26th Conference on Hurricanes and Tropical Meteorology

Wednesday, 5 May 2004
Comparison of convective environments in deep tropical and extratropical atmospheres with 19892002 radiosonde data
Richelieu Room (Deauville Beach Resort)
Lan Yi, National University of Singapore, Singapore; and H. Lim
Poster PDF (79.4 kB)
A quantitative evaluation of convective environments in tropical and extratropical atmospheres is performed by using twice daily radiosonde data at three stations for a 14 year period from 1989 to 2002. The three stations are (1) Singapore Changi airport (SIN) at 1.36oN, 103.98oE, (2) Little Rock of Arkansas US (LR) at 34.73oN, 92.23oW, and (3) Beijing China (BJ) at 39.93oN, 116.28oE. The elevations of the three stations are 16 m, 78 m, and 55 m, respectively. Nearly 30,000 soundings are inspected in this study.

In SIN, less than 5 m/s wind shears between 0-6 km occur 80% of time, and 5-10 m/s shears occur 19% of time, and 10-15 m/s, only 1% of time. Stronger wind shears (10-15 m/s) appear about 10 times more frequently (10%) in LR, while each of the 0-5 m/s and 5-10 m/s shears accounts for 40% of the total frequency distribution. The frequency distribution of various wind shears in BJ is somewhat in the range between SIN and LR. For the convective available potential energy (CAPE), SIN has about 1000-2000 J/kg 60% of time, while it is 10% less in LR, and there is a further 10% decrease in BJ. There are more spreads of higher (>3000 J/kg) and lower CAPE (0~250 J/kg) values in the midlatitude stations than in the tropical station. For the convective inhibition (CIN), BJ has more frequencies of large CIN (>100 J/kg) than LR and SIN, with CIN = 340 20 J/kg occurring 9% of time in BJ, 1.5% in LR and 0.2% in SIN. For CIN = 20 10 J/kg, it occurs 75% of time in SIN, 45% of time in LR, and 10% in BJ. Comparison of the lifting condensation level (LCL), level of free convection (LFC), and Equilibrium Level (EL) among the three stations discloses that the LCL and the LFC in the tropical atmosphere are lower than those in the extratropical atmosphere by about 100 hPa, and the EL is approximately 40-400 hPa higher depending on the season, therefore, tropical convection is generally lower and deeper.

The atmospheric lapse rate, static stability, and potential stability are also examined on the climatological scale for these three stations. Consistency is found between the differences in these quantities and those in the tropical and extratropical convection organization and development. Further understanding is pursued of the Rotunno, Klemp, and Weisman (RKW) theory (Rotunno et al 1988), and the gravity wave-CISK theory (Raymond 1975), and their applicability to the forecast of convective self organization in the tropical atmosphere.

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