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Scientific Investigations Report 2008–5201

Scientific Investigations Report 2008–5201

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Meteorological Data

Daily Lakewide Meteorological Conditions

Lakewide daily average meteorological conditions shown in figure 7 provide information about the general behavior of these environmental parameters throughout the lake during the 2005 and 2006 field season. Time series plots of 2005 data are included to provide an interannual comparison. Daily average wind speed was mostly less than 5 m/s from June through August during both years. However, in 2005 lakewide daily median wind speed exceeded 5 m/s during some days in mid-June and late August. In both years, daily average wind speed beginning in September was more variable. Average air temperature followed similar patterns in both years gradually increasing from June through July and then gradually decreasing from August through October. Average relative humidity largely followed the inverse of air temperature patterns in both years. These patterns of air temperature and relative humidity are typical of the hot, dry summers of the Upper Klamath Lake basin. Average daytime solar radiation was more variable and periodically less intense through much of July and August 2006 relative to 2005, indicating that these months were somewhat cloudier in 2006.

Wind Histograms

Wind speed and direction determine the circulation patterns of the water in Upper Klamath Lake. This phenomenon has been verified with a hydrodynamic model of the lake (Wood and others, 2008) and with the placement of acoustic Doppler current profilers in the lake (Wood and others, 2006). Because the wind and the currents are so tightly coupled, the preliminary modeling effort also determined that spatially accurate wind data from the entire lake is required, rather than data collected from only a single site. Before meteorological measurements were collected at several sites on and around the lake in 2005, little was understood about wind characteristics at different locations on the lake. In 2006, meteorological data were collected at the same sites as 2005 in continued support of the modeling effort (fig. 2).

Wind histograms (fig. 8) provide a summary of wind direction and speed at each site. These histograms show the relative frequency of occurrence of wind in four speed categories from each 5-degree direction category around 360 degrees of direction. The wind speed histogram bars are stacked in each 5-degree direction category, with bars for the strongest winds on top. Because the histograms show simple counts of direction readings categorized by wind speed, no temporal filters were applied to the data used in these plots.

Wind characteristics at each site were nearly identical to characteristics shown on the histograms from 2005 (Hoilman and others, 2008). The prevailing westerly winds in the northern one-third of the lake measured at site MDN MET and WMR MET, were funneled by the topography surrounding the main body of the lake into a narrow range in northwesterly winds measured at site MDL MET. This same narrow range of northwesterly winds was observed for most winds greater than 5 m/s at the land-based HDB MET and SSHR MET sites in the southern part of the lake, although winds less than 5 m/s primarily came from the northeast and south at site HDB MET. The range of prevailing northwesterly winds at site SSHR MET is narrower than at site MDL MET, perhaps because the lake basin narrows between the surrounding ridges at the southern end. Overall, data from 2005 and 2006 indicate that the prevailing winds over the northern part of the lake are westerly, and these prevailing winds become northwesterly over the middle and southern part of the lake.

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