Showing papers in "Bulletin of the American Meteorological Society in 1996"

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...

Clouds and the Earth's Radiant Energy System (CERES): An Earth Observing System Experiment

Abstract: Clouds and the Earth's Radiant Energy System (CERES) is an investigation to examine the role of cloud/radiation feedback in the Earth's climate system. The CERES broadband scanning radiometers are an improved version of the Earth Radiation Budget Experiment (ERBE) radiometers. The CERES instruments will fly on several National Aeronautics and Space Administration Earth Observing System (EOS) satellites starting in 1998 and extending over at least 15 years. The CERES science investigations will provide data to extend the ERBE climate record of top-of-atmosphere shortwave (SW) and longwave (LW) radiative fluxes CERES will also combine simultaneous cloud property data derived using EOS narrowband imagers to provide a consistent set of cloud/radiation data, including SW and LW radiative fluxes at the surface and at several selected levels within the atmosphere. CERES data are expected to provide top-of-atmosphere radiative fluxes with a factor of 2 to 3 less error than the ERBE data Estimates of radiative fluxes at the surface and especially within the atmosphere will be a much greater challenge but should also show significant improvements over current capabilities.

Indices of Climate Change for the United States

Abstract: A framework is presented to quantify observed changes in climate within the contiguous United States through the development and analysis of two indices of climate change, a Climate Extremes Index (CEI) and a U.S. Greenhouse Climate Response Index (GCRI). The CEI is based on an aggregate set of conventional climate extreme indicators, and the GCRI is composed of indicators that measure changes in the climate of the United States that have been projected to occur as a result of increased emissions of greenhouse gases. The CEI supports the notion that the climate of the United States has become more extreme in recent decades, yet the magnitude and persistence of the changes are not large enough at this point to conclude that the increase in extremes reflects a nonstationary climate. Nonetheless, if impacts due to extreme events rise exponentially with the index, then the increase may be quite significant in a practical sense. Similarly, the positive trend of the U.S. GCRI during the twentieth centu...

GPS Sounding of the Atmosphere from Low Earth Orbit: Preliminary Results

Abstract: This paper provides an overview of the methodology of and describes preliminary results from an experiment called GPS/MET (Global Positioning System/Meteorology), in which temperature soundings are obtained from a low Earth-orbiting satellite using the radio occultation technique. Launched into a circular orbit of about 750-km altitude and 70° inclination on 3 April 1995, a small research satellite, MicroLab 1, carried a laptop-sized radio receiver. Each time this receiver rises and sets relative to the 24 operational GPS satellites, the GPS radio waves transect successive layers of the atmosphere and are bent (refracted) by the atmosphere before they reach the receiver, causing a delay in the dual-frequency carrier phase observations sensed by the receiver. During this occultation, GPS limb sounding measurements are obtained from which vertical profiles of atmospheric refractivity can be computed. The refractivity is a function of pressure, temperature, and water vapor and thus provides informat...

Impacts and Responses to the 1995 Heat Wave: A Call to Action

Abstract: The short but intense heat wave in mid-July 1995 caused 830 deaths nationally, with 525 of these deaths in Chicago. Many of the dead were elderly, and the event raised great concern over why it happened. Assessment of causes for the heat wave–related deaths in Chicago revealed many factors were at fault, including an inadequate local heat wave warning system, power failures, questionable death assessments, inadequate ambulance service and hospital facilities, the heat island, an aging population, and the inability of many persons to properly ventilate their residences due to fear of crime or a lack of resources for fans or air conditioning. Heat-related deaths appear to be on the increase in the United States. Heat-related deaths greatly exceed those caused by other life-threatening weather conditions. Analysis of the impacts and responses to this heat wave reveals a need to 1) define the heat island conditions during heat waves for all major cities as a means to improve forecasts of threatening condition...

