The Experts below are selected from a list of 6588 Experts worldwide ranked by ideXlab platform
D Perezramirez - One of the best experts on this subject based on the ideXlab platform.
-
Precipitable Water vapor over oceans from the maritime aerosol network evaluation of global models and satellite products under clear sky conditions
Atmospheric Research, 2019Co-Authors: D Perezramirez, A Smirnov, R T Pinker, Roberto Roman, Maksym Petrenko, Wen Chen, Charles Ichoku, Stefan Noel, Gonzalo Gonzalez Abad, H LyamaniAbstract:Abstract We present results from an evaluation of Precipitable Water vapor (W) over remote oceanic areas as derived from global reanalysis models and from satellites against observations from the Maritime Aerosol Network (MAN) for cloudless skies during the period of 2004–2017. They cover polar, mid latitude and tropical oceanic regions and represent a first effort to use MAN observations for such evaluation. The global reanalysis model products evaluated in this study are from the Modern-Era Retrospective analysis for Research and Applications Version 2 (MERRA-2), the European Centre for Medium-Range Weather Forecasts (ECMWF) Interim Reanalysis (ERA I), and the Climate Forecast System Reanalysis (CFSR) model. The satellite products evaluated are from the Moderate Resolution Imaging Spectroradiometer (MODIS), the Polarization and Directionality of the Earth's Reflectances (POLDER), the Global Ozone Monitoring Experiment (GOME-2), the Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY), and the Atmospheric Infra-red Sounder (AIRS). Satellite retrievals of W are based on the attenuation of solar reflected light by Water vapor absorption bands, except those from AIRS that rely on brightness temperature measurements. A very good agreement is observed between the model estimates and MAN, with mean differences of ~5% and standard deviations of ~15%. These results are within the uncertainties associated with the models and the measurements, indicating the skill of the reanalysis models to estimate W over oceans under clear sky conditions. Mean differences of W between the satellite and MAN products are ~11, 6.7, 12, −7, and 3% for MODIS, POLDER, GOME-2, SCIAMACHY and AIRS respectively, while their standard deviations are 31, 29, 28, 20 and 17%. These differences reveal the need to address inconsistencies among different satellite sensors and ground-based measurements to reduce the uncertainties associated with the retrievals.
-
evaluation of aeronet Precipitable Water vapor versus microwave radiometry gps and radiosondes at arm sites
Journal of Geophysical Research, 2014Co-Authors: D Perezramirez, David N Whiteman, A Smirnov, H Lyamani, B N Holben, R T Pinker, Marcos Andrade, L AladosarboledasAbstract:In this paper we present comparisons of Aerosol Robotic Network (AERONET) Precipitable Water vapor (W) retrievals from Sun photometers versus radiosonde observations and other ground-based retrieval techniques such as microwave radiometry (MWR) and GPS. The comparisons make use of the extensive measurements made within the U.S. Department of Energy Atmospheric Radiation Measurement Program (ARM), mainly at their permanent sites located at the Southern Great Plains (Oklahoma, U.S.), Nauru Islands, and Barrow (Alaska, U.S.). These places experience different types of weather which allows the comparison of W under different conditions. Radiosonde and microwave radiometry data were provided by the ARM program while the GPS data were obtained from the SOUMINET network. In general, W obtained by AERONET is lower than those obtained by MWR and GPS by ~6.0–9.0% and ~6.0–8.0%, respectively. The AERONET values are also lower by approximately 5% than those obtained from the numerous balloon-borne radiosondes launched at the Southern Great Plains. These results point toward a consistent dry bias in the retrievals of W by AERONET of approximately 5–6% and a total estimated uncertainty of 12–15%. Differences with respect to MWR retrievals are a function of solar zenith angle pointing toward a possible bias in the MWR retrievals. Finally, the ability of AERONET Precipitable Water vapor retrievals to provide long-term records of W in diverse climate regimes is demonstrated.
U Platt - One of the best experts on this subject based on the ideXlab platform.
-
global trends 1996 2003 of total column Precipitable Water observed by global ozone monitoring experiment gome on ers 2 and their relation to near surface temperature
Journal of Geophysical Research, 2006Co-Authors: Thomas Wagner, Steffen Beirle, M Grzegorski, U PlattAbstract:[1] We have analyzed global trends of total column Precipitable Water from measurements of the Global Ozone Monitoring Experiment (GOME) on the European Research Satellite (ERS-2) for the period January 1996 to June 2003. In contrast to other satellite retrieval methods of total column Precipitable Water, our analysis does not rely on a priori assumptions or additional information; thus it is particularly well suited to trend studies. The chosen wavelength range in the red spectral region ensures similar sensitivity for observations over land and ocean and thus a consistent global picture. To minimize the influence of clouds on the Water vapor trends, we selected observations under mainly clear-sky conditions. The temporal evolution of the monthly or yearly averaged total column Precipitable Water, especially in the tropics, is highly correlated to that of the near-surface temperature, indicating that the global atmospheric humidity is mainly driven by Clausius-Clapeyron's principle. The magnitude of the dependence on near-surface temperature indicates a strong Water vapor feedback. The spatial patterns of the Water vapor trends show both positive and negative signs. Especially over the oceans, trend patterns very similar to those of near-surface temperature are found. In contrast, over Northern Hemispheric continents the trend patterns are much less correlated, and even opposite trends for Water vapor and the near-surface temperatures are found. During the period 1996–2002 the globally and yearly averaged total column Precipitable Water increased by 2.8 ± 0.8% (excluding the ENSO period).
