Regional Tropical Precipitation Change Mechanisms in ECHAM4/OPYC3 under Global Warming*

Abstract

Mechanisms of global warming impacts on regional tropical precipitation are examined in a coupled atmosphere–ocean general circulation model (ECHAM4/OPYC3). The pattern of the regional tropical precipitation changes, once established, tends to persist, growing in magnitude as greenhouse gases increase. The sulfate aerosol induces regional tropical precipitation anomalies similar to the greenhouse gases but with opposite sign, thus reducing the early signal. Evidence for two main mechanisms, the upped-ante and the anomalous gross moist stability (M′) mechanisms (previously proposed in an intermediate complexity model), is found in this more comprehensive coupled general circulation model. Preferential moisture increase occurs in convection zones. The upped-ante mechanism signature of dry advection from nonconvective regions is found in tropical drought regions on the margins of convection zones. Here advection in both the atmospheric boundary layer and lower free troposphere are found to be important, with an additional contribution from horizontal temperature transport in some locations. The signature of the M′ mechanism—moisture convergence due to increased moisture in regions of large mean vertical motion—enhances precipitation within strong convective regions. Ocean dynamical feedbacks can be assessed by net surface flux, the main example being the El Niño–like shift of the equatorial Pacific convection zone. Cloud–radiative feedbacks are found to oppose precipitation anomalies over ocean regions.

Mass balance of a slope glacier on Kilimanjaro and its sensitivity to climate

“…This suggestion is consistent with global warming and regional moisture changes, particularly in the tropics (e.g. Chou et al, 2006).…”

Tropical drying trends in global warming models and observations

“…The ''uppedante'' mechanism (11) for drought tendency hypothesizes a differential moistening between convective and nonconvective regions as warming increases the ''ante'' of moisture required to sustain convection. Decreases in precipitation occur on the margins of the convection zones in regions of strong low-level inflow into the convection zones, as has been shown to occur in two model studies (12,13). This mechanism depends on the details of the simulated wind climatology relative to the moisture gradient, and thus the location of the drying is hypothesized to be sensitive among models.…”

The Tropical Response to Extratropical Thermal Forcing in an Idealized GCM: The Importance of Radiative Feedbacks and Convective Parameterization

“…In these two studies, the changes in circulation strength and CCEW speed are interpreted with the concept of ''gross moist stability'' (Neelin and Held 1987;Emanuel et al 1994;Neelin 2007). When the gross moist stability is smaller, theoretical work suggests a stronger and narrower precipitating region (Bretherton and Sobel 2002;Chou and Neelin 2004), slower CCEWs (Neelin et al 1987;Neelin and Yu 1994;Frierson et al 2004), and a larger response to perturbations (Neelin and Su 2005;Chou et al 2006). Thus, in this section, we study the response of the model to the convection scheme parameter RH SBM , which changes the tropical gross moist stability.…”