Roy W. Spencer

Bio: Roy W. Spencer is an academic researcher from University of Alabama in Huntsville. The author has contributed to research in topics: Radiometer & Global warming. The author has an hindex of 34, co-authored 80 publications receiving 5427 citations. Previous affiliations of Roy W. Spencer include University of Wisconsin-Madison & Marshall Space Flight Center.

Precipitation retrieval over land and ocean with the SSM/I - Identification and characteristics of the scattering signal

Abstract: The subject of this study is the identification of precipitation in warm and cold land and ocean environments from the Defense Meteorological Satellite Program's (DMSP) Special Sensor Micmwave/Imager (SSM/I). The high sensitivity of the SSM/I 85.5 GHz channels to volume scattering by precipitation, especially ice above the freezing level, is the basis for this identification. This ice scattering process causes SSM/I 85.5 GHz brightness temperatures to occasionally fall below 100 K. It is demonstrated that the polarization diversity available at 85.5 GHz from the SSM/I allows discrimination between low brightness temperatures due to surface water bodies versus those due to precipitation. An 85.5 GHz polarization corrected temperature (PCT) is formulated to isolate the precipitation effect. A PCT threshold of 255 K is suggested for the delineation of precipitation. This threshold is shown to be lower than what would generally be expected from nonprecipitating cloud water alone, yet high enough to s...

The Advanced Microwave Scanning Radiometer for the Earth Observing System (AMSR-E), NASDA's contribution to the EOS for global energy and water cycle studies

Abstract: The Advanced Microwave Scanning Radiometer for the Earth Observing System (AMSR-E) was developed and provided to the National Aeronautics and Space Administration's EOS Aqua satellite by the National Space Development Agency of Japan, as one of the indispensable instruments for Aqua's mission. AMSR-E is a modified version of AMSR that was launched December 2002 aboard the Advanced Earth Observing Satellite-II (ADEOS-II). It is a six-frequency dual-polarized total-power passive microwave radiometer that observes water-related geophysical parameters supporting global change science and monitoring efforts. The hardware improvements over existing spaceborne microwave radiometers for Earth imaging include the largest main reflector of its kind and addition of 6.925-GHz channels. These improvements provide finer spatial resolution and the capability to retrieve sea surface temperature and soil moisture information on a global basis. This paper provides an overview of the instrument characteristics, mission objectives, and data products.

Global Oceanic Precipitation from the MSU during 1979—91 and Comparisons to Other Climatologies

Abstract: The construction and general features of a new monthly oceanic precipitation data set compiled from Microwave Sounding Unit (MSU) data gathered by TIROS-N satellites are described. Rainfall is estimated from the intensity of warming in MSU channel 1 (50.3 GHz) brightness temperatures above a 15-percent cumulative frequency distribution threshold after correction for airmass temperature. The average channel 1 warming above the threshold is calibrated into precipitation units with five to ten years of monthly accumulations from 132 raingages distributed around the globe. Comparisons between the satellite and raingage measurements of the average annual cycle in monthly precipitation are presented for 75 raingages from different climatic regions.

SSM/I Rain Retrievals within a Unified All-Weather Ocean Algorithm

Abstract: A new method for the physical retrieval of rain rates from satellite microwave radiometers is presented. The method is part of a unified ocean parameter retrieval algorithm that is based on the fundamental principles of radiative transfer. The algorithm simultaneously finds near-surface wind speed W, columnar water vapor V, columnar cloud liquid water L, rain rate R, and effective radiating temperature TU for the upwelling radiation. Comparisons with radiosondes demonstrate that the algorithm is able to retrieve water vapor when rain is present. For rain rates from 1 to 15 mm h−1, the rms difference between the retrieved water vapor and the radiosonde value is 5 mm. A novel feature of the rain retrieval method is a beamfilling correction that is based upon the ratio of the retrieved liquid water absorption coefficients at 37 and 19 GHz. This spectral ratio decreases by about 40% when heavy and light rain coexist within the SSM/I footprint as compared to the case of uniform rain. This correction i...

