Processes Controlling the Seasonally Varying Emergence of Forced Arctic Longwave Radiation Changes
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Jonah K. Shaw↗
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Effects of surface coating on the shortwave and longwave radiative effects of dust aerosol in comparison with external mixing: A theoretical study
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Zhibo Zhang↗
Impact of downward longwave radiative deficits on Antarctic sea-ice extent predictability during the sea ice growth period
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Ivana Cerovečki↗
Diabatic heating fields and the generation of available potential energy during FGGE
Global diabatic heating is estimated using fields of directly computed heating components, in particular those due to shortwave radiation, longwave radiation, sensible heating, and latent heating produced every 6 hours. The role of average fields of diabatic heating in the generation of available potential energy is examined. It is observed that latent heating is most significant in generating available potential energy.
Salstein, David A.↗
Black Carbon and Precipitation: an Energetics Perspective
Black carbon aerosols (BC) influence precipitation through a range of processes. The climate response to the presence of BC is however highly dependent on its vertical distribution. Here, we analyze the changes in the energy budget and precipitation impacts of adding a layer of BC at a range of altitudes in two independent global climate models. The models are run with atmosphere‐only and slab ocean model setup to analyze both fast and slow responses, respectively. Globally, precipitation changes are tightly coupled to the energy budget. We decompose the precipitation change into contributions from absorption of solar radiation, atmospheric longwave radiative cooling, and sensible heat flux at the surface. We find that for atmosphere‐only simulations, BC rapidly suppress precipitation, independent of altitude, mainly because of strong atmospheric absorption. This reduction is offset by increased atmospheric radiative longwave cooling and reduced sensible heat flux at the surface, but not of sufficient magnitude to prevent reduced precipitation. On longer timescales, when the surface temperature is allowed to respond, we find that the precipitation increase associated with surface warming can compensate for the initial reduction, particularly for BC in the lower atmosphere. Even though the underlying processes are strikingly similar in the two models, the resulting change in precipitation and temperature by BC differ quite substantially.
black carbon aerosols↗
Relationship between the longwave cloud radiative forcing at the surface and the top of the atmosphere
In order to achieve global coverage, any surface radiation climatology has to be based on satellite observations. In the last decade several schemes have been devised to obtain the surface solar insolation from top of the atmosphere reflected solar radiation. More recently, attempts have been made to infer the components of longwave radiation at the surface from satellite sounder data using a radiative transfer model. In addition to the radiative transfer scheme, these methods require assumptions about the effective emitting temperature of cloud tops and bases. Modeling studies have shown that although there are strong correlations between the solar upwelling radiative flux and surface flux, this is not true of the longwave. However, if the clear sky component is considered separately such that the cloud longwave forcing at the top and at the surface are compared, a slightly different picture emerges. During the FIRE Cirrus IFO, surface radiation measurements were made at several sites and coincident satellite overpass data was also collected. It may be possible to extract the longwave cloud radiative forcing at the top and surface from these data. If relationships are verifiable by observations, this information can be useful for the extraction of the surface longwave radiation from satellite data. The radiative transfer schemes used to convert upwelling spectral radiances into a downwelling longwave radiation can provide the clear sky component. The cloud radiative forcing at the top of the atmosphere can then modify the surface fluxes according to relationships shown. It should be noted that this procedure may be considered only for temporal averages and not for instantaneous deductions of surface fluxes. This would be most useful in compiling monthly mean regional climatologies of the surface longwave fluxes.
HARSHVARDHAN↗
Cloud forcing and the net longwave surface radiation
A method is suggested which determines the monthly mean longwave radiation at the surface over the oceans using currently available satellite data sets. An independent estimate of the frequency of occurrence of clouds or cloud top heights is not required. A climatological relationship between the LWCRF (longwave cloud radiation forcing) at the top of the atmosphere and surface may be substituted. This ratio is obtained from a GMC simulation but in principle could be obtained observationally, although global coverage is doubtful. A flow diagram shows the procedure used to obtain maps for the monthly mean net upward longwave flux at the surface.
HARSHVARDHAN↗
Spectral Longwave Cloud Radiative Forcing as Observed by AIRS
AIRS V6 products contain the spectral contributions to Outgoing Longwave Radiation (OLR), clear-sky OLR (OLR(sub CLR)), and Longwave Cloud Radiative Forcing (LWCRF) in 16 bands from 100 cm(exp -1) to 3260 cm(exp -1). We show climatologies of selected spectrally resolved AIRS V6 products over the period of September 2002 through August 2016. Spectrally resolved LWCRF can better describe the response of the Earth system to cloud and cloud feedback processes. The spectral LWCRF enables us to estimate the fraction of each contributing factor to cloud forcing, i.e.: surface temperature, mid to upper tropospheric water vapor, and tropospheric temperature. This presentation also compares the spatial characteristics of LWCRF from AIRS, CERES_EBAF Edition-2.8, and MERRA-2. AIRS and CERES LWCRF products show good agreement. The OLR bias between AIRS and CERES is very close to that of OLR(sub CLR). This implies that both AIRS and CERES OLR products accurately account for the effect of clouds on OLR.
Cloud radiative forcing↗
An Assessment of the Surface Longwave Direct Radiative Effect of Airborne Saharan Dust During the NAMMA Field Campaign
In September 2006, NASA Goddard s mobile ground-based laboratories were deployed to Sal Island in Cape Verde (16.73degN, 22.93degW) to support the NASA African Monsoon Multidisciplinary Analysis (NAMMA) field study. The Atmospheric Emitted Radiance Interferometer (AERI), a key instrument for spectrally characterizing the thermal IR, was used to retrieve the dust IR aerosol optical depths (AOTs) in order to examine the diurnal variability of airborne dust with emphasis on three separate dust events. AERI retrievals of dust AOT are compared with those from the coincident/collocated multifilter rotating shadow-band radiometer (MFRSR), micropulse lidar (MPL), and NASA Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) sensors. The retrieved AOTs are then inputted into the Fu-Liou 1D radiative transfer model to evaluate local instantaneous direct longwave radiative effects (DRE(sub LW)) of dust at the surface in cloud-free atmospheres and its sensitivity to dust microphysical parameters. The top-of-atmosphere DRE(sub LW) and longwave heating rate profiles are also evaluated. Instantaneous surface DRE(sub LW) ranges from 2 to 10 W/sq m and exhibits a strong linear dependence with dust AOT yielding a DRE(sub LW) of 16 W/sq m per unit dust AOT. The DRE(sub LW) is estimated to be approx.42% of the diurnally averaged direct shortwave radiative effect at the surface but of opposite sign, partly compensating for the shortwave losses. Certainly nonnegligible, the authors conclude that DRE(sub LW) can significantly impact the atmospheric energetics, representing an important component in the study of regional climate variation.
Hansell, R. A.↗
Radiation in controlled environments: influence of lamp type and filter material
Radiation in controlled environments was characterized using fluorescent and various high-intensity-discharge (HID) lamps, including metal halide, low-pressure sodium, and high-pressure sodium as the radiation source. The effects of water, glass, or Plexiglas filters on radiation were determined. Photosynthetic photon flux (PPF, 400 to 700 nm), spectra (400 to 1000 nm), shortwave radiation (285-2800 nm), and total radiation (300 to 100,000 nm) were measured, and photosynthetically active radiation (PAR, 400 to 700 nm) and longwave radiation (2800 to 100,000 nm) were calculated. Measurement of PPF alone was not an adequate characterization of the radiation environment. Total radiant flux varied among lamp types at equal PPF. HID lamps provided a lower percentage of longwave radiation than fluorescent lamps, but, when HID lamps provided PPF levels greater than that possible with fluorescent lamps, the amount of longwave radiation was high. Water was the most effective longwave radiation filter. Glass and Plexiglas similarly filtered longwave more than shortwave radiation, but transmission of nonphotosynthetic shortwave radiation was less with Plexiglas than glass. The filter materials tested would not be expected to influence photomorphogenesis because radiation in the action spectrum of phytochrome was not altered, but this may not be the only pigment involved.
NASA Discipline Life Support Systems↗
A parameterization for longwave surface radiation from sun-synchronous satellite data
A parameterization is presented for computing downward, upward, and net longwave radiation at the earth's surface using data from NOAA sun-synchronous satellites. The parameterization is applied to satellite soundings for April, 1982 over a large region of the tropical Pacific Ocean. Sensitivity studies were used to estimate the random and systematic errors in computed fluxes due to probable errors in TOVS-derived parameters. It is suggested that large biases in the results due to errors in TOVS-derived parameters may be corrected with data from the International Satellite Cloud Climatology Project.
Gupta, Shashi K.↗
A parameterization for longwave surface radiation from satellite data - Recent improvements
Several improvements have been made recently to the parameterization for surface longwave radiation described by Gupta (1989). Model constants have been modified in order to use meteorological data from the International Satellite Cloud Climatology Project instead of from the TIROS Operational Vertical Sounder data, primarily to take advantage of the vastly superior cloud information available from the former. Additional modifications were made to improve the estimation of cloud effect in the presence of low-level clouds. The latter modifications reduced the systematic error of the overcast-sky fluxes from 10.0 to 1.7 W/sq m and the random error from +/- 18.9 to +/- 6.3 W/sq m when compared to the fluxes computed with a detailed radiative transfer model.
Gupta, Shashi K.↗
Downward longwave surface radiation from sun-synchronous satellite data - Validation of methodology
An extensive study has been carried out to validate a satellite technique for estimating downward longwave radiation at the surface. The technique, mostly developed earlier, uses operational sun-synchronous satellite data and a radiative transfer model to provide the surface flux estimates. The satellite-derived fluxes were compared directly with corresponding ground-measured fluxes at four different sites in the United States for a common one-year period. This provided a study of seasonal variations as well as a diversity of meteorological conditions. Dome heating errors in the ground-measured fluxes were also investigated and were corrected prior to the comparisons. Comparison of the monthly averaged fluxes from the satellite and ground sources for all four sites for the entire year showed a correlation coefficient of 0.98 and a standard error of estimate of 10 W/sq m. A brief description of the technique is provided, and the results validating the technique are presented.
Darnell, W. L.↗
A numerical simulation of seasonal stratospheric climate. I - Zonal temperatures and winds
Two numerical experiments were designed to isolate the effects of seasonal and latitudinal variations in longwave radiative transfer processes. The first experiment aimed at computing the rate of temperature change in the stratosphere due to longwave radiative transfer by CO2, H2O and O3 from Ramanathan's (1976) radiative-convective model applied to the troposphere-stratosphere circulation. The second experiment employs the Newtonian cooling approximation in which the rate of temperature change in the stratosphere by longwave radiative transfer is set equal to the product of the Newtonian cooling coefficient 'h' and the departure of the local temperature from a reference temperature. It is shown that the latitudinal temperature distribution of the lower stratosphere is maintained by the combined effects of dynamics, O3 solar heating and the longwave radiative coupling between troposphere and stratosphere. The latitudinal gradient in the troposphere-stratosphere longwave radiative coupling is maximum during winter and spring. The radiative response time (1/h) of the middle and upper stratosphere undergoes significant latitudinal and seasonal variations, largely due to the temperature dependence of h.
Ramanathan, V.↗
Sensitivity of Downward Longwave Surface Radiation to Moisture and Cloud Changes in a High-elevation Region
Several studies have suggested enhanced rates of warming in high-elevation regions since the latter half of the twentieth century. One of the potential reasons why enhanced rates of warming might occur at high elevations is the nonlinear relationship between downward longwave radiation (DLR) and specific humidity (q). Using ground-based observations at a high-elevation site in southwestern Colorado and coincident satellite-borne cloud retrievals, the sensitivity of DLR to changes in q and cloud properties is examined and quantified using a neural network method. It is also used to explore how the sensitivity of DLR to q (dDLR/dq) is affected by cloud properties. When binned by season, dDLR/dq is maximum in winter and minimum in summer for both clear and cloudy skies. However, the cloudy-sky sensitivities are smaller, primarily because (1) for both clear and cloudy skies dDLR/dq is proportional to 1/q, for q>0.5 g/kg, and (2) the seasonal values of q are on average larger in the cloudy-sky cases than in clear-sky cases. For a given value of q, dDLR/dq is slightly reduced in the presence of clouds and this reduction increases as q increases. In addition, DLR is found to be more sensitive to changes in cloud fraction when cloud fraction is large. In the limit of overcast skies, DLR sensitivity to optical thickness decreases as clouds become more opaque. These results are based on only one high-elevation site, so the conclusions here need to be tested at other high-elevation locations.
