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Longwave Radiation (longwave + radiation)

Distribution by Scientific Domains
Earth and Environmental Science88%

Kinds of Longwave Radiation

  • outgoing longwave radiation
    		•

    Selected Abstracts

    The surface radiation budget over North America: gridded data assessment and evaluation of regional climate models

    INTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 15 2009
    Marko Markovic
    Abstract While surface station observations of downwelling radiation offer accuracy at high temporal resolution, they do not easily allow an evaluation of model surface radiation budgets (SRB) over a wide geographical area. We evaluate three gridded SRB data sets against detailed observations from six surface radiation sites from the US surface radiation (SURFRAD) network. We subsequently use the most accurate surrogate observational data set for evaluation of model-simulated SRB. The data sets assessed are: ERA40,reanalysis of European Centre for Medium-Range Weather Forecasts (ECMWF), North American Regional Reanalysis (NARR),regional reanalysis of National Centres for Environmental Prediction (NCEP) and the surface radiative budget (SRB) from the International Satellite Cloud Climatology Project (ISCCP). Due to varying constraints with respect to temporal coverage of each data set, the evaluation period used in this study is 1996,2001, inclusive. The ERA40 downwelling longwave radiation (DLR) appears the most accurate surrogate observation, while both ERA40 and ISCCP show accurate results when the incoming shortwave radiation (ISR) is considered across the annual cycle. Winter DLR is less accurate in ISCCP with a positive bias and lack of very low (<200 Wm,2) flux values. The NARR SRB shows a large positive bias in the ISR throughout the annual cycle, linked to a significant underestimate of cloud cover. The ERA40 data are subsequently used to evaluate the simulated SRB in three regional climate models across North America. With respect to solar radiation, cloud cover biases are seen to be crucial, while for longwave fluxes both cloud fraction and in-cloud water content are important to simulate correctly. Inclusion of trace gases beyond H2O, CO2 and O3 appears necessary for an accurate calculation of clear-sky longwave radiation. Error compensation frequently occurs between the various components contributing to a model total-sky SRB. This is important to consider when trying to identify the underlying causes of errors in the simulated total SRB. Copyright © 2009 Royal Meteorological Society [source]

    Remote weather associated with North Pacific subtropical sea level high properties

    INTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 5 2007
    Richard Grotjahn
    Abstract Remote events influencing North Pacific (NP) subtropical high properties in monthly and daily data are identified. Variability in the NP during summer is far more strongly dominated by midlatitude events than in South Pacific (SP); low-pass filtering is required to see tropical associations. The dominant pattern in composites, correlations, and regressions is a midlatitude wave train. A stronger NP high was led by higher sea-level pressure (SLP) just east of Japan and lower SLP over central Canada and to a lesser extent over western tropical Pacific. Various mechanisms have been proposed to force the NP high: (1)Heating over southwestern North America (with cooling off the west coast). However, higher temperatures over North America follow stronger SLP over the NP high and occur much further east than postulated. Higher SLP occurs where temperatures are lower over western North America and adjacent ocean. Thermal pattern is consistent with temperature advection between NP high and Canadian low. (2)Precipitation over and near Central America. However, SLP increase on the SE side of the high is led by higher SLP (and higher outgoing longwave radiation (OLR)) along the west coast of Mexico and Central America. Normalized regressions find a very weak lower OLR in North American monsoon preceding stronger NP high, but the region is much smaller in size and magnitude than other significant areas. (3)Precipitation over Indonesia and southeast Asia. Statistics provide some support for lower SLP and OLR over Indonesia preceding higher SLP in the center, west, and northwest sides of NP high. The lower SLP and OLR appear to migrate into southeast Asia, perhaps independently, perhaps from stronger NP high. (4)The NP high has a strong connection to El Niño during winter, but no significant link during summer. Only the south side of NP high appears (weakly) linked to the Madden Julian oscillation (MJO). Copyright © 2006 Royal Meteorological Society [source]

    Snow disappearance in Eastern Siberia and its relationship to atmospheric influences

    INTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 2 2007
    Yoshihiro Iijima
    Abstract In the present study, we examine the climatological features and interannual variations in snow disappearance within the Lena River Basin, Eastern Siberia, during a recent 15-year period (1986,2000), and the relationship of snow disappearance to atmospheric conditions. According to the climatology of the day of the year on which snow disappears, the boundary of snow disappearance within the Lena River Basin migrates rapidly northward from mid-April until early June, with minimum interannual variation occurring in the middle part of the basin. In addition, the preceding snow disappearance is apparent in the central Lena River Basin. Melting of snow within the Lena River Basin commonly occurs within 30 days of complete snow disappearance under certain atmospheric conditions: daily mean air temperature in excess of , 10 °C, greater than 2 hPa of water vapor pressure, and, hence, more than 170 W m,2 of downward longwave radiation under clear sky conditions. Composite analysis using a reanalysis dataset demonstrates that the increase in air temperature and water vapor that accompanies snow melting is due to wet (and warm) air advection in conjunction with enhanced water vapor convergence over the central Lena River Basin during the 30-day period prior to snow disappearance. Copyright © 2006 Royal Meteorological Society. [source]

