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A net decrease in the Earth's cloud, aerosol, and surface 340 nm reflectivity during the past 33 yr (1979–2011)
Abstract and Figures
Measured upwelling radiances from Nimbus-7 SBUV (Solar Backscatter Ultraviolet) and seven NOAA SBUV/2 instruments have been used to calculate the 340 nm Lambertian equivalent reflectivity (LER) of the Earth from 1979 to 2011 after applying a common calibration. The 340 nm LER is highly correlated with cloud and aerosol cover because of the low surface reflectivity of the land and oceans (typically 2 to 6 RU, reflectivity units, where 1 RU Combining double low line 0.01 Combining double low line 1.0%) relative to the much higher reflectivity of clouds plus nonabsorbing aerosols (typically 10 to 90 RU). Because of the nearly constant seasonal and long-term 340 nm surface reflectivity in areas without snow and ice, the 340 nm LER can be used to estimate changes in cloud plus aerosol amount associated with seasonal and interannual variability and decadal climate change. The annual motion of the Intertropical Convergence Zone (ITCZ), episodic El Niño Southern Oscillation (ENSO), and latitude-dependent seasonal cycles are apparent in the LER time series. LER trend estimates from 5 zonal average and from 2 × 5 , latitude × longitude, time series show that there has been a global net decrease in 340 nm cloud plus aerosol reflectivity. The decrease in cos2(latitude) weighted average LER from 60 S to 60 N is 0.79 ± 0.03 RU over 33 yr, corresponding to a 3.6 ± 0.2% decrease in LER. Applying a 3.6% cloud reflectivity perturbation to the shortwave energy balance partitioning given by Trenberth et al. (2009) corresponds to an increase of 2.7 W m-2 of solar energy reaching the Earth's surface and an increase of 1.4% or 2.3 W m-2 absorbed by the surface, which is partially offset by increased longwave cooling to space. Most of the decreases in LER occur over land, with the largest decreases occurring over the US (-0.97 RU decade-1), Brazil (-0.9 RU decade-1), and central Europe (-1.35 RU decade-1). There are reflectivity increases near the west coast of Peru and Chile (0.8 ± 0.1 RU decade-1), over parts of India, China, and Indochina, and almost no change over Australia. The largest Pacific Ocean change is -2 ± 0.1 RU decade-1 over the central equatorial region associated with ENSO. There has been little observed change in LER over central Greenland, but there has been a significant decrease over a portion of the west coast of Greenland. Similar significant decreases in LER are observed over a portion of the coast of Antarctica for longitudes -160 to -60 and 80 to 150.
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... A longer 39-year record of UV measurements from NASA and NOAA satellites does allow the study of these very important pre-CERES events. Previous work by Herman et al. [5] and Weaver et al. [6] construct a record of the Lambertian equivalent reflectivity (LER) from the UV measurements. LER is the reflectivity derived for the Earth's surface, bounding a purely Rayleigh atmosphere, consistent with measured the top of atmosphere (TOA) radiance; an assumption is that the surface is Lambertian, and the effects of aerosols and clouds are included in the LER of the scene. ...
... This may explain our agreement with the SW CERES cloud albedo despite the simple assumptions we made in our BCA derivation: A single droplet distribution, single cloud layer height, and a single phase (water). These advantages motivated Herman et al. [5], Weaver et al. [6], and now this work to derive a record of cloudiness from the suite of UV satellite instruments dating from 1980. ...
... Our negligible BCA trend of 0.01 decade −1 (45°S to 45°N) appeared to disagree with the quite significant −0.24 LER decade −1 (60°S to 60°N) estimate of Herman et al. [5]. Their LER was produced using SBUV intensities calibrated only over Antarctica. ...
