Computer Science – Sound
Scientific paper
Dec 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agufm.a11b0852l&link_type=abstract
American Geophysical Union, Fall Meeting 2006, abstract #A11B-0852
Computer Science
Sound
3319 General Circulation (1223), 3334 Middle Atmosphere Dynamics (0341, 0342), 3362 Stratosphere/Troposphere Interactions, 3389 Tides And Planetary Waves, 3394 Instruments And Techniques
Scientific paper
The stratospheric Brewer-Dobson circulation transports air from the troposphere into the stratosphere in the Tropics, from the Tropics through mid-latitudes to the poles, and downward from the stratosphere into the troposphere at middle and high latitudes. The circulation is composed of diabatic and adiabatic terms, the former resulting from radiative heating rates internal to the atmosphere, and the latter resulting from the deposition of the Eliassen-Palm (E-P) flux associated with planetary-scale atmospheric waves. The adiabatic term is also referred to as the residual mean circulation in the context of isobaric coordinates. While heating rates can be estimated by radiation calculations given profiles of temperature and water vapor, the Eliassen- Palm flux must be deduced from longitudinal fluctuations in horizontal winds and temperature not easily measured on global scales. The Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) carries occultation GPS receivers on each LEO satellite in a six-satellite constellation. Because GPS radio occultation directly measures the geopotential height of constant pressure surfaces from space, it is possible to use the high density of radio occultation data from COSMIC to derive geostrophic or linear winds on scales of ~1000 km daily and thus estimate E-P flux. We have simulated the reconstruction of winds and E-P fluxes from the NCEP reanalysis after simulating a COSMIC-like distribution of radio occultation soundings. We do so by interpolating height and temperature fields in the NCEP reanalysis to occultation geolocations, applying a Bayesian mapping technique to map the interpolated heights and temperatures every day, deriving geostrophic winds, and computing correlations of horizontal winds and temperature. The correlations make up the meridional and vertical components of the E-P flux vector. Finally we compare these E-P fluxes to the exact E-P fluxes in the NCEP reanalysis. Reconstructions of both the horizontal and vertical components of the E-P flux capture the large-scale characteristics of the "true" E-P flux very well. The amplitude of the vertical component of the E-P flux is reconstructed with good accuracy (~10%), but the horizontal component is not reconstructed as well (~40%). [Note that the vertical component of the E-P flux is almost solely responsible for the adiabatic component of the Brewer-Dobson circulation.] The errors in recovery of the amplitudes of the components of the E-P flux are due in roughly equal parts to the analysis of the height fields and the approximation of horizontal winds from these height fields. Improvement in the analysis of the height and temperatures fields is possible, and techniques superior to the geostrophic approximation can be used to better estimate horizontal winds.
Anderson James G.
Leroy Sébastien
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