Albedo Trends Research Articles

Towards Multidecadal Consistent Meteosat Surface Albedo Time Series

Monitoring of land surface albedo dynamics is important for the understanding of observed climate trends. Recently developed multidecadal surface albedo data products, derived from a series of geostationary satellite data, provide the opportunity to study long term surface albedo dynamics at the regional to global scale. Reliable estimates of temporal trends in surface albedo require carefully calibrated and homogenized long term satellite data records and derived products. The present paper investigates the long term consistency of a new surface albedo product derived from Meteosat First Generation (MFG) geostationary satellites for the time period 1982–2006. The temporal consistency of the data set is characterized. The analysis of the long term homogeneity reveals some discrepancies in the time series related to uncertainties in the characterization of the sensor spectral response of some of the MFG satellites. A method to compensate for uncertainties in the current data product is proposed and evaluated.

PLUTO AND CHARON WITH THEHUBBLE SPACE TELESCOPE. II. RESOLVING CHANGES ON PLUTO’S SURFACE AND A MAP FOR CHARON

We present new imaging of the surface of Pluto and Charon obtained during 2002–2003 with the Hubble Space Telescope (HST) Advanced Camera for Surveys (ACS) instrument. Using these data, we construct two-color albedo maps for the surfaces of both Pluto and Charon. Similar mapping techniques are used to re-process HST/Faint Object Camera (FOC) images taken in 1994. The FOC data provide information in the ultraviolet and blue wavelengths that show a marked trend of UV-bright material toward the sunlit pole. The ACS data are taken at two optical wavelengths and show widespread albedo and color variegation on the surface of Pluto and hint at a latitudinal albedo trend on Charon. The ACS data also provide evidence for a decreasing albedo for Pluto at blue (435 nm) wavelengths, while the green (555 nm) data are consistent with a static surface over the one-year period of data collection. We use the two maps to synthesize a true visual color map of Pluto's surface and investigate trends in color. The mid- to high-latitude region on the sunlit pole is, on average, more neutral in color and generally higher albedo than the rest of the surface. Brighter surfaces also tend to be more neutral in color and show minimal color variations. The darker regions show considerable color diversity arguing that there must be a range of compositional units in the dark regions. Color variations are weak when sorted by longitude. These data are also used to constrain astrometric corrections that enable more accurate orbit fitting, both for the heliocentric orbit of the barycenter and the orbit of Pluto and Charon about their barycenter.

OMEGA long wavelength channel: Data reduction during non-nominal stages

The Observatoire pour la Minéralogie, l’Eau, les Glaces et l’Activité (OMEGA) instrument is a visible and near-infrared imaging spectrometer on board the European Mars Express (MEx) mission. The on-board calibration (OBC) performed at the beginning of observations on each orbit reveals that the photometric response of the C channel (1.0–2.5 μm) has been very stable since orbit insertion in January 2004. On the contrary the L channel (2.5–5.1 μm) response has varied significantly during the mission, and only orbits for which the response is close to nominal could be used with confidence. The spatial coverage of ice-free surfaces in this wavelength range is consequently limited to only ∼30%, mainly during northern spring and summer. This paper presents the empirical method used to derive new instrumental transfer functions (ITF) for the non-nominal orbits. This method consists of analyzing the variation of the signal between several observations of a same region acquired at nominal and non-nominal calibration states. In the cases where the mineralogy and the atmospheric conditions between the two observations are the same, the variation in reflectance spectra is only due to the ITF variation, which provides a new ITF. We then associate these new ITFs with their corresponding OBCs to model a relationship between both. The resulting model enables us to provide a new ITF for each orbit for which the OBC is available. The new ITFs derived for the entire dataset have been validated (1) through a comparison of the C and L channel global albedo trends and (2) through a comparison of the surface temperatures derived from the L channel with those calculated from the General Circulation Model (GCM) numerical simulation of the LMD released in the Martian Climate Database. The non-nominal data processed with adapted ITFs for orbits up to 3050 increase the non-icy surface coverage of Mars to ∼70% including all seasons.

