The Experts below are selected from a list of 38043 Experts worldwide ranked by ideXlab platform
Joel R Norris - One of the best experts on this subject based on the ideXlab platform.
-
trends in aerosol radiative effects over china and japan inferred from observed Cloud Cover solar dimming and solar brightening
Journal of Geophysical Research, 2009Co-Authors: Joel R Norris, Martin WildAbstract:[1] This study examines multidecadal changes in surface downward shortwave (SW) radiation flux, total Cloud Cover, SW Cloud effect, and related parameters over China and Japan during 1960–2004 using monthly gridded data from the Global Energy Balance Archive, synoptic Cloud reports, and the International Satellite Cloud Climatology Project. We use the concept of Cloud Cover radiative effect, defined as the change in downward SW flux produced by a change in Cloud Cover, to quantify and remove the impact of Cloud Cover anomalies on surface solar flux. This will allow radiative effects of long-term changes in anthropogenic aerosol to be more clearly distinguished from natural weather and climate variability. As fit by a linear trend between 1971 and 1989, surface solar flux decreased by a statistically significant 11 W m−2 per decade over China and decreased by a nonsignificant 1 W m−2 per decade over Japan. The small decline over Japan can be entirely explained by an increase in Cloud Cover, but changes in Cloud Cover made negligible contribution to the 1971–1989 solar flux trend over China. Between 1990 and 2002, surface solar flux increased by a statistically significant 8 W m−2 per decade over Japan and increased by a nonsignificant 4 W m−2 per decade over China. Half of the 1990–2002 solar flux trend over China and one third of the trend over Japan can be attributed to a reduction in Cloud Cover. The 1971–1989 decrease in surface solar flux over China and the 1990–2002 increase in surface solar flux over Japan are both spatially widespread and exhibit consistent sign across seasons.
-
trends in aerosol radiative effects over europe inferred from observed Cloud Cover solar dimming and solar brightening
Journal of Geophysical Research, 2007Co-Authors: Joel R Norris, Martin WildAbstract:residual flux declined by a statistically significant 2.7–3.5 W m � 2 per decade during 1971–1986 and rose by a statistically significant 2.0–2.3 W m � 2 per decade during 1987–2002. The fact that independent grid boxes exhibit mostly negative trends in the earlier period and mostly positive trends in the later period demonstrates that these longterm variations in SW flux are real and widespread over Europe. Changes in Cloud Cover cannot account for the trends in surface SW flux since Cloud Cover actually slightly decreased during 1971–1986 and slightly increased during 1987–2002. The most likely explanation is changes in anthropogenic aerosol emissions that led to more scattering and absorption of SW radiation during the earlier period of solar ‘‘dimming’’ and less scattering and absorption during the later period of solar ‘‘brightening.’’
-
multidecadal changes in near global Cloud Cover and estimated Cloud Cover radiative forcing
Journal of Geophysical Research, 2005Co-Authors: Joel R NorrisAbstract:The first paper was Multidecadal changes in near-global Cloud Cover and estimated Cloud Cover radiative forcing, by J. R. Norris (2005, J. Geophys. Res. - Atmos., 110, D08206, doi: lO.l029/2004JD005600). This study examined variability in zonal mean surface-observed upper-level (combined midlevel and high-level) and low-level Cloud Cover over land during 1971-1 996 and over ocean during 1952-1997. These data were averaged from individual synoptic reports in the Extended Edited Cloud Report Archive (EECRA). Although substantial interdecadal variability is present in the time series, long-term decreases in upper-level Cloud Cover occur over land and ocean at low and middle latitudes in both hemispheres. Near-global upper-level Cloud Cover declined by 1.5%-sky-Cover over land between 1971 and 1996 and by 1.3%-sky-Cover over ocean between 1952 and 1997. Consistency between EECRA upper-level Cloud Cover anomalies and those from the International Satellite Cloud Climatology Project (ISCCP) during 1984-1 997 suggests the surface-observed trends are real. The reduction in surface-observed upper-level Cloud Cover between the 1980s and 1990s is also consistent with the decadal increase in all-sky outgoing longwave radiation reported by the Earth Radiation Budget Satellite (EMS). Discrepancies occur between time series of EECRA and ISCCP low-level Cloud Cover due to identified and probable artifacts in satellite and surface Cloud data. Radiative effects of surface-observed Cloud Cover anomalies, called "Cloud Cover radiative forcing (CCRF) anomalies," are estimated based on a linear relationship to climatological Cloud radiative forcing per unit Cloud Cover. Zonal mean estimated longwave CCRF has decreased over most of the globe. Estimated shortwave CCRF has become slightly stronger over northern midlatitude oceans and slightly weaker over northern midlatitude land areas. A long-term decline in the magnitude of estimated shortwave CCRF occurs over low-latitude land and ocean, but comparison with EMS all-sky reflected shortwave radiation during 1985-1997 suggests this decrease may be underestimated.
