COLD AIR POOLS IN CROOKED CREEK VALLEY, WHITE MOUNTAINS, CA

Crooked Creek is a subalpine valley in the White Mountains of California east of the town of Bishop, CA. A cold air pool results when temperatures at lower elevations, such a valley, are colder than the temperatures of surrounding slopes and ridges. This causes an inverted lapse rate or temperature inversion where lower elevations are colder than higher elevations. Tree growth had been inhibited in the bottom of the valley by the cold air pool. However, young trees are now growing at elevations below the established treeline defined by large, mature limber and bristlecone pines (Pinus flexilis and Pinus longaeva). This suggests that in recent decades the inversion strength has decreased. This study’s goals are to determine the strength and frequency of the inversions in Crooked Creek. To calculate inversions, the annual average temperature, humidity, precipitation, and wind speed collected from the Crooked Creek Weather Station for each year from 2006-2010 was analyzed. Since inversions are typically a nighttime phenomenon, only data from night hours, 2000 to 0600, were used to evaluate weather conditions that are indicators of cold air pools. Contrary to expectations, the Crooked Creek weather history shows that humid nights had stronger inversions. Higher wind speeds reduce the ability for a cold air pool to form since it causes turbulence and mixing of cold and warm air. Although too short a time frame to be statistically significant, from 2006 to 2010 there was a slight increase in temperature and a decrease in wind speed and humidity. Thus, two of three factors that increase inversions in general decreased over the four year span. In addition to the strength, the shape of the cold air pool was analyzed. Temperature loggers were deployed in the valley in transects running up the slope to better show the relationship between temperature and elevation. In Crooked Creek valley, the pool was about 30 meters deep with the pool being about 10 degrees Celsius colder than the air above. The air was coldest coming down from a saddle in the valley to the N, rather than the broad opening to the SW.