Japan Geoscience Union Meeting 2021

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[E] Oral

A (Atmospheric and Hydrospheric Sciences ) » A-AS Atmospheric Sciences, Meteorology & Atmospheric Environment

[A-AS01] Large-scale moisture and organized cloud systems

Fri. Jun 4, 2021 1:45 PM - 3:10 PM Ch.07 (Zoom Room 07)

convener:Satoru Yokoi(Japan Agency for Marine-Earth Science and Technology), Hiroaki Miura(The University of Tokyo), Atsushi Hamada(University of Toyama), Masaki Satoh(Atmosphere and Ocean Research Institute, The University of Tokyo), Chairperson:Satoru Yokoi(Japan Agency for Marine-Earth Science and Technology), Atsushi Hamada(University of Toyama)

1:50 PM - 2:10 PM

[AAS01-02] Moisture-temperature relationships of tropical precipitation and some implications for tropical wave dynamics.

★Invited Papers

*Fiaz Ahmed1, David Neelin1, Ángel Adames2 (1.University of California Los Angeles, 2.University of Wisconsin )

Keywords:Tropical precipitation, Moisture

Decades-long satellite and ground observations show that tropical precipitation is highly sensitive to moisture variations. However, tropical precipitation arises from convection, and must therefore also be sensitive to temperature (or rather lapse rate) variations. The observed sensitivities of precipitation to moisture and temperature perturbations are unified and contextualized in a buoyancy framework. In this framework, temperature and moisture fluctuations map to plume buoyancy fluctuations that ultimately govern precipitation. The quantitative details of this framework are constrained by remote sensing observations and reanalysis data. The ideas of convective Quasi-equilibrium (QE) and the convective adjustment have natural expressions in this framework: precipitation emerges when temperature and moisture anomalies are adjusted by convection to maintain near-neutral buoyancy. This picture permits us to showcase the competition between convective adjustment and gravity wave adjustment in a linearized beta-plane model. At small scales, gravity waves erase temperature perturbations much faster than convection so shortwave tropical fluctuations evolve as “moisture modes”. At large scales, convection consumes buoyancy anomalies faster than gravity waves can erase temperature anomalies. Longwave tropical fluctuations therefore evolve as QE modes with a non-negligible temperature signature. A simple test using reanalysis thermodynamic data suggests that the MJO is likely a mixed mode situated between the limits of QE and moisture modes. Water vapor fluctuations dominate tropical thermodynamic variations. However, the role of temperature fluctuations—particularly for planetary-scale tropical transients—must not be discounted.