Antarctic ice sheet and sea ice regional albedo and temperature change, 1981–2000, from AVHRR Polar Pathfinder data

Spring–summer (November, December, January) ice sheet and sea ice regional surface albedo, surface temperature, sea ice concentration and sea ice extent averages and trends from 1981 to 2000 have been calculated for the Antarctic area. In this research the AVHRR Polar Pathfinder 5-km EASE-Grid Composites and the combined SMMR and SSMI data sets from the National Snow and Ice Data Center (NSIDC), Boulder, Colorado have been employed. A regional analysis has been made for five longitudinal sectors around Antarctica: the Weddell Sea (WS), the Indian Ocean (IO), the Pacific Ocean (PO), the Ross Sea (RS) and the Bellingshausen–Amundsen Sea (BS). The IO and PO sectors show ice sheet albedos of 0.85 and temperatures of − 25 °C. The corresponding values in the RS and BS sectors are 0.80 and − 16 °C respectively. The sea ice albedo is about 0.60 in the RS, BS and WS sectors and 0.55 in the IO and PO sectors. The average sea ice temperature varies around − 12 °C. All the sectors show slight increasing spring–summer albedo trends and decreasing spring–summer temperature trends and similar interannual variability in albedo and surface temperature. The steepest ice sheet albedo trend of 0.0019 ± 0.0009/yr is found in the RS sector. The steepest sea ice albedo trend of 0.0044 ± 0.0017 /yr occurs in the PO sector. The steepest temperature trends for both the ice sheet and sea ice occur in the BS sector, having values of − 0.075 ± 0.040 °C/yr and − 0.107 ± 0.027 °C/yr respectively. The sea ice concentration shows slight increasing trends, the highest being in the PO sector (0.3 ± 0.12%/yr), whereas the sea ice extent trends are near zero with the exception of the RS sector (14,700 ±8600 km 2/yr) and the BS sector (− 13,000 ± 6400 km 2/yr).

Latitude‐dependent long‐term variations in polar mesospheric clouds from SBUV version 3 PMC data

Previous studies have suggested that there should be secular trends in polar mesospheric cloud (PMC) occurrence frequency and brightness on decadal timescales and that those trends would be strongest at the lowest latitudes of the PMC existence region. We have analyzed the 27‐year PMC data set created from Solar Backscatter Ultraviolet (SBUV, SBUV/2) satellite instruments for long‐term variations in albedo using three latitude bands (50°–64°, 64°–74°, 74°–82°). The improved version 3 data set includes revisions to the PMC detection algorithm to produce more consistent results in all measurement conditions. A detailed error analysis yields an approximate uncertainty of 1–2% for seasonally averaged 252‐nm albedo values. Adjustments for local time variations in PMC brightness between different satellite data sets were derived to ensure accurate trend calculations. Multiple linear regression fits show that albedo variations are anticorrelated with solar activity in all latitude bands, with a stronger response at high latitudes. The albedo increase from solar maximum to solar minimum ranges from +2% at 50°–64°S to +17% at 74°–82°N. Secular trends in albedo are positive, with long‐term changes over 27 years ranging from +12% to +20% depending on hemisphere and latitude. The derived long‐term trend in PMC albedo at 50°–64° is smaller than that of higher latitudes. This result contradicts previous suggestions that PMC brightness changes might be most rapid at low latitudes. The albedo response to solar variations is larger in the Northern Hemisphere, while long‐term trends are approximately the same in both hemispheres.

Comparison of MISR and CERES top‐of‐atmosphere albedo

The Clouds and the Earth's Radiant Energy System (CERES) and the Multi‐angle Imaging SpectroRadiometer (MISR) on Terra satellite measure the Earth's top‐of‐atmosphere (TOA) albedo in broadband and narrowband, respectively. This study presents the first direct comparison of the CERES and MISR albedos. An algorithm for converting the MISR spectral albedos to broadband is derived. The MISR and CERES albedos for overcast ocean scenes are compared between 75°S–75°N for solar zenith angles ≤75°. For overcast 1° × 1° ocean regions, the relative differences and the relative root‐mean‐square (RMS) differences between the MISR and CERES albedos are ∼0.8% and ∼4.3%, respectively. Accounting for a ∼2.0% error in the MISR albedos due to narrow‐to‐broadband albedo conversion errors, the RMS difference between the MISR and CERES albedos due to angular distribution model (ADM) differences is estimated to be ∼3.8%. The remarkable consistency between the CERES and MISR albedos for overcast oceans suggests that both instrument teams have derived accurate corrections for the radiance anisotropy of cloud scenes. This consistency will strongly enhance the confidence in the temporal trends of cloud albedo measured by the CERES and have significant impact on climate studies.

Comment on “A multi-data comparison of shortwave climate forcing changes” by Pallé et al.

Comment on “A multi-data comparison of shortwave climate forcing changes” by Pallé et al.

