may warm the lower atmosphere, but they cool the upper atmosphere, because of the density of the atmospheric layer.

As the atmosphere cools the density will increase, which ultimately may impact satellite operations through increased drag over time.

The SABER dataset is the first global, long-term, and continuous record of the Nitric oxide (NO) and Carbon dioxide (CO2) emissions from the thermosphere.

“We suggest that the dataset of radiative cooling of the thermosphere by NO and CO2 constitutes a first climate data record for the thermosphere,” says Mlynczak.

The TIMED data provide a fundamental climate data record for validation of upper atmosphere climate models which is an essential step in making accurate predictions of climate change in the high atmosphere. SABER provides the first long-term measurements of natural variability in key terms of the upper atmosphere climate. As the TIMED mission continues, these data derived from SABER will become important in assessing long term changes due to the increase of carbon dioxide in the atmosphere.

The findings were presented at the American Geophysical Union fall meeting in San Francisco.

Source: NASA Langley