-
has northern indian ocean Cloud Cover changed due to increasing anthropogenic aerosol
Geophysical Research Letters, 2001Co-Authors: Joel R NorrisAbstract:The recent Indian Ocean Experiment (INDOEX) observed high aerosol concentrations with a sizeable soot fraction over the northern Indian Ocean. This aerosol mix substantially absorbs solar radiation, and recent modeling studies have proposed that the resulting atmospheric heating reduces daytime Cloud Cover. The present study tests this hypothesis by investigating whether low-level Cloud Cover has decreased over the northern Indian Ocean between 1952 and 1996, a time period when south Asian anthropogenic emissions have greatly increased. The observed slight increase in Cloud Cover indicates that other processes must compensate soot solar heating. A similar increase in Cloud Cover observed over the relatively clean southern Indian Ocean suggests the increase over the northern Indian Ocean does not have a special regional anthropogenic aerosol origin.
Jiancheng Shi - One of the best experts on this subject based on the ideXlab platform.
-
Cloud Cover over the tibetan plateau and eastern china a comparison of era5 and era interim with satellite observations
Climate Dynamics, 2020Co-Authors: Yonghui Lei, Husi Letu, Huazhe Shang, Jiancheng ShiAbstract:This study examines the progress made by reanalyses and satellite products in the estimation of Cloud Cover over China: the ECMWF reanalyses ERA5 and ERA-Interim, geostationary satellite observation Himawari-8 (H8) and the International Satellite Cloud Climatology Project H-series (ISCCP) product. There is great similarity in spatial patterns of Cloud Cover in reanalyses and satellite observations, especially between ERA5 and H8. Distinct characteristics of the seasonal evolution of Cloud Cover are shown over the Tibetan Plateau (TP), the southeast (SE) and northeast (NE) of China. Differences in magnitudes of Cloud Cover exist. Overestimations are about 10% for reanalyses and about 20% for ISCCP in compared with certain Cloud Cover in H8. When probable Cloud (about 10%) in H8 is included in the estimation, biases reduce the most in ERA5. The Cloud hit rate (CHR) and false alarm rate (FAR) in against H8 and ISCCP reveal that simulated Clouds in ERA5 have been improved especially over eastern China, but with limited improvement over TP in compared with ERA-Interim. Diurnal variations of Cloud Cover are characterized by increases during daytime over those three regions. Amplifications of diurnal variation vary over different regions and months. Satellite observations and ERA5 indicate distinguished diurnal cycle of Cloud Cover over TP, while further investigation based on ERA5 reveals coherent diurnal cycle in meteorological environment. Long-term changes of Cloud Cover highlight decreasing trends over TP and particular during March in past decades based on ISCCP and ERA5, which require further investigation in future.
-
diurnal cycle and seasonal variation of Cloud Cover over the tibetan plateau as determined from himawari 8 new generation geostationary satellite data
Scientific Reports, 2018Co-Authors: Huazhe Shang, Yonghui Lei, Husi Letu, Takashi Nakajima, Ziming Wang, Tianxing Wang, Jiancheng ShiAbstract:Analysis of Cloud Cover and its diurnal variation over the Tibetan Plateau (TP) is highly reliant on satellite data; however, the accuracy of Cloud detection from both polar-orbiting and geostationary satellites over this area remains unclear. The new-generation geostationary Himawari-8 satellites provide high-resolution spatial and temporal information about Clouds over the Tibetan Plateau. In this study, the Cloud detection of MODIS and AHI is investigated and validated against CALIPSO measurements. For AHI and MODIS, the false alarm rate of AHI and MODIS in Cloud identification over the TP was 7.51% and 1.94%, respectively, and the Cloud hit rate was 73.55% and 80.15%, respectively. Using hourly Cloud-Cover data from the Himawari-8 satellites, we found that at the monthly scale, the diurnal cycle in Cloud Cover over the TP tends to increase throughout the day, with the minimum and maximum Cloud fractions occurring at 10:00 a.m. and 18:00 p.m. local time. Due to the limited time resolution of polar-orbiting satellites, the underestimation of MODIS daytime average Cloud Cover is approximately 4.00% at the annual scale, with larger biases during the spring (5.40%) and winter (5.90%).
