Clear-sky Planetary Albedo Research Articles

Planetary albedo decline over Northwest India contributing to near surface warming

The increase in frequency and severity of heat waves during the pre-monsoon season (March–May) over Northwest India in recent decades is alarming. This study investigates the causative mechanism for warming through the forcing induced by planetary albedo changes over Northwest India, a hotspot for land-cover change. We use satellite-measured planetary albedo (α) and satellite-derived land-use-land-cover (LULC) data to estimate the impact of LULC changes from 2001 to 2018 on α and the associated radiative forcing. Over Northwest India, significant area under native land-cover, viz., barren, shrub and grass-lands, has been converted to cropland. The associated land-cover-induced changes have perturbed the radiation-budget by modifying the absorption of shortwave radiation, thereby contributing to the pronounced reduction of α as observed over this region. The diurnal-mean α has decreased by 0.016 ± 0.001 from 2001 to 2018 during pre-monsoon season which dominates α-decrease during the annual cycle over this region and contributes to the overall decreasing trend over India. Conversion of barren and shrub-lands to cropland is observed to be the greatest contributor to the α-decrease as compared to other land-cover changes. The radiative forcing due to decline in diurnal-mean α over Northwest India from 2001 to 2018 is highest during pre-monsoon at 5.99 ± 0.34 W/m2. This α-induced forcing averaged over the global land surface (0.02 W/m2) is equivalent to the corresponding direct forcing from rise in atmospheric methane concentrations during this period. We find an enhancement in near-surface heating to be associated with change in α; the decreasing trend in α during pre-monsoon has substantially enhanced near-surface extreme effective temperatures by 3.15 ± 2.61 K thus far and may further lead to more extreme heatwaves in future. Further, our findings highlight a decreasing (warming) and increasing (cooling) trend in clear-sky planetary albedo respectively over Northwest India and coastal regions, suggesting that sudden climate change could occur if one forcing dominates over the other.

Toward the Influence of Clouds on the Shortwave Radiation Budget of the Earth–Atmosphere System Estimated from Satellite Data

Abstract The purpose of this paper is to investigate the influence of cloudiness on the shortwave radiation budget at the top of the atmosphere, at the surface, and, as a residual, for the atmosphere itself. The data used for this study are derived exclusively from satellite measurements. Calculations for the top of the atmosphere are based entirely on measurements of the Earth Radiation Budget Experiment (ERBE). For the solar radiation budget at the surface, the incoming surface solar radiation is derived from Meteosat data and the surface albedo is calculated from ERBE clear-sky planetary albedo measurements by applying an atmospheric correction scheme. As results, maps of absorbed solar radiation for the total earth–atmosphere system, the surface, and for the atmosphere are presented for the area of investigation, ±60° longitude and latitude. To infer the contribution of clouds, the concept of cloud radiative forcing is applied to these different datasets. It is shown that the solar cloud forcing at th...

Removal of Atmospheric Effects prom AVHRR Albedos

Based on numerical simulations, coefficients are determined to be used in a linear relationship between clear-sky planetary albedo and surface albedo. Thew coefficients are given as functions of solar zenith angle and atmospheric parameters for both the AVHRR (Advanced Very High Resolution Radiometer) channels 1 and 2 separately. The atmospheric effects in these channels are systematically different, because of the different spectral behavior of atmospheric parameters. Accordingly the use of the narrowband coefficients will improve the determination of surface properties from AVHRR data, compared with analogous methods using broadband coefficients.

Determination of the clear-sky planetary albedo from AVHRR using a bi-directional reflectance model

Clear-sky planetary albedos are derived from NOAA-9 AVHRR data during 1986 over the U.S. Great Plains with several distinct surface types (shrubland, grassland, deciduous and coniferous forests). The cloud-free observations are selected using a combination of absolute threshold and spatial coherence cloud-screening procedures. The broadband albedo is approximated from the narrow-band visible and near-infrared albedos. Bi-directional reflectivity models are applied to account for the effect of Sun-target-sensor geometry. The corrected albedos are converted to daily means using a directional model to account for the dependence upon sun angle. The results indicate a significant reduction in variability of the observed albedos. The efficiency of the model application is demonstrated on two examples: 1) using time series of cloud-free observations over one target and 2) using one daily image of mapped data in July, 1986.

A Simple Method for Estimating Monthly Mean Albedo of Land Surfaces From AVHRR Data

It is suggested that the observed periodicity of cloud-free, visible and near-infrared data from the Advanced Very High Resolution Radiometer (AVHRR) onboard NOAA-9 for a particular target can be efficiently used for deriving the monthly mean clear-sky planetary albedo. The broadband albedo is approximated by a linear combination of visible and near-infrared albedos. The new method of 9-day compositing distributes the clear-sky observations over the sun-target-sensor geometry combinations and weights them by the occurrence of each combination during a particular month. It is shown that the monthly mean clear-sky planetary albedo can be estimated solely from the visible and near-infrared data in a model-independent manner. The surface albedo is then obtained by applying a simple atmospheric correction to the derived clear-sky planetary albedo. A comparison of the results of the present method and those obtained by using the “minimum albedo” method indicates that the latter may lead to an underestimation of monthly values because of the angular variation in clear-sky observed albedos. The derived surface albedos are compared with those reported in climatological studies based on ground observations.

