Darbas:

not interfere with the very high frequencies. This precipitation static, as it is called, tends to be most severe near the freezing level and where turbulence and up and down drafts occur.
Hail. Hailstones are capable of inflicting serious damage to an airplane. Hail is encountered at levels between 10000 and 30000 feet. It is, on occasion, also encountered in clear air outside the cloud as especially active cells throw it upward and outward.
Icing. In a thunderstorm is encountered at or above the freezing level in the areas of heaviest turbulence during the mature stage of the storm. The altitudes within a few thousand feet of the freezing level, above or below, are especially dangerous.
Pressure. Rapid changes in barometric pressure associated with the storm cause altimeter readings to become very unreliable. The barometric pressure ahead of a thunderstorm falls abruptly as the storm approaches then rises quickly when the rain comes, and returns to normal when the storm subsides. Occasionally after a storm, the pressure falls below normal. Then rises to near normal again. All this can happen in a matter of 10 to 15 minutes.
Rain. The thunderstorm contains vast amounts of liquid water droplets suspended or carried aloft by the updrafts. This water can be as damaging as hail to an aircraft penetrating the thunderstorm at high speed. The heavy rain showers associated with thunderstorms encountered during approach and landing can reduce visibility and cause retraction on the windscreen of the aircraft, producing an illusion that the runway threshold is lower than it actually is. Water lying on the runway can cause hydroplaning, which destroys the braking action needed to bring the aircraft to a stop within the confines of the airport runway. Hydroplaning can also lead to loss of control during take-off.
Severe Thunderstorms are defined as convective storms with frequent lighting, accompanied by local wind gusts of 97 kilometers per hour, or hail that is 2 centimeters in diameter or larger. Severe thunderstorms can also have tornadoes. Movement of the severe storm is usually caused by the presence of a mid-latitude cyclone cold front or a dry line some 100 to 300 kilometers ahead of a cold front. In the spring and early summer, frontal cyclones are common weather events that move from west to east in the mid-latitudes.

At the same time, the ground surface in the mid-latitudes is receiving elevated levels of insulation, which creates ideal conditions for air mass thunderstorm formation. When the cold front or dry line of a frontal cyclone comes in contact with this warm air it pushes it like a bulldozer both horizontally and vertically.
If this air has a high humidity and extends some distance to the east, the movement of the mid-latitude cyclone enhances vertical uplift in storm and keeps the thunderstorms supplied with moisture and energy. Thus, the mid-latitude cyclone converts air mass thunderstorms into severe thunderstorms that last for many hours. Severe thunderstorms usually extend all the way to the tropopause and can be seen in satellite imagery as storms producing overshooting tops.
Severe thunderstorms dissipate only when no more warm moist air is encountered. This condition occurs several hours after nightfall when the atmosphere begins to cool off.

3.2 THUNDERSTORM AVOIDANCE

Because of the severe hazards enumerated above, attempting to penetrate a thunderstorm is asking for trouble. In the case of flight, airplane pilots, the best advice on how to fly through a thunderstorm is summed up in one word—DON'T.

Detour around storms as early as possible when encountering them enroute. Stay at least 5 miles away from a thunderstorm with large overhanging areas because of the danger of encountering hail. Stay even farther away from a thunderstorm identified as very severe as turbulence may be encountered as much as 15 or more nautical miles away. Vivid and frequent lightning indicates the probability of a severe thunderstorm.
Any thunderstorm with tops at 35,000 feet or higher should be regarded as extremely hazardous. Avoid landing or taking off at any airport in close proximity to an approaching thunderstorm or squall line.
Do not fly under a thunderstorm even if you can see through to the other side, since turbulence may be severe. Especially, do not attempt to fly underneath a thunderstorm formed by orographic lift. The wind flow that is responsible for the formation of the thunderstorm is likely to create dangerous up and down drafts and turbulence between the mountain peaks.
Reduce airspeed to maneuvering speed when in the vicinity of a thunderstorm or at the first indication of turbulence.
Do not fly into a cloud mass containing scattered embedded thunderstorms unless you have airborne radar.
Do not attempt to go through a narrow clear space between two thunderstorms. The turbulence there may be more severe than through the storms themselves. If the clear space is several miles in width, however, it may be safe to attempt to fly through the center, but always go through at the highest possible altitude. When flying around a thunderstorm, it is better to fly around the right side of it. The wind circulates anti-clockwise and you will get more favorable winds. If circumstances are such that you must penetrate a thunderstorm, the following few simple rules may help you to survive the ordeal:
1) Go straight through a front, not across it, so that you will get through the storm in the minimum amount of time.
2) Hold a reasonably constant heading that will get you through the storm cell in the shortest possible time.
3) Before entering the storm, reduce the airspeed to the airplane's maneuvering airspeed to minimize structural stresses.
4) Turn the cockpit lights full bright. (This helps to minimize the risk of lightning blindness.) Check the pilot head. Fasten seat belts. Secure loose objects in the cabin.
5) Try to maintain a constant attitude and power setting. (Vertical drafts past the pitot head and clogging by rain cause erratic airspeed readings.)
6) Avoid unnecessary maneuvering (to prevent adding maneuver loads to those already imposed by turbulence).
7) Determine the freezing level and avoid the icing zone. Avoid dark areas of the cell and, at night, those areas of heavy lightning.

