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WSP06088
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Last modified
1/26/2010 2:21:12 PM
Creation date
10/12/2006 1:25:42 AM
Metadata
Fields
Template:
Water Supply Protection
File Number
8210.470
Description
Pacific Southwest Interagency Committee
State
CO
Basin
Colorado Mainstem
Water Division
5
Date
12/1/1962
Author
PSIAC
Title
Limitations in Hydrologic Data as Applied to Studies of Water Control and Water Management - December 1962
Water Supply Pro - Doc Type
Report/Study
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<br />001405 <br /> <br />1II. 2 <br /> <br />" <br /> <br />At s~e stations, a continuous trace of temperature is obtained <br />from a thermograph instrument. Most of such instruments are clock- <br />driven and .will operate up to 8 days without servicing. They are not <br />as accurate as the official mercury~in-glass or alcohol-in-glass <br />therm~eters, but records from them may be adjusted to readings from <br />those offioial therm~eters. <br /> <br />" <br /> <br />Hourly air temperatures are taken at approximately 300 Weather <br />Bureau stations in the United states, also at some Federal Aviation <br />Agencr,y stations. <br /> <br />Upper~air temperatures are measured at selected Weather Bureau <br />stations, by" radiosonde flights every 12 hours up to an altitude of <br />about 100,000 feet. <br /> <br />Dependability of observations <br />Effects of exposure <br /> <br />Temperatures measured at stations on steep south- or west~facing <br />slopes are likely to average too high, owing to the angle of the sun's <br />rays in daytime and to drainage of cold air away from the slope at <br />night. Theil"Mometers exposed on a roof top usually indicate higher <br />minimum temperatures than those at the standard level, owing to the <br />usual night'-time temperature "inversion" near the land surface. <br />Temperature' observations taken in a hollow usually will show average <br />minima much lower than in the surrounding area, owing to night-time <br />drainage of: cold air. Although the effect is small, average temperatures <br />in urban areas tend to be greater than in adjacent rural areas., Generally, <br />the average temperature at a city station has been found to increase as . <br />the city expands. These effects should be weighed if the records are to <br />be used for disclosing climatic trends or for detailed correlation analyses. <br />Accumulation of snow around a temperature station may bring the point of <br />observation too close to the effective land surface and so within a oon- <br />representat:Lvll layer of a:Lr. In such instances, rough adjustments may <br />be made according to a generalized vertical temperature profile. <br /> <br />. <br /> <br />Other sources of error <br /> <br />y <br /> <br />Possible errors in temperature measurements include those due to <br />reading a ~um therm~eter in the hori~ontal position; in a minimum <br />thermometer:, the indicator displaced by vibration; sepal'ation of the <br />alcohol or lllercury colunm in the thermometer; and, "retre.ater" max:imuJn <br />thermometerS. In such instances of instrumental error, also in errors of <br />technique, commonly there is no rational basis for adjusting the published <br />records of temperature. <br /> <br />
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