    Intraseasonal oscillations and the South China Sea summer monsoon onset

    INTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 12 2005
    Wen Zhou
    Abstract This paper investigates the role of intraseasonal oscillations (ISOs) in the onset of the South China Sea summer monsoon (SCSSM). Two major components of ISO (10,20-day and 30,60-day modes) are identified. The coupling of these two intraseasonal modes during the pre-monsoon period of the SCSSM are investigated by examining the filtered outgoing longwave radiation (OLR), low-level circulation, apparent heat source and apparent moisture sink from October of a previous calendar year to September of a calendar year. The zonal and meridional propagations of the 10,20-day and 30,60-day modes are found to be different, which reflects their different roles in the establishment and development of the SCSSM. The northwestward propagation of the 10,20-day mode is associated with the weakening of the subtropical high over the western Pacific, while the northeastward propagation of the 30,60-day mode originates from convection over the equatorial Indian Ocean. A hypothesis is then proposed to explain the observed variabilities in the SCSSM onset. When the equatorial Indian Ocean exhibits a 30,60-day mode oscillation, an initially weak convection develops into a large convection band (or monsoon trough). Meanwhile, a convective disturbance of the 10,20-day mode is induced when this monsoon trough extends to the western Pacific. These two processes then collaborate to cause a weakening of the subtropical anticyclone over the South China Sea. Because the monsoon trough associated with the 30,60-day mode subsequently propagates northward into the Bay of Bengal (BOB), the induced vortex together with the 10,20-day westward-migrating convection from the equatorial western Pacific will substantially increase the effect of horizontal advection of moisture and heat, thus destabilizing the atmosphere and weakening the subtropical ridge there. Westerlies can then penetrate and prevail over the SCS region, and the SCSSM onset occurs. Copyright © 2005 Royal Meteorological Society. [source]

    Remote weather associated with South Pacific subtropical sea-level high properties

    INTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 7 2004
    Richard Grotjahn
    Abstract The subtropical highs in sea-level pressure (SLP) are little studied and incompletely understood. In recent years, three groups of theories, i.e. tropical divergent circulations, subtropical Rossby wavetrains, and midlatitude frontal cyclone interactions, have been proposed for remote maintenance of these highs. The latter is presented here as a remote forcing of these highs for the first time in the reviewed literature. The focus of the study is upon illuminating associations between these mechanisms and the South Pacific subtropical high in SLP (SP high). Precipitation, outgoing longwave radiation, velocity potential, and divergent winds are used as proxy markers for the remote forcing mechanisms. The tools used include composites, one-point correlations, autocorrelations, cross-correlations, and cross-spectra. Observational evidence, in monthly and daily data, is examined that appears to support each mechanism. Associations seen in monthly data are better understood in daily data at various lags. Convection over Amazonia, coordinated with suppressed convection in the western tropical Pacific, leads to enhanced SLP on the tropical side of the high. Midlatitude weather systems are the strongest influence upon the maximum SLP and the SLP on the higher latitude side of the high. The western side is associated with both middle-and lower-latitude phenomena, such as the South Pacific convergence zone. Various properties of the high have a strong period around 45 days. Associations to the Madden,Julian oscillation and El Niño,southern oscillation are explored and are strong only for the tropical side of the SP high. Copyright © 2004 Royal Meteorological Society [source]

    Patterns of convection in the tropical pacific and their influence on New Zealand weather

    INTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 2 2002
    John W. Kidson
    Abstract Characteristic patterns of convection in the tropical Pacific Ocean have previously been inferred from analysis of outgoing longwave radiation (OLR), and associated with year-to-year variations in El Niño (EN),Southern Oscillation events. This study examines both the effects of these convection patterns on the New Zealand climate, and the more general influence of tropical convection on the New Zealand sector of the Southern Hemisphere. The Southern Hemisphere circulation, as a whole, is found to be most strongly influenced by equatorial convection near the Philippines, and in a broad band over the central Pacific. Where increased convection occurs west of 160°E, La Niña-like (LN) conditions prevail. When the anomalous convective activity is located near the dateline, in ,moderate' EN conditions, SW flow prevails over New Zealand. This gives way to stronger WSW anomalies as the centre of convection is displaced further eastwards and a second centre of reduced convection becomes prominent west of the dateline in strong EN (EN+) events. The changes in wind regimes over the New Zealand region implied by the hemispheric 1000 hPa height fields are supported by mean sea-level pressure differences between a number of New Zealand and adjacent island stations. Indices of the zonal flow show a weak reduction in strength of the westerlies for LN OLR composites, and no apparent effects for EN composites, whereas EN+ conditions strongly favour above-normal westerlies. The meridional flow over New Zealand is skewed towards more frequent southerlies in both the EN and EN+ composites, whereas LN conditions favour northerly flow anomalies. A change is also observed in the frequency of New Zealand-area ,weather regimes'. Enhanced convection centred on 5°S and east of the dateline, as found in the EN+ composites, leads to an increase in zonal regimes and a corresponding decrease in blocking regimes. The direct influence of tropical OLR variations on New Zealand temperature and precipitation has also been assessed. These indicate that the response is not simply one of degree. Different spatial anomaly patterns in the climatic elements result from the varying regional circulation patterns, and these need to be considered if present climate-forecasting schemes are to be improved. Copyright © 2002 Royal Meteorological Society. [source]

    Guidelines for Riparian Vegetative Shade Restoration Based Upon a Theoretical Shaded-Stream Model,

    JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, Issue 6 2008
    David R. DeWalle
    Abstract:, Guidelines for riparian vegetative shade restoration were developed using a theoretical model of total daily radiation received by a shaded stream. The model assumed stream shading by nontransmitting, vertical or overhanging, solid vegetation planes in infinitely long reaches. Radiation components considered in the model were direct beam shortwave on the stream centerline, diffuse atmospheric shortwave, shortwave reflected by vegetation, atmospheric longwave, and longwave emitted by vegetation. Potential or extraterrestrial shortwave irradiation theory was used to compute beam shortwave radiation received at the stream centerline, and view factor theory was used to compute diffuse radiation exchange among stream, vegetation, and atmospheric planes. Model shade effects under clear skies were dominated by reductions in receipt of direct beam shortwave radiation. Model shade effects with cloudy skies were dominated by the "view factor effect" or the decreases in diffuse shortwave and longwave radiation from the atmosphere balanced against increases in longwave radiation from vegetation. Model shade effects on shortwave radiation reflected by vegetation were found to be negligible. The model was used to determine the vegetation height (H) to stream width (W) ratios needed to achieve 50, 75, and 90 % shade restoration for mid-latitude conditions on clear and cloudy days. Ratios of vegetation height to stream width, for dense nontransmitting vegetation, generally ranged from 1.4 to 2.3 for 75% shade restoration at a mid-latitude site (40°N). The model was used to show H/W needed for E-W vs. N-S stream azimuths, varying stream latitudes between 30° and 50°N, channels with overhanging vegetation, channels undergoing width changes, as well as the limits to shade restoration on very wide channels. [source]

    Quasi-biennial oscillations in spectral aerosol optical depth

    ATMOSPHERIC SCIENCE LETTERS, Issue 4 2009
    S. Naseema Beegum
    Abstract Analysis of long-term time series of monthly mean aerosol optical depths (AOD) at four tropical stations over Asia and Africa revealed the presence of significant annual oscillations (AO) and quasi-biennial oscillations (QBO). While the AOs were the dominant features, the QBOs in AOD (QBOAOD) were also quite strong and were well associated with the QBO in stratospheric zonal wind (QBOU). At the equatorial stations, QBOAOD were out of phase with QBOU, while they were in phase at the off-equatorial stations. However, QBO in both outgoing longwave radiation (OLR) and rainfall showed an out-of-phase relationship with QBOAOD at all stations. Copyright © 2009 Royal Meteorological Society [source]

    Estimating the top-of-atmosphere longwave radiative forcing due to Saharan dust from satellite observations over a west African surface site

    ATMOSPHERIC SCIENCE LETTERS, Issue 3 2007
    H. E. Brindley
    Abstract This paper presents a methodology for estimating the longwave top-of-atmosphere direct radiative forcing due to Saharan dust aerosol from satellite observations made by the Spinning Enhanced Visible and Infrared Imager (SEVIRI) and Geostationary Earth Radiation Budget (GERB) instruments. Narrow-band observations from SEVIRI are used to detect dust presence and quantify its loading, while GERB provides an estimate of the dust impact on the total outgoing longwave radiation. Applying the technique to observations made over the Banizoumbou surface station in Niger through March,June 2006 indicates a midday longwave forcing efficiency of 17 ± 5 W m,2 per unit aerosol optical depth. Copyright © 2007 Royal Meteorological Society [source]