scholarly journals Year-Round Observation of Longwave Radiative Flux Divergence in Greenland

2007 ◽  
Vol 46 (9) ◽  
pp. 1469-1479 ◽  
Author(s):  
S. W. Hoch ◽  
P. Calanca ◽  
R. Philipona ◽  
A. Ohmura
Keyword(s):  
Longwave Radiation ◽  
Radiative Flux ◽  
Radiative Cooling ◽  
Flux Divergence ◽  
Tower Structure ◽  
Order Of Magnitude ◽  
The Mean ◽  
Temperature Tendency ◽  
Radiation Measurements ◽  
Longwave Flux

Abstract Longwave radiative flux divergence within the lowest 50 m of the atmospheric boundary layer was observed during the Eidgenössische Technische Hochschule (ETH) Greenland Summit experiment. The dataset collected at 72°35′N, 38°30′W, 3203 m MSL is based on longwave radiation measurements at 2 and 48 m that are corrected for the influence of the supporting tower structure. The observations cover all seasons and reveal the magnitude of longwave radiative flux divergence and its incoming and outgoing component under stable and unstable conditions. Longwave radiative flux divergence during winter corresponds to a radiative cooling of −10 K day−1, but values of −30 K day−1 can persist for several days. During summer, the mean cooling effect of longwave radiative flux divergence is small (−2 K day−1) but exhibits a strong diurnal cycle. With values ranging from −35 K day−1 around midnight to 15 K day−1 at noon, the heating rate due to longwave radiative flux divergence is of the same order of magnitude as the observed temperature tendency. However, temperature tendency and longwave radiative flux divergence are out of phase, with temperature tendency leading the longwave radiative flux divergence by 3 h. The vertical variation of the outgoing longwave flux usually dominates the net longwave flux divergence, showing a strong divergence at nighttime and a strong convergence during the day. The divergence of the incoming longwave flux plays a secondary role, showing a slight counteracting effect. Fog is frequently observed during summer nights. Under such conditions, a divergence of both incoming and outgoing fluxes leads to the strongest radiative cooling rates that are observed. Considering all data, a correlation between longwave radiative flux divergence and the temperature difference across the 2–48-m layer is found.

scholarly journals Radiative Flux Estimation from a Broadband Radiometer Using Synthetic Angular Models in the EarthCARE Mission Framework. Part I: Methodology

2011 ◽  
Vol 50 (5) ◽  
pp. 974-993 ◽  
Author(s):  
Carlos Domenech ◽  
Ernesto Lopez-Baeza ◽  
David P. Donovan ◽  
Tobias Wehr
Keyword(s):  
Longwave Radiation ◽  
Scientific Basis ◽  
Radiative Flux ◽  
Monte Carlo Algorithm ◽  
Retrieval Algorithm ◽  
Atmospheric Conditions ◽  
Flux Divergence ◽  
Distribution Models ◽  
Diverse Range ◽  
Physical Constraints

AbstractThe forthcoming broadband radiometer (BBR) on board the Earth Clouds, Aerosols, and Radiation Explorer (EarthCARE) will provide quasi-instantaneous top-of-atmosphere radiance measurements for three different viewing angles. The role of BBR data will be to constrain the vertical radiative flux divergence profiles derived from EarthCARE measurements. Thus, the development of an instantaneous radiance-to-flux conversion procedure is of paramount importance. This paper studies the scientific basis for determining fluxes from radiances measured by the BBR instrument. This is an attempt to evaluate a possible solution and assess its potential advantages and drawbacks. The approach considered has been to construct theoretical angular distribution models (ADMs) based on the multiangular pointing feature of this instrument. This configuration provides extra information on the anisotropy of the observed radiance field, which can be employed to construct accurate inversion schemes. The proposal relies on radiative transfer calculations performed with a Monte Carlo algorithm. Considering the intrinsic difficulty associated with addressing the range of atmospheric conditions needed to determine reliable ADMs, a synthetic database has been thoroughly constructed that considers a diverse range of surface, atmospheric, and cloud conditions that are conditioned to the EarthCARE orbit and physical constraints. Three inversion methodologies have been specifically designed for the BBR flux retrieval algorithm. In particular, an optimized classical inversion procedure in which the definition of an effective radiance leads to derive fluxes with averaged errors up to 1.2 and 5.2 W m−2 for shortwave clear and cloudy sky and 1.5 W m−2 for longwave radiation scenes and a linear combination of the three instantaneous radiances from which averaged errors up to 0.4 and 2.7 W m−2 for shortwave clear and cloudy sky and 0.5 W m−2 for longwave scenes can be obtained.

scholarly journals Turbulence and Radiation in Stratocumulus-Topped Marine Boundary Layers: A Case Study from VOCALS-REx

2014 ◽  
Vol 53 (1) ◽  
pp. 117-135 ◽  
Author(s):  
Virendra P. Ghate ◽  
Bruce A. Albrecht ◽  
Mark A. Miller ◽  
Alan Brewer ◽  
Christopher W. Fairall
Keyword(s):  
Vertical Velocity ◽  
Marine Boundary Layer ◽  
Velocity Structure ◽  
Radiative Flux ◽  
Radiative Cooling ◽  
Flux Divergence ◽  
A Value ◽  
Velocity Variance ◽  
Velocity Scale ◽  
Surface Buoyancy

AbstractObservations made during a 24-h period as part of the Variability of the American Monsoon Systems (VAMOS) Ocean–Cloud–Atmosphere–Land Study Regional Experiment (VOCALS-REx) are analyzed to study the radiation and turbulence associated with the stratocumulus-topped marine boundary layer (BL). The first 14 h exhibited a well-mixed (coupled) BL with an average cloud-top radiative flux divergence of ~130 W m−2; the BL was decoupled during the last 10 h with negligible radiative flux divergence. The averaged radiative cooling very close to the cloud top was −9.04 K h−1 in coupled conditions and −3.85 K h−1 in decoupled conditions. This is the first study that combined data from a vertically pointing Doppler cloud radar and a Doppler lidar to yield the vertical velocity structure of the entire BL. The averaged vertical velocity variance and updraft mass flux during coupled conditions were higher than those during decoupled conditions at all levels by a factor of 2 or more. The vertical velocity skewness was negative in the entire BL during coupled conditions, whereas it was weakly positive in the lower third of the BL and negative above during decoupled conditions. A formulation of velocity scale is proposed that includes the effect of cloud-top radiative cooling in addition to the surface buoyancy flux. When scaled by the velocity scale, the vertical velocity variance and coherent downdrafts had similar magnitude during the coupled and decoupled conditions. The coherent updrafts that exhibited a constant profile in the entire BL during both the coupled and decoupled conditions scaled well with the convective velocity scale to a value of ~0.5.

scholarly journals ENSO surface longwave radiation forcing over the tropical Pacific

2007 ◽  
Vol 7 (8) ◽  
pp. 2013-2026 ◽  
Author(s):  
K. G. Pavlakis ◽  
D. Hatzidimitriou ◽  
E. Drakakis ◽  
C. Matsoukas ◽  
A. Fotiadi ◽  
...  
Keyword(s):  
Time Series ◽  
El Niño ◽  
El Nino ◽  
Longwave Radiation ◽  
Western Pacific ◽  
Radiative Cooling ◽  
Central Pacific ◽  
The Mean ◽  
Downwelling Longwave Radiation ◽  
The Western Pacific

Abstract. We have studied the spatial and temporal variation of the surface longwave radiation (downwelling and net) over a 21-year period in the tropical and subtropical Pacific Ocean (40 S–40 N, 90 E–75 W). The fluxes were computed using a deterministic model for atmospheric radiation transfer, along with satellite data from the ISCCP-D2 database and reanalysis data from NCEP/NCAR (acronyms explained in main text), for the key atmospheric and surface input parameters. An excellent correlation was found between the downwelling longwave radiation (DLR) anomaly and the Niño-3.4 index time-series, over the Niño-3.4 region located in the central Pacific. A high anti-correlation was also found over the western Pacific (15–0 S, 105–130 E). There is convincing evidence that the time series of the mean downwelling longwave radiation anomaly in the western Pacific precedes that in the Niño-3.4 region by 3–4 months. Thus, the downwelling longwave radiation anomaly is a complementary index to the SST anomaly for the study of ENSO events and can be used to asses whether or not El Niño or La Niña conditions prevail. Over the Niño-3.4 region, the mean DLR anomaly values range from +20 Wm−2 during El Niño episodes to −20 Wm−2 during La Niña events, while over the western Pacific (15–0 S, 105–130 E) these values range from −15 Wm−2 to +10 Wm−2, respectively. The long- term average (1984–2004) distribution of the net downwelling longwave radiation at the surface over the tropical and subtropical Pacific for the three month period November-December-January shows a net thermal cooling of the ocean surface. When El Niño conditions prevail, the thermal radiative cooling in the central and south-eastern tropical Pacific becomes weaker by 10 Wm−2 south of the equator in the central Pacific (7–0 S, 160–120 W) for the three-month period of NDJ, because the DLR increase is larger than the increase in surface thermal emission. In contrast, the thermal radiative cooling over Indonesia is enhanced by 10 Wm−2 during the early (August–September–October) El Niño phase.

On the Cooling-to-Space Approximation

2020 ◽  
Vol 77 (2) ◽  
pp. 465-478 ◽  
Author(s):  
Nadir Jeevanjee ◽  
Stephan Fueglistaler
Keyword(s):  
Radiative Transfer ◽  
Radiative Flux ◽  
Analytical Theory ◽  
Radiative Cooling ◽  
Atmospheric Layer ◽  
Flux Divergence ◽  
Theoretical Justification ◽  
Vertical Coordinate ◽  
Validity Criteria ◽  
Radiative Exchange

Abstract The cooling-to-space (CTS) approximation says that the radiative cooling of an atmospheric layer is dominated by that layer’s emission to space, while radiative exchange with layers above and below largely cancel. Though the CTS approximation has been demonstrated empirically and is thus fairly well accepted, a theoretical justification is lacking. Furthermore, the intuition behind the CTS approximation cannot be universally valid, as the CTS approximation fails in the case of pure radiative equilibrium. Motivated by this, we investigate the CTS approximation in detail. We frame the CTS approximation in terms of a novel decomposition of radiative flux divergence, which better captures the cancellation of exchange terms. We also derive validity criteria for the CTS approximation, using simple analytical theory. We apply these criteria in the context of both gray gas pure radiative equilibrium (PRE) and radiative–convective equilibrium (RCE) to understand how the CTS approximation arises and why it fails in PRE. When applied to realistic gases in RCE, these criteria predict that the CTS approximation should hold well for H2O but less so for CO2, a conclusion we verify with line-by-line radiative transfer calculations. Along the way we also discuss the well-known “τ = 1 law,” and its dependence on the choice of vertical coordinate.

scholarly journals ENSO surface longwave radiation forcing over the tropical Pacific

2006 ◽  
Vol 6 (6) ◽  
pp. 12895-12928 ◽  
Author(s):  
K. G. Pavlakis ◽  
D. Hatzidimitriou ◽  
E. Drakakis ◽  
C. Matsoukas ◽  
A. Fotiadi ◽  
...  
Keyword(s):  
Time Series ◽  
El Niño ◽  
El Nino ◽  
Longwave Radiation ◽  
Western Pacific ◽  
Radiative Cooling ◽  
Central Pacific ◽  
The Mean ◽  
Downwelling Longwave Radiation ◽  
The Western Pacific