A new global water vapor dataset

Abstract: A comprehensive and accurate global water vapor dataset is critical to the adequate understanding of water vapor`s role in the earth`s climate system. To begin to satisfy this need, the authors have produced a blended dataset made up of global, 5-yr (1988-92), 1{degrees} x 1{degrees} spatial resolution, atmospheric water vapor (WV) and liquid water path products. These new products consist of both the daily total column-integrated composites and a multilayered WV product at three layers (1000-700, 700-500, 500-300 mb). The analyses combine WV retrievals from the Television and Infrared Operational Satellite (TIROS) Operational Verticle Sounder (TOVS), the Special Sensor Microwave/Imager, and radiosonde observations. The global, verticle-layered water vapor dataset was developed by slicing the blended total column water vapor using layer information from TOVS and radiosonde. Also produced was a companion, over oceans only, liquid water path dataset. Satellite observations of liquid water path are growing in importance since many of the global climate models are now either incorporating or contain liquid water as an explicit variable. The complete dataset (all three products) has been named NVAP, an acronym for National Aeronautics and Space Administration Water Vapor Project. This paper provides examples of the new dataset as well as scientificmore » analysis of the observed annual cycle and the interannual variability of water vapor at global, hemispheric, and regional scales. A distinct global annual cycle is shown to be dominated by the Northern Hemisphere observations. Planetary-scale variations are found to relate well to recent independent estimates of tropospheric temperature variations. Maps of regional interannual variability in the 5-yr period show the effect of the 1992 ENSO and other features. 43 refs., 12 figs., 2 tabs.« less

A Historical Perspective of U.S. Climate Divisions

Abstract: The history of climatic divisions in the contiguous United States has been pieced together from fragmentary documentation. Each of the 48 contiguous states has been subdivided into climatic divisions. Divisional boundaries are now standardized, and a set of climatic variables for time-invariant divisional boundaries has been compiled for the period of record beginning in 1895. This paper documents the origins of climatic divisions, the computational methodology of an area-invariant divisional dataset maintained by the National Climatic Data Center, and the strengths and weaknesses of divisional data.

An eight-year (1987-1994) time series of rainfall, clouds, water vapor, snow cover, and sea ice derived from SSM/I measurements

Abstract: The Special Sensor Microwave/Imager (SSM/I), first placed into operation in July 1987, has been making measurements of earth-emitted radiation for over eight years. These data are used to estimate both atmospheric and surface hydrological parameters and to generate a time series of global monthly mean products averaged to a 1° lat × 1° long grid. Specifically, this includes monthly estimates of rainfall and its frequency, cloud liquid water and cloud frequency, water vapor, snow cover frequency, and sea ice frequency. This study uses seasonal mean values to demonstrate the spatial and temporal distributions of these hydrological variables. Examples of interannual variability such as the 1993 flooding in the Mississippi Valley and the 1992–93 snow cover changes over the United States are used to demonstrate the utility of these data for regional applications.

The Promise of GPS in Atmospheric Monitoring

Abstract: This paper provides an overview of applications of the Global Positioning System (GPS) for active measurement of the Earth's atmosphere. Microwave radio signals transmitted by GPS satellites are delayed (refracted) by the atmosphere as they propagate to Earth-based GPS receivers or GPS receivers carried on low Earth orbit satellites. The delay in GPS signals reaching Earth-based receivers due to the presence of water vapor is nearly proportional to the quantity of water vapor integrated along the signal path. Measurement of atmospheric water vapor by Earth-based GPS receivers was demonstrated during the GPS/STORM field project to be comparable and in some respects superior to measurements by ground-based water vapor radiometers. Increased spatial and temporal resolution of the water vapor distribution provided by the GPS/STORM network proved useful in monitoring the moisture-flux convergence along a dryline and the decrease in integrated water vapor associated with the passage of a midtropospheri...