8) Do not use the autopilot. It is a constant altitude device and will dive the airplane to compensate for updrafts, causing excessive airspeed, or will cause the plane to climb in a downdraft creating the risk of a stall.
3.3 INFORMATION FOR A PILOT

To minimize the hazards to air navigation that are constantly being manufactured in the so-called weather factory, a vast world-wide meteorological organization has been built up, to collect, analyze and broadcast information relative to the ever changing flight environment or the upper air. There are some instruments and ways to measure the weather: weather radar, weather satellites, airplanes that gather data, computers information analyses.
Airborne weather radar is one of the best instrument aids that a pilot can have in locating and avoiding thunderstorms. It is able to detect and display on the cockpit radar screen any significant weather that lies ahead on the flight route.
. DOPPLER RADAR is a key forecasting tool

All weather radars send out radio waves from an antenna. Objects in the air, such as rain drops, snow crystals, hail stones or even insects and dust, scatter or reflect some of the radio waves back to the antenna. All weather radars, including Nexrad, electronically convert the reflected radio waves into pictures showing the location and intensity of precipitation.
Doppler radars also measure the frequency change in returning radio waves. Waves reflected by something moving away from the antenna change to a lower frequency. Waves from an object moving toward the antenna change to a higher frequency.


The computer that's a part of a Doppler radar uses the frequency changes to show directions and speeds of the winds blowing around the raindrops, insects and other objects that reflected the radio waves. Scientists and forecasters have learned how to use these pictures of wind motions in storms, or even in clear air, to more clearly understand what's happening now and what's likely to happen in the next hour or two.

METAR is routine weather report issued at hourly or half-hourly intervals. It is a description of the meteorological elements observed at an airport at a specific time.
Example: METAR KPIT 091955Z COR 22015G25KT 3/4SM R28L/2600FT TSRA OVC010CB 18/16 A2992 RMK SLP045 T01820159

SPECI is special weather report issued when there is significant deterioration or improvement in airport weather conditions, such as significant changes of surface winds, visibility, cloud base height and occurrence of severe weather. The format of the SPECI report is similar to that of the METAR and the elements used have the same meaning. The identifier METAR or SPECI at the beginning of the weather report differentiates them.

A METAR/SPECI report usually contains the following information:
Originating airport name, METAR/SPECI issue time, wind direction/speed/gust, wind direction variation,
visibility, runway visual range, weather during time of observation, cloud, air temperature/dew-point, QNH (pressure measured at airport with adjustment made to suit aeronautical use), weather during the past hour but not at time of observation, wind shear information, trend-type landing forecast.
Example: EYVI 251730 120V18009KT 3000 TSSHRA SCT008CB 14/12 Q1012=

A TAF conveys the following meteorological information:
Originating airport name, TAF validity period, wind direction/speed/gust, visibility, weather, cloud, icing, turbulence, significant change of weather elements, maximum and minimum temperature.
When forecast temperatures are included in accordance with regional air navigation agreement, the maximum and minimum temperatures expected to occur during the period of validity of the aerodrome forecast should be given, together with their corresponding times of occurrence. An amended forecast may be issued subject to certain criteria and is prefixed by the keyword TAF AMD.
Example:
TAF VHHH 160400Z 160606 13018KT 9000 BKN020 BECMG 0608
SCT015CB BKN020 TEMPO 0812 17025G40KT 1000 TSRA SCT010CB
BKN020 FM1200 15015KT 9999 NSW BKN020 BKN100 TN26/22Z TX30/06Z=

3.4 IN-FLIGHT ADVISORIES (WARNINGS)

Warn pilots of potentially hazardous weather. They include SIGMETs, CONVECTIVE SIGMETs, AIRMETs, and Center Weather Advisories (CWA). SIGMETs warn of hazardous conditions of importance to all aircraft i.e. severe icing or turbulence, dust storms, sandstorms, and volcanic ash. AIRMETs warn of less severe conditions which may be hazardous to some aircraft or pilots. SIGMETs

are issued as needed. AIRMET bulletins are issued routinely and supplement the Area Forecast (FA). CONVECTIVE SIGMETs are issued hourly for thunderstorms in the continuous U.S. Center Weather Advisories, issued as needed, are detailed advisories of conditions which meet or approach SIGMET or AIRMET criteria.

