Ask Jack: Upper Air Temperatures
Q: I am trying to find out how many degrees Fahrenheit the temperature decreases with each 1,000 feet of elevation. Thanks for your response. -Harry, Phoenix, Ariz.
A: The exact rate at which the temperature changes with elevation differs from day to day and place to place, but I suspect that you are looking for something like an average rate. For example, you might be thinking of going hiking or climbing in northern Arizona’s 10,000-plus foot mountains and wonder what clothing to take based on the temperature at your lower elevation home.
For informal uses like this, assuming that the temperature drops by approximately 3.5 degrees F for each 1,000 feet you go up works well enough. This figure would also help you estimate likely temperatures in mountains based on averages for lower elevation weather stations in the same region.
When more precise values are needed, such as determining how an aircraft will perform at a cruising altitude, you need to obtain the actual and forecast temperatures for the time and places where you’ll be flying. Pilots obtain this data during an ordinary pre-flight weather briefing.
The actual change in temperature with altitude at a particular time and place is called the environmental lapse rate. This is sometimes confused with the “dry adiabatic lapse rate” of 5.4 degrees F per 1,000 feet, which is the rate as which rising air cools. As explained in Chapter 4 of The AMS Weather Book the temperature of the surrounding air does not affect this rate of cooling when the air rises. This chapter also explains why changes in the environmental lapse rate determine whether the atmosphere is stable or unstable and thus what kind of weather is likely.
The arrival of colder or warmer air at ground level is a weather change that directly affects us. The arrival of cold air aloft also brings important weather changes. When cold air moves in aloft it makes the atmosphere more unstable, which in turn makes clouds, rain, and thunderstorms more likely.
Differences in the air’s temperature aloft also determine the speeds and directions of upper air winds, as shown in the graphic on pages 60 and 61 of the AMS Weather Book. This is one of the reasons that observations of upper air temperatures are so important. The Looking aloft” section on pages 137 to 138 of the AMS Weather Book explains how weather balloons and aircraft obtain these observations.
If you want to check the actual weather balloon readings from any location in the world where balloons are launched, you can go to the University of Wyoming upper-air soundings Web pages, select the part of the earth you want to look at, the type of display you want –text list is the easiest to understand–and the date and time range of the observations you want. You then click on one of the weather stations shown on the map.
The resulting table shows the observations from all of the reported heights. Starting on the left, the items in each column are the atmospheric pressure in hectopascales (the same as millibars), the height above sea level in meters, and the temperature at that height in Celsius degrees. As you learn more about meteorology you’ll come to understand what the other columns show for each altitude.