A Multiyear Global Surface Wind Velocity Dataset Using SSM/I Wind Observations

Abstract: The Special Sensor Microwave Imagers (SSM/I) aboard three DMSP satellites have improved a large dataset of surface wind speeds over the global oceans from July 1987 to the present. These data are characterized by high resolution, coverage, and accuracy, but their application has been limited by the lack of directional information. In an effort to extend the applicability of these data , methodology has been developed to assign directions to the SSM/I wind speeds and to produce analyses using these data. Following extensive testing, this methodology has been used to generate a seven and one-half year dataset (from July 1987 through December 1994) of global SSM/I wind vectors. These data are currently being used in a variety of atmospheric and oceanic applications and are available to interested investigators. Recent results presented in this paper show the accuracy of the SSM/I wind velocities, the ability of these data to improve surface wind analyses, and the propagation of a synoptic-scale convergent cortex in the Tropics that can be tracked from year to year in annual mean SSM/I wind fields. 11 refs., 5 figs., 2 tabs.

The Philadelphia Hot Weather–Health Watch/Warning System: Development and Application, Summer 1995

Abstract: Last summer, Philadelphia, Pennsylvania, instituted a new Hot Weather-Health Watch/Warning System (PWWS) to alert the city's residents of potentially oppressive weather situations that could negatively affect health. In addition, the system was used by the Philadelphia Department of Public Health for guidance in the implementation of mitigation procedures during dangerous weather. The system is based on a synoptic climatological procedure that identifies “oppressive” air masses historically associated with increased human mortality. Airmass occurrence can be predicted up to 48 h in advance with use of model output statistics guidance forecast data. The development and statistical basis of the system are discussed, and an analysis of the procedure's ability to forecast weather situations associated with elevated mortality counts is presented. The PWWS, through greater public awareness of excessive heat conditions, may have played an important role in reducing Philadelphia's total heat-related deat...

The July 1995 Heat Wave in the Midwest: A Climatic Perspective and Critical Weather Factors

Abstract: A brief but intense heat wave developed in the central and eastern United States in mid-July 1995, causing hundreds of fatalities. The most notable feature of this event was the development of very high dewpoint temperature (Td) over the southern Great Lakes region and the Upper Mississippi River Basin. At many locations, hourly values of Td set new records. The combination of high air and dewpoint temperatures resulted in daily average apparent temperatures exceeding 36°C over a large area on some days. A comparison with past heat waves shows that this was the most intense short-duration heat wave in at least the last 48 years at some locations in the southern Great Lakes region and Upper Mississippi River Basin. An analysis of historical data for Chicago, where the majority of fatalities occurred, indicates the intensity of this heat wave was exceeded only by a few periods in the 1910s and 1930s. Impacts in the Chicago urban center were exacerbated by an urban heat island that raised nocturnal temperatu...

Observations of the infrared radiative properties of the ocean-implications for the measurement of sea surface temperature via satellite remote sensing

Abstract: The Atmospheric Emitted Radiance Interferometer (AERI) was used to measure the infrared radiative properties and the temperature of the Gulf of Mexico during a 5-day oceanographic cruise in January 1995. The ocean skin temperature was measured with an accuracy believed to be better than 0.1°C. The surface reflectivity/emissivity was determined as a function of view angle and sea state. The radiative properties are in good theoretical consistency with in situ measurements of ocean bulk temperature and the meteorological observations made from the oceanographic vessel. The AERI and in situ measurements provide a strong basis for accurate global specifications of sea surface temperature and ocean heat flux from satellites and ships.

Results from the GPCP Algorithm Intercomparison Programme

Abstract: Three algorithm intercomparison experiments have recently been conducted as part of the Global Precipitation Climatology Project with the goal of (a) assessing the skill of current satellite rainfall algorithms, (b) understanding the differences between them, and (c) moving toward improved algorithms. The results of these experiments are summarized and intercompared in this paper. It was found that the skill of satellite rainfall algorithms depends on the regime being analyzed, with algorithms producing very good results in the tropical western Pacific and over Japan and its surrounding waters during summer, but relatively poor rainfall estimates over western Europe during late winter. Monthly rainfall was estimated most accurately by algorithms using geostationary infrared data, but algorithms using polar data [Advanced Very High Resolution Radiometer and Special Sensor Microwave/Imager (SSM/1)l were also able to produce good monthly rainfall estimates when data from two satellites wore availabl...

