Dynamical Properties of the Tropical Atmosphere Derived from Radiosonde Observations at San Cristobal and Singapore

Abstract

Operational radiosonde data at San Cristóbal (0.90 S, 89.62 W; eastern Pacific) are compared with those at Singapore (1.37 N, 103.98 E; western Pacific) intending to explore the differences in the dynamical properties of the tropopause region and in the activities of atmospheric waves between the eastern and the western tropical Pacific. The interannual variations in the meteorological parameters of the tropopause region are found to be almost synchronized between the two stations and do not show direct correspondence with the time evolution of El Niñ o. These evidences, as opposed to the general expectation of the strong influence of sea surface temperature variations on the tropopause properties, suggest that the tropospheric dynamical forcing is not a prevailing factor that drives the interannual variation of the tropical tropopause properties for these stations. The dynamical parameters of the tropopause region are affected by passages of vertically propagating atmospheric waves that characterize the time evolution of daily sounding data. The variations with the time scales of 15 to 20 days are identified as equatorial Kelvin waves of zonal wave number 1, which is consistent with the observed out-ofphase relationship between the two stations. The perturbations in the tropospheric temperature and wind are also brought about by those waves with the typical time scales of several days. These waves are more pronounced over San Cristóbal than in Singapore. As the convections are more active and reach higher altitude in the western than in the eastern Pacific, this evidence implies that the altitude rather than the strength of convection is more important in characterizing the daily fluctuations of the tropical troposphere. The differences between the two stations in the time evolution and magnitude of the quasibiennial oscillation in the equatorial stratosphere are found to be marginal, although occasional differences in the onset time and the magnitude of zonal wind acceleration could be pointed out.

Seasonal and interannual variations of temperature in the tropical tropopause layer (TTL) over Indonesia based on operational rawinsonde data during 1992–1999

“…The peak-to-peak difference is largest ($6 K) at 18.5 km (70 hPa). The annual variation observed over Indonesia is similar to that observed at other longitudinal sections in the tropics [Reed and Vicek, 1969;Reid and Gage, 1996;Seidel et al, 2001;Hasebe and Koyata, 2004;Fortuin et al, 2006]. The longitudinal homogeneity of the annual variation was also confirmed using satellite data, and the correlation between the annual variation of the lower-stratospheric temperature and annual change in total ozone became clear [Shiotani, 1992].…”

Space‐time variability of equatorial Kelvin waves and intraseasonal oscillations around the tropical tropopause

“…Though the maximum values and their seasonality at 150 hPa are almost similar to those at 100 hPa, the longitudinal distribution is quite different; the active longitudes are found in the Eastern Hemisphere at 100 hPa, but in the Western Hemisphere at 150 hPa. Observations on Kelvin waves have been done mostly in the Eastern Hemisphere as introduced in section 1, but there is evidence for the existence as shown by Fujiwara et al [2001] and Hasebe and Koyata [2004] using radiosonde data at San Cristóbal Island (0.9°S, 89.6°W) in the eastern Pacific. The seasonal and longitudinal variations of Kelvin wave activities at 200 hPa and 250 hPa are basically similar to those at 150 hPa except that the square amplitudes are smaller than those at 150 hPa (not shown).…”