Abstract. We have studied the spatial and temporal variation of the surface longwave radiation (downwelling and net) over a 21-year period in the tropical and subtropical Pacific Ocean (40 S–40 N, 90 E–75 W). The fluxes were computed using a deterministic model for atmospheric radiation transfer, along with satellite data from the ISCCP-D2 database and reanalysis data from NCEP/NCAR (acronyms explained in main text), for the key atmospheric and surface input parameters. An excellent correlation was found between the downwelling longwave radiation (DLR) anomaly and the Niño-3.4 index time-series, over the Niño-3.4 region located in the central Pacific. A high anti-correlation was also found over the western Pacific (15–0 S, 105–130 E). There is convincing evidence that the time series of the mean downwelling longwave radiation anomaly in the western Pacific precedes that in the Niño-3.4 region by 3–4 months. Thus, the downwelling longwave radiation anomaly is a complementary index to the SST anomaly for the study of ENSO events and can be used to asses whether or not El Niño or La Niña conditions prevail. Over the Niño-3.4 region, the mean DLR anomaly values range from +20 Wm−2 during El Niño episodes to –20 Wm−2 during La Niña events, while over the western Pacific (15–0 S, 105–130 E) these values range from –15 Wm−2 to +10 Wm−2, respectively. The long- term average (1984–2004) distribution of the net surface longwave radiation to the surface over the tropical and subtropical Pacific for the three month period November-December-January shows a net thermal cooling of the ocean surface. When El Niño conditions prevail, the thermal radiative cooling in the central and south-eastern tropical Pacific becomes weaker by 10 Wm−2 south of the equator in the central Pacific (7–0 S, 160–120 W) for the three-month period of NDJ, because the DLR increase is larger than the increase in surface thermal emission. In contrast, the thermal radiative cooling over Indonesia is enhanced by 10 Wm−2 during the early (August–September–October) El Niño phase.

On the influence of CO2 on the radiative flux divergence

Tellus ◽  
1968 ◽  
Vol 20 (2) ◽  
pp. 294-299
Author(s):  
Wilford G. Zdunkowski ◽  
Larry L. Stowe
Keyword(s):  
Radiative Flux ◽  
Flux Divergence

scholarly journals Relaxation Times in Strictly Disk Systems

1971 ◽  
Vol 10 ◽  
pp. 15-19
Author(s):  
George B. Rybicki
Keyword(s):  
Numerical Experiments ◽  
Relaxation Times ◽  
Galactic Structure ◽  
Large Numbers ◽  
Order Of Magnitude ◽  
Vlasov Limit ◽  
The Mean ◽  
Gravitating Systems

AbstractIt is shown that the time of relaxation by particle encounters of self-gravitating systems in the plane interacting by 1/r2 forces is of the same order of magnitude as the mean orbit time. Therefore such a system does not have a Vlasov limit for large numbers of particles, unless appeal is made to some non-zero thickness of the disk. The relevance of this result to numerical experiments on galactic structure is discussed.

A Statistical Model of Cloud Vertical Structure Based on Reconciling Cloud Layer Amounts Inferred from Satellites and Radiosonde Humidity Profiles

2005 ◽  
Vol 18 (17) ◽  
pp. 3587-3605 ◽  
Author(s):  
William B. Rossow ◽  
Yuanchong Zhang ◽  
Junhong Wang
Keyword(s):  
Statistical Model ◽  
Vertical Structure ◽  
Atmospheric Temperature ◽  
Radiative Flux ◽  
Cloud Layer ◽  
Cloud Base ◽  
Polar Regions ◽  
Flux Divergence ◽  
Climate Scale ◽  
Humidity Profiles

Abstract To diagnose how cloud processes feed back on weather- and climate-scale variations of the atmosphere requires determining the changes that clouds produce in the atmospheric diabatic heating by radiation and precipitation at the same scales of variation. In particular, not only the magnitude of these changes must be quantified but also their correlation with atmospheric temperature variations; hence, the space–time resolution of the cloud perturbations must be sufficient to account for the majority of these variations. Although extensive new global cloud and radiative flux datasets have recently become available, the vertical profiles of clouds and consequent radiative flux divergence have not been systematically measured covering weather-scale variations from about 100 km, 3 h up to climate-scale variations of 10 000 km, decadal inclusive. By combining the statistics of cloud layer occurrence from the International Satellite Cloud Climatology Project (ISCCP) and an analysis of radiosonde humidity profiles, a statistical model has been developed that associates each cloud type, recognizable from satellite measurements, with a particular cloud vertical structure. Application of this model to the ISCCP cloud layer amounts produces estimates of low-level cloud amounts and average cloud-base pressures that are quantitatively closer to observations based on surface weather observations, capturing the variations with latitude and season and land and ocean (results are less good in the polar regions). The main advantage of this statistical model is that the correlations of cloud vertical structure with meteorology are qualitatively similar to “classical” information relating cloud properties to weather. These results can be evaluated and improved with the advent of satellites that can directly probe cloud vertical structures over the globe, providing statistics with changing meteorological conditions.

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