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Radiosondes
Radiosondes
Since the weather we experience is due to dynamic processes that take place throughout the atmosphere, we need to know what is taking place through the entire atmosphere. These observations are primarily taken with the aid of radiosondes.The radiosonde is a small, expendable instrument package that is suspended below balloon filled with either hydrogen or helium. As the radiosonde rises, sensors on the radiosonde measure values of pressure, temperature, and relative humidity.
These sensors are linked to a battery powered radio transmitter that sends the sensor measurements to a ground receiver. By tracking the position of the radiosonde in flight via GPS (global positioning system), information on wind speed and direction aloft is also obtained.
Worldwide, most radiosonde observations are taken at 00Z and 12Z daily (What is ‘Z’ time?). With worldwide coordination of these upper air observations we can get a good picture of the various pressure and wind patterns across the globe. For the United States mainland observation sites, the local times for these observations are centered around 6 AM and 6 PM daily.
Technically, a radiosonde observation provides onlypressure, temperature, and relative humidity data. When the position of a radiosonde is tracked (so that wind speed and direction can be determined) it is called a rawinsonde observation.Most stations around the world take rawinsonde observations. However, meteorologists and other data users frequently refer to a rawinsonde observation as a radiosonde observation.
The radiosonde flight can last in excess of two hours, and during this time the radiosonde can ascend to over 115,000 feet (35,000 m) and drift more than 125 miles (200 km) from the release point. During the flight, the radiosonde is exposed to temperatures as cold as -130°F (-92°C) and air pressure of only a few hundredths of what is found on the Earth’s surface.
When the balloon has expanded beyond its elastic limit (about 20 feet in diameter) and bursts, the radiosonde returns to Earth via a small parachute. This slows its descent, minimizing the danger to life and property.
If found, radiosondes can be reconditioned and used again saving the taxpayer some money. If you find a fallen NWSradiosonde, it is safe to handle. Cut the string to the burst balloon and place it in a trash receptacle.
Next, remove the plastic mailbag attached to the handle of the radiosonde and place the instrument inside the bag. Hand the package to your postal carrier. Postage is prepaid if the instrument is returned in the United States.Worldwide, there are about 1,300 upper-air stations. Observations are made by the NWS at 92 stations – 69 in the conterminous United States, 13 in Alaska, nine in the Pacific, and one in Puerto Rico.NWS supports the operation of 10 other stations in the Caribbean. Through international agreements data are exchanged between countries worldwide.
How Are Radiosonde Data Used?
Radiosonde observations are used over a broad spectrum of efforts including:
- Input for computer-based weather prediction models,
- Local severe storm, aviation, and marine forecasts,
- Weather and climate change research,
- Input for air pollution research, and
- Ground truth for satellite data.
Data from a radiosonde observation is plotted on a seemingly complicated chart called a “Skew-T” but provides is a wealth of information concerning the state of the atmosphere.
Hydrologic Cycle
The Hydrologic Cycle
The hydrologic cycle involves the continuous circulation of water in the Earth-Atmosphere system. At its core, the water cycle is the motion of the water from the ground to the atmosphere and back again. Of the many processes involved in the hydrologic cycle, the most important are…
- evaporation
- transpiration
- condensation
- precipitation
- runoff
Evaporation
Evaporation is the change of state in a substance from a liquid to a gas. In meteorology, the substance we are concerned about the most is water.
For evaporation to take place, energy is required. The energy can come from any source: the sun, the atmosphere, the earth, or objects on the earth such as humans.
Everyone has experienced evaporation personally. When the body heats up due to the air temperature or through exercise, the body sweats, secreting water onto the skin.
The purpose is to cause the body to use its heat to evaporate the liquid, thereby removing heat and cooling the body. It is the same effect that can be seen when you step out of a shower or swimming pool. The coolness you feel is from the removing of bodily heat to evaporate the water on your skin.
Transpiration
Transpiration is the evaporation of water from plants through stomata. Stomata are small openings found on the underside of leaves that are connected to vascular plant tissues. In most plants, transpiration is a passive process largely controlled by the humidity of the atmosphere and the moisture content of the soil. Of the transpired water passing through a plant only 1% is used in the growth process of the plant. The remaining 99% is passed into the atmosphere.
