Latent heat

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

The Effect of Diurnal Sea Surface Temperature Warming on Climatological Air–Sea Fluxes

Abstract: Diurnal sea surface warming affects the fluxes of latent heat, sensible heat, and upwelling longwave radiation. Diurnal warming most typically reaches maximum values of 3°C, although very localized events may reach 7°–8°C. An analysis of multiple years of diurnal warming over the global ice-free oceans indicates that heat fluxes determined by using the predawn sea surface temperature can differ by more than 100% in localized regions over those in which the sea surface temperature is allowed to fluctuate on a diurnal basis. A comparison of flux climatologies produced by these two analyses demonstrates that significant portions of the tropical oceans experience differences on a yearly average of up to 10 W m−2. Regions with the highest climatological differences include the Arabian Sea and the Bay of Bengal, as well as the equatorial western and eastern Pacific Ocean, the Gulf of Mexico, and the western coasts of Central America and North Africa. Globally the difference is on average 4.45 W m−2. The...

Is Oceanic Heat Transport Significant in the Climate System

Abstract: It has long been believed that the transport of heat by the ocean circulation is of importance to atmospheric climate. Circulation of the Atlantic Ocean warms and moistens western Europe, the argument goes, and, because of the pivotal role of the Atlantic/Arctic region, also affects global climate (e.g., Stommel 1979). Indeed, major oceanographic field programs have been launched by many nations, based on this premise. In the US, NOAA issues quarterly assessments of subtropical North Atlantic meridional heat transport (http://www.aoml.noaa.gov/phod/soto/mht/reports/ index.php). Estimates from ocean observations show the annual-mean, northward heat transport by the global circulation to decrease by about 1.5 pW (10W) between latitudes 25° N and 50° N, with nearly 1 pW of that within the narrow Atlantic sector alone (see Bryden and Imawaki 2001, who estimate the uncertainty of individual section heat transports at 0.3 pW). This effect of the oceanic meridional overturning forces an enormous upward flux of heat and moisture in subtropical latitudes, providing a significant fraction of the zonally integrated atmospheric northward energy flux (which peaks at between 3 and 5.2 pW, as discussed further below). Occurring dominantly in wintertime, oceanic warmth and moisture energize the Pacific and Atlantic storm tracks. Combined action of atmosphere and ocean carries this energy northward, with great impact on all facets of high-latitude climate. Northern Atlantic climate hovers in the midst of debates over the dynamical origins and impacts of the global oceanic meridional overturning circulation (MOC), and its contribution to the coupled atmosphere–ocean system. Still, the

Numerical evaluation of subsurface soil water evaporation derived from sensible heat balance

Abstract: [1] A recently introduced measurement approach allows in situ determination of subsurface soil water evaporation by means of heat-pulse probes (HPP). The latent heat component of subsurface evaporation is estimated from the residual of the sensible heat balance. This heat balance method requires measurement of vertical soil temperature and estimates of thermal properties for soil water evaporation determination. Our objective was to employ numerically simulated thermal and hydraulic processes using constant or diurnally cycled surface boundary conditions to evaluate and understand this technique. Three observation grid spacings, namely, 6 mm (tri-needle HPP), 3 mm (penta-needle HPP) and 1 mm, along with three soil textures (sand, silt, and silty clay) were used to test the heat balance method. The comparison of heat balance–based evaporation rate estimates with an independent soil profile water balance revealed substantial errors when thermal conductivity was averaged spatially across the evaporation front. Since the conduction component of heat flux is the dominant process at the evaporation front, the estimation of evaporation rate was significantly improved using depth-dependent instead of a space-averaged . A near-surface “undetectable zone” exists, where the heat balance calculation is irreconcilable, resulting in underestimation of total subsurface evaporation. The method performs better for medium- and coarse-textured soils than for fine-textured soils, where portions of the drying front may be maintained longer within the undetectable zone. Using smaller temperature sensor spacing near the soil surface minimized underestimation from the undetectable zone and improved accuracy of total subsurface evaporation rate estimates.

Contribution of impervious surfaces to urban evaporation

Abstract: Observational data and the Princeton urban canopy model, with its detailed representation of urban heterogeneity and hydrological processes, are combined to study evaporation and turbulent water vapor transport over urban areas. The analyses focus on periods before and after precipitation events, at two sites in the Northeastern United States. Our results indicate that while evaporation from concrete pavements, building rooftops, and asphalt surfaces is discontinuous and intermittent, overall these surfaces accounted for nearly 18% of total latent heat fluxes (LE) during a relatively wet 10 day period. More importantly, these evaporative fluxes have a significant impact on the urban surface energy balance, particularly during the 48 h following a rain event when impervious evaporation is the highest. Thus, their accurate representation in urban models is critical. Impervious evaporation after rainfall is also shown to correlate the sources of heat and water at the earth surface, resulting in a conditional scalar transport similarity over urban terrain following rain events.

Analysis of transpiration results from the RICE and PILPS Workshop

Abstract: Results from the 14 land surface parameterization schemes involved in the PILPS-RICE Workshop are compared for a soya crop growing season (from June to September). During this period, the transpiration flux dominates the total surface evapotranspiration and observed data from HAPEX-MOBILHY are available for comparison. Results indicate that during the month of June half of the models fall within the uncertainty range of the observations. The scatter between models behaviour is explained by three major reasons: • The functional dependency between soil moisture and transpiration; • the initial moisture content at the beginning of the period; • the vertical discretization within the soil and the extension of the root system that defines the soil water holding capacity for plants Examination of diurnal cycles of evaporation reveals that formulations based on the supply-demand concept are very sensitive to the specification of the root zone. This analysis underlines the need for more sensitivity experiments to be done with the current forcing data set and more detailed datasets to be collected in future field experiments (e.g. latent heat flux during all the growing season, root zone distribution).