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Water vapor variance measurements using a Raman lidarBecause of the importance of atmospheric water vapor variance, we have analyzed data from the NASA/Goddard Raman lidar to obtain temporal scales of water vapor mixing ratio as a function of altitude over observation periods extending to 12 hours. The ground-based lidar measures water vapor mixing ration from near the earth's surface to an altitude of 9-10 km. Moisture profiles are acquired once every minute with 75 m vertical resolution. Data at each 75 meter altitude level can be displayed as a function of time from the beginning to the end of an observation period. These time sequences have been spectrally analyzed using a fast Fourier transform technique. An example of such a temporal spectrum obtained between 00:22 and 10:29 UT on December 6, 1991 is shown in the figure. The curve shown on the figure represents the spectral average of data from 11 height levels centered on an altitude of 1 km (1 plus or minus .375 km). The spectra shows a decrease in energy density with frequency which generally follows a -5/3 power law over the spectral interval 3x10 (exp -5) to 4x10 (exp -3) Hz. The flattening of the spectrum for frequencies greater than 6x10 (exp -3) Hz is most likely a measure of instrumental noise. Spectra like that shown in the figure are calculated for other altitudes and show changes in spectral features with height. Spectral analysis versus height have been performed for several observation periods which demonstrate changes in water vapor mixing ratio spectral character from one observation period to the next. The combination of these temporal spectra with independent measurements of winds aloft provide an opportunity to infer spatial scales of moisture variance.
Document ID
19920021797
Acquisition Source
Legacy CDMS
Document Type
Conference Paper
Authors
Evans, K.
(Hughes STX, Inc., Lanham MD., United States)
Melfi, S. H.
(NASA Goddard Space Flight Center Greenbelt, MD, United States)
Ferrare, R.
(Universities Space Research Association Columbia, MD., United States)
Whiteman, D.
(NASA Goddard Space Flight Center Greenbelt, MD, United States)
Date Acquired
September 6, 2013
Publication Date
July 1, 1992
Publication Information
Publication: NASA. Langley Research Center, 16th International Laser Radar Conference, Part 2
Subject Category
Meteorology And Climatology
Accession Number
92N31041
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

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