Learning Lesson: Leaf it to Me
Condensation
Condensation is the process whereby water vapor in the atmosphere is changed into a liquid state. In the atmosphere condensation may appear as clouds or dew. Condensation is the process whereby water appears on the side of an uninsulated cold drink can or bottle.
Condensation is not a matter of one particular temperature but of a difference between two temperatures; the air temperature and the dewpoint temperature. At its basic meaning, the dew point is the temperature where dew can form.
Actually, it is the temperature that, if the air is cool to that level, the air becomes saturated. Any additional cooling causes water vapor to condense. Foggy conditions often occur when air temperature and dew point are equal.
Condensation is the opposite of evaporation. Since water vapor has a higher energy level than that of liquid water, when condensation occurs, the excess energy in the form of heat energy is released. This release of heat aids in the formation of hurricanes.
Learning Lesson: Sweatin’ to the Coldies
Precipitation
Precipitation is the result when the tiny condensation particles grow too large, through collision and coalescence, for the rising air to support, and thus fall to the earth. Precipitation can be in the form of rain, hail, snow or sleet.
Precipitation is the primary way we receive fresh water on earth. On average, the world receives about 38½” (980 mm) each year over both the oceans and land masses.
Learning Lesson: The Rain Man
Runoff
Runoff occurs when there is excessive precipitation and the ground is saturated (cannot absorb any more water). Rivers and lakes are results of runoff. There is some evaporation from runoff into the atmosphere but for the most part water in rivers and lakes returns to the oceans.
If runoff water flows into the lake only (with no outlet for water to flow out of the lake), then evaporation is the only means for water to return to the atmosphere. As water evaporates, impurities or salts are left behind. The result is the lake becomes salty as in the case of the Great Salt Lake in Utah or Dead Sea in Israel.
Evaporation of this runoff into the atmosphere begins the hydrologic cycle over again. Some of the water percolates into the soil and into the ground water only to be drawn into plants again for transpiration to take place.
Earth-Atmosphere Energy Balance
The Earth-Atmosphere Energy Balance
The earth-atmosphere energy balance is the balance between incoming energy from the Sun and outgoing energy from the Earth. Energy released from the Sun is emitted as shortwave light and ultraviolet energy. When it reaches the Earth, some is reflected back to space by clouds, some is absorbed by the atmosphere, and some is absorbed at the Earth’s surface.
Learning Lesson: Canned Heat
However, since the Earth is much cooler than the Sun, its radiating energy is much weaker (long wavelength) infrared energy. We can indirectly see this energy radiate into the atmosphere as heat, rising from a hot road, creating shimmers on hot sunny days.
The earth-atmosphere energy balance is achieved as the energy received from the Sun balances the energy lost by the Earth back into space. In this way, the Earth maintains a stable average temperature and therefore a stable climate. Using 100 units of energy from the sun as a baseline the energy balance is as follows:
| Incoming energy | Outgoing energy | ||
|---|---|---|---|
| Units | Source | Units | Source |
| +100 | Short wave radiation from the sun. | -23 | Short wave radiation reflected back to space by clouds. |
| -7 | Short wave radiation reflected to space by the earth’s surface. | ||
| -49 | Longwave radiation from the atmosphere into space. | ||
| -9 | Longwave radiation from clouds into space. | ||
| -12 | Longwave radiation from the earth’s surface into space. | ||
| +100 | Total Incoming | -100 | Total Outgoing |
| Incoming energy | Outgoing energy | ||
|---|---|---|---|
| Units | Source | Units | Source |
| +19 | Absorbed short wave radiation by gases in the atmosphere. | -9 | Long wave radiation emitted to space by clouds. |
| +4 | Absorbed short wave radiation by clouds. | -49 | Long wave radiation emitted to space by gases in atmosphere. |
| +104 | Absorbed longwave radiation from earth’s surface. | -98 | Longwave radiation emitted to earth’s surface by gases in atmosphere. |
| +5 | From convective currents (rising air warms the atmosphere). | ||
| +24 | Condensation /Deposition of water vapor (heat is released into the atmosphere by process). | ||
| +156 | Total Incoming | -156 | Total Outgoing |
| Incoming energy | Outgoing energy | ||
|---|---|---|---|
| Units | Source | Units | Source |
| +47 | Absorbed short wave radiation from the sun. | -116 | Long wave radiation emitted by the surface. |
| +98 | Absorbed longwave radiation from gases in atmosphere. | -5 | Removal of heat by convection (rising warm air). |
| -24 | Heat required by the processes of evaporation and sublimation and therefore removed from the surface. | ||
| +145 | Total Incoming | -145 | Total Outgoing |
The absorption of infrared radiation trying to escape from the Earth back to space is particularly important to the global energy balance. Energy absorption by the atmosphere stores more energy near its surface than it would if there was no atmosphere.
