Flight Training - September 2012 - 39

standard sea-level pressure of 1013.15 millibars (mb), which is equivalent to 29.92 inches of mercury in the inches-ofmercury pressure system the NWS uses for public forecasts and pilots use for altimeter settings.
THE 500-MB CHART (below) is a closeup view of the map at left of the eastern United States and Canada. It helps to illustrate how temperature differences create upper-atmosphere winds. The weather balloon launched by the Environment Canada weather station at Maniwaki, Quebec, northwest of Montreal, found the 500-mb pressure level at 5,120 meters above sea level. At roughly the same time the balloon launched by the NWS at Key West, Florida, measured 500-mb 5,880 meters above sea level. We’ll consider only pressures aloft over Key West and Maniwaki and the pressures at only at 5,120 meters above sea level at each station. Since the 500-mb pressure over Key West was all the way up at 5,880 meters, the pressure there at 5,120 meters was higher than at Maniwaki. This pressure creates a force trying to push air from Key West to Maniwaki.

A 500-MILLIBAR chart showing the general flow of the winds aloft roughly 18,000 feet above sea level. The wavy black lines show the north-south pattern of wind and upper-atmosphere pressure (long wave). An upper-air ridge (elongated area of high pressure) is shown over the northern Rockies and an upper-air trough is seen over the southeast, with possible foul weather at the surface.

osities. As airplanes begin flying higher in the 1930s, pilots began encountering what we now call “jet stream” winds, but no one could figure out how they fit with what scientists then knew about weather. Pilots of World War II aircraft that routinely flew higher than 20,000 feet regularly told meteorologists about encountering 150-mph headwinds or tailwinds. After the war, the U.S. military funded university research into these then-mysterious winds. This research led to today’s knowledge of how jet streams fit into the global air circulation. It also led to regular observations of high-altitude winds, temperatures, and humidity that helped improve all weather forecasts, for both the weather aloft and at the surface.
LOOKING OVER WEATHER maps showing various levels of the upper atmosphere is a good way to begin understanding weather aloft. These maps are different from surface weather maps you’re probably used to. Surface maps show the sea-level air pressures at the stations on the chart, even when the stations are not at sea level. They also show centers of high and low pressure and fronts. Instead of showing the pressures at fixed altitudes, as you might expect, upper

air charts show the altitudes of specified pressures measured by weather balloons. The charts show the pressure altitude of specific pressures in millibars. Pressure altitude is the altitude measured by a properly calibrated altimeter set at the

THESE MAPS ARE details of the larger 500-mb chart (top). A indicates Maniwaka, Quebec. B indicates Key West. Black lines swoop across the map with black numbers that show the height in meters of the 500-mb pressure level along the line (add a zero to numbers for the height in meters). Dashed red lines and red numbers show temperature in Celsius. Blue wind arrows show wind direction and barbs or flags show wind speed. Violet numbers show the height in meters of 500-mb pressure observed by a radiosonde. Green minus numbers show the dew point depression in Celsius, which is the number of degrees between the dew point and the temperature.

SEPTEMBER 2012 FLIGHT TRAINING

/ 39



Flight Training - September 2012

Table of Contents for the Digital Edition of Flight Training - September 2012

Flight Training - September 2012
Contents
President’s Perspective
Right Seat
Letters
Flying Low and Slow
How It Works
Success Story AOPA Summit News
After the Checkride
ASI News Tech Tip
Since You Asked
Training Products News
Flying Carpet
Give Yourself a Lift
Radiohead
Everything I Know About Flying I Learned in the Traffic Pattern
Technique
Weather
Checkride
Flight Lesson
Drone Incoming
Career Advisor
Tech Talk
You Can Do It
The Landing 'Time Machine'
Advertiser Index
Debrief
Flight Training - September 2012 - Flight Training - September 2012
Flight Training - September 2012 - Cover2
Flight Training - September 2012 - Contents
Flight Training - September 2012 - 2
Flight Training - September 2012 - 3
Flight Training - September 2012 - President’s Perspective
Flight Training - September 2012 - 5
Flight Training - September 2012 - Right Seat
Flight Training - September 2012 - 7
Flight Training - September 2012 - Letters
Flight Training - September 2012 - 9
Flight Training - September 2012 - Flying Low and Slow
Flight Training - September 2012 - 11
Flight Training - September 2012 - How It Works
Flight Training - September 2012 - Success Story AOPA Summit News
Flight Training - September 2012 - After the Checkride
Flight Training - September 2012 - ASI News Tech Tip
Flight Training - September 2012 - Since You Asked
Flight Training - September 2012 - 17
Flight Training - September 2012 - Training Products News
Flight Training - September 2012 - 19
Flight Training - September 2012 - Flying Carpet
Flight Training - September 2012 - 21
Flight Training - September 2012 - Give Yourself a Lift
Flight Training - September 2012 - 23
Flight Training - September 2012 - 24
Flight Training - September 2012 - 25
Flight Training - September 2012 - 26
Flight Training - September 2012 - 27
Flight Training - September 2012 - Radiohead
Flight Training - September 2012 - 29
Flight Training - September 2012 - 30
Flight Training - September 2012 - 31
Flight Training - September 2012 - Everything I Know About Flying I Learned in the Traffic Pattern
Flight Training - September 2012 - 33
Flight Training - September 2012 - 34
Flight Training - September 2012 - 35
Flight Training - September 2012 - Technique
Flight Training - September 2012 - 37
Flight Training - September 2012 - Weather
Flight Training - September 2012 - 39
Flight Training - September 2012 - 40
Flight Training - September 2012 - Checkride
Flight Training - September 2012 - 42
Flight Training - September 2012 - 43
Flight Training - September 2012 - Flight Lesson
Flight Training - September 2012 - Drone Incoming
Flight Training - September 2012 - Career Advisor
Flight Training - September 2012 - 47
Flight Training - September 2012 - Tech Talk
Flight Training - September 2012 - You Can Do It
Flight Training - September 2012 - The Landing 'Time Machine'
Flight Training - September 2012 - 51
Flight Training - September 2012 - Advertiser Index
Flight Training - September 2012 - 53
Flight Training - September 2012 - 54
Flight Training - September 2012 - 55
Flight Training - September 2012 - Debrief
Flight Training - September 2012 - Cover3
Flight Training - September 2012 - Cover4
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