Black-sky cloud albedo (BCA) is derived from satellite UV 340 nm observations from NOAA and NASA satellites to infer long-term (1980–2018) shortwave cloud albedo variations induced by volcano eruptions, the El Niño–Southern Oscillation, and decadal warming. While the UV cloud albedo has shown no long-term trend since 1980, there are statistically significant reductions over the North Atlantic and over the marine stratocumulus decks off the coast of California; increases in cloud albedo can be seen over Southeast Asia and over cloud decks off the coast of South America. The derived BCA assumes a C-1 water cloud model with varying cloud optical depths and a Cox–Munk surface BRDF over the ocean, using radiances calibrated over the East Antarctic Plateau and Greenland ice sheets during summer.
... One of the most important indirect forcing that might have potential to influence the terrestrial climate is variation in cloud cover through cosmic rays. As we know the cloud cover obstructs the flow of solar radiation, which directly implies that the clouds can control the incident amount of solar radiation reaching the surface of the Earth during the day time, and it also controls the amount of heat that lost during overnight that is cooling of near surface environment [39][40][41] . Sunspots are the indicators of state of the solar magnetic activity and therefore they also represent the amount of solar modulation of galactic cosmic rays, and hence their intensity at Earth [42] . ...
In past few decades, climate has manifested numerous shifts in its trend. Various natural and anthropogenic factors have influenced the dynamics and the trends of climate change at longer time scale. To understand the long term climate fluctuations, we have analyzed forty years (1978 - 2018) data of ten climatic parameters that are responsible to influence the climate dynamics. The parameters involved in the present study are total solar irradiance (TSI), ultra violet (UV) index, cloud cover, carbon dioxide (CO2) abundances, multivariate (ENSO) index, volcanic explosivity index (VEI), global surface temperature (GST) anomaly, global sea ice extent, global mean sea level and global precipitation anomaly. Using the above mentioned climate entities; we have constructed a proxy index to study the quantitative measure of the climate change. In this process these indicators were aggregated to a single proxy index as global climate index (GCI) that has measured the strength of present climate change in semblance with the past natural variability. To construct GCI, the principal component analysis (PCA) has been used on yearly based data for the period 1978 - 2018. Actually PCA is a statistical tool with which we can reduce the dimensionality of the data and it retains most of the variation in the new data set. Further, we have confined our study to natural climate drivers and anthropogenic climate drivers. Our result has indicated that the strongest climate change has been occurred globally by the end of the year 2018 in comparison to late 1970’s natural variability.
Nadir-viewed intensities (radiances) from nine UV sensing satellite instruments are calibrated over the East Antarctic Plateau and Greenland during summer. The calibrated radiances from these UV instruments ultimately will provide a global long-term record of cloud trends and cloud response from ENSO events since 1980. We first remove the strong solar zenith angle dependence from the intensities using an empirical approach rather than a radiative transfer model. Then small multiplicative adjustments are made to these solar zenith angle normalized intensities in order to minimize differences when two or more instruments temporally overlap. While the calibrated intensities show a negligible long-term trend over Antarctica and a statistically insignificant UV albedo trend of −0.05 % per decade over the interior of Greenland, there are small episodic reductions in intensities which are often seen by multiple instruments. Three of these darkening events are explained by boreal forest. Other events are caused by surface melting or volcanoes. We estimate a 2-sigma uncertainty of 0.35 % for the calibrated radiances.
As the important coal bases in northwestern China, the hydrological and ecological environment of Ordos, northern Shaanxi (Shanbei) and Shanxi Province has attracted more and more attention. Terrestrial water storage anomaly (TWSA) and soil moisture anomaly (SMA) and groundwater storage anomaly (GWSA), as important water storage, play a critical role in the distribution and growth of vegetation. In this paper, the multi‐source remote sensing data were used to analyze the spatial‐temporal changes and relationships of water storage and ecological environment from 2002 to 2020. The numerical results showed the TWSA and GWSA in the study area had a decreasing trend and the rates were ‐7.512mm/a, ‐8.268mm/a, respectively. On the contrary, the SMS appeared an increasing trend and the rate was 0.840mm/a. By trend variation and correlation analysis, we found GWSA is the main part in the variation of TWSA. By further analysis, it was found that the climate factors are not the major factors causing the variation of GWSA, but the coal mining activities and artificial irrigation activities, which is especially clear in the Taihang Mountains in eastern of Shanxi Province. The ecological environment has been improving, and water storage and climate factors played a different role in different regions. The warm and suitable climate conditions and the increased 0‐40cm soil water promoted the growth of vegetation and the improvement of ecological environment. The research results are helpful to understand the impacts of water storage on the ecological environment in high‐intensity coal mining areas.