SIGMET
Example:
LFFF SIGMET SST 5 VALID 240900/241100 LFPW
FRANCE UIR ISOL TO OCNL CB OBS/FCST TOP BLW FL380 ON FIR
MARSEILLE S OF 45N MOV N SLW NC=
LFFF SIGMET SST 4 VALID 240700/240900 LFPW
FRANCE UIR ISOL TO OCNL CB OBS/FORCS TOP BLW FL/380 ON FIR
MARSILLE S OF 45N MOV N NC=

AIRMET/ GAMET
GAMET is used to report forecasted or actual en-route weather phenomena that may affect aircraft in flight. An AIRMET (AIRman's METeorological Information) is used to report forecasted or actual en-route weather phenomena for aircraft flying at low altitude, typically under 100 meters and Visual Flight Rule (VFR) pilots. GAMET and AIRMET are sold as optional modules.
There are three AIRMETs - Sierra, Tango, and Zulu.
AIRMET Sierra describes IFR conditions and/or extensive mountain obscurations.
AIRMET Tango describes moderate turbulence, sustained surface winds of 30 knots or greater, and/or nonconvective low-level wind shear.
AIRMET Zulu describes moderate icing and provides freezing level heights.
After the first issuance each day, scheduled or unscheduled bulletins are numbered sequentially for easier identification.
Example of AIRMET Tango issued for the Salt Lake City FA area:
SLCT WA 121345
AIRMET TANGO UPDT 2 FOR TURB VALID UNTIL 122000
AIRMET TURB...NV UT CO AZ NM
FROM LKV TO CHE TO ELP TO 60S TUS TO YUM TO EED TO RNO TO LKV
OCNL MOD TURB BLW FL180 DUE TO MOD SWLY/WLY WNDS. CONDS CONTG BYD 20Z THRU 02Z.
AIRMET TURB...NV WA OR CA CSTL WTRS
FROM BLI TO REO TO BTY TO DAG TO SBA TO 120W FOT TO 120W TOU TO BLI
OCNL MOD TURB BTWN FL180 AND FL400 DUE TO WNDSHR ASSOCD WITH JTSTR. CONDS CONTG BYD 20Z THRU 02Z
Example of GAMET
PSYS: 12 L 998 HPA N54.0 E06.0 MOV SE 15KT WKN
12 COLD FRONT LINE EHGG - EDDK MOV E 20KT NC
WIND/T: 2000 FT AMSL 230/15KT PS09
FL050 250/25KT PS03
FL100 260/40KT MS07
CLD: BKN SC 2000 FT AMSL /FL050 SCT CB TOP 1400FT
FZLVL: FL065
MNM QNH: 1002 HPA


INFERENCE

The pilot can today avail himself of last minute weather reports and forecasts along all the regularly established air routes. In addition, he can secure much valuable weather data with reference to areas located off the organized airways. He must, however, possess sufficient and adequate weather sense, to be able to size up and deal with sudden changing conditions, which may be encountered at any stage during flight. Weather conditions can be influenced by great variety of synoptic situations, which determine the flight conditions as well. The most obvious “problems” in the sky, during the flight, can be clouds and associated phenomena. As aviators, we learn in our basic aviation meteorology that thunderstorms are the most dangerous clouds of all species that produce significant hazards that could seriously jeopardize the safety of flying. It has aptly been described as a cumulus cloud gone wild. It is always accompanied by thunder and lightning, strong vertical drafts, severe gusts and turbulence, heavy rain and sometimes hail. It is a weather condition of which a pilot should be enormously respectful. Since over 44,000 thunderstorms occur daily over the earth, every pilot is sure occasionally to come in contact with one Because of the severe hazards enumerated above, attempting to penetrate a thunderstorm is asking for trouble. In the case of flight, airplane pilots, the best advice on how to fly through, close or under a thunderstorm is summed up in one word—DON'T.



LITERATURE

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2. http://liftoff.msfc.nasa.gov/academy/space/atmosphere.html
3. http://www.cyberair.com/tower/faa/app/p8740-5.html
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5. http://www.erh.noaa.gov/er/cae/svrwx/downburst.htm
6. http://doppler.unl.edu/users/phowell/sworks.html#module
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9. http://www.srh.weather.gov/jetstream/tropics/tc.htm
10. http://apollo.lsc.vsc.edu/classes/met130/notes/chapter6/clouds_intro.html
11. http://www.cityofportsmouth.com/school/dondero/msm/weather/index.html
12. http://seaborg.nmu.edu/Clouds/default.html
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18. http://www.uwm.edu/~kahl/Images/i2.html#top
19. http://www.alamance-nc.com/fire/index.html
20. http://www.weatherpictures.nl/index.html
21. http://www.allstar.fiu.edu/aerojava/
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23. http://www.inclouds.com/index.html
24. http://www.solarviews.com/eng/cloud1.htm#views
25. http://www.weather.gov.hk/contente.htm
26. http://www.met.tamu.edu/class/METAR/metar-pg3.html#General
27. http://www.flightsimaviation.com/index.php?p=glossaries&s=avterms#top