Equatorial Kelvin Waves Observed with GPS Occultation Measurements (CHAMP and SAC-C)

Abstract

Structure and propagation of equatorial Kelvin waves during May 2001 and December 2002 are observed from the temperature profiles in the upper troposphere and the lower stratosphere using CHAMP and SAC-C GPS radio occultation data. Kelvin waves derived from temperature fluctuations characterize eastward phase propagation in time-longitude section and eastward phase tilts with height in altitude-longitude section between 10 and 30 km. The phase progression spans the range indicating the continuity of Kelvin waves from the upper troposphere to the lower stratosphere. Results show that near the tropopause, Kelvin waves fluctuate temperature by 2 K in general, with wave periods of 12.5-14 days for zonal wave number 1 and 9.3-11.0 days for wave number 2, and vertical wavelengths of 7.6-8.5 km in 2001 and of 4.4-5.8 km in 2002.

Characteristics of 10-day Kelvin Wave Observed with Radiosondes and CHAMP/GPS Occultation during the CPEA Campaign (April-May, 2004)

“…In addition, balloons were released eight times a day for five days during the intensive observation period ( (739) and 65% (552) ascended higher than 25 km and 30 km, respectively. Consistent with earlier balloon studies (e.g., Tsuda et al 2004), the balloons generally reached higher altitudes (by approximately 2 km on average) during the daytime compared to the nighttime, with the maximum difference at PD (4.1 km). However, at KL and SG, balloon burst occurred at lower altitudes during the daytime, as shown in Table 2.…”

“…In order to see the horizontal structure of the waves, simultaneous CHAMP/ GPS RO observations are utilized. For extraction of Kelvin waves with zonal wave numbers of 1 and 2 from GPS RO data, the procedure implemented by Tsai et al (2004) is closely followed. We selected the latitude within G10 from equator in order to avoid mixing of waves other than the Kelvin waves, with the height coverage of 10-30 km.…”

“…Therefore, the fitted Ts' are generated every three days and are shifted by one day (three-day running fitting). This method can be effectively used to study Kelvin waves with periods greater than approximately 10 days and with reduced amplitudes for less than seven-day oscillations (Tsai et al 2004;Randel and Wu 2005).…”

“…However, the observations by GPS/ MET were restricted to limited times (prime times). Using one-year GPS RO data with German (CHAMP) and Argentine (SAC-C) satellites, Tsai et al (2004) reported evidence of Kelvin waves in the lower stratosphere. Randel and Wu (2005) extended the study with special emphasis on how these Kelvin waves are influenced by background stratospheric winds and their relation to tropical deep convection.…”

Observations of the 7-day Kelvin Wave in the Tropical Atmosphere During the CPEA Campaign

“…Highly accurate and relatively better vertical resolution (@100 m) of temperature measurements in the troposphere and lower stratosphere have become possible with the advent of the GPS radio occultation technique. Using the GPS measurements, Tsai et al (2004) showed evidence of Kelvin waves spanning the upper troposphere and lower stratosphere (UTLS) region. Randel and Wu (2005) further extended the analysis and observed long-period (@20 days) waves with short vertical wavelengths of 4-8 km.…”