A Comparison between Circulation Statistics Computed from Conventional Data and NMC Hough Analyses

Richard D. Rosen Environmental Research & Technology, Inc., Concord, MA 01742

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David A. Salstein Environmental Research & Technology, Inc., Concord, MA 01742

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Abstract

Statistics concerning the budgets of angular momentum heat and water vapor over the Northern Hemisphere are computed by two different methods for the winter of 1976–77. The first method employs an objective analysis scheme applied to the set of conventional upper air sounding obtained from the hemispheric network of rawinsonde stations. The second method uses grid-point values produced daily by the NMC global Hough analysis based on data from several sources. Our results show that the gridded Hough data do not contain mean meridional circulations, thus seriously limiting their usefulness for studies in which these cells play a major role. In addition, the gridded data appear to yield unreasonably large values of water vapor. On the other hand, they produce a realistic temperature structure and seem quite adequate for use in studies of midlatitude waves and their transports. They have also proven much easier to work with than the conventional station data. We find, too, that these station data have their own deficiencies caused largely by gaps in the rawinsonde network, such as those resulting from the loss of several ocean weather ship stations since 1973.

Our study also provides an added appreciation for the highly amplified nature of atmospheric waves during the 1976–77 winter. A strong conversion of kinetic energy from its eddy to zonal mean state and a large standing eddy heat flux are both evident. Additionally, transient eddy momentum fluxes were found to peak at 230 mb, a level not usually included in previous general circulation statistics.

Abstract

Statistics concerning the budgets of angular momentum heat and water vapor over the Northern Hemisphere are computed by two different methods for the winter of 1976–77. The first method employs an objective analysis scheme applied to the set of conventional upper air sounding obtained from the hemispheric network of rawinsonde stations. The second method uses grid-point values produced daily by the NMC global Hough analysis based on data from several sources. Our results show that the gridded Hough data do not contain mean meridional circulations, thus seriously limiting their usefulness for studies in which these cells play a major role. In addition, the gridded data appear to yield unreasonably large values of water vapor. On the other hand, they produce a realistic temperature structure and seem quite adequate for use in studies of midlatitude waves and their transports. They have also proven much easier to work with than the conventional station data. We find, too, that these station data have their own deficiencies caused largely by gaps in the rawinsonde network, such as those resulting from the loss of several ocean weather ship stations since 1973.

Our study also provides an added appreciation for the highly amplified nature of atmospheric waves during the 1976–77 winter. A strong conversion of kinetic energy from its eddy to zonal mean state and a large standing eddy heat flux are both evident. Additionally, transient eddy momentum fluxes were found to peak at 230 mb, a level not usually included in previous general circulation statistics.

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