Global Ocean Circulation from Satellite Altimetry and High-Resolution Computer Simulation

Abstract: The sea surface elevation relative to the geoid, a dynamic boundary condition for the three-dimensional oceanic pressure field, is being determined over the global ocean every 10 days by a precision radar altimeter aboard the TOPEX/POSEIDON satellite. This is the most accurate altimeter data stream to date for the study of the ocean general circulation and its variability. The authors compare results from 2 years (October 1992-October 1994) of the satellite observations to computer simulations for the same period using a state-of-the-art ocean general circulation model driven by realistic winds from an atmospheric weather-prediction model. The average horizontal resolution of the model is 1/5° (varying from 30 km at the equator to 6 kin at the polar latitudes), the highest for a global simulation performed to date. Comparisons of the mean circulation, the mesoscale variability, the amplitude, and phase of the annual cycle, as well as intraseasonal and interannual changes show that the simulations...

Improvements in Quantitative Precipitation Forecasts with the Eta Regional Model at the National Centers for Environmental Prediction: The 48-km Upgrade

Abstract: Since 9 June 1993, the eta coordinate regional model has been run twice daily at the National Centers for Environmental Prediction (NCEP, previously the National Meteorological Center) as the NCEP's “early” operational model. Its performance is regularly monitored in a variety of ways, with particular attention given to precipitation forecasts. Throughout this period, the eta model has demonstrated significantly increased accuracy in forecasting daily precipitation amounts compared to NCEP's Nested Grid Model (NGM). The model has shown a smaller but equally consistent advantage in skill against that of NCEP's global spectral model. Precipitation scores of these three operational models for the 6-month period March–August 1995 are presented. This interval is chosen because the 6-month-long periods September–February and March–August have been used in previous model comparisons and because an upgraded version of the eta model, run at 48-km resolution, was also regularly executed twice daily during the March...

The ISLSCP initiative I global datasets: Surface boundary conditions and atmospheric forcings for land-atmosphere studies

Abstract: A comprehensive series of global datasets for land-atmosphere models has been collected, formatted to a common grid, and released on a set of CD-ROMs. This paper describes the motivation for and th...

Hurricane Andrew in Florida: Dynamics of a Disaster

Abstract: Four meteorological factors aggravated the devastation when Hurricane Andrew struck South Florida: completed replacement of the original eyewall by an outer, concentric eyewall while Andrew was still at sea; storm translation so fast that the eye crossed the populated coastline before the influence of land could weaken it appreciably; extreme wind speed, 82 m s− 1 winds measured by aircraft flying at 2.5 km; and formation of an intense, but nontornadic, convective vortex in the eyewall at the time of landfall. Although Andrew weakened for 12 h during the eyewall replacement, it contained vigorous convection and was reintensifying rapidly as it passed onshore. The Gulf Stream just offshore was warm enough to support a sea level pressure 20–30 hPa lower than the 922 hPa attained, but Andrew hit land before it could reach this potential. The difficult-to-predict mesoscale and vortex-scale phenomena determined the course of events on that windy morning, not a long-term trend toward worse hurricanes.

Reply to comment on 'Tthe ELDORA/ASTRAIA airborne doppler weather radar: High-resolution observations from TOGA COARE''

Abstract: Abstract The ELDORA/ASTRAIA (Electra Doppler Radar/Analyese Stereoscopic par Impulsions Aeroporte) airborne Doppler weather radar was recently placed in service by the National Center for Atmospheric Research and the Centre d'etude des Environnements Terrestre et Planetaires in France. After a multiyear development effort, the radar saw its first field tests in the TOGA COARE (Tropical Oceans-Global Atmosphere Coupled Ocean-Atmosphere Response Experiment) field program during January and February 1993. The ELDORA/ASTRAIA radar (herein referred to as ELDORA) is designed to provide high-resolution measurements of the air motion and rainfall characteristics of very large storms, storms that are frequently too large or too remote to be adequately observed by ground-based radars. This paper discusses the measurement requirements and the design goals of the radar and concludes with an evaluation of the performance of the system using data from TOGA COARE. The performance evaluation includes data from two cases....

