Atmospheric diurnal variations observed with GPS radio occultation soundings

Abstract

Abstract. The diurnal variation, driven by solar forcing, is a fundamental mode 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 nearly uniform global coverage with high vertical resolution, all-weather and diurnal sampling capability. This paper analyzes the diurnal variations of temperature and refractivity from three-year (2007)(2008)(2009)) COSMIC RO measurements in the troposphere and stratosphere between 30 • S and 30 • N. The RO observations reveal both propagating and trapped vertical structures of diurnal variations, including transition regions near the tropopause where data with high vertical resolution are critical. In the tropics the diurnal amplitude in refractivity shows the minimum around 14 km and increases to a local maximum around 32 km 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 stratopause to the upper troposphere with a vertical wavelength of about 25 km. At ∼32 km the seasonal variation of the tidal amplitude maximizes at the opposite side of the equator relative to the solar forcing. The vertical structure of tidal amplitude shows strong seasonal variations and becomes asymmetric along the equator and tilted toward the summer hemisphere in the solstice months. Such asymmetry becomes less prominent in equinox months.

Impact of land convection on temperature diurnal variation in the tropical lower stratosphere inferred from COSMIC GPS radio occultations

“…above 26 km are the manifestation of migrating tide. The vertical structure, the amplitude and the winter maximum of the tide fully agree with those derived from the CHAMP and COSMIC data (Pirscher et al, 2010;Xie et al, 2010), and the simulations of the Canadian Middle Atmosphere Model (McLandress, 2002). According to these authors, the seasonal variation is attributed to an interference of latitudinal symmetric and anti-symmetric vertically propagating modes of waves with different vertical wavelengths.…”

“…The downward phase propagation of the temperature anomalies in the mid-stratosphere is the well-known signature of migrating tides already reported by previous studies exploiting COSMIC data and showing an increase of amplitude with height and a local maximum in winter (Pirscher et al, 2010;Xie et al, 2010). The temperature diurnal cycle in the lower stratosphere in local summer, of larger amplitude in the SH, is out of phase with the upper-tropospheric diurnal cycle, which displays a late-afternoon warming due to latent heat release during the development phase of convection followed by a nighttime cloud radiative cooling.…”

“…Several studies of the temperature diurnal cycle associated with migrating tide in the stratosphere at low and mid-latitudes are available (e.g. Zeng et al, 2008;Xie et al, 2010;Pircher et al, 2010) but noticeably never distinguishing between continents and oceans.…”

Advances and limitations of atmospheric boundary layer observations with GPS occultation over southeast Pacific Ocean

“…The six-satellite COSMIC constellation is in six inclined orbits with 30 • orbit plane separation, which allow full 24-h local time sampling within one-month at low and mid latitudes (e.g., Pirscher et al, 2010;Xie et al, 2010b). Such diurnal sampling capability is a very appealing feature for compiling the climatology.…”

Exploring Earth's atmosphere with radio occultation: contributions to weather, climate and space weather

“…More recently, Pirscher et al (2010) and Xie et al (2010) used COSMIC observations to study diurnal tides (Figs. 16 and 17).…”