Latent heat

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

Infiltration of water into snow

Abstract: Measurements from a rectangular grid of thermistors set in a maritime snowpack are used to study the infiltration of water during two midwinter rain on snow events. The progress of wetting is tracked in real time by monitoring changes in the position of the zero-degree isotherm. Rates and patterns of infiltration are calculated for each event. Infiltration was not uniform, and water penetrated through localized channels that often occupied less than 50% of the total volume of the snowpack. The evolution of wetting was strongly influenced by the snow stratigraphy. In one case the snowpack contained multiple ice layers, and vertical flow was impeded and diverted laterally for several hours at each layer. In the other case the snowpack was more homogeneous, and water concentrated in channels and penetrated to depth more rapidly. The measurements of temperature are also used to calculate the components of heat transfer within the snow during each rain event. Heat transfer in dry snow occurs primarily by conduction, and rates are relatively slow. However, introduction of liquid water results in the release of latent heat when water freezes on contact with subfreezing snow at the wetting front. The release of latent heat dominates heat transfer and has the potential to warm the snowpack rapidly. Rates of freezing needed to satisfy the heat equation are calculated. In both cases studied, less than 4% of the total influx of rainwater needed to change phase. Most of the rain remained liquid and wet the snow or drained through the snowpack.

Warming of the arctic ice-ocean system is faster than the global average since the 1960s

Abstract: [1] Model results and observations both indicate warming of the world ocean from 1955 to 2003. Forced by reanalysis data, the model also shows that the warming of the arctic ice–ocean system is faster than the global average since the 1960s; there is a small but widespread increase in heat content of the Arctic Ocean's waters and a larger increase of latent heat embodied in the ocean's decreasing ice cover. From 1966 to 2003 the modeled mean world ocean temperature in the upper 700 m increased 0.097°C and by 0.137°C according to observations (Levitus et al., 2005); the modeled mean temperature adjusted for sea ice in the corresponding layer of the Arctic Ocean increased 0.203°C. The warming of the world ocean is associated with an increase in global surface air temperature, downward longwave radiation, and therefore net heat flux. The faster warming of the arctic ice–ocean system is associated with an amplified increase in arctic surface air temperature, downward longwave radiation, and net heat flux.

Satellite assessment of land surface evapotranspiration for the pan-Arctic domain

Abstract: [1] Regional evapotranspiration (ET), including water loss from plant transpiration and soil evaporation, is essential to understanding interactions between land-atmosphere surface energy and water balances. Vapor pressure deficit (VPD) and surface air temperature are key variables for stomatal conductance and ET estimation. We developed an algorithm to estimate ET using the Penman-Monteith approach driven by Moderate Resolution Imaging Spectroradiometer (MODIS)-derived vegetation data and daily surface meteorological inputs including incoming solar radiation, air temperature, and VPD. The model was applied using alternate daily meteorological inputs, including (1) site level weather station observations, (2) VPD and air temperature derived from the Advanced Microwave Scanning Radiometer (AMSR-E) on the EOS Aqua satellite, and (3) Global Modeling and Assimilation Office (GMAO) reanalysis meteorology-based surface air temperature, humidity, and solar radiation data. Model performance was assessed across a North American latitudinal transect of six eddy covariance flux towers representing northern temperate grassland, boreal forest, and tundra biomes. Model results derived from the three meteorology data sets agree well with observed tower fluxes (r > 0.7; P < 0.003; root mean square error of latent heat flux <30 W m−2) and capture spatial patterns and seasonal variability in ET. The MODIS-AMSR-E–derived ET results also show similar accuracy to ET results derived from GMAO, while ET estimation error was generally more a function of algorithm parameterization than differences in meteorology drivers. Our results indicate significant potential for regional mapping and monitoring daily land surface ET using synergistic information from satellite optical IR and microwave remote sensing.