AVIATION WEATHER –METEOROLOGY
WHAT THE FAA REQURES YOU TO KNOW ABOUT AVIATION METEROLOGY.
You must have knowledge of elements related to weather information by analyzing weather reports, charts, and forecasts from various sources withemphasis on:
•METAR, TAF, and FA
•Surface Analysis Charts
•Radar Summary Charts
•Winds and Temperature Aloft Charts
•Significant Weather Prognostic Charts
•Convective Outlook Charts
•AWOS, ASOS and ATIS Report
You must be able to make a competent “go/no-go”decision based on available weather information.
To enable you to do this we must study weather theory, patterns,hazards, forecasting, printed/ and graphic weather products, and sources of weather info.
Know US Time Zones (continental)
PST MST CST EST(FL)
-3 -2 -1 ***
-1 **TO** +1 +2
Types of Time
Civilian (Local) AM and PM
Military 00:01 to 24:00, Civilian time 1 PM become 13:00 (PM time +12)
ALL aviation reporting are given inUniversal Coordinated Time (UTC)
which is designated as Zulu (Z)This is GMT (Greenwich Mean Time)
To convert Local to Zulu as you will do in preparing a flight plan:
- Convert Local to Military
- Add Zulu Offset (Florida for EDT = +4, EST = +5)
To convert Zulu to Local as you will do in interpreting weather reports
- Subtract Offset (Florida EDT = -4, EST = -5
- If hour is greater than 12, then subtract 12
Likely problem on Aeronautical Knowledge Exam involving conversion
Take off from Denver at 1PM (MDT) and fly to Ogallala NE (CDT)
Depart at 1 PM for 2 hour flight. What is the ETA in Zulu Time?
a. What is the Z time at Denver (1 PM) military time is 13:00 then add +6=1900Z
b. What is the estimated time of arrival (ETA) at Ogallala 19+2= 2100Z
What is local time at Ogallala? 2100-5=1600, -12 = 4 PM
Return to Denver departing 2200Z, what is local ETA at Denver?
a. 22+2=24Z, -6 for Zulu offset =18:00 mil, -12 for local time is 6 PM
METEOROLOGY –BASIC WEATHER THEORY
Pressure Altitude
Pressure altitude is the height above a standard datum plane (SDP), which is a theoretical level where the weight of the atmosphere is 29.92 "Hg (1,013.2 mb) as measured by a barometer.
Density Altitude
SDP is a theoretical pressure altitude, but aircraft operate in a nonstandard atmosphere and the term density altitude is used for correlatingaerodynamic performance in the nonstandard atmosphere. Density altitude is the vertical distance above sea level in the standard atmosphere at which a given density is to be found. The density of air has significant effects on the aircraft’s performance because as air becomes less dense, it reduces:
•Power because the engine takes in less air.
•Thrust because a propeller is less efficient in thin air.
•Lift because the thin air exerts less force on the airfoils.
Effect of Pressure on Density
Since air is a gas, it can be compressed or expanded. When air is compressed, a greater amount of air can occupy a given volume. If the pressure is doubled, the density is doubled; if the pressure is lowered, the density is lowered.
Effect of Temperature on Density
Increasing the temperature of a substance decreases its density.Thus, the density of air varies inversely with temperature. This statement is true only at a constant pressure.
Effect of Humidity (Moisture) on Density
Water vapor is lighter than air; consequently, as the water content of the air increases, the air becomes less dense, increasing density altitude and decreasing performance.
METEOROLOGY –BASIC WEATHER THEORY
High: Area of higher pressure surrounded by area of lower pressure
Elongated area of high pressure is called a “Ridge.”
Low: Area of lower pressure surrounded by area of high pressure
Elongated area of low pressure is called a “Trough”
Elongated area of neutral pressure (intersection of Ridge & Trough) is called a “Col”
Isobars reveals the pressure gradient or change in pressure over distance.
Isobars and Pressure Gradients Difference in pressure create WIND. The closer the isobars the higher the pressure gradient and associated winds.
*Isobars reveal the pressure gradient of an area of high- or low-pressure areas.
Take advantage of winds from pressure regions.
*Favorable winds near a high pressure system.
Convective currents cause the bumpy, turbulent air sometimes experienced when flying at lower altitudes during warmer weather. On a low altitude flight over varying surfaces, updrafts are likely to occur over pavement or barren places, and downdrafts often occur over water or expansive areas of vegetation like a group of trees. Typically, these turbulent conditions can be avoided by flying at higher altitudes, even above cumulus cloud layers.
*Convective turbulence avoidance.
METEOROLOGY –PLANETARY BOUNDRY LAYER
The planetary boundary layer (PBL) is also known as the atmospheric boundary layer (ABL)is a marked thermal layer at approximately the 850 ML level (5000-7000). You will see a marked drop in temperature because of a thermal inversion right at the PLB. Due to aerodynamic drag, there is a wind gradient in the wind flow just a few hundred meters above the earth's surface—the surface layer of the planetary boundary layer. the wind gradient effect could cause a reduction of 40% to 50% of the geostrophic wind speed aloft (balance between the Coriolis effect and the pressure gradient) while over open water or ice, the reduction may be only 20% to 30%. Wind speed increases with increasing height above the ground.
Be aware that when we look at Winds Aloft (FB) forecasts. You are likely to see marked changes in air temperature and wind speed between published 6000 and 9000 foot forecasts.
GLOBAL WIND FORCES
Convective Heating and Cooling sets up basic global circulation patterns
You can learn by yourself with the material below:
- Pilot's Handbook of Aeronautical Knowledge [PHAK]
- Online Meteorology Guide
Note: only a member of this blog may post a comment.