The average surface temperature of the moon, which has no atmosphere, is 0°F (-18°C). By contrast, the average surface temperature of the Earth is 59°F (15°C). This heating effect is called the greenhouse effect.
Transfer of heat energy
The Transfer of Heat Energy
The heat source for our planet is the sun. Energy from the sun is transferred through space and through the earth’s atmosphere to the earth’s surface. Since this energy warms the earth’s surface and atmosphere, some of it is or becomes heat energy. There are three ways heat is transferred into and through the atmosphere:
- radiation
- conduction
- convection
Radiation
If you have stood in front of a fireplace or near a campfire, you have felt the heat transfer known as radiation. The side of your body nearest the fire warms, while your other side remains unaffected by the heat. Although you are surrounded by air, the air has nothing to do with this transfer of heat. Heat lamps, that keep food warm, work in the same way. Radiation is the transfer of heat energy through space by electromagnetic radiation.
Most of the electromagnetic radiation that comes to the earth from the sun is invisible. Only a small portion comes as visible light. Light is made of waves of different frequencies. The frequency is the number of instances that a repeated event occurs, over a set time. In electromagnetic radiation, its frequency is the number of electromagnetic waves moving past a point each second.
Our brains interpret these different frequencies into colors, including red, orange, yellow, green, blue, indigo, and violet. When the eye views all these different colors at the same time, it is interpreted as white. Waves from the sun which we cannot see are infrared, which have lower frequencies than red, and ultraviolet, which have higher frequencies than violet light. [more on electromagnetic radiation] It is infrared radiation that produce the warm feeling on our bodies.
Most of the solar radiation is absorbed by the atmosphere and much of what reaches the earth’s surface is radiated back into the atmosphere to become heat energy. Dark colored objects, such as asphalt, absorb radiant energy faster that light colored objects. However, they also radiate their energy faster than lighter colored objects.
Learning Lesson: Melts in your bag, not in your hand
Conduction
Conduction is the transfer of heat energy from one substance to another or within a substance. Have you ever left a metal spoon in a pot of soup being heated on a stove? After a short time the handle of the spoon will become hot.
This is due to transfer of heat energy from molecule to molecule or from atom to atom. Also, when objects are welded together, the metal becomes hot (the orange-red glow) by the transfer of heat from an arc.
This is called conduction and is a very effective method of heat transfer in metals. However, air conducts heat poorly.
Convection
Convection is the transfer of heat energy in a fluid. This type of heating is most commonly seen in the kitchen when you see liquid boiling.
Air in the atmosphere acts as a fluid. The sun’s radiation strikes the ground, thus warming the rocks. As the rock’s temperature rises due to conduction, heat energy is released into the atmosphere, forming a bubble of air which is warmer than the surrounding air. This bubble of air rises into the atmosphere. As it rises, the bubble cools with the heat contained in the bubble moving into the atmosphere.
As the hot air mass rises, the air is replaced by the surrounding cooler, more dense air, what we feel as wind. These movements of air masses can be small in a certain region, such as local cumulus clouds, or large cycles in the troposphere, covering large sections of the earth. Convection currents are responsible for many weather patterns in the troposphere.
Air Pressure
Air Pressure
atmosphere decreases with height.