Precise Monitoring of Global Temperature Trends from Satellites

Abstract: Passive microwave radiometry from satellites provides more precise atmospheric temperature information than that obtained from the relatively sparse distribution of thermometers over the earth's surface. Accurate global atmospheric temperature estimates are needed for detection of possible greenhouse warming, evaluation of computer models of climate change, and for understanding important factors in the climate system. Analysis of the first 10 years (1979 to 1988) of satellite measurements of lower atmospheric temperature changes reveals a monthly precision of 0.01 degrees C, large temperature variability on time scales from weeks to several years, but no obvious trend for the 10-year period. The warmest years, in descending order, were 1987, 1988, 1983, and 1980. The years 1984, 1985, and 1986 were the coolest.

The NCEP/NCAR 40-Year Reanalysis Project

Abstract: The NCEP and NCAR are cooperating in a project (denoted “reanalysis”) to produce a 40-year record of global analyses of atmospheric fields in support of the needs of the research and climate monitoring communities. This effort involves the recovery of land surface, ship, rawinsonde, pibal, aircraft, satellite, and other data; quality controlling and assimilating these data with a data assimilation system that is kept unchanged over the reanalysis period 1957–96. This eliminates perceived climate jumps associated with changes in the data assimilation system. The NCEP/NCAR 40-yr reanalysis uses a frozen state-of-the-art global data assimilation system and a database as complete as possible. The data assimilation and the model used are identical to the global system implemented operationally at the NCEP on 11 January 1995, except that the horizontal resolution is T62 (about 210 km). The database has been enhanced with many sources of observations not available in real time for operations, provided b...

Contribution of Working Group II to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change

Abstract: Drafting Authors: Neil Adger, Pramod Aggarwal, Shardul Agrawala, Joseph Alcamo, Abdelkader Allali, Oleg Anisimov, Nigel Arnell, Michel Boko, Osvaldo Canziani, Timothy Carter, Gino Casassa, Ulisses Confalonieri, Rex Victor Cruz, Edmundo de Alba Alcaraz, William Easterling, Christopher Field, Andreas Fischlin, Blair Fitzharris, Carlos Gay García, Clair Hanson, Hideo Harasawa, Kevin Hennessy, Saleemul Huq, Roger Jones, Lucka Kajfež Bogataj, David Karoly, Richard Klein, Zbigniew Kundzewicz, Murari Lal, Rodel Lasco, Geoff Love, Xianfu Lu, Graciela Magrín, Luis José Mata, Roger McLean, Bettina Menne, Guy Midgley, Nobuo Mimura, Monirul Qader Mirza, José Moreno, Linda Mortsch, Isabelle Niang-Diop, Robert Nicholls, Béla Nováky, Leonard Nurse, Anthony Nyong, Michael Oppenheimer, Jean Palutikof, Martin Parry, Anand Patwardhan, Patricia Romero Lankao, Cynthia Rosenzweig, Stephen Schneider, Serguei Semenov, Joel Smith, John Stone, Jean-Pascal van Ypersele, David Vaughan, Coleen Vogel, Thomas Wilbanks, Poh Poh Wong, Shaohong Wu, Gary Yohe