Changes in Earth's Albedo Measured by Satellite

NASA global satellite data provide observations of Earth's albedo, i.e., the fraction of incident solar radiation that is reflected back to space. The satellite data show that the last four years are within natural variability and fail to confirm the 6% relative increase in albedo inferred from observations of earthshine from the moon. Longer global satellite records will be required to discern climate trends in Earth's albedo.

Monitoring the perennial martian northern polar cap with MGS MOC

We have used the Mars Global Surveyor Mars Orbiter Camera Wide Angle (MGS MOC WA) dataset to study albedo trends on the martian northern residual cap. Six study regions were selected, the Chasma Boreale source region, three regions near the center of the cap (“fish hook” region, latitude = 87°; “bottle opener” region, latitude = 87°, “steep-shallow” region, latitude = 85°), and two lower latitude regions (crater, latitude = 77°, and polar outlier, latitude = 82°), and the albedos of these six regions were examined. These regions were chosen due to their good temporal coverage in the MOC dataset, as well as having been studied by other researchers (Bass et al., 2000, Icarus 144, 382–396; Calvin and Titus, 2004, Lunar Planet. Sci. XXXV, Abstract 1455). The picture which emerges is complex. Most areas experience a combination of darkening and brightening through the northern summer; only one area consistently brightens (the polar outlier region). A good deal of interannual repeatability in each region's albedo behavior is seen, however. Possible causes for the observed complex behaviors include dust deposition from late summer storms, sintering of frost grains over the course of the summer, and cold trapping of volatiles on bright, cold surfaces.

Surface albedo measurements over Antarctic sites in summer

Surface albedo data from several Antarctic sites were compared to determine spatial and temporal variability in albedo. The highest degree of variability was observed at Hells Gate Station on the Ross Sea coast. The temperature close to the melting point and the reduced katabatic winds during summer allowed a strong metamorphism of the snow. At Neumayer, a coastal station by the Weddell Sea, snowfall and drifting snow were more frequent, and the surface albedo was constantly high. The albedo increased by an average of 0.07 from clear days to days with snowfall and overcast sky. Surprisingly, the hourly variation in albedo at Hells Gate Station showed a trend similar to the one observed at Neumayer Station and at Dome Concordia Station on the high plateau, when only those days with fresh snow at the surface were considered. The albedo steadily decreased during the day for solar zenith angles less than 80°. Snow metamorphism, sublimation during the day, and refreezing and/or crystal formation/precipitation during the night can explain the observed trend. To represent the daily trend in albedo over ice and fresh snow, we propose two parameterizations, which can be easily applied over other Arctic and Antarctic sites in summer. Small‐ and large‐scale surface roughness elements can result in distortion in the measured albedo. The data at Reeves Névé Station show the effect produced on the albedo by changing slightly the sampling area immediately over a sastruga.

Long-term global distribution of earth's shortwave radiation budget at the top of atmosphere

Abstract. The mean monthly shortwave (SW) radiation budget at the top of atmosphere (TOA) was computed on 2.5° longitude-latitude resolution for the 14-year period from 1984 to 1997, using a radiative transfer model with long-term climatological data from the International Satellite Cloud Climatology Project (ISCCP-D2) supplemented by data from the National Centers for Environmental Prediction – National Center for Atmospheric Research (NCEP-NCAR) Global Reanalysis project, and other global data bases such as TIROS Operational Vertical Sounder (TOVS) and Global Aerosol Data Set (GADS). The model radiative fluxes at TOA were validated against Earth Radiation Budget Experiment (ERBE) S4 scanner satellite data (1985–1989). The model is able to predict the seasonal and geographical variation of SW TOA fluxes. On a mean annual and global basis, the model is in very good agreement with ERBE, overestimating the outgoing SW radiation at TOA (OSR) by 0.93 Wm-2 (or by 0.92%), within the ERBE uncertainties. At pixel level, the OSR differences between model and ERBE are mostly within ±10 Wm-2, with ±5 Wm-2 over extended regions, while there exist some geographic areas with differences of up to 40 Wm-2, associated with uncertainties in cloud properties and surface albedo. The 14-year average model results give a planetary albedo equal to 29.6% and a TOA OSR flux of 101.2 Wm-2. A significant linearly decreasing trend in OSR and planetary albedo was found, equal to 2.3 Wm-2 and 0.6% (in absolute values), respectively, over the 14-year period (from January 1984 to December 1997), indicating an increasing solar planetary warming. This planetary SW radiative heating occurs in the tropical and sub-tropical areas (20° S–20° N), with clouds being the most likely cause. The computed global mean OSR anomaly ranges within ±4 Wm-2, with signals from El Niño and La Niña events or Pinatubo eruption, whereas significant negative OSR anomalies, starting from year 1992, are also detected.