-
water vapor retrieval over Cloud Cover area on land using amsr e and modis
IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, 2014Co-Authors: Jiancheng ShiAbstract:This study mainly discusses atmospheric water vapor retrieval over Cloud Cover area on land with the help of a newly developed surface emissivity parameter estimation method in microwave bands. In the retrieval method, the atmospheric water vapor sensitivity parameter-ratio of brightness temperature polarization difference at frequencies 18.7 and 23.8 GHz (ΔTb 1.87 /ΔTb 23.8 )-is used to retrieve water vapor, and the surface emissivity parameter-ratio of surface emissivity polarization difference at frequencies 18.7 and 23.8 GHz (Δe 18.7 /Δe 23.8 ) that corresponds to ΔTb 18.7 /ΔTb 23.8 is a key parameter that affects the final precision of retrieved atmosphere water vapor. In order to estimate Δe 18.7 /Δe 23.8 in Cloudy condition, we first estimated the value of Δe 18.7 /Δe 23.8 in clear condition using Advanced Microwave Scanning Radiometer for EOS (AMSR-E) brightness temperature and related MODIS atmospheric products. At the same time, it was found that gradient information derived separately from ΔTb 18.7 /ΔTb 23.8 and Δe 18.7 /Δe 23.8 and very good correlation with each other. Based on this good correlation, the Δe 18.7 /Δe 23.8 in Cloudy condition was estimated using corresponding==and adjacent 8 days Δe 18.7 /Δe 23.8 in clear condition. With the estimated Δe 18.7 /Δe 23.8 , we retrieved atmospheric column water vapor using lookup table method in Cloudy condition over land. As a validation source data, the SuomiNet GPS-retrieved precipitable water (PW) vapor is used to validate the retrieved water vapor in this study. According to validation, the correlation coefficient of the two is 0.94 and the root-mean-square-error (RMSE) is 4.85 mm. It is a great improvement in water vapor retrieval using microwave in Cloud Cover area on land.
Martin Wild - One of the best experts on this subject based on the ideXlab platform.
-
trends in aerosol radiative effects over china and japan inferred from observed Cloud Cover solar dimming and solar brightening
Journal of Geophysical Research, 2009Co-Authors: Joel R Norris, Martin WildAbstract:[1] This study examines multidecadal changes in surface downward shortwave (SW) radiation flux, total Cloud Cover, SW Cloud effect, and related parameters over China and Japan during 1960–2004 using monthly gridded data from the Global Energy Balance Archive, synoptic Cloud reports, and the International Satellite Cloud Climatology Project. We use the concept of Cloud Cover radiative effect, defined as the change in downward SW flux produced by a change in Cloud Cover, to quantify and remove the impact of Cloud Cover anomalies on surface solar flux. This will allow radiative effects of long-term changes in anthropogenic aerosol to be more clearly distinguished from natural weather and climate variability. As fit by a linear trend between 1971 and 1989, surface solar flux decreased by a statistically significant 11 W m−2 per decade over China and decreased by a nonsignificant 1 W m−2 per decade over Japan. The small decline over Japan can be entirely explained by an increase in Cloud Cover, but changes in Cloud Cover made negligible contribution to the 1971–1989 solar flux trend over China. Between 1990 and 2002, surface solar flux increased by a statistically significant 8 W m−2 per decade over Japan and increased by a nonsignificant 4 W m−2 per decade over China. Half of the 1990–2002 solar flux trend over China and one third of the trend over Japan can be attributed to a reduction in Cloud Cover. The 1971–1989 decrease in surface solar flux over China and the 1990–2002 increase in surface solar flux over Japan are both spatially widespread and exhibit consistent sign across seasons.
-
trends in aerosol radiative effects over europe inferred from observed Cloud Cover solar dimming and solar brightening
Journal of Geophysical Research, 2007Co-Authors: Joel R Norris, Martin WildAbstract:residual flux declined by a statistically significant 2.7–3.5 W m � 2 per decade during 1971–1986 and rose by a statistically significant 2.0–2.3 W m � 2 per decade during 1987–2002. The fact that independent grid boxes exhibit mostly negative trends in the earlier period and mostly positive trends in the later period demonstrates that these longterm variations in SW flux are real and widespread over Europe. Changes in Cloud Cover cannot account for the trends in surface SW flux since Cloud Cover actually slightly decreased during 1971–1986 and slightly increased during 1987–2002. The most likely explanation is changes in anthropogenic aerosol emissions that led to more scattering and absorption of SW radiation during the earlier period of solar ‘‘dimming’’ and less scattering and absorption during the later period of solar ‘‘brightening.’’
S Cavazzani - One of the best experts on this subject based on the ideXlab platform.
-
sky quality meter and satellite correlation for night Cloud Cover analysis at astronomical sites
Monthly Notices of the Royal Astronomical Society, 2020Co-Authors: S Cavazzani, S Ortolani, A Bertolo, R Binotto, Pietro Fiorentin, Giovanni Carraro, I SavianeAbstract:The analysis of the night Cloud Cover is very important for astronomical observation in real time, considering a typical observation time of about 15 minutes, and to have a statistics of the night Cloud Cover. In this paper we use the SQM (Sky Quality Meter) for high resolution temporal analysis of the La Silla and Asiago (Ekar observatory) sky: 3 and 5 minutes respectively. We investigate the annual temporal evolution of the natural contributions of the sky in a site not influenced by artificial light at night (ALAN) and one highly influenced respectively. We also make a correlation between GOES and AQUA satellites data and ground-based SQM data to confirm a relationship between the SQM data and Cloud Cover. We develop an algorithm that allows the use of the SQM for night Cloud detection and we reach a correlation of 97.2\% at La Silla and 94.6\% at Asiago with the nighttime Cloud Cover detected by the GOES and AQUA satellites. Our algorithm also classifies the photometric (PN) and spectroscopic nights (SN). We measure 59.1\% PN and 21.7\% SN for a total percentage of clear nights of 80.8\% at La Silla in 2018. The respective Ekar observatory values are 31.1\% PN, 24.0\% SN and 55.1\% of total clear nights time. Application to the SQM network would involve the development of long-term statistics and big data forecasting models, for site testing and real-time astronomical observation.
R L Miller - One of the best experts on this subject based on the ideXlab platform.
-
Cloud Cover increase with increasing aerosol absorptivity a counterexample to the conventional semidirect aerosol effect
Journal of Geophysical Research, 2010Co-Authors: R L Miller, Jan PerlwitzAbstract:[1] We reexamine the aerosol semidirect effect using a general circulation model and four cases of the single-scattering albedo of dust aerosols. Contrary to the expected decrease in low Cloud Cover due to heating by tropospheric aerosols, we find a significant increase with increasing absorptivity of soil dust particles in regions with high dust load, except during Northern Hemisphere winter. The strongest sensitivity of Cloud Cover to dust absorption is found over land during Northern Hemisphere summer. Here even medium and high Cloud Cover increase where the dust load is highest. The Cloud Cover change is directly linked to the change in relative humidity in the troposphere as a result of contrasting changes in specific humidity and temperature. More absorption by aerosols leads to larger diabatic heating and increased warming of the column, decreasing relative humidity. However, a corresponding increase in the specific humidity exceeds the temperature effect on relative humidity. The net effect is more low Cloud Cover with increasing aerosol absorption. The higher specific humidity where Cloud Cover strongly increases is attributed to an enhanced convergence of moisture driven by dust radiative heating. Although in some areas our model exhibits a reduction of low Cloud Cover due to aerosol heating consistent with the conventional description of the semidirect effect, we conclude that the link between aerosols and Clouds is more varied, depending also on changes in the atmospheric circulation and the specific humidity induced by the aerosols. Other absorbing aerosols such as black carbon are expected to have a similar effect.
-
tropical thermostats and low Cloud Cover
Journal of Climate, 1997Co-Authors: R L MillerAbstract:Abstract The ability of subtropical stratus low Cloud Cover to moderate or amplify the tropical response to climate forcing such as increased CO2 is considered. Cloud radiative forcing over the subtropics is parameterized using an empirical relation between stratus Cloud Cover and the difference in potential temperature between 700 mb (a level that is above the trade inversion) and the surface. This relation includes the empirical negative correlation between SST and low Cloud Cover and is potentially a positive feedback to climate forcing. Since potential temperature above the trade inversion varies in unison across the Tropics as a result of the large-scale circulation and because moist convection relates tropospheric temperature within the convecting region to variations in surface temperature and moisture, the subtropical potential temperature at 700 mb depends upon surface conditions within the convecting region. As a result, subtropical stratus Cloud Cover and the associated feedback depend upon the...