-
el nino induced anomalies in global data sets of total column Precipitable Water and cloud cover derived from gome on ers 2
Journal of Geophysical Research, 2005Co-Authors: T Wagner, Steffen Beirle, Michael Grzegorski, S Sanghavi, U PlattAbstract:[1] Global data sets of total column Precipitable Water and cloud cover derived from the Global Ozone Monitoring Experiment (GOME) are analyzed with respect to anomalies induced by the strong El Nino 1997/1998. In contrast to other satellite observations of Water vapor, the GOME nadir observations in the visible spectral range are of similar sensitivity over both land and ocean. In addition, they are sensitive in particular to the Water vapor concentration close to the surface where a major fraction of the Water vapor column is present. Information on the atmospheric cloud cover was derived from the observed broadband intensity as well as the oxygen (O2) absorption. While the first quantity is mainly a measure of geometrical cloud fraction, the latter also yields information on the cloud altitude. We investigated the time series of monthly mean values as well as anomalies calculated for a 6-month period during the El Nino 1997/1998. For all three quantities we found strong anomalies over large areas and for extended periods. Especially for the total column Precipitable Water, significant anomalies were found even in mid and high latitudes indicating substantial changes in the hydrological cycle and the global circulation patterns.
Frank J Wentz - One of the best experts on this subject based on the ideXlab platform.
-
intercomparison of total Precipitable Water measurements made by satellite borne microwave radiometers and ground based gps instruments
Journal of Geophysical Research, 2015Co-Authors: Carl Mears, Junhong Wang, Deborah K Smith, Frank J WentzAbstract:High-quality, high temporal resolution measurements of total Precipitable Water (TPW) can be made by evaluating the vapor-dependent delay of radio signals reaching land-based Global Positioning System (GPS) receivers from GPS satellites. These measurements are available since the mid-1990s when the GPS system became operational. Over the world's oceans, satellite-borne microwave imaging radiometers have been making measurements of TPW for more than 25 years. In this work, we perform an intercomparison of collocated TPW measurements made by these two disparate systems using measurements from 26 GPS stations located on small islands. The two types of measurements agree well, with typical satellite-station mean differences of less than 1.0 kg m−2. Analysis revealed several cases of inhomogeneities in the GPS data set, and two deficiencies in the Remote Sensing Systems satellite data, demonstrating the usefulness of intercomparison for improving the accuracy of both types of data. After the individual station, biases were removed, the standard deviation of the overall differences between individual satellites and GPS measurements ranged between 1.60 and 1.94 kg m−2. Twelve GPS stations had overlap time periods long enough to evaluate difference trends, yielding 59 satellite-station pairs when paired with different satellites. More than half of the pairs (39 of 59) did not show a significant trend. The 20 pairs with significant trends did not show trends of predominantly one sign, suggesting that neither system is plagued by a system-wide drift in TPW.
-
Precipitable Water and surface humidity over global oceans from special sensor microwave imager and european center for medium range weather forecasts
Journal of Geophysical Research, 1992Co-Authors: Timothy W Liu, Wenqing Tang, Frank J WentzAbstract:Global fields of Precipitable Water W from the special sensor microwave imager were compared with those from the European Center for Medium Range Weather Forecasts (ECMWF) model. They agree over most ocean areas; both data sets capture the two annual cycles examined and the interannual anomalies during an ENSO episode. They show significant differences in the dry air masses over the eastern tropical-subtropical oceans, particularly in the Southern Hemisphere. In these regions, comparisons with radiosonde data indicate that overestimation by the ECMWF model accounts for a large part of the differences. As a check on the W differences, surface-level specific humidity Q derived from W, using a statistical relation, was compared with Q from the ECMWF model. The differences in Q were found to be consistent with the differences in W, indirectly validating the Q-W relation. In both W and Q, SSMI was able to discern clearly the equatorial extension of the tongues of dry air in the eastern tropical ocean, while both ECMWF and climatological fields have reduced spatial gradients and weaker intensity.
Nobuyuki Kikuchi - One of the best experts on this subject based on the ideXlab platform.
-
on the sciences obtained from adeos ii mission
Remote Sensing, 2005Co-Authors: Akimasa Sumi, Keiji Imaoka, Nobuyuki KikuchiAbstract:The scientific results, present status, and future plan of the ADEOS-II mission, especially for AMSR and GLI sensor, are presented in the paper. Five specific sensors aboard the ADEOS-II satellite were designed for making overall observation of land, atmosphere, ocean, and cryosphere from the sun-synchronous polar orbit. The AMSR and GLI are two of the primary sensors aboard the ADEOS-II satellite. The AMSR, a microwave scanner, retrieved the physical parameters related to global Water cycle such as total Precipitable Water, cloud liquid Water, precipitations and soil moisture. One the other hand, the GLI, a near ultraviolet to infrared imager, had captured many environmental events such as volcano eruptions, forest fires, and dust events with moderate spatial resolution of 250 m or 1 km. It also observed ocean colors, sea surface temperature, vegetation indices, aerosol and cloud properties, and Precipitable Water over land area. The ADEOS-II science activities continue in future. The primary objective of the next phase is the data utilization toward the future satellite missions, and the synergy of satellite data and climate models.
-
retrieval of Precipitable Water using adeos ii gli near infrared data
Fourth International Asia-Pacific Environmental Remote Sensing Symposium 2004: Remote Sensing of the Atmosphere Ocean Environment and Space, 2004Co-Authors: Makoto Kuji, Nobuyuki Kikuchi, Akihiro UchiyamaAbstract:Retrieval of vertically integrated Water vapor amount (Precipitable Water) is proposed using near infrared channels of Global Imager onboard Advanced Earth Observing Satellite-II (GLI/ADEOS-II). The principle of retrieval algorithm is based upon that adopted with Moderate Resolution Imaging Spectroradiometer (MODIS) onboard Earth Observing System (EOS) satellite series. Simulations were carried out with GLI Signal Simulator (GSS) to calculate the radiance ratio between Water vapor absorbing bands and non-absorbing bands. As a result, it is found that for the case of high spectral reflectance background (a bright target) such as the land surface, the calibration curves are sensitive to the Precipitable Water variation. It turns out that aerosol loading has little influence on the retrieval over a bright target for the aerosol optical thickness less than about 1.0 at 500 nm wavelength. A preliminary analysis of GLI data was also carried out and the retrieved result is discussed. It is also anticipated that simultaneous retrieval of the Water vapor amount using GLI data along with other channels will lead to improved accuracy of the determination of surface geophysical properties, such as vegetation, ocean color, and snow and ice, through the better atmospheric correction.
Steffen Beirle - One of the best experts on this subject based on the ideXlab platform.
-
global trends 1996 2003 of total column Precipitable Water observed by global ozone monitoring experiment gome on ers 2 and their relation to near surface temperature
Journal of Geophysical Research, 2006Co-Authors: Thomas Wagner, Steffen Beirle, M Grzegorski, U PlattAbstract:[1] We have analyzed global trends of total column Precipitable Water from measurements of the Global Ozone Monitoring Experiment (GOME) on the European Research Satellite (ERS-2) for the period January 1996 to June 2003. In contrast to other satellite retrieval methods of total column Precipitable Water, our analysis does not rely on a priori assumptions or additional information; thus it is particularly well suited to trend studies. The chosen wavelength range in the red spectral region ensures similar sensitivity for observations over land and ocean and thus a consistent global picture. To minimize the influence of clouds on the Water vapor trends, we selected observations under mainly clear-sky conditions. The temporal evolution of the monthly or yearly averaged total column Precipitable Water, especially in the tropics, is highly correlated to that of the near-surface temperature, indicating that the global atmospheric humidity is mainly driven by Clausius-Clapeyron's principle. The magnitude of the dependence on near-surface temperature indicates a strong Water vapor feedback. The spatial patterns of the Water vapor trends show both positive and negative signs. Especially over the oceans, trend patterns very similar to those of near-surface temperature are found. In contrast, over Northern Hemispheric continents the trend patterns are much less correlated, and even opposite trends for Water vapor and the near-surface temperatures are found. During the period 1996–2002 the globally and yearly averaged total column Precipitable Water increased by 2.8 ± 0.8% (excluding the ENSO period).
-
el nino induced anomalies in global data sets of total column Precipitable Water and cloud cover derived from gome on ers 2
Journal of Geophysical Research, 2005Co-Authors: T Wagner, Steffen Beirle, Michael Grzegorski, S Sanghavi, U PlattAbstract:[1] Global data sets of total column Precipitable Water and cloud cover derived from the Global Ozone Monitoring Experiment (GOME) are analyzed with respect to anomalies induced by the strong El Nino 1997/1998. In contrast to other satellite observations of Water vapor, the GOME nadir observations in the visible spectral range are of similar sensitivity over both land and ocean. In addition, they are sensitive in particular to the Water vapor concentration close to the surface where a major fraction of the Water vapor column is present. Information on the atmospheric cloud cover was derived from the observed broadband intensity as well as the oxygen (O2) absorption. While the first quantity is mainly a measure of geometrical cloud fraction, the latter also yields information on the cloud altitude. We investigated the time series of monthly mean values as well as anomalies calculated for a 6-month period during the El Nino 1997/1998. For all three quantities we found strong anomalies over large areas and for extended periods. Especially for the total column Precipitable Water, significant anomalies were found even in mid and high latitudes indicating substantial changes in the hydrological cycle and the global circulation patterns.