Intercomparison of hydrologic processes in AMIP GCMs

Abstract: Results of an intercomparison study under the Atmospheric Model Intercomparison Project (AMIP) to assess the abilities of 29 global climate models (GCMS) in simulating various aspects of regional and hydrologic processes in response to observed sea surface temperature and sea ice boundary forcings are presented. The authors find that the models generally portray an earthlike climate to approximately 10%–20% of the global land surface temperature (=14.8°C) and global precipitation (=2.3 mm day−1). While a majority of the models have a reasonable global water budget, about a quarter of the models show significant errors in the total global water balance. While the model frequency distributions of heavy precipitation associated with deep convection are in reasonable agreement with observations, a systematic underestimate of the frequency of occurrence of light precipitation events (< 1 mm day−1) is present in almost all the AMIP models, especially over continental desert regions and over tropical an...

On the Existence and Strength of the Summer Subtropical Anticyclones. Bernhard Haurwitz Memorial Lecture.

Abstract: The subtropical anticyclones are usually related to radiative cooling and the descending arm of the Hadley Cell. This explanation works well for the winter anticyclone belt. However, the summer subtropical anticyclones are in most measures stronger, as well as being more longitudinally localized, than their winter counterparts. The nature of the circulations in the summer and winter subtropics, and the Tropics are compared. It is hypothesized that the basic cause of the summer anticyclones is the monsoonal latent heat release over the neighboring continents to the east. As this diabatic heating pushes poleward to near 25° latitude, so deep descent is induced poleward and westward of it. Orographic effects can act to localize this descent. Enhanced radiative cooling and suppressed convection are then viewed as amplifiers of the descent. Under this descent is the equatorward moving air of an anticyclone, which is centered to the west. This wind acts to drive oceanic upwelling, leading to cold sea surface temperatures and reinforcement of the suppression of convection.

The ELDORA/ASTRAIA Airborne Doppler Weather Radar: High-Resolution Observations from TOGA COARE

Abstract: The ELDORA/ASTRAIA (Electra Doppler Radar/Analyese Stereoscopic par Impulsions Aeroporte) airborne Doppler weather radar was recently placed in service by the National Center for Atmospheric Research and the Centre d'etude des Environnements Terrestre et Planetaires in France. After a multiyear development effort, the radar saw its first field tests in the TOGA COARE (Tropical Oceans-Global Atmosphere Coupled Ocean-Atmosphere Response Experiment) field program during January and February 1993. The ELDORA/ASTRAIA radar (herein referred to as ELDORA) is designed to provide high-resolution measurements of the air motion and rainfall characteristics of very large storms, storms that are frequently too large or too remote to be adequately observed by ground-based radars. This paper discusses the measurement requirements and the design goals of the radar and concludes with an evaluation of the performance of the system using data from TOGA COARE. The performance evaluation includes data from two cases....

The CERES/ARM/GEWEX Experiment (CAGEX) for the Retrieval of Radiative Fluxes with Satellite Data

Abstract: Results from a temporally intensive, limited area, radiative transfer model experiment are on-line for investigating the vertical profile of shortwave and longwave radiative fluxes from the surface to the top of the atmosphere (TOA). The CERES/ARM/GEWEX Experiment (CAGEX) Version 1 provides a record of fluxes that have been computed with a radiative transfer code; the atmospheric sounding, aerosol, and satellite-retrieved cloud data on which the computations have been based; and surface-based measurements of radiative fluxes and cloud properties from ARM for comparison. The computed broadband fluxes at TOA show considerable scatter when compared with fluxes that are inferred empirically from narrowband operational satellite data. At the surface, LW fluxes computed with an alternate sounding dataset compare well with pyrgeometer measurements. In agreement with earlier work, the authors find that the calculated SW surface insulation is larger than the measurements for clear-sky and total-sky condit...

