Atmos. Chem. Phys. Discuss., 9, 25409-25441, 2009
© Author(s) 2009. This work is distributed
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This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
Atmospheric diurnal and semi-diurnal variations observed with GPS radio occultation soundings
F. Xie1,*, D. L. Wu1, C. O. Ao1, and A. J. Mannucci1
1Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA
*now at: Joint Institute for Regional Earth System Science and Engineering (JIFRESSE), University of California, Los Angeles, California, 90095, USA

Abstract. Diurnal and semi-diurnal variations, driven by solar forcing, are two fundamental modes in the Earth's weather and climate system. Radio occultation (RO) measurements from the six COSMIC satellites (Constellation Observing System for Meteorology Ionosphere and Climate) provide rather uniform global coverage with high vertical resolution, all-weather and diurnal sampling capability. This paper analyzes the diurnal and semi-diurnal variations of both temperature and refractivity from two-year (2007–2008) COSMIC RO measurements in the troposphere and stratosphere. The RO observations reveal both propagating and trapped vertical structures of diurnal and semi-diurnal variations, including transition regions near the tropopause where data with high vertical resolution are critical. In the tropics the diurnal amplitude in refractivity decreases with altitude from a local maximum in the planetary boundary layer and reaches the minimum around 14 km and then further increase amplitude in the stratosphere. The upward propagating component of the migrating diurnal tides in the tropics is clearly captured by the GPS RO measurements, which show a downward progression in phase from upper troposphere to the stratopause with a vertical wavelength of about 25 km. Below 500 hPa (~5.5 km), seasonal variations of the peak diurnal amplitude in the tropics follow the solor forcing change in latitude, while at 30 km the seasonal pattern reverses with the diurnal amplitude peaking at the opposite side of the equator relative to the solar forcing. Polar regions shows large diurnal variations in the stratosphere with strong seasonal variations and the cause(s) of these variations require further investigations.

Citation: Xie, F., Wu, D. L., Ao, C. O., and Mannucci, A. J.: Atmospheric diurnal and semi-diurnal variations observed with GPS radio occultation soundings, Atmos. Chem. Phys. Discuss., 9, 25409-25441, doi:10.5194/acpd-9-25409-2009, 2009.
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