Latent heat

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

Validation of the NOAH-OSU land surface model using surface flux measurements in Oklahoma

Abstract: [1] Oklahoma Atmospheric Surface-Layer Instrumentation System (OASIS) measurements of net radiation (Rn), latent heat flux (LH), sensible heat flux (SH), and ground heat flux (GH) were used to validate the NOAH-Oregon State University Land Surface Model (NOAH-OSU LSM). A 1-year study period was used. Rn, LH, SH and GH data from seven sites were screened based on an energy balance closure criterion (daily/hourly sum of the flux components within the range of −10 to +10 W m−2). The vegetation fraction used in the model was computed using both the Gutman-Ignatov (G-I) and the Carlson-Ripley (C-R) schemes. The simulated net radiation and ground heat fluxes seem less sensitive to the choice of schemes for computing green vegetation fraction, while latent and sensible heat flux show more sensitivity particularly for soil dry-down period. Therefore, the G-I approach was used for the validation study, as it is widely used and linear in its form. The daily aggregated model outputs showed that the predicted Rn had a positive bias of 0.8 MJ m−2 d−1 and an RMSE of 1.6 MJ m−2 d−1 when averaged over all seven sites. The seven-site average bias in LH was about 0.9 MJ m−2 d−1 with an RMSE of 2.5 MJ m−2 d−1. The bias in SH and GH was low and positive with an RMSE of about 2.2 MJ m−2 d−1 in SH estimation. The hourly average output showed similar results, with the exception that GH had a negative bias. The overall performance of the NOAH-OSU LSM was good for a diverse set of Oklahoma conditions.

Determination of regional distributions and seasonal variations of land surface heat fluxes from Landsat‐7 Enhanced Thematic Mapper data over the central Tibetan Plateau area

Abstract: [1] In this study, a parameterization method based on Landsat-7 ETM data and field observations has been proposed and tested for deriving surface reflectance, surface temperature, NDVI, MSAVI, vegetation coverage, LAI, net radiation flux, soil heat flux, sensible heat flux and latent heat flux over heterogeneous landscape. As a case study, the methodology was applied to the experimental area of the CAMP/Tibet, which located at the central Tibetan Plateau. Two scenes of Landsat-7 ETM data were used in this study. The scene of 9 June 2002 was selected as a case of summer, and the scene of 2 December 2002 was selected as a case of winter. To validate the proposed methodology, the ground-measured surface reflectance, surface temperature, net radiation flux, soil heat flux, sensible heat flux and latent heat flux are compared to Landsat-7 ETM derived values. The results show that the derived surface variables and land surface heat fluxes in two different months over the study area are in good accordance with the land surface status. These parameters show a wide range due to the strong contrast of surface features. Also, the estimated land surface variables and land surface heat fluxes are in good agreement with ground measurements, and all their absolute percent difference is less than 9.9% in the validation sites. It is therefore concluded that the proposed methodology is successful for the retrieval of land surface variables and land surface heat fluxes using the Landsat-7 ETM data and filed observations over the study area.

An Investigation of the Presence of Atmospheric Rivers over the North Pacific during Planetary-Scale Wave Life Cycles and Their Role in Arctic Warming

Abstract: Heretofore, the tropically excited Arctic warming (TEAM) mechanism put forward that localized tropical convection amplifies planetary-scale waves, which transport sensible and latent heat into the Arctic, leading to an enhancement of downward infrared radiation and Arctic surface warming. In this study, an investigation is made into the previously unexplored contribution of the synoptic-scale waves and their attendant atmospheric rivers to the TEAM mechanism. Reanalysis data are used to conduct a suite of observational analyses, trajectory calculations, and idealized model simulations. It is shown that localized tropical convection over the Maritime Continent precedes the peak of the planetary-scale wave life cycle by ~10–14 days. The Rossby wave source induced by the tropical convection excites a Rossby wave train over the North Pacific that amplifies the climatological December–March stationary waves. These amplified planetary-scale waves are baroclinic and transport sensible and latent heat pol...

How Well Can We Measure the Vertical Wind Speed? Implications for Fluxes of Energy and Mass

Abstract: Sonic anemometers are capable of measuring the wind speed in all three dimen- sions at high frequencies (10-50 Hz), and are relied upon to estimate eddy-covariance-based fluxes of mass and energy over a wide variety of surfaces and ecosystems. In this study, wind-velocity measurement errors from a three-dimensional sonic anemometer with a non- orthogonal transducer orientation were estimated for over 100 combinations of angle-of- attack and wind direction using a novel technique to measure the true angle-of-attack and wind speed within the turbulent atmospheric surface layer. Corrections to the vertical wind speed varied from −5 to 37% for all angles-of-attack and wind directions examined. When applied to eddy-covariance data from three NOAA flux sites, the wind-velocity corrections increased the magnitude of CO2 fluxes, sensible heat fluxes, and latent heat fluxes by ≈11%, with the actual magnitude of flux corrections dependent upon sonic anemometer, surface type, and scalar. A sonic anemometer that uses vertically aligned transducers to measure the vertical wind speed was also tested at four angles-of-attack, and corrections to the ver- tical wind speed measured using this anemometer were within ±1% of zero. Sensible heat fluxes over a forest canopy measured using this anemometer were 15% greater than sensible heat fluxes measured using a sonic anemometer with a non-orthogonal transducer orienta- tion. These results indicate that sensors with a non-orthogonal transducer orientation, which includes the majority of the research-grade three-dimensional sonic anemometers currently in use, should be redesigned to minimize sine errors by measuring the vertical wind speed using one pair of vertically aligned transducers.