The Impact of Omega Dropwindsondes on Operational Hurricane Track Forecast Models

Abstract: Since 1982, the Hurricane Research Division (HRD) has conducted a series of experiments with research aircraft to enhance the number of observations in the environment and the core of hurricanes threatening the United States. During these experiments, the National Oceanic and Atmospheric Administration WP-3D aircraft crews release Omega dropwindsondes (ODWs) at 15–20-min intervals along the flight track to obtain profiles of wind, temperature, and humidity between flight level and the sea surface. Data from the ODWs are transmitted back to the aircraft and then sent via satellite to the Tropical Prediction Center and the National Centers for Environmental Prediction (NCEP), where the observations become part of the operational database. This paper tests the hypothesis that additional observations improve the objective track forecast models that provide operational guidance to the hurricane forecasters. The testing evaluates differences in forecast tracks from models run with and without the ODW d...

Ultraviolet Index Forecasts Issued by the National Weather Service

Abstract: The National Weather Service (NWS), in collaboration with the Environmental Protection Agency (EPA), now issues an Ultraviolet (UV) index forecast. The UV index (UVI) is a mechanism by which the American public is forewarned of the next day's noontime intensity of UV radiation at locations within the United States. The EPA's role in this effort is to alert the public of the dangerous health effects of overexposure to, and the accumulative effects of, UV radiation. The EPA also provides ground-level monitoring data for use in ongoing verification of the UVI. The NWS estimates the UVI using existing atmospheric measurements, forecasts, and an advanced radiative transfer model. This paper discusses the justification for a forecasted index, the nature of UV radiation, the methodology of producing the UVI, and results from verifying the UVI. Since the UVI is an evolving product, a short discussion of necessary improvements and/or refinements is included at the end of this article.

ELDORA observations during VORTEX 95

Abstract: Airborne radar platforms have played an increasingly important role in advancing our understanding of storms that are either too remote or occur too infrequently for ground-based radars. Recognizing this potential, the National Center for Atmospheric Research and the Centre de Recherche en Physique de l'Environnment Terrestre et Planetaire have designed and developed ELDORA (Electra Doppler Radar), a tail Doppler radar with the following unique capabilities: 1) increased accuracy and sensitivity by averaging more independent samples in the radar pulse volume, 2) higher spatial resolution in the along-track direction by using a faster rotation rate of the antenna, and 3) a large unambiguous velocity measuring interval by means of a dual pulse repetition frequency. Although the first field deployment of ELDORA occurred in 1993, it was not until VORTEX (Verification of the Origins of Rotation in Tornadoes Experiment) that the system was operating up to its full capabilities. Examples of the radar's ...

Defining Mesoscale Convective Systems by Their 85-GHz Ice-Scattering Signatures

Abstract: Mesoseale Convective systems are composed of numerous deep convective cells with varying amounts of large, convectively produced ice particles aloft. The magnitude of the 85-GHz brightness temperature depression resulting from scattering by large ice is believed to be related to the convective intensity and to the magnitude of the convective fluxes through a deep layer. The 85-GHz ice-scattering signature can be used to map the distribution of organized mesoscale regions of convectively produced large ice particles. The purpose of this article is to demonstrate the usefulness of the 85-GHz ice-scattering signature for describing the frequency, convective intensity, and geographic distribution of mesoscale convective systems. Objective criteria were developed to identify mesoscale convective systems from raw data from January, April, July, and October 1993. To minimize the effects of background contamination and to ensure that bounded areas contained convective elements, a “mesoscale convective sy...

The Antarctic zone flux experiment

Abstract: In winter the eastern Weddell Sea in the Atlantic sector of the Southern Ocean hosts some of the most dynamic air–ice–sea interactions found on earth. Sea ice in the region is kept relatively thin by heat flux from below, maintained by upper-ocean stirring associated with the passage of intense, fast-moving cyclones. Ocean stratification is so weak that the possibility of deep convection exists, and indeed, satellite imagery from the Weddell Sea in the 1970s shows a large expanse of open water (the Weddell Polynya) that persisted through several seasons and may have significantly altered global deep-water production. Understanding what environmental conditions could again trigger widespread oceanic overturn may thus be an important key in determining the role of high latitudes in deep-ocean ventilation and global atmospheric warming. During the Antarctic Zone Flux Experiment in July and August 1994, response of the upper ocean and its ice cover to a series of storms was measured at two drifting stations s...