Atmospheric diurnal variations observed with GPS radio occultation soundings
- ISSN: 16807316
- DOI: 10.5194/acp-10-6889-2010
The diurnal variation, driven by solar forcing, is a fundamental mode in\nthe Earth's weather and climate system. Radio occultation (RO)\nmeasurements from the six COSMIC satellites (Constellation Observing\nSystem for Meteorology, Ionosphere and Climate) provide nearly uniform\nglobal coverage with high vertical resolution, all-weather and diurnal\nsampling capability. This paper analyzes the diurnal variations of\ntemperature and refractivity from three-year (2007-2009) COSMIC RO\nmeasurements in the troposphere and stratosphere between 30 degrees S\nand 30 degrees N. The RO observations reveal both propagating and\ntrapped vertical structures of diurnal variations, including transition\nregions near the tropopause where data with high vertical resolution are\ncritical. In the tropics the diurnal amplitude in refractivity shows the\nminimum around 14 km and increases to a local maximum around 32 km in\nthe stratosphere. The upward propagating component of the migrating\ndiurnal tides in the tropics is clearly captured by the GPS RO\nmeasurements, which show a downward progression in phase from\nstratopause to the upper troposphere with a vertical wavelength of about\n25 km. At similar to 32 km the seasonal variation of the tidal amplitude\nmaximizes at the opposite side of the equator relative to the solar\nforcing. The vertical structure of tidal amplitude shows strong seasonal\nvariations and becomes asymmetric along the equator and tilted toward\nthe summer hemisphere in the solstice months. Such asymmetry becomes\nless prominent in equinox months.