Latent heat

About: Latent heat is a research topic. Over the lifetime, 13503 publications have been published within this topic receiving 302811 citations.

The Daytime Evolution of the Atmospheric Boundary Layer and Convection over the Tibetan Plateau: Observations and Simulations

Abstract: Based on field observations, theoretical analyses, and numerical simulations, this study investigates the structure and the evolution of the atmospheric boundary layer (ABL) and convection over the Tibetan Plateau during the dry season. Both field observations and numerical simulations show that the convection over the plateau evolves from dry shallow convection in the morning to wet deep convection in the afternoon. The shallow convection is organized, and its major wavelength is controlled by mesoscale hills. The deep convection is not very regular. Both nonlinear scale interactions and latent heat release from convection may play significant roles in the development of the deep convection. However, the deep convection near mountains is related to an interactive process between mountain‐valley circulations and rain evaporative cooling. The mountain‐valley circulations in the afternoon can be either upslope or downslope. The plateau ABL can extend to heights of almost 3 km above the ground surface, and is characterized by a well‐mixed layer of potential temperature. The energy budget in the ABL indicates that the sensible heat is the dominant energy for sustaining the ABL growth, and radiations also play a significant role, but the rain evaporative cooling below the wet convection suppresses ABL development. The ABL evolution is strongly associated with the convective activities. The convection not only efficiently exchanges the quantities between the near‐surface layer and the upper layer, but also enhances the air entrainment near the top of the ABL.

Finite Amplitude Convection Through a Phase Boundary

Abstract: Summary A finite amplitude, numerical model of convective motions through a phase boundary is studied. The phase change is assumed to occur over a finite vertical transition zone in the fluid and thus a continuously stratified model is considered. The motions are driven by horizontal temperature gradients on the boundaries or super-critical vertical stratification. In the case of Rayleigh instability, the numerical results reproduce the neutral curve previously obtained in the analytic solution of the linearized problem. When the parameters of the problem are chosen to simulate the olivine-spinel transition in the upper mantle, the following results are obtained: (1) the vertical scale of motion is the entire depth of the fluid; (2) the horizontal scale is not significantly changed from the case of a single phase fluid; (3) the amplitude of the motion is not significantly changed, due to buoyancy changes at the phase boundary being offset by corresponding sources and sinks of latent heat; and (4) the phase boundary varies in depth by as much as 30 km when the vertical velocities are of the order of 10–1 cm yr–1.

Crystallization, sublimation, and gas release in the interior of a porous comet nucleus

Abstract: A numerical code is developed for evolutionary calculations of the thermal structure and composition of a porous comet nucleus made of water ice, in amorphous or crystalline form, other volatiles, dust, and gases trapped in amorphous ice. Bulk evaporation, crystallization, gas release, and free (Knudsen) flow of gases through the pores are taken into account. The numerical scheme yields exact conservation laws for mass and energy. The code is used to study the effect of bulk evaporation of ice in the interior of a comet nucleus during crystallization. It is found that evaporation controls the temperature distribution; the vapor prevents cooling of the crystallized layer of ice, by recondensation and release of latent heat. Thus high temperatures are maintained below the surface of the nucleus and down to depths of tens or hundreds of meters, even at large heliocentric distances, as long as crystallization goes on. Gas trapped in the ice and released during the phase transition flows both toward the interior and toward the surface and out of the nucleus. The progress of crystallization is largely determined by the contribution of gas fluxes to heat transfer.

Air-Sea Fluxes With a Focus on Heat and Momentum

Abstract: Turbulent and radiative exchanges of heat between the ocean and atmosphere (hereafter heat fluxes), ocean surface wind stress, and state variables used to estimate them, are Essential Ocean Variables (EOVs) and Essential Climate Variables (ECVs) influencing weather and climate. This paper describes an observational strategy for producing 3-hourly, 25-km (and an aspirational goal of hourly at 10-km) heat flux and wind stress fields over the global, ice-free ocean with breakthrough 1-day random uncertainty of 15 W m-2 and a bias of less than 5 W m-2. At present this accuracy target is met only at OceanSITES reference station moorings and research vessels (RVs) that follow best practices. To meet these targets globally, in the next decade, satellite-based observations must be optimized for boundary layer measurements of air temperature, humidity, sea surface temperature, and ocean wind stress. In order to tune and validate these satellite measurements, a complementary global in situ flux array, built around an expanded OceanSITES network of time series reference station moorings, is also needed. The array would include 500 - 1000 measurement platforms, including autonomous surface vehicles, moored and drifting buoys, RVs, the existing OceanSITES network of 22 flux sites, and new OceanSITES expanded in 19 key regions. This array would be globally distributed, with 1 - 3 measurement platforms in each nominal 10° by 10° boxes. These improved moisture and temperature profiles and surface data, if assimilated into Numerical Weather Prediction (NWP) models, would lead to better representation of cloud formation processes, improving state variables and surface radiative and turbulent fluxes from these models. The in situ flux array provides globally distributed measurements and metrics for satellite algorithm development, product validation, and for improving satellite-based, NWP and blended flux products. In addition, some of these flux platforms will also measure direct turbulent fluxes, which can be used to improve algorithms for computation of air-sea exchange of heat and momentum in flux products and models. With these improved air-sea fluxes, the ocean’s influence on the atmosphere will be better quantified and lead to improved long-term weather forecasts, seasonal-interannual-decadal climate predictions, and regional climate projections.