The atoms and molecules that make up the various layers in the atmosphere are constantly moving in random directions. Despite their tiny size, when they strike a surface they exert a force on that surface in what we observe as pressure.
Each molecule is too small to feel and only exerts a tiny bit of force. However, when we sum the total forces from the large number of molecules that strike a surface each moment, then the total observed pressure can be considerable.
Air pressure can be increased (or decreased) one of two ways. First, simply adding molecules to any particular container will increase the pressure. A larger number of molecules in any particular container will increase the number of collisions with the container’s boundary which is observed as an increase in pressure.
A good example of this is adding (or subtracting) air in an automobile tire. By adding air, the number of molecules increase as well a the total number of the collisions with the tire’s inner boundary. The increased number of collisions forces the tire’s pressure increase to expand in size.
The second way of increasing (or decreasing) is by the addition (or subtraction) of heat. Adding heat to any particular container can transfer energy to air molecules. The molecules therefore move with increased velocity striking the container’s boundary with greater force and is observed as an increase in pressure.
Learning Lesson: Air: A weighty subject
Since molecules move in all directions, they can even exert air pressure upwards as they smash into object from underneath. In the atmosphere, air pressure can be exerted in all directions.
In the International Space Station, the density of the air is maintained so that it is similar to the density at the earth’s surface. Therefore, the air pressure is the same in the space station as the earth’s surface (14.7 pounds per square inch).
Learning Lesson: A Pressing Engagement
Learning Lesson: Going with the Flow
Back on Earth, as elevation increases, the number of molecules decreases and the density of air therefore is less, meaning a decrease in air pressure. In fact, while the atmosphere extends more than 15 miles (24 km) up, one half of the air molecules in the atmosphere are contained within the first 18,000 feet (5.6 km).
Because of this decrease in pressure with height, it makes it very hard to compare the air pressure at ground level from one location to another, especially when the elevations of each site differ. Therefore, to give meaning to the pressure values observed at each station, we convert the station air pressures reading to a value with a common denominator.
The common denominator we use is the sea-level elevation. At observation stations around the world the air pressure reading, regardless of the observation station elevation, is converted to a value that would be observed if that instrument were located at sea level.
The two most common units in the United States to measure the pressure are “Inches of Mercury” and “Millibars”. Inches of mercury refers to the height of a column of mercury measured in hundredths of inches. This is what you will usually hear from the NOAA Weather Radio or from your favorite weather or news source. At sea level, standard air pressure is 29.92 inches of mercury.
Millibars comes from the original term for pressure “bar”. Bar is from the Greek “báros” meaning weight. A millibar is 1/1000th of a bar and is approximately equal to 1000 dynes (one dyne is the amount of force it takes to accelerate an object with a mass of one gram at the rate of one centimeter per second squared). Millibar values used in meteorology range from about 100 to 1050. At sea level, standard air pressure in millibars is 1013.2. Weather maps showing the pressure at the surface are drawn using millibars.
Although the changes are usually too slow to observe directly, air pressure is almost always changing. This change in pressure is caused by changes in air density, and air density is related to temperature.
Warm air is less dense than cooler air because the gas molecules in warm air have a greater velocity and are farther apart than in cooler air. So, while the average altitude of the 500 millibar level is around 18,000 feet (5,600 meters) the actual elevation will be higher in warm air than in cold air.
Learning Lesson: Crunch Time
The L’s represent the position of the lowest pressure.
The most basic change in pressure is the twice daily rise and fall in due to the heating from the sun. Each day, around 4 a.m./p.m. the pressure is at its lowest and near its peak around 10 a.m./p.m. The magnitude of the daily cycle is greatest near the equator decreasing toward the poles.
On top of the daily fluctuations are the larger pressure changes as a result of the migrating weather systems. These weather systems are identified by the blue H’s and red L’s seen on weather maps.
Learning Lesson: Measure the Pressure: The “Wet” Barometer
How are changes in weather related to changes in pressure?
From his vantage point in England in 1848, Rev. Dr. Brewer wrote in his A Guide to the Scientific Knowledge of Things Familiar the following about the relation of pressure to weather:
The FALL of the barometer (decreasing pressure)
- In very hot weather, the fall of the barometer denotes thunder. Otherwise, the sudden falling of the barometer denotes high wind.
