Showing papers in "Bulletin of the American Meteorological Society in 1992"

AMIP: The Atmospheric Model Intercomparison Project.

Abstract: The Atmospheric Model Intercomparison Project (AMIP) is an international effort to determine the systematic climate errors of atmospheric models under realistic conditions, and calls for the simulation of the climate of the decade 1979-1988 using the observed monthly averaged distributions of sea surface temperature and sea ice as boundary conditions. Organized by the Working Group on Numerical Experimentation as a contribution to the World Climate Research Programme, AMIP involves the international atmospheric modeling community in a major test and intercomparison of model performance; in addition to an agreed-to set of monthly averaged output variables, each of the participating models will generate a daily history of state. These data will be stored and made available in standard format by the Program for Climate Model Diagnosis and Intercomparison at the Lawrence Livermore National Laboratory. Following completion of the computational phase of AMIP in 1993, emphasis will shift to a series of diagnostic sub-projects, now being planned, for the detailed examination of model performance and the simulation of specific physical processes and phenomena. AMIP offers an unprecedented opportunity for the comprehensive evaluation and validation of current atmospheric models, and is expected to provide valuable information for model improvement.

TOGA COARE: The Coupled Ocean-Atmosphere Response Experiment.

Abstract: Despite significant progress in the Tropical Ocean–Global Atmosphere (TOGA) program, a number of major hurdles remain before the primary objective, prediction of the variability of the coupled ocean-atmosphere system on time scales of months to years, can be achieved. Foremost among these hurdles is understanding the physics that maintains and perturbs the western Pacific warm pool, the region of the warmest sea surface temperature in the open oceans, which coexists with the largest annual precipitation and latent heat release in the atmosphere. Even though it is believed that the warm pool is a “center of action” for the El Nino-Southern Oscillation (ENSO) phenomena in the ocean and the atmosphere, successful simulation of the warm pool has remained an elusive goal. To gain a clear understanding of global climate change, the ENSO phenomenon, and the intraseasonal variability of the coupled atmosphere–ocean system, it is clear that a better specification of the coupling of the ocean and the atmosphere is ...

AN AMS CONTINUING SERIES: GLOBAL CHANGE--AMIP: The Atmospheric Model Intercomparison Project

Abstract: The Atmospheric Model Intercomparison Project (AMIP) is an international effort to determine the systematic climate errors of atmospheric models under realistic conditions, and calls for the simulation of the climate of the decade 1979–1988 using the observed monthly averaged distributions of sea surface temperature and sea ice as boundary conditions. Organized by the Working Group on Numerical Experimentation as a contribution to the World Climate Research Programme, AMIP involves the international atmospheric modeling community in a major test and intercomparison of model performance; in addition to an agreed-to set of monthly averaged output variables, each of the participating models will generate a daily history of state. These data will be stored and made available in standard format by the Program for Climate Model Diagnosis and Intercomparison at the Lawrence Livermore National Laboratory. Following completion of the computational phase of AMIP in 1993, emphasis will shift to a series of diagnosti...

Nonclassical mesoscale circulations caused by surface sensible heat-flux gradients

Abstract: Significant spatial heterogeneities of daytime surface sensible heat flux are common over land within mesoscale domains. Thermally induced circulations, similar to the sea/lake breeze [termed nonclassical mesoscale circulations (NCMCs)], are anticipated in these situations. Growing research interest in NCMCs has developed in the recent decade. In this article, general quantifications of NCMC characteristics are sun/eyed based on modeling and observational studies, along with further elaborations on specific NCMCs. The numerical modeling studies have indicated NCMCs with intensity comparable to the sea breeze in the ideal situations of sharp contrast between extended wet soil or crop and adjacent dry land areas. Similar results were obtained when contrasts of cloud with clear sky and snow with snow-free areas were considered. For less ideal contrasts, as well as for thermal contrasts generated by some other types of forcing, weaker NCMCs were simulated. The limited observational studies have suggested that...

Reconstruction and Analysis of Spring Rainfall over the Southeastern U.S. for the Past 1000 Years

Abstract: Tree-ring chronologies can provide surprisingly accurate estimates of the natural variability of important climate parameters such as precipitation and temperature during the centuries prior to the industrial Revolution. Bald cypress tree-ring chronologies have been used to reconstruct spring rainfall for the past 1000 years in North Carolina, South Carolina, and Georgia. These rainfall reconstructions explain from 54% to 68% of the spring rainfall variance in each state, and are well verified against independent rainfall measurements. In fact, these tree-ring data explain only 6% to 13% less statewide rainfall variance than is explained by the same number of instrumental raingage records. The reconstructions indicate that the spring rainfall extremes and decade-long regimes witnessed during the past century of instrumental observation have been a prominent feature of southeastern United States climate over the past millennium. These spring rainfall regimes are linked in part to anomalies in the seasonal expansion and migration of the subtropical anticyclone over the North Atlantic. The western sector of the Bermuda high often ridges strongly westward into the southeastern United States during dry springs, but during wet springs it is usually located east of its mean position and well offshore. Similar anomalies in the western sector of themore » Bermuda high occurred during multidecadal regimes of spring rainfall over the Southeast. During the relatively dry springs from 1901 to 1939, the high often ridged into the Southeast, but the western periphery of the high was more frequently located offshore during the relatively wet period from 1940 to 1980. Spring and summer rainfall extremes and decade-long regimes over the Southeast are frequently out of phase, and the tendency for wet (dry) springs to be followed by dry (wet) summers also appears to reflect anomalies in the zonal position of the Bermuda high during spring and summer.« less

The Down Under Doppler and Electricity Experiment (DUNDEE): Overview and Preliminary Results

Abstract: DUNDEE (Down Under Doppler and Electricity Experiment) is described. DUNDEE was carded out in the vicinity of Darwin, Northern Territory, Australia, during the wet seasons of November 1988 through February 1989, and November 1989 through February 1990. The general goal of DUNDEE was to investigate the dynamical and electrical properties of tropical mesoscale convective systems and isolated deep convective storms. Darwin, situated at the southern tip of the “maritime continent,” experiences both monsoon and “break” period conditions during the wet season. We discuss the observational network deployed for DUNDEE and present preliminary scientific results. One particularly interesting observation is a large contrast in the frequency of total lightning between break period convection (high lightning rates) and convection in the monsoon trough (low lightning rates). A relationship between CAPE (convective available potentional energy) and total flash rate is presented and discussed to explain this obs...

Inadvertent Weather Modification in Urban Areas: Lessons for Global Climate Change

Abstract: Large metropolitan areas in North America, home to 65% of the nation's population, have created major changes in their climates over the past 150 years. The rate and amount of the urban climate change approximate those being predicted globally using climate models. Knowledge of urban weather and climate modification holds lessons for the global climate change issue. First, adjustments to urban climate changes can provide guidance for adjusting to global change. A second lesson relates to the difficulty but underscores the necessity of providing scientifically credible proof of change within the noise of natural climatic variability. The evolution of understanding about how urban conditions influence weather reveals several unexpected outcomes, particularly relating to precipitation changes. These suggest that similar future surprises can be expected in a changed global climate, a third lesson. In-depth studies of how urban climate changes affected the hydrologic cycle, the regional economy, and human acti...

Sensitivity of Runoff to Climate Change: A Hortonian Approach

Abstract: This Horton Memorial Lecture reviews the approach of Robert Horton (1875–1945) to key problems in hydrology, meteorology, and geography and then speculates on how Horton might today approach the problem of analyzing the sensitivity of catchment runoff to climate change. It is suggested that the techniques used by Horton can give us an insight into the nature of the latter problem through a partial analysis of the phenomena involved.

Nonlinear Prediction, Chaos, and Noise

Abstract: We present a brief overview of some new methodologies for making predictions on time-series data. These ideas stern from two rapidly growing fields: nonlinear dynamics (choas) theory and parallel distributed processing. Examples are presented that show the usefulness of such methods in making short-term predictions. It is suggested that such methodologies are capable of distinguishing between chaos and noise. Implications of these ideas and methods in the study of weather and climate are discussed.

A Deterministic Approach to the Validation of Historical Daily Temperature and Precipitation Data from the Cooperative Network.

Abstract: It is widely known that the TD3200 (Summary of the Day Cooperative Network) database held by the National Climatic Data Center contains tens of thousands of erroneous daily values resulting from data-entry, data-recording, and data-reformatting errors. TD3200 serves as a major baseline dataset for detecting global climate change. It is of paramount importance to the climate community that these data be as error-free as possible. Many of these errors are systematic in nature. If a deterministic approach is taken, using empirically developed criteria, many if not most of these errors can be corrected or removed. A computer program utilizing Backus Normal Form structure design and a series of chain-linked tests in the form of encoded rules has been developed as a means of modeling the human subjective process of inductive data review. This objective automated correction process has proven extremely effective. A manual review and validation of 138 stations of a 1300-station subset of TD3200 data closely match...

Gust Factors Applied to Hurricane Winds

Abstract: An important consideration in the design of structures is their response to extreme winds. This is especially true in regions affected by hurricanes. In this research, gust factors derived from hurricane wind-speed records are compared with those derived by Durst and others from open-scale records obtained in well-developed, extratropical storms. Based on records obtained from four hurricanes and 11 different recording stations, it is concluded that an upward adjustment of the Durst gust factors for the estimation of hurricane gust speeds may be in order. Anomalously high gust factors observed for hurricane winds in inland areas suggest the need for additional study. Also, it is concluded that a reexamination of the statistics of gust factors obtained from extratropical storm data would be useful in clearly identifying the appropriate probability distribution function.

Observing Precipitation through Dual-Polarization Radar Measurements

Abstract: Dual-polarization radar measurements of precipitation are primarily influenced by the size, shape, orientation, and phase of scattering hydrometeors. As a result, these measurements can serve as a tool for remote identification of hydrometeor characteristics. This paper presents an overview of the definitions, observed values, and applications of differential reflectivity (ZDR) and linear depolarization ratio (LDR) measurements. Brief examples of these measurements are given for widespread stratiform precipitation, a rapidly developing convective cell, and a severe hailstorm. The results outline the role that ZDR can play in the differentiation of rain and solid precipitation, identification of supercooled raindrops above the 0°C level, and identification of hail at the surface. LDR measurements are seen to reveal contrasts in ice-particle shape, orientation, and particle phase. These contrasts are of particular benefit toward delineation of hail regions aloft and identification of mixed-phase particle gr...

Precipitation types in the transition region of winter storms

Abstract: Winter storms often produce snow, freezing rain, and ice pellets. The characteristics and formation of these forms of precipitation as well as their location within storms are reviewed. Phenomena such as accretion and fog can be related to this precipitation as well.

Autonomous aerosondes for economical atmospheric soundings anywhere on the globe

Abstract: Considerable interest in the use of autonomous aircraft for atmospheric measurements in remote and hazardous areas worldwide has arisen over recent years. Their application in tropical cyclone reconnaissance is under study by the World Meteorological Organization and the International Council for Scientific Unions under the United Nations International Decade for Natural Disaster Reduction. More diverse experiments, particularly for stratospheric operations, are being planned by agencies in the United States. The aerosonde can provide an economical and flexible element in these international initiatives. The concept is for a small aircraft (weighing less than 20 kg) with on-board meteorological sensors to provide radiosonde-quality observations at any location on the globe. Individual missions could span several thousand kilometers and several days' duration, using the Global Positioning System for autonomous navigation, and satellite relay for data return and flight-plan updates. With a supercharged engi...

Winter Icing and Storms Project (WISP).

Abstract: Field studies in support of the Winter Icing and Storms Project (WISP) were conducted in the Colorado Front Range area from 1 February to 31 March 1990 (WISP90) and from 15 January to 5 April 1991 (WISP91). The main goals of the project are to study the processes leading to the formation and depletion of supercooled liquid water in winter storms and to improve forecasts of aircraft icing. During the two field seasons, 2 research aircraft, 4 Doppler radars, 49 Mesonet stations, 7 CLASS sounding systems, 3 microwave radiometers, and a number of other facilities were deployed in the Front Range area. A comprehensive dataset was obtained on 8 anticyclonic storms, 16 cyclonic storms, and 9 frontal passages. This paper describes the objectives of the experiment, the facilities employed, the goals and results of a forecasting exercise, and applied research aspects of WISP. Research highlights are presented for several studies under way to illustrate the types of analysis being pursued. The examples chosen includ...

Programs of the National Data Buoy Center

Abstract: Platforms of the National Data Buoy Center provide vital meteorological and oceanographic observations from data-sparse marine areas worldwide. The data are essential for real-time weather forecasting and research programs. This paper provides information on the data-acquisition systems, networks, monitoring capabilities, data processing and dissemination, data quality and availability and related technology development for these platforms.

The resolution of global spectral models

Abstract: Physics Depal1ment, University of Quebec at MontrealMontreal, Quebec, CanadaThe letter of Professor Pielke (1991) suggesting adefinition of horizontal resolution of gridpoint modelsprompts me to reciprocate with a short essay on acorresponding analysis for global spectral models.The horizontal structure of dependent variables inspectral models is represented by series expansion ofspherical harmonics Y;;', where 0 ::s Jml ::s n (e.g.,Kubota 1959); the transform method (Machenhauerand Rasmussen 1972) is used to calculate nonlinearterms on a Gaussian latitude-longitude grid in allmodern spectral models. Triangular truncation (O.$: n.$: N) of the series is often used, as it offers uniformresolution on a spherical domain. As this note will tryto show, there does not seem to be any straightfor-ward way to define an equivalent mesh size for spec-tral models; this makes the estimation of effectiveresolution even more difficult than in gridpoint models.A sometimes quoted estimate of spectral-modelresolution consists in the average spacing betweenGaussian latitudes of the transform grid; for triangulartruncