Variability of Water Vapor, Infrared Radiative Cooling, and Atmospheric Instability for Deep Convection in the Equatorial Western Pacific

Chidong Zhang Division of Meteorology and Physical Oceanography, Rosenstiel School of Marine and Atmospheric Science, University of Miami, Miami, Florida

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Ming-Dah Chou Laboratory for Atmospheres, NASA/Goddard Space Flight Center, Greenbelt, Maryland

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Abstract

In the troposphere of the equatorial western Pacific, the water vapor variability dominates the temperature variability in changing the clear-sky infrared (IR) cooling rate. The large water vapor variability, especially its bimodal distribution at certain levels of the upper troposphere, leads to distinct structures of the clear-sky IR radiative cooling rate. The IR cooling rate, its maximum normally in the upper troposphere (∼300 hPa) and minimum in the lower troposphere (∼650 hPa), tends to become vertically uniform when the upper troposphere is abnormally dry. A local, maximum IR cooling rate may occur in the boundary layer when the lower troposphere becomes extraordinarily dry. The changes in IR cooling due to the water vapor variability affect the rate of generation of convective available potential energy (CAPE) and the conditional instability for deep convection. Little or no mean rainfall over an area of roughly 3 × 105 km2 is observed when either the rate of generation of CAPE suffers from a reduction (magnitude of 50 J kg−1 day−1) or IR cooling decreases with height. The observed variability of water vapor results from both local vertical processes and the large-scale horizontal circulation. Horizontal advection accounts for a large fraction of the drying that is responsible for the changes in the IR cooling profile and in the atmospheric instability for deep convection. These results suggest that interactions among water vapor, radiation, and deep convection must be assessed by fully taking the large-scale circulation into consideration. This study is based on an analysis of upper-air soundings collected during the Tropical Ocean Global Atmosphere Coupled Ocean–Atmosphere Response Experiment Intensive Observing Period and calculations of a radiative transfer model.

Corresponding author address: Prof. Chidong Zhang, 4600 Rickenbacker Causeway, MPO, Miami, FL 33149-1098.

Email: czhang@rsmas.miami.edu

Abstract

In the troposphere of the equatorial western Pacific, the water vapor variability dominates the temperature variability in changing the clear-sky infrared (IR) cooling rate. The large water vapor variability, especially its bimodal distribution at certain levels of the upper troposphere, leads to distinct structures of the clear-sky IR radiative cooling rate. The IR cooling rate, its maximum normally in the upper troposphere (∼300 hPa) and minimum in the lower troposphere (∼650 hPa), tends to become vertically uniform when the upper troposphere is abnormally dry. A local, maximum IR cooling rate may occur in the boundary layer when the lower troposphere becomes extraordinarily dry. The changes in IR cooling due to the water vapor variability affect the rate of generation of convective available potential energy (CAPE) and the conditional instability for deep convection. Little or no mean rainfall over an area of roughly 3 × 105 km2 is observed when either the rate of generation of CAPE suffers from a reduction (magnitude of 50 J kg−1 day−1) or IR cooling decreases with height. The observed variability of water vapor results from both local vertical processes and the large-scale horizontal circulation. Horizontal advection accounts for a large fraction of the drying that is responsible for the changes in the IR cooling profile and in the atmospheric instability for deep convection. These results suggest that interactions among water vapor, radiation, and deep convection must be assessed by fully taking the large-scale circulation into consideration. This study is based on an analysis of upper-air soundings collected during the Tropical Ocean Global Atmosphere Coupled Ocean–Atmosphere Response Experiment Intensive Observing Period and calculations of a radiative transfer model.

Corresponding author address: Prof. Chidong Zhang, 4600 Rickenbacker Causeway, MPO, Miami, FL 33149-1098.

Email: czhang@rsmas.miami.edu

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  • Ackerman, T. P., K.-N. Liou, F. P. J. Valero, and L. Pfister, 1988: Heating rates in tropical anvils. J. Atmos. Sci.,45, 1606–1623.

  • Arakawa, A., and W. H. Schubert, 1974: Interaction of a cumulus cloud ensemble with the large-scale environment: Part I. J. Atmos. Sci.,31, 674–701.

  • Brown, R. G., and C. Zhang, 1997: Variability of midtropospheric moisture and its effect on cloud-top height distribution during TOGA COARE. J. Atmos. Sci.,54, 2760–2774.

  • Chen, S. S., R. A. Houze, and B. E. Mapes, 1996: Multiscale variability of deep convection in relation to large-scale circulation in TOGA COARE. J. Atmos. Sci.,53, 1380–1409.

  • Chou, M.-D., and M. J. Suarez, 1994: An efficient thermal infrared radiation parameterization for use in general circulation models. NASA Tech. Memo. 104606, Vol. 3, 85 pp.

  • ——, and W. Zhao, 1997: Estimation and model validation of surface solar radiation and cloud radiative forcing using TOGA COARE measurements. J. Climate,10, 610–620.

  • Cole, H., 1993: The TOGA COARE ISS radiosonde temperature and humidity sensor errors. NCAR Tech. Rep., 28 pp. [Available from Surface and Sounding System Facility, NCAR, Boulder, CO 80303.].

  • Cox, S. K., and K. T. Griffith, 1979: Estimates of radiative divergence during phase III of the GARP Atlantic Tropical Experiment: Part II. Analysis of Phase III results. J. Atmos. Sci.,36, 586–601.

  • Dharssi, I., R. Kershaw, and W. K. Tao, 1997: Sensitivity of a simulated tropical squall line to long-wave radiation. Quart. J. Roy. Meteor. Soc.,123, 187–206.

  • Doherty, G. M., and R. E. Newell, 1984: Radiative effects of changing atmospheric water vapour. Tellus,36B, 149–162.

  • Emanuel, K. A., 1994: Atmospheric Convection. Oxford University Press, 580 pp.

  • Fitzjarrald, D. R., and M. Garstang, 1981: Vertical structure of the tropical boundary layer. Mon. Wea. Rev.,109, 1512–1526.

  • Guan, H., R. Davies, and M. K. Yau, 1995: Longwave radiative cooling rates in axially symmetric clouds. J. Geophys. Res.,100 (D2), 3213–3220.

  • Gutzler, D. S., 1993: Uncertainties in climatological tropical humidity profiles: Some implications for estimating the greenhouse effect. J. Climate,6, 978–982.

  • Hu, Q., and D. A. Randall, 1994: Low-frequency oscillations in radiative-convective systems. J. Atmos. Sci.,51, 1089–1099.

  • Kain, J. S., and J. M. Fritsch, 1990: A one-dimensional entraining/detraining plume model and its application in convective parameterization. J. Atmos. Sci.,47, 2784–2802.

  • Lin, X., and R. H. Johnson, 1996a: Kinematic and thermodynamic characteristics of the flow over the western Pacific warm pool during TOGA COARE. J. Atmos. Sci.,53, 695–715.

  • ——, and ——, 1996b: Heating, moistening, and rainfall over the western Pacific warm pool during TOGA COARE. J. Atmos. Sci.,53, 3367–3383.

  • Lucas, C., 1997: Environmental effects on mesoscale convective systems. Proc. 22d Conf. on Hurricanes and Tropical Meteorology, Fort Collins, CO, Amer. Meteor. Soc., 162–163.

  • Madden, R. A., and P. R. Julian, 1971: Description of a 40–50 day oscillation in the zonal wind in the tropical Pacific. J. Atmos. Sci.,28, 702–708.

  • ——, and ——, 1972: Description of global-scale circulation cells in the Tropics with a 40–50 day period. J. Atmos. Sci.,29, 1109–1123.

  • Mapes, B. E., and R. A. Houze, 1995: Diabatic divergence profiles in western Pacific mesoscale convective systems. J. Atmos. Sci.,52, 1807–1828.

  • ——, and P. Zuidema, 1996: Radiative-dynamical consequences of dry tongues in the tropical troposphere. J. Amos. Sci.,53, 620–638.

  • Mehta, A. V., and E. A. Smith, 1997: Variability of radiative cooling during the Asian summer monsoon and its influence on intraseasonal waves. J. Atmos. Sci.,54, 941–966.

  • McClatchey, R. A., R. W. Fenn, J. E. A. Selby, F. E. Volz, and J. S. Garing, 1972: Optical properties of the atmosphere, 3d ed. AFCRL-72-0497, 108 pp. [NTIS N7318412].

  • Numaguti, A., R. Oki, K. Nakamura, K. Tsuboki, N. Misawa, T. Asai, and Y.-M. Kodama, 1995: 4–5-day-period variation and low-level dry air observed in the equatorial western Pacific during the TOGA COARE IOP. J. Meteor. Soc. Japan,73, 267–290.

  • Parsons, D., and Coauthors, 1994: The integrated sounding system: Descriptions and preliminary observations from TOGA COARE. Bull. Amer. Meteor. Soc.,75, 553–567.

  • Ramsey, P. G., and D. G. Vincent, 1995: Computation of vertical profiles of longwave radiative cooling over the equatorial Pacific. J. Atmos. Sci.,52, 1555–1572.

  • Randall, D. A., Q. Hu, K.-M. Xu, and S. K. Krueger, 1994: Radiative-convective disequilibrium. Atmos. Res.,31, 315–327.

  • Rogers, C. D., and C. D. Walshaw, 1965: The computation of infra-red cooling rate in planetary atmospheres. Quart. J. Roy. Meteor. Soc.,92, 67–92.

  • Sherwood, S., 1995: The maintenance of the tropical water vapor distribution. Ph.D. thesis, University of California, San Diego, 181 pp.

  • Sheu, R.-S., and G. Liu, 1995: Atmospheric humidity variations associated with westerly wind bursts during Tropical Ocean Global Atmosphere (TOGA) Coupled Ocean Atmosphere Response Experiment (COARE). J. Geophys. Res.,100, 25 759–25 768.

  • Spencer, R. W., 1993: Global oceanic precipitation from the MSU during 1979–91 and comparisons to other climatologies. J. Climate,6, 1301–1326.

  • Stommel, H., 1947: Entrainment of air into a cumulus cloud. J. Meteor.,4, 91–94.

  • Udelhofen, P. M., and D. L. Hartmann, 1995: Influence of tropical cloud systems on the relative humidity in the upper troposphere. J. Geophys. Res.,100, 7423–7440.

  • Väisälä, 1990: HMP 35C humidity and temperature probe. Väisälä, Inc., 9 pp. [Available from Väisälä Inc., 100 Commerce Way, Woburn, MA 01801-1068.].

  • Webster, P. J., and G. L. Stephens, 1980: Tropical upper-tropospheric extended clouds: Inferences from Winter MONEX. J. Atmos. Sci.,37, 1521–1541.

  • ——, and R. Lukas, 1992: TOGA COARE: The coupled ocean–atmosphere response experiment. Bull. Amer. Meteor. Soc.,73, 1377–1416.

  • Yanai, M., S. Esbensen, and J.-H. Chu, 1973: Determination of bulk properties of tropical cloud clusters from large-scale heat and moisture budgets. J. Atmos. Sci.,30, 611–627.

  • Zhang, C., and H. H. Hendon, 1997: On propagating and standing components of the intraseasonal oscillation in tropical convection. J. Atmos. Sci.,54, 741–752.

  • Zipser, E. J., 1969: The role of organized unsaturated convective downdrafts in the structure and rapid decay of an equatorial disturbance. J. Appl. Meteor.,8, 799–814.

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