The ERA‐40 re‐analysis

Abstract: ERA-40 is a re-analysis of meteorological observations from September 1957 to August 2002 produced by the European Centre for Medium-Range Weather Forecasts (ECMWF) in collaboration with many institutions. The observing system changed considerably over this re-analysis period, with assimilable data provided by a succession of satellite-borne instruments from the 1970s onwards, supplemented by increasing numbers of observations from aircraft, ocean-buoys and other surface platforms, but with a declining number of radiosonde ascents since the late 1980s. The observations used in ERA-40 were accumulated from many sources. The first part of this paper describes the data acquisition and the principal changes in data type and coverage over the period. It also describes the data assimilation system used for ERA-40. This benefited from many of the changes introduced into operational forecasting since the mid-1990s, when the systems used for the 15-year ECMWF re-analysis (ERA-15) and the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) re-analysis were implemented. Several of the improvements are discussed. General aspects of the production of the analyses are also summarized. A number of results indicative of the overall performance of the data assimilation system, and implicitly of the observing system, are presented and discussed. The comparison of background (short-range) forecasts and analyses with observations, the consistency of the global mass budget, the magnitude of differences between analysis and background fields and the accuracy of medium-range forecasts run from the ERA-40 analyses are illustrated. Several results demonstrate the marked improvement that was made to the observing system for the southern hemisphere in the 1970s, particularly towards the end of the decade. In contrast, the synoptic quality of the analysis for the northern hemisphere is sufficient to provide forecasts that remain skilful well into the medium range for all years. Two particular problems are also examined: excessive precipitation over tropical oceans and a too strong Brewer-Dobson circulation, both of which are pronounced in later years. Several other aspects of the quality of the re-analyses revealed by monitoring and validation studies are summarized. Expectations that the ‘second-generation’ ERA-40 re-analysis would provide products that are better than those from the firstgeneration ERA-15 and NCEP/NCAR re-analyses are found to have been met in most cases. © Royal Meteorological Society, 2005. The contributions of N. A. Rayner and R. W. Saunders are Crown copyright.

Global Precipitation: A 17-Year Monthly Analysis Based on Gauge Observations, Satellite Estimates, and Numerical Model Outputs

Abstract: Gridded fields (analyses) of global monthly precipitation have been constructed on a 2.5° latitude–longitude grid for the 17-yr period from 1979 to 1995 by merging several kinds of information sources with different characteristics, including gauge observations, estimates inferred from a variety of satellite observations, and the NCEP–NCAR reanalysis. This new dataset, which the authors have named the CPC Merged Analysis of Precipitation (CMAP), contains precipitation distributions with full global coverage and improved quality compared to the individual data sources. Examinations showed no discontinuity during the 17-yr period, despite the different data sources used for the different subperiods. Comparisons of the CMAP with the merged analysis of Huffman et al. revealed remarkable agreements over the global land areas and over tropical and subtropical oceanic areas, with differences observed over extratropical oceanic areas. The 17-yr CMAP dataset is used to investigate the annual and interannual variab...

Annular Modes in the Extratropical Circulation. Part I: Month-to-Month Variability*

Abstract: The leading modes of variability of the extratropical circulation in both hemispheres are characterized by deep, zonally symmetric or ‘‘annular’’ structures, with geopotential height perturbations of opposing signs in the polar cap region and in the surrounding zonal ring centered near 458 latitude. The structure and dynamics of the Southern Hemisphere (SH) annular mode have been extensively documented, whereas the existence of a Northern Hemisphere (NH) mode, herein referred to as the Arctic Oscillation (AO), has only recently been recognized. Like the SH mode, the AO can be defined as the leading empirical orthogonal function of the sea level pressure field or of the zonally symmetric geopotential height or zonal wind fields. In this paper the structure and seasonality of the NH and SH modes are compared based on data from the National Centers for Environmental Prediction‐National Center for Atmospheric Research reanalysis and supplementary datasets. The structures of the NH and SH annular modes are shown to be remarkably similar, not only in the zonally averaged geopotential height and zonal wind fields, but in the mean meridional circulations as well. Both exist year-round in the troposphere, but they amplify with height upward into the stratosphere during those seasons in which the strength of the zonal flow is conducive to strong planetary wave‐mean flow interaction: midwinter in the NH and late spring in the SH. During these ‘‘active seasons,’’ the annular modes modulate the strength of the Lagrangian mean circulation in the lower stratosphere, total column ozone and tropopause height over mid- and high latitudes, and the strength of the trade winds of their respective hemispheres. The NH mode also contains an embedded planetary wave signature with expressions in surface air temperature, precipitation, total column ozone, and tropopause height. It is argued that the horizontal temperature advection by the perturbed zonal-mean zonal wind field in the lower troposphere is instrumental in forcing this pattern. A companion paper documents the striking resemblance between the structure of the annular modes and observed climate trends over the past few decades.