- In frosty weather, the fall of the barometer denotes thaw.
- If wet weather happens soon after the fall of the barometer, expect but little of it.
- In wet weather if the barometer falls expect much wet.
- In fair weather, if the barometer falls much and remains low, expect much wet in a few days, and probably wind.
- The barometer sinks lowest of all for wind and rain together; next to that wind, (except it be an east or north-east wind).
The RISE of the barometer (increasing pressure)
- In winter, the rise of the barometer presages frost.
- In frosty weather, the rise of the barometer presages snow.
- If fair weather happens soon after the rise of the barometer, expect but little of it.
- In wet weather, if the mercury rises high and remains so, expect continued fine weather in a day or two.
- In wet weather, if the mercury rises suddenly very high, fine weather will not last long.
- The barometer rises highest of all for north and east winds; for all other winds it sinks.
The barometer UNSETTLED (unsteady pressure)
- If the motion of the mercury be unsettled, expect unsettled weather.
- If it stands at “MUCH RAIN” and rises to “CHANGEABLE” expect fair weather of short continuance.
- If it stands at “FAIR” and falls to “CHANGEABLE”, expect foul weather.
- Its motion upwards, indicates the approach of fine weather; its motion downwards, indicates the approach of foul weather.
These pressure observations hold true for many other locations as well but not all of them. Storms that occur in England, located near the end of the Gulf Stream, bring large pressure changes. In the United States, the largest pressure changes associated with storms will generally occur in Alaska and northern half of the continental U.S. In the tropics, except for tropical cyclones, there is very little day-to-day pressure change and none of the rules apply.
Layers of the Atmosphere
Layers of the Atmosphere – Courtesy NOAA
The envelope of gas surrounding the Earth changes from the ground up. Five distinct layers have been identified using…
- thermal characteristics (temperature changes),
- chemical composition,
- movement, and
- density.
Each of the layers are bounded by “pauses” where the greatest changes in thermal characteristics, chemical composition, movement, and density occur.
Exosphere
This is the outermost layer of the atmosphere. It extends from the top of the thermosphere to 6,200 miles (10,000 km) above the earth. In this layer, atoms and molecules escape into space and satellites orbit the earth. At the bottom of the exosphere is the thermopause located around 375 miles (600 km) above the earth.
Thermosphere
Between about 53 miles (85 km) and 375 miles (600 km) lies the thermosphere. This layer is known as the upper atmosphere. While still extremely thin, the gases of the thermosphere become increasingly more dense as one descends toward the earth.
As such, incoming high energy ultraviolet and x-ray radiation from the sun begins to be absorbed by the molecules in this layer and causes a large temperature increase.
Because of this absorption, the temperature increases with height. From as low as -184°F (-120°C) at the bottom of this layer, temperatures can reach as high as 3,600°F (2,000°C) near the top.
However, despite the high temperature, this layer of the atmosphere would still feel very cold to our skin due to the very thin atmosphere. The high temperature indicates the amount of the energy absorbed by the molecules but with so few in this layer, the total number of molecules is not enough to heat our skin.
Take it to the MAX! The Ionosphere
Mesosphere
This layer extends from around 31 miles (50 km) above the Earth’s surface to 53 miles (85 km). The gases, including the oxygen molecules, continue to become more dense as one descends. As such, temperatures increase as one descends rising to about 5°F (-15°C) near the bottom of this layer.
The gases in the mesosphere are now thick enough to slow down meteors hurtling into the atmosphere, where they burn up, leaving fiery trails in the night sky. Both the stratosphere (next layer down) and the mesosphere are considered the middle atmosphere. The transition boundary which separates the mesosphere from the stratosphere is called the stratopause.
Stratosphere
The Stratosphere extends around 31 miles (50 km) down to anywhere from 4 to 12 miles (6 to 20 km) above the Earth’s surface. This layer holds 19 percent of the atmosphere’s gases but very little water vapor.