The long‐term variation of North Pacific and North Atlantic sea surface temperatures (SSTs) is shown to be associated with multidecadal trends of surface solar radiation in North America, Europe, and Asia. Long‐term, large‐scale warm SST anomalies lead to a mid‐level planetary wave anomaly pattern of geopotential height ridges over the warm water and dynamically‐induced lower heights on either side, sometimes extending over adjacent continents. Geopotential height troughs over the continents encourage more cloud cover and dimming of surface solar radiation. Conversely, cool SST anomalies correspond to a pattern of lower mid‐level geopotential heights over the cool water and compensating high pressure on either side that encourages decreasing cloud cover and brightening over the continents, if the wave positioning is favorable. Additionally, these effects are observed to be latitude dependent, showing stronger SST‐geopotential height associations in the northern half of the Northern Hemisphere. The change from continental dimming to brightening and the reversal of North Pacific SST trends are nearly simultaneous. A similar SST‐geopotential height association is seen in the North Atlantic and leads to brightening and dimming in Europe and North America, but there is a ∼12‐year lag between the transition of dimming to brightening and SST reversals there, which is yet unexplained. The next step is to support these connections and their latitudinal dependence with carefully designed numerical experiments that consider variable greenhouse gas and aerosol concentrations.
The record of downwelling solar irradiance and other surface radiation budget components for the U.S. has been extended through 2019 using SURFRAD Network data. Brightening of surface solar irradiance of +7.36 Wm⁻²/decade occurred from 1996 through 2012. In 2013, surface solar radiation sharply decreased to the long‐term mean (representing 1996–2019) and remained near that level through 2017. Successive decreases in 2018 and 2019 yielded a dimming trend of −3.90 Wm⁻²/decade after 2012, but with a high uncertainty owing to the observed variability and brief period covered. Individually, all stations but Penn State showed brightening trends consistent with the network average, and surface solar irradiance decreased at all stations after 2012. Total surface net radiation showed similar tendencies but the reversal from increasing to decreasing was more gradual because of the response of surface net longwave to the changing solar input. Aerosol optical depth decreased continuously throughout the tenure of the network but accounted for only 3% of the variability of surface solar irradiance, while cloud fraction explained 62%. The mean cloud fraction was 2.4% greater during the dimming period than the brightening period but showed no trends due to high interannual variability. However, annual anomalies of direct‐normal solar radiation, which relate to sun duration and clouds, generally increased to 2012 and then decreased thereafter. Collectively, these results indicate that changing cloud cover was the primary source of brightening and dimming over the U.S. from 1996 to 2019.
Significance
Socioeconomic development in low- and middle-income countries is thought to increase emissions of air pollutants, such as nitrogen dioxide (NO 2 ). In Africa, fossil fuel use has nearly doubled since 2000, but vegetation fires—which cause substantial NO 2 pollution—have declined, partly as a result of human activity. Satellite observations show that during the biomass burning season, NO 2 concentrations in Africa’s northern fire region declined by 4.5% between 2005 and 2017, potentially benefitting hundreds of millions of people. Statistical modeling suggests that this decline is associated with declining vegetation fires. During the biomass burning season, higher levels of economic productivity are associated with lower NO 2 concentrations, suggesting that socioeconomic development in this region is resulting in net improvements to air quality.