Satellite observation of surface albedo over the Qinghai-Xizang Plateau Region

A method has been developed to determine the surface albedo over the Qinghai-Xizang Plateau region from NOAA polar orbiter AVHRR (Advanced Very High Resolution Radiometer) data. The empirical relationship between clear-sky planetary and surface albedos is established the basis of surface global radiation measurements and the specified ratio between atmospheric reflection and absoption of solar radiation. The method is applied to the Qinghai-Xizang region with several measurements during the period of Sep. to Nov., 1985. A comparison is presented between the estimated surface albedos and that of surface observation. The results show that the presented method is suitable to detecting the spatial and temporal variation of surface albedo and is relevant for climatological studies. The possible error sources and improvements are discussed as well.

Simulations of the meteosat visible sensor response to changing boundary conditions

Computational experiments have been conducted to simulate the METEOSAT visible sensor's response to varying surfaces and clear-sky atmospheric conditions, as a function of solar zenith angle. The possible bias in observations obtained with this limited spectral response sensor, was assessed. The filtered clear-sky planetary albedo, as observed with the METEOSAT was compared with the (0.305 - 2.5 μm) unfiltered planetary albedo, under the same environmental conditions. Four cases of wavelength-independent surface albedo (0%, 10%, 20%, 30%) and four cases of realistic wavelength dependent surface albedo (snow; meadow; dry sand; water) have been simulated. The complexity of the narrow/broadband spectral relationship of the clear-sky planetary albedo has been demonstrated. The simulations have shown that while under certain assumptions the two were in close agreement, the relationship would strongly depend on the assumptions made on the spectral dependence of the surface reflectivity.

On the relationship between clear-sky planetary and surface albedos: a parameterization for simple energy balance climate models

In simple energy balance climate models all physical and dynamical processes are parameterized in terms of the single unknown variable: the surface temperature. To simulate the ice-albedo feedback, the surface albedo is usually assumed to be a function of surface temperature. But to compute the absorbed solar radiation in such models one requires the top-of-the atmosphere albedo: the planetary albedo. In the present study, a simple linear relationship is derived between planetary albedo and surface albedo for the case of clear skies. The relationship is based upon a regression equation derived from simulations and has a standard error of estimate of 0.028. The estimation of planetary albedo from surface albedo is checked by comparing zonally averaged clear-sky planetary albedos, estimated from zonally averaged surface albedos, to satellite determinations of zonally averaged minimum albedos for monthly mean conditions. The minimum albedos are assumed to be representative of the clear-sky planetary albedos. The results show root-mean square differences of 0.05 between the estimated clear-sky planetary albedos and the minimum albedos. More accurate relationships can be obtained if one uses an additional parameter - the solar zenith angle. In this case, the standard errors of estimate are reduced to 0.017 for a zenith angle of 0°, 0.018 for a zenith angle of 60° and 0.021 for a zenith angle of 85°.

Effects of concurrent snow and cloud cover on planetary albedo

The effects of snow and cloud cover on planetary albedo are examined using observations from NOAA polar orbiting satellites. Reflected radiation was measured in the visible range (0.5 – 0.7 μm). Planetary albedos resulting from different cloud/snow cover conditions are compared using Northern Hemisphere snow cover maps, surface weather charts, satellite photos and data on land surface types. None of the cases studied show that concurrent cloud and snow cover produces significantly different planetary albedos than cloud cover alone. Cloud cover alone is found to yield higher planetary albedos than snow cover alone; the difference being greatest over forested areas. With and without snow cover present, clear-sky planetary albedos over farming and grazing lands (snow(0.45), no snow(0.15)) are found to be significantly higher than those over forested regions (snow(0.33), no snow(0.11)). Variations in satellite zenith angle are not found to produce significant effects in most cases studied.

On the Relationship between Clear-Sky Planetary and Surfae Albedos

Based on simulations, a simple linear relationship is derived between planetary albedo and the surface albedo for the case of clear skies. This relationship enables one to estimate the planetary albedo, given only the surface albedo, and vice versa. The standard error of estimate is 0.028. The estimation of planetary albedo from surface albedo is checked by comparing zonally averaged clear-sky planetary albedos estimated from zonally averaged surface albedos, to satellite determinations of zonally averaged minimum albedos for monthly mean conditions. The minimum albedos are assumed to be representative of the clear-sky planetary albedos. The results show root-mean square differences of 0.05 between the estimated clear-sky planetary albedos and them albedos. More accurate relationships can be obtained if one uses an additional parameter-the solar zenith angle. In this case, the standard errors of estimate are reduced to 0.017 for a zenith angle of 0°,0/018 for a zenith angle of 60° and 0.021 for a zenith of 85°.

Solar and Thermal Radiation Measurements to 32 km at Low Solar Elevations

Abstract The instrumentation and flight results of a balloonborne package of radiometers which measure the upward and downward fluxes of both shortwave and longwave atmospheric radiation are described. Ten flights wore conducted at Mildura and at Longreach, Australia. In most cases the balloon was launched just prior to dawn so that ascent data were obtained covering the period of sunrise, and float data (at altitudes between 21.5 and 31.5 km) were obtained covering the range of solar elevations from 4° to 45°. Composite experimental curves of the clear-sky planetary albedo, net radiation balance, and upward long-wave flux at the top of the atmosphere are presented as functions of solar elevation; the results from which these curves are constructed are remarkably consistent from one time and place to another, and can be regarded as representative for most of continental Australia. Angular intensity distributions of the short-wave radiation emerging from the top of the clear atmosphere are derived from all...