In this region the temperature increases with height. Heat is produced in the process of the formation of Ozone and this heat is responsible for temperature increases from an average -60°F (-51°C) at tropopause to a maximum of about 5°F (-15°C) at the top of the stratosphere.
This increase in temperature with height means warmer air is located above cooler air. This prevents “convection” as there is no upward vertical movement of the gases. As such the location of the bottom of this layer is readily seen by the ‘anvil-shaped’ tops of cumulonimbus clouds.
Troposphere
Known as the lower atmosphere almost all weather occurs in this region. The troposphere begins at the Earth’s surface and extends from 4 to 12 miles (6 to 20 km) high.
The height of the troposphere varies from the equator to the poles. At the equator it is around 11-12 miles (18-20 km) high, at 50°N and 50°S, 5½ miles and at the poles just under four miles high.
As the density of the gases in this layer decrease with height, the air becomes thinner. Therefore, the temperature in the troposphere also decreases with height in response. As one climbs higher, the temperature drops from an average around 62°F (17°C) to -60°F (-51°C) at the tropopause.
Introduction to the Atmosphere
Introduction to the Atmosphere – Courtesy NOAA
The atmosphere is a cloud of gas and suspended solids extending from the Earth’s surface out many thousands of miles, becoming increasingly thinner with distance but always held by the Earth’s gravitational pull.
The atmosphere surrounds the Earth and holds the air we breathe; it protects us from outer space; and holds moisture (clouds), gases, and tiny particles. In short, the atmosphere is the protective bubble in which we live.
| Gas | Symbol | Content | ||
|---|---|---|---|---|
| Nitrogen | N2 | 78.084% |  |
99.998% |
| Oxygen | O2 | 20.947% | ||
| Argon | Ar | 0.934% | ||
| Carbon dioxide | CO2 | 0.033% | ||
| Neon | Ne | 18.20 parts per million | ||
| Helium | He | 5.20 parts per million | ||
| Krypton | Kr | 1.10 parts per million | ||
| Sulfur dioxide | SO2 | 1.00 parts per million | ||
| Methane | CH4 | 2.00 parts per million | ||
| Hydrogen | H2 | 0.50 parts per million | ||
| Nitrous oxide | N2O | 0.50 parts per million | ||
| Xenon | Xe | 0.09 parts per million | ||
| Ozone | O3 | 0.07 parts per million | ||
| Nitrogen dioxide | NO2 | 0.02 parts per million | ||
| Iodine | I2 | 0.01 parts per million | ||
| Carbon monoxide | CO | trace | ||
| Ammonia | NH3 | trace | ||
This protective bubble consists of several gases (listed in the table to the right) with the top four making up 99.998% of all gases. Of the dry composition of the atmosphere nitrogen, by far, is the most common. Nitrogen dilutes oxygen and prevents rapid burning at the Earth’s surface. Living things need it to make proteins.
Oxygen is used by all living things and is essential for respiration. It is also necessary for combustion or burning.
Argon is used in light bulbs, in double-pane windows, and used to preserve the original Declaration of Independence and the Constitution. Plants use carbon dioxide to make oxygen. Carbon dioxide also acts as a blanket that prevents the escape of heat into outer space.
These percentages of atmospheric gases are for a completely dry atmosphere. The atmosphere is rarely, if ever, dry. Water vapor (water in a ‘gas’ state) is nearly always present up to about 4% of the total volume.
| Water Vapor | Nitrogen | Oxygen | Argon |
|---|---|---|---|
| 0% | 78.084% | 20.947% | 0.934% |
| 1% | 77.30% | 20.70% | 0.92% |
| 2% | 76.52% | 20.53% | 0.91% |
| 3% | 75.74% | 20.32% | 0.90% |
| 4% | 74.96% | 20.11% | 0.89% |
In the Earth’s desert regions (30°N/S) when dry winds are blowing, the water vapor contribution to the composition of the atmosphere will be near zero.
Water vapor contribution climbs to near 3% on extremely hot/humid days. The upper limit, approaching 4%, is found in tropical climates. The table shows the changes in atmospheric composition with the inclusion of different amounts of water vapor.
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