Meteorological Measurements

Meteorological Measurements at the 70^th Street East Blow Sand Site

RES Environmental installed a 10-meter wind speed and direction monitor at the 70^th Street East blow sand site in the fall of 2002. Figures 4, 5, & 6 show typical wind patterns during a storm winter (January-February), a windy spring (April-May) and a typical summer (July – August).

The Mojave Desert, and more specifically the Antelope Valley, is a windy location during the early spring through fall. In the afternoon, thermally driven winds are typically in the 7-12 m/sec range. March through about early June are the windiest months, resulting from a combination of both thermal and synoptically driven winds. During the long hot summer, the winds are predominately from the southwest. Beginning in November though about February, there is a more northerly component to the winds, in response to the “offshore” fair weather winds which dominate the desert during this period. During this particular January-February 2003, there were a lot a strong winds from the southeast, an indicator of the numerous storms passing through the area.

From field observations, we know that when wind gusts exceed 30 mph, saltation of disturbed Antelope Valley soil can begin, resulting in blowing dust and elevated PM levels. Table 7 displays the number of gusts (winds of at least 3 sec duration) by month for 2004. As expected, the least windy period was during the winter months of November – February. However, March 2004 was relatively calm. During this period we had a strong ridge of high pressure over this part of the western US resulting in light northeasterly offshore surface winds. As expected the windiest months were April - May with the highest gust occurring on May 10 at 1700. During this 2004 summer, there were also several windy periods because of generally weak troughiness over the southwestern US. October, normally one of the lowest wind speed months had elevated winds because of early season storms and strong troughs over the western US associated with weak El Nino conditions.