Arctic sea ice regional albedo variability and trends, 1982–1998

Whole‐summer and monthly sea ice regional albedo averages for June, July, and August from 1982 to 1998 have been processed from advanced very high resolution radiometer data. Time series for albedo, sea ice concentration, sea ice extent, and surface air temperature have been calculated for the sea ice cover for the Northern Hemisphere as a whole and for six subregions: the Arctic Ocean, the Kara and Barents Seas, the Greenland Sea, the Labrador Sea, Hudson Bay, and the Canadian archipelago. The slope of the summer albedo trend for the Northern Hemisphere is −0.0007 ± 0.0008/year. The largest monthly slope (−0.0016 ± 0.0011/year) is found for June, and the lowest slope (−0.0004 ± 0.0014/year) is found for August. Among the subregions the Greenland Sea has the steepest negative summer trend of −0.0038 ± 0.0012/year during the period, while for the Arctic Ocean the albedo trend is near zero. The calculated trends for the summer sea ice concentration and extent for the Northern Hemisphere are also negative, with a slopes of −0.093 ± 0.069%/year and −42,300 ± 15,200 km2/yr, respectively. In general, the albedo in the central Arctic is between 0.5 and 0.7. The highest albedo values are mainly found in the Arctic Ocean north of Greenland. The lowest albedo (0.2–0.3) occurs in the fringe area of the Arctic Ocean, e.g., on the coasts of Alaska and Siberia. Low albedo values also exist on the east coast of Greenland and in Hudson Bay.

Effects of aerosol and SST gradients on marine stratocumulus albedo

Airborne data are reported on the effect of sea surface temperature and aerosol gradients on the albedo of marine stratocumulus clouds off the coast of central California. Both types of gradients, at the magnitudes and spatial scales observed, produce significant and comparable trends in the cloud albedo (∼15% changes over 40 km).

Assessment of Greenland albedo variability from the advanced very high resolution radiometer Polar Pathfinder data set

The advanced very high resolution radiometer Polar Pathfinder (APP) data set is used to examine the variability of the surface albedo over Greenland. Analysis of the APP albedo record from 1981 to 1998 show anomalously low albedo during 1995 and 1998 over most of the ice sheet as compared with the other years. The low albedo encountered during these years suggests that the ice sheet experienced considerable melt in 1995 and 1998, particularly near the western margin of the ice sheet. Conversely, anomalously high albedos were found in 1992 as a result of colder temperatures and hence less melt following the eruption of Mount Pinatubo. The relationship between the annual North Atlantic Oscillation (NAO) index and the mean summer albedo from all the stations reveals a positive correlation of 0.44 and a positive correlation of 0.55 for the southern part of the ice sheet. Therefore variations in the mean summer albedo over Greenland can, in part, be explained by variations in the NAO such that during periods of intensification of the normal mode of the NAO the mean summer albedo is above normal. Trend analysis reveals an overall downward trend in surface albedo from 1981 to 1998, which agrees with recent trends in melt and precipitation. However, the trend was found not to be statistically significant but rather influenced by the low albedo in recent years.

Satellite-observed variability and trend in sea-ice extent, surface temperature, albedo and clouds in the Arctic

AbstractRecent observations of a decreasing ice extent and a possible thinning of the ice cover in the Arctic make it imperative that detailed studies of the current Arctic environment are made, especially since the region is known to be highly sensitive to a potential change in climate. A continuous dataset of microwave, thermal infrared and visible satellite data has been analyzed for the first time to concurrently study in spatial detail the variability of the sea-ice cover, surface temperature, albedo and cloud statistics in the region from 1987 to 1998. Large warming anomalies during the last four years (i.e. 1995−98) are indeed apparent and spatially more extensive than previous years. The largest surface temperature anomaly occurred in 1998, but this was confined mainly to the western Arctic and the North American continent, while cooling occurred in other areas. The albedo anomalies show good coherence with the sea-ice concentration anomalies except in the central region, where periodic changes in albedo are observed, indicative of interannual changes in duration and areal extent of melt ponding and snow-free ice cover. The cloud-cover anomalies are more difficult to interpret, but are shown to be well correlated with the expected warming effects of clouds on the sea-ice surface. The results from trend analyses of the data are consistent with a general warming trend and an ice-cover retreat that appear to be even larger during the last dozen years than those previously reported.

