Search results for "Longwave"
showing 10 items of 25 documents
On the angular variation of thermal infrared emissivity of inorganic soils
2012
[1] Land surface temperature (LST), a key parameter for many environmental studies, can be most readily estimated by using thermal infrared (TIR) sensors onboard satellites. Accurate LST are contingent upon simultaneously accurate estimates of land surface emissivity (e), which depend on sensor viewing angle and the anisotropy of optical and structural properties of surfaces. In the case of inorganic bare soils (IBS), there are still few data that quantify emissivity angular effects. The present work deals with the angular variation of TIR emissivity for twelve IBS types, representative of nine of the twelve soil textures found on Earth according to United States Department of Agriculture c…
A typology for intraseasonal oscillations
2013
This descriptive study attempts to document the diversity of intraseasonal oscillations (ISO) propagative and spatial patterns, as inferred from outgoing longwave radiation (OLR) variability. Main ISO events over the Indo-Pacific Warm Pool are first extracted using a local mode analysis (LMA) applied on the 20–120-d filtered OLR on the 1979–2008 period. One hundred and sixty-nine individual ISO are detected. Their propagative patterns are then objectively regrouped into a few types using a hierarchical agglomerative classification. Three alternative partitionings are retained, depending on the level of details expected from the typology. ISO events first regroup naturally into two well-sepa…
Flux retrieval optimization with a nonscanner along-track broadband radiometer
2003
[1] The theoretical behavior of broadband flux retrieval is analyzed with the aid of a radiance field database. Several angular inversion models are developed for different viewing configurations, with special emphasis in a nonscanner along-track design concept. Results show that the performance of these angular models depends on the viewing zenith angle (VZA). When cloud cover is predominant within the observed scene, VZAs around 55° (shortwave) and 50° (longwave) minimize the error when deriving fluxes. These results might help in the design of future missions where the main idea is to obtain accurate instantaneous measurements of top of atmosphere reflected and emitted fluxes. Such measu…
Sensitivity of the atmospheric temperature profile to the aerosol absorption in the presence of dust
2014
Abstract Radiative transfer simulations in the shortwave (SW) and longwave (LW) spectral regions have been carried out to investigate the time evolution of the atmospheric heating/cooling rates and their influence on the temperature profiles under different vertical distributions of the aerosol absorption. The case study is based on measurements made at Rome, Italy, on 20 June 2007, when a dust layer was present above the urban boundary layer (BL) and the column aerosol optical depth at 550 nm was about 0.37. Column-integrated aerosol optical depth and single scattering albedo, as well as vertical profiles of aerosol extinction and meteorological variables have been derived from observation…
Altitude-resolved shortwave and longwave radiative effects of desert dust in the Mediterranean during the GAMARF campaign: Indications of a net daily…
2015
Desert dust interacts with shortwave (SW) and longwave (LW) radiation, influencing the Earth radiation budget and the atmospheric vertical structure. Uncertainties on the dust role are large in the LW spectral range, where few measurements are available and the dust optical properties are not well constrained. The first airborne measurements of LW irradiance vertical profiles over the Mediterranean were carried out during the Ground-based and Airborne Measurements of Aerosol Radiative Forcing (GAMARF) campaign, which took place in spring 2008 at the island of Lampedusa. The experiment was aimed at estimating the vertical profiles of the SW and LW aerosol direct radiative forcing (ADRF) and …
Variability of the African convection centre as viewed by outgoing longwave radiation records and relationships with sea-surface temperature patterns
1995
International audience; The main African convection centre (ACC) is delimited by the 5"-square areas with outgoing longwave radiation less than 235 W m-' in the domain 17.5°N-17.5"S and 18"W-46"E. Four parameters (latitude and longitude of the centre of gravity, mean intensity, and extension) were analysed during the period June 1974 to December 1991. The relationships between the variability of the ACC and the main sea-surface temperature (SST) patterns were then studied. Correlation and composite analyses demonstrate that the first principal component of SST, representing mainly the variability of the eastern and the central tropical Pacific, is associated strongly with the extension and …
Observations and snow model simulations of winter energy balance terms within and between different coniferous forests in Southern Boreal Finland
2015
Variation of canopy properties between different forest types is seldom taken into account in hydrological and climate models, and consideration of variation inside a forest is normally omitted. In this work, three data sets on near surface energy balance terms (incoming shortwave and longwave radiation; air and snow–soil interface temperatures) were collected in the southern boreal coniferous zone in Finland during three winters below different types of forest canopies. The aim was to evaluate the ability of a snow mass and energy balance model with a canopy module to reproduce the observed differences in below-canopy incoming radiations and snow–soil interface temperature. Clear differenc…
Observed changes in the life time and amplitude of the madden-julian oscillation associated with interannual ENSO sea surface temperature anomalies
2007
Abstract The Madden–Julian oscillation (MJO) is analyzed using the reanalysis zonal wind– and satellite outgoing longwave radiation–based indices of Wheeler and Hendon for the 1974–2005 period. The average lifetime of the MJO events varies with season (36 days for events whose central date occurs in December, and 48 days for events in September). The lifetime of the MJO in the equinoctial seasons (March–May and October–December) is also dependent on the state of El Niño–Southern Oscillation (ENSO). During October–December it is only 32 days under El Niño conditions, increasing to 48 days under La Niña conditions, with similar values in northern spring. This difference is due to faster eastw…
Influence of the Madden-Julian Oscillation on Southern African summer rainfall
2007
Rain-causing mechanisms over Southern Africa (south of 15˚S) involve both tropical and temperate dynamics. Most studies focused on the synoptical timescale, while the intraseasonal (20-120 days) variability has more been neglected to date. This study aims at determining whether the dominant mode of intraseasonal variability in the Tropics, namely the Madden-Julian Oscillation (MJO), has a significant impact on Southern African rainfall and associated atmospheric dynamics. The examination of outgoing longwave radiation (OLR) over Southern Africa shows indeed significant intraseasonal fluctuations at the 30-60 day timescale, i.e. in the pe- riods that are typically reminiscent of the MJO. In ord…
Surface soil humidity retrieval using remote sensing techniques: a triangle method validation
2010
Soil humidity plays a key-role in hydrological and agricultural processes. In the rainfall-runoff processes the knowledge of its spatial distribution is fundamental to accurately model these phenomena. Furthermore in agronomy and agricultural sciences, assessing the water content of the root zone is required in order to optimize the plant productivity and to improve the irrigation systems management. Despite the importance of this variable the in situ measurements techniques based on Time Domain Reflectometry (TDR) or on the standard thermo-gravimetric methods, are neither cost-effective nor representative of its spatial and temporal variability. Indirect estimations via Earth Observation (…