Moisture Tendency Equations in a Tropical Atmosphere

Abstract

Direct diagnostic evaluation of the moisture tendency in the moisture equation is very difficult in practice because two poorly measured terms, moisture convergence and precipitation, dominate the equation. Using the near constancy in space and time of the tropical temperature profile, a variety of energy and entropy based equations have been employed to obtain indirect estimates of the moisture budget. In this paper rigorous versions of the energy and entropy equations are developed. The strengths and weakness of these two formulations are complementary, allowing the authors to estimate moistening and drying tendencies with high confidence when the two formulations are used together. This study applies the theory to data from Tropical Ocean Global Atmosphere Coupled Ocean–Atmosphere Response Experiment (TOGA COARE). The results demonstrate how convection regulates the tropospheric humidity, drying the atmosphere when it becomes too moist, and moistening it when it becomes too dry.

Tropical cyclogenesis and mid-level vorticity

“…This is likely an expression of moisture quasi- the nature of the convection occurring within the vortex. Normal deep convection over the high SSTs of the western tropical Pacific and surrounding areas tends to exhibit topheavy convective mass flux profiles due to the prevalence of large stratiform rain areas associated with the convection (Mapes andHouze, 1993, 1995;Back and Bretherton, 2006;López and Raymond, 2005;. Similar results are found in the western Atlantic and Caribbean (Gjorgjievska and Raymond, 2013).…”

“…López and Raymond (2005) provide further evidence that moisture quasi-equilibrium acts in the tropical environment. These results, based on observations of convection in the western tropical Pacific, show that convection exports moist entropy laterally if the saturation deficit is small and imports entropy if it is large.…”

“…The mesoscale downdrafts occur when convection is dominated by large, organised convective systems with widespread stratiform rain areas. Bottom-heavy profiles occur when these systems do not exist (Zipser, 1969(Zipser, , 1977Houze, 1977;Leary and Houze, 1980;López and Raymond, 2005;etc. ).…”

Multiple equilibria in a cloud‐resolving model using the weak temperature gradient approximation

“…[13] Observations suggest that the sign of NGMS in a convecting region is related to the level of nondivergence in the horizontally averaged circulation [López-Carrillo and Raymond, 2005;Back and Bretherton, 2006]. In particular, when convergence is concentrated at low levels, as expected in the early stages of the development of deep convection, a vertical pressure integral of moist entropy or moist static energy divergence gives a net import of these quantities.…”

Roles of convective heating and boundary-layer moisture asymmetry in slowing down the convectively coupled Kelvin waves

“…Similar arbitrary values of the "effective static stability" parameter were assigned in the simple models for MJO that consists of a first baroclinic mode free atmosphere and a well-mixed planetary boundary layer (PBL) (e.g., Wang and Li 1994;Li and Wang 1994;Xie and Wang 1996). Given that there was uncertainty in estimating the atmospheric vertical velocity, caution was warned to diagnose the "gross moist stability" or the "effective static stability" (Yu et al 1998;López Carrillo and Raymond 2005;Back and Bretherton 2006). Motivated by the previous studies, we intend to diagnose, using a new generation of reanalysis dataset, the "effective static stability" associated with CCKW, in order to reveal how much reduction of CCKW phase speed is attributed to the diabatic heating and whether or not additional mechanism is needed to explain the observed phase speed.…”