Estimation of the parameter error propagation in inversion based BRDF observations at single sun position

In multiangular remote sensing observations, the variable range of the solar zenith angle (SZN) is narrow. We takes the linear kernel-driven model as an example to analyze the parameter error propagation in inversion by using the observations at single sun position and to show that in such case it is unreliable to invert the BRDF tendency with SZN. To improve the algorithm, we suggest adding certain constraint for the changing trend of albedo with SZN in the model inversion.

Dry-season radiation balance of land covers replacing forest in northern Thailand

The results of numerous general circulation model (GCM) experiments of climatic effects of extensive tropical deforestation include significant reductions in regional precipitation. However, the simulated precipitation decrease is highly dependent on the large albedo shift associated with the assumed conversion of forest into grassland. Land cover change surveys of the Amazon and Thailand suggest that secondary vegetation at various growth stages, rather than grassland, is the dominant feature of deforested land. In this paper, we present field measurements, taken during the dry season, of radiative characteristics of various deforested land surfaces in montane northern Thailand, including secondary vegetation. Dry-season albedo at nine sites in the village of Pang Khum, Chiang Mai Province, ranged from 0.085 for irrigated bare soil to 0.171 for 3-year secondary vegetation. As a result of increased albedo and higher daytime surface temperature at exposed dry soil sites, net radiation is reduced substantially. Regional mean dry-season albedo is estimated to have increased from 0.13 to 0.144 by 1980 for all of northern Thailand, and from 0.13 to 0.14 by 1983 for the southern portion of Sam Mun watershed, the 10 000 ha area immediately surrounding the study site. Continuing significant upward trends in regional albedo at both spatial scales are suggested by the estimates. However, our measurements suggest a maximum deforestation-induced albedo increase of about 0.04, half that used to simulate the effects of deforestation in most GCM experiments. It is likely, therefore, that simulated reductions in precipitation in the region due to deforestation will not be seen in model runs using more realistic scenarios of post-deforestation land cover characteristics.

Climate changes indicated by trends in snow cover duration and surface albedo in Estonia

Climate changes indicated by trends in snow cover duration and surface albedo in Estonia

Spatial and Temporal Variations in Surface Albedo of a Subarctic Landscape Using Surface-based Measurements and Remote Sensing

Spatial and temporal variation in summertime albedo of a subarctic landscape near the Hudson Bay coast is examined using ground-based measurements and Landsat Thematic Mapper (TM) imagery. Temporal variation in surface albedo was determined using an extensive data set from six tower sites with multiple years of data. Four distinct patterns in evolution of the seasonal trend in daily albedo were discovered for the six sites and appeared to be related to vegetation and surface moisture characteristics. All sites showed an albedo response to solar zenith angles greater than 60 degrees, at smaller zenith angles hourly albedo was a good representation of daily values.TM imagery from a dry year (1984) and a wet year (1991) were used to derive maps of albedo for the study area. Spatial variation of albedo was examined within representative training areas centered on the six tower sites. The magnitude of spatial variation in albedo was typically less than 0.04 for all sites. Spatial variability was slightly greater in the wet year. A one pixel transect of albedo across the study area showed the largest difference between lakes and terrestrial surfaces. However, within the terrestrial zones, alternating patches of open forest and tundra and differences in wetness create a coherent pattern in albedo across the landscape.

CHANGES IN MONO-, DI-,AND POLYAMINE LEVELS IN CITRUS FRUIT TISSUES DURING FRUIT ENLARGEMENT

Mono-, di- and polyamines are known to influence growth and development processes in plant organs. Because of the complexity of citrus fruit, we investigated the relative distribution and changes occurring in endogenous levels of the free form of these compounds in the three major fruit tissues (i.e., flavedo, albedo, and juice vesicles) of the `Washington' navel orange (Citrus sinensis L. Osbeck) during the period of exponential growth (i.e., from 2 to 8 cm in diameter). In young fruit (2 to 4 cm), putrescine levels were highest in juice vesicles > flavedo > albedo, decreasing during growth to a minimum when fruit were 4 to 5 cm in diameter. Fully grown fruit undergoing maturation exhibited a significant increase in putrescine with albedo > flavedo > juice vesicles. Spermidine followed similar trends in albedo and flavedo, but decreased in the endocarp. Spermine levels steadily declined in all tissues with fruit growth to barely detectable amounts when fruit reached full size. Phenylethylamine was absent in the flavedo, whereas tyramine and dopamine were present in significant amounts, especially during early fruit growth. The significance of these changes to fruit growth and development will be discussed.