cloud physics↗
A three-D circulation model study of the radiative-dynamic coupling within the stratosphere
The role of radiative transfer processes in the general circulation of the stratosphere was studied by comparing the thermal and dynamical structure of the stratosphere as simulated by two controlled numerical experiments performed with the aid of a spectral 3-dimensional quasi-geostrophic circulation model. In the first experiment, a detailed radiative transfer model is employed to treat the longwave radiative transfer in the stratosphere. In the second experiment, longwave radiative transfer is accounted for by employing the Newtonian cooling approximation. It is found that the exchange of longwave radiation between the troposphere and lower stratosphere has a net heating effect on the lower stratosphere. It is shown that this heating effect contributes partly to the maintenance of the warm high-latitude belt in the lower stratosphere during winter and spring seasons. The strong temperature dependence of the Newtonian cooling coefficient plays an important role in determining the zonal temperatures and has a significant influence on the transmissivity of stratosphere to propagating planetary scale waves.
Ramanathan, V.↗
Evaluation of surface energy and radiation balance systems on the Konza Prairie
Four Surface Energy and Radiation Balance Systems (SERBS) were installed and operated for two weeks in Kansas during July of 1986. Surface energy and radiation balances were investigated on six sites on the Konza Prairie about 3 km south of Manhattan, Kansas. Measurements were made to allow the computation of these radiation components: total solar and diffuse radiation, reflected solar radiation, net radiation, and longwave radiation upward and downward. Measurements were made to allow the computation of the sensible and latent heat fluxes by the Bowen ratio method using differential psychrometers on automatic exchange mechanisms. The report includes a description of the experimental sites, data acquisition systems and sensors, data acquisitions system operating instructions, and software used for data acquisition and analysis. In addition, data listings and plots of the energy balance components for all days and systems are given.
Fritschen, Leo J.↗
Earth System Model Parameter Adjustment Using a Green's Functions Approach
We demonstrate the practicality and effectiveness of using a Green's functions estimation approach for adjusting uncertain parameters in an Earth system model (ESM). This estimation approach has previously been applied to an intermediate-complexity climate model and to individual ESM components, e.g., ocean, sea ice, or carbon cycle components. Here, the Green's functions approach is applied to a state-of-the-art ESM that comprises a global atmosphere/land configuration of the Goddard Earth Observing System (GEOS) coupled to an ocean and sea ice configuration of the Massachusetts Institute of Technology general circulation model (MITgcm). Horizontal grid spacing is approximately 110 km for GEOS and 37–110 km for MITgcm. In addition to the reference GEOS-MITgcm simulation, we carried out a series of model sensitivity experiments, in which 20 uncertain parameters are perturbed. These “control” parameters can be used to adjust sea ice, microphysics, turbulence, radiation, and surface schemes in the coupled simulation. We defined eight observational targets: sea ice fraction, net surface shortwave radiation, downward longwave radiation, near-surface temperature, sea surface temperature, sea surface salinity, and ocean temperature and salinity at 300 m. We applied the Green's functions approach to optimize the values of the 20 control parameters so as to minimize a weighted least-squares distance between the model and the eight observational targets. The new experiment with the optimized parameters resulted in a total cost reduction of 9 % relative to a simulation that had already been adjusted using other methods. The optimized experiment attained a balanced cost reduction over most of the observational targets. We also report on results from a set of sensitivity experiments that are not used in the final optimized simulation but helped explore options and guided the optimization process. These experiments include an assessment of sensitivity to the number of control parameters and to the selection of observational targets and weights in the cost function. Based on these sensitivity experiments, we selected a specific definition for the cost function. The sensitivity experiments also revealed a decreasing overall cost as the number of control variables was increased. In summary, we recommend using the Green's functions estimation approach as an additional fine-tuning step in the model development process. The method is not a replacement for modelers' experience in choosing and adjusting sensitive model parameters. Instead, it is an additional practical and effective tool for carrying out final adjustments of uncertain ESM parameters.
Green's Function↗