Abstract. Nadir viewed intensities (radiances) from nine UV sensing satellite instruments are calibrated over the East Antarctic Plateau and Greenland during summer. The calibrated radiances from these UV instruments ultimately will provide a global long-term record of cloud trends and cloud response from ENSO events since 1980. We first remove the strong solar zenith angle dependence from the intensities using an empirical approach rather than a radiative transfer model. Then small multiplicative adjustments are made to these solar zenith angle normalized intensities in order to minimize differences when two or more instruments temporally overlap. While the calibrated intensities show negligible long-term trend over Antarctica, and a statistically insignificant UV albedo trend of −0.05 % per decade over the interior of Greenland, there are small episodic reductions in intensities which are often seen by multiple instruments. Three of these darkening events are explained by boreal forest fires using trajectory modeling analysis. Other events are caused by surface melting or volcanoes. We estimate a 2-sigma uncertainty of 0.35 % for the calibrated radiances.
Surface melt on the coastal Antarctic ice sheet (AIS) determines the viability of its ice shelves and the stability of the grounded ice sheet, but very few in situ melt rate estimates exist to date. Here we present a benchmark dataset of in situ surface melt rates and energy balance from nine sites in the eastern Antarctic Peninsula (AP) and coastal Dronning Maud Land (DML), East Antarctica, seven of which are located on AIS ice shelves. Meteorological time series from eight automatic and one staffed weather station (Neumayer), ranging in length from 15 months to almost 24 years, serve as input for an energy-balance model to obtain consistent surface melt rates and energy-balance results. We find that surface melt rates exhibit large temporal, spatial and process variability. Intermittent summer melt in coastal DML is primarily driven by absorption of shortwave radiation, while non-summer melt events in the eastern AP occur during föhn events that force a large downward directed turbulent flux of sensible heat. We use the in situ surface melt rate dataset to evaluate melt rates from the regional atmospheric climate model RACMO2 and validate a melt product from the QuikSCAT satellite.
The climate of high, mid-latitude mountains appears to be warming faster than the global average, but evidence for such elevation-dependent warming (EDW) at higher latitudes is presently scarce. Here, we use a comprehensive network of remote meteorological stations, proximal radiosonde measurements, downscaled temperature reanalysis, ice cores, and climate indices to investigate the manifestation and possible drivers of EDW in the St. Elias Mountains, subarctic Yukon, Canada. Linear trend analysis of comprehensively validated annual downscaled North American Regional Reanalysis (NARR) gridded surface air temperatures for the years 1979 to 2016 indicates a warming rate of 0.028°C a ⁻¹ between 5500 and 6000 m a.s.l., which is ∼1.6 times larger than the global average warming rate between 1970 and 2015. The warming rate between 5500 and 6000 m a.s.l. was ∼ 1.5 times greater than the rate at the 2000 to 2500 m a.s.l. bin (0.019°C a ⁻¹ ), which is similar to the majority of warming rates estimated worldwide over similar elevation gradients. Accelerated warming since 1979, measured by radiosondes, indicates a maximum rate at 400 hPa (∼7010 m a.s.l.). EDW in the St. Elias region therefore appears to be driven by recent warming of the free troposphere. MODIS satellite data show no evidence for an enhanced snow albedo feedback above 2500 m a.s.l., and declining trends in sulfate aerosols deposited in high elevation ice cores suggests a modest increase in radiative forcing at these elevations. In contrast, increasing trends in water vapour mixing ratio at the 500 hPa level measured by radiosonde suggests that a long-wave radiation vapour feedback is contributing to EDW.
Satellite measurements using the backscattered ultraviolet technique provide a powerful method for the ob-servation of stratospheric ozone. However, rapid input signal variations over three to four orders of magnitude in several minutes can lead to problems with instrument response. Inflight data have recently been used to characterize a ''hysteresis'' problem on the NOAA-9 SBUV/2 instrument, which affects measurements made shortly after emerging from darkness. Radiance values observed under these conditions can be up to 2%–3% lower than expected. A correction has been derived for NOAA-9 data that is solar zenith angle dependent and varies in amplitude and time. Typical changes to affected polar total ozone values are on the order of 1% but can reach 5% in some cases. Profile ozone changes are altitude dependent, with maximum values of 4%–5% at 1 hPa. The NOAA-11 and NOAA-14 SBUV/2 instruments have a much smaller hysteresis effect than that observed for NOAA-9 SBUV/2 due to a change in photomultiplier tubes. The Nimbus-7 SBUV instrument also shows a hysteresis effect, which has not been fully characterized at this time.
This paper describes the calibration process for the Solar Backscatter
Ultraviolet (SBUV) Version 8.6 (V8.6) ozone data product. Eight SBUV
instruments have flown on NASA and NOAA satellites since 1970, and a
continuous data record is available since November 1978. The accuracy of
ozone trends determined from these data depends on the calibration and
long-term characterization of each instrument. V8.6 calibration
adjustments are determined at the radiance level, and do not rely on
comparison of retrieved ozone products with other instruments. The
primary SBUV instrument characterization is based on prelaunch
laboratory tests and dedicated on-orbit calibration measurements. We
supplement these results with "soft" calibration techniques using
carefully chosen subsets of radiance data and information from the
retrieval algorithm output to validate each instrument's calibration.
The estimated long-term uncertainty in albedo is approximately
±0.8-1.2% (1σ) for most of the instruments. The overlap
between these instruments and the Shuttle SBUV (SSBUV) data allows us to
intercalibrate the SBUV instruments to produce a coherent V8.6 data set
covering more than 32 yr. The estimated long-term uncertainty in albedo
is less than 3% over this period.
This paper describes the calibration process for the Solar Backscatter
Ultraviolet (SBUV) Version 8.6 (V8.6) ozone data product. Eight SBUV
instruments have flown on NASA and NOAA satellites since 1970, and a
continuous data record is available since November 1978. The accuracy of
ozone trends determined from these data depends on the calibration and
long-term characterization of each instrument. V8.6 calibration
adjustments are determined at the radiance level, and do not rely on
comparison of retrieved ozone products with other instruments. The
primary SBUV instrument characterization is based on prelaunch
laboratory tests and dedicated on-orbit calibration measurements. We
supplement these results with "soft" calibration techniques using
carefully chosen subsets of radiance data and information from the
retrieval algorithm output to validate each instrument's calibration.
The estimated long-term uncertainty in albedo is approximately
±0.8-1.2% (1σ) for most of the instruments. The overlap
between these instruments and the Shuttle SBUV (SSBUV) data allows us to
intercalibrate the SBUV instruments to produce a coherent V8.6 data set
covering more than 32 yr. The estimated long-term uncertainty in albedo
is less than 3% over this period.
This study explores how global precipitation and tropospheric water vapor content vary on the interdecadal/long-term time scale during past three decades (1988–2010 for water vapor), in particular to what extent the spatial structures of their variations relate to changes in surface temperature. EOF analyses of satellite-based products indicate that the first two modes of global precipitation and columnar water vapor content anomalies are in general related to the El Niño-Southern oscillation. The spatial patterns of their third modes resemble the corresponding linear fits/trends estimated at each grid point, which roughly represent the interdecadal/long-term changes happening during the same time period. Global mean sea surface temperature (SST) and land surface temperature have increased during the past three decades. However, the water vapor and precipitation patterns of change do not reflect the pattern of warming, in particular in the tropical Pacific basin. Therefore, other mechanisms in addition to global warming likely exist to account for the spatial structures of global precipitation changes during this time period. An EOF analysis of longer-record (1949–2010) SST anomalies within the Pacific basin (60oN–60oS) indicates the existence of a strong climate regime shift around 1998/1999, which might be associated with the Pacific decadal variability (PDV) as suggested in past studies. Analyses indicate that the observed linear changes/trends in both precipitation and tropospheric water vapor during 1988–2010 seem to result from a combined impact of global mean surface warming and the PDV shift. In particular, in the tropical central-eastern Pacific, a band of increases along the equator in both precipitation and water vapor sandwiched by strong decreases south and north of it are likely caused by the opposite effects from global-mean surface warming and PDV-related, La Niña-like cooling in the tropical central-eastern Pacific. This narrow band of precipitation increase could also be considered an evidence for the influence of global mean surface warming.
Numerous studies report that ultraviolet (UV) radiation is harmful to living organisms and detrimental to human health. Growing concerns regarding the increased levels of UV-B radiation that reach the earth's surface have led to the development of ground- and space-based measurement programs. Further study is needed on the measurement, modeling, and effects of UV radiation. The chapters of this book describe the research conducted across the globe over the past three decades in the areas of: (1) current and predicted levels of UV radiation and its associated impact on ecosystems and human health, as well as economic and social implications; (2) new developments in UV instrumentation, advances in calibration (ground- and satellite-based), measurement methods, modeling efforts, and their applications; and (3) the effects of global climate change on UV radiation. © Tsinghua University Press, Beijing and Springer-Verlag Berlin Heidelberg 2010. All rights are reserved.
This chapter investigates variations in cloudiness and changes in the Earth’s radiation budget (ERB), including their connection with other parameters of the climate system. Anthropogenic aerosol emissions cause a perturbation to the physical and radiative properties of clouds. The chapter examines the radiative impacts of anthropogenic aerosol emissions on cloudiness, and also indicates the importance of small cloud and ERB changes and the difficulties encountered in measuring them. Cloud simulation and climate sensitivity observed in global climate models are discussed as well.
The Solar Backscatter Ultraviolet and Total Ozone Mapping Spectrometer (SBUV/TOMS) experiment scheduled for launch on NIMBUS G is an expanded capability version of the Backscatter Ultraviolet (BUV) instrument, which has been providing useful data for deducing ozone vertical profiles since its launch aboard the NIMBUS-4 satellite in April 1970. Evaluation of the BUV data has led to a number of design changes on the SBUV/TOMS that will improve our knowledge of the global stratospheric ozone distribution. The BUV instrument sounded ozone in the nadir direction only, and under certain orbital conditions the data were influenced by charged particles in the earth's radiation belts. The SBUV/TOMS instrument has a wider wavelength range, a cross-course mapper, and special provisions for minimizing the effects of space radiation. The BUV instrument is a double (tandem) Ebert-Fastie spectrophotometer measuring spectral intensities at 12 wavelengths from 2555 A to 3398 A with a 10-A bandpass. The SBUV is similar in design to the BUV. It features a state-of-the-art double monochromator that maximizes throughput while providing good wavelength resolution, accuracy, and very high stray-light rejection (106). The TOMS is an ozone mapping system utilizing a close replica of the first monochromator of the SBUV.
Satellite drift is a historical issue affecting the consistency of those few satellite records capable of being used for studies on climate time scales. Here, the authors address this issue for the Pathfinder Atmospheres Extended (PATMOS-x)/Advanced Very High Resolution Radiometer (AVHRR) cloudiness record, which spans three decades and 11 disparate sensors. A two-harmonic sinusoidal function is fit to a mean diurnal cycle of cloudiness derived over the course of the entire AVHRR record. The authors validate this function against measurements from Geostationary Operational Environmental Satellite (GOES) sensors, finding good agreement, and then test the stability of the diurnal cycle over the course of the AVHRR record. It is found that the diurnal cycle is subject to some interannual variability over land but that the differences are somewhat offset when averaged over an entire day. The fit function is used to generate daily averaged time series of ice, water, and total cloudiness over the tropics, where it is found that the diurnal correction affects the magnitude and even the sign of long-term cloudiness trends. A statistical method is applied to determine the minimum length of time required to detect significant trends, and the authors find that only recently have they begun generating satellite records of sufficient length to detect trends in cloudiness.