This preview shows page 1. Sign up to view the full content.
Unformatted text preview: arking lot surrounded by grass. The air over the parking lot will be heated more
and start to rise. So now our parcel starts out at 35°C and the surrounding air is
30°, with an ELR of 5°C per 1000 meters. At 500 meters, the parcel will be 30°
and the surrounding air will be 27.5°. At 1000 meters, the parcel will be 25° and
so will the surrounding air, so the parcel will stop rising. This is a stable situation.
But what if the dew point for that air is 26°? The parcel will reach 26° at 900
meters, before it met the temperature of the surrounding air. Now, the parcel is
rising at the WALR, at 6°C per 1000 meters, so it will continue to rise because it
will always be warmer than the surrounding air. This is an unstable situation and
it will result in rain. Convectional precipitation is caused by differential heating
of the ground surface. If there is enough rising and enough moisture available,
the rising air results in rain. Some of our summer rain is caused by this situation. Atmospheric Moisture:7 Stable Unstable Altitude, m WALR 1000
0 25 30 35
Temperature, °C DALR
ELR 25 30 35
Temperature, °C Orographic Precipitation
Another way of getting the air to rise is to push it over mountains. This is called
orographic precipitation. Imagine the Sierra Nevada in California. Relatively
moist air blows off the Pacific Ocean, carried by the Westerlies and then they run
into the base of the Sierra at 500 meters above sea level, where the air in our
hypothetical example is 30°C. The air will be pushed up by the wind and cool at
the DALR. Let’s say that dew...
View Full Document
This document was uploaded on 10/27/2011 for the course GEOG 1401 at Texas Tech.
- Fall '08