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U.S. GEOLOGICAL SURVEY
Scientific Investigations Report 2008–5026

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Meteorological Conditions

The graphs of lakewide daily median meteorological conditions (fig. 6) provide information about the general behavior of these environmental parameters in the vicinity of the lake throughout the field season. Daily median wind speed generally was constant throughout the study. Some particularly windy periods occurred in mid-June, late August, and mid-September, when lakewide daily median wind speed exceeded 5 m/s. Air temperature gradually increased from June through July and then gradually decreased from August through October. Relative humidity generally followed the inverse of air temperature patterns. Variability in solar radiation was low through July and August; indicating that conditions during these months were mostly sunny. Greater variability in mid-June and again from September onward indicates more periods of cloudiness during these times. These patterns of air temperature, relative humidity, and solar radiation are typical of the hot, dry summers of the Upper Klamath Lake basin.

Wind speed and direction ultimately determine the circulation of the water in Upper Klamath Lake. This phenomenon has been verified with a hydrodynamic model of the lake (Cheng and others, 2005) and with the placement of acoustic Doppler current profilers in the lake (Wood and others, 2006). The hydrodynamic model describes a general clockwise circulation pattern of water in Upper Klamath Lake under northwesterly winds (fig. 7), which are prevalent during the summer.

Because the wind and the currents are so closely related, the preliminary modeling effort also demonstrated the need to collect spatially accurate wind data, rather than data from a single site. Before meteorological measurements were collected at several sites on and around the lake (fig. 2), little was understood about wind characteristics in the vicinity of the lake.

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. The histograms display simple counts of direction readings categorized by wind speed; no temporal filters were applied to the data used in these plots.

The histograms reveal that wind characteristics in the northern part of the lake, represented by MDN MET, differed from those in the main body of the lake, represented by MDL MET. In the northern part of the lake, winds were likely to come from the southwest-to-northwest sector, including most winds greater than 5 m/s, which have more potential to drive lake currents. In the main body of the lake, most winds in all speed categories came from a relatively narrow band to the northwest, because the topographic ridges to the east and west funnel the winds into a narrow range of direction over the main body of the lake. This same narrow band of northwesterly winds was observed for most winds greater than 5 m/s at the land-based HDB MET and SSHR MET sites farther south, although winds less than 5 m/s came primarily from the northeast and south at HDB MET and primarily from the south at SSHR MET. This observation indicates that strong winds blowing from the northwest over the main body of the lake typically continue in this direction over the southern part of the lake. At the land-based meteorological sites in the northern part of the lake, the strongest winds typically came from the northwest at BLB MET and from the west at WMR MET, reinforcing the inference drawn from the MDN MET histogram that westerly winds dominate in the northern part of Upper Klamath Lake.

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