Detailed Analysis of Horizontal Wave Parameters using Radio Occultation Data

A. HASER, T. SCHMIDT, A. DE LA TORRE, J. WICKERT, J. FISCHER

Hawaii

Conferencia; CHAPMAN CONFERENCE; 2011

American Geophysical Union

Ern et al. (2004) introduced a method to derive horizontal wave parameters along the adjacent line of two vertical temperature profiles. The horizontal wavenumber kh is given by the ratio of the phase shift
ij and the spatail distance
xij between the regardet profiles at one altitude kh =
ij/
xij . We apply this method to GPS radio occultation (RO) profiles from the six-satellites constellation COSMIC/FORMOSAT-3, delivering approximately 2500 temperature profiles daily. The RO technique is a limb sounding method that is sensitive to gravity waves with small ratios of vertical to horizontal wavelength. To extract the real horizontal wavelength, a third measurement is needed. In the early mission months (April to Decmber 2006) several triads of RO profiles are found, due to the close flying arrangement of the satellites. Before we apply this method to our dataset, a theoretical analysis is made. A sensitivity study of the Ern method shows, that the results for the horizontal wavenumber and therefore all follow up products (like wavelength or momentum flux) have a high dependency on the horizontal distances of the measured profiles. Therefore the phase shift must have a lower limit, which raises with increasing distance between the profiles. Another restrain is, that the regarded profiles must be within one pi-phase for the Ern method to deliver the real horizonral wavelength, once the regarded profiles are futher apart, the results for horizontal wavelength will represent an upper boundary of the wavelength. Restrictions like the dominant vertical wavelength and a phase shift and the wavenumber comparission will be discussed. Additionally a case study in the Andes mountains is presented, delivering wavelength between 30 and 300 km for altitudes from 20 to 27 km. These results are verified using the Weather and Forecast model (WRF). From global analysis for August 1 and December 2006, results for the horizontal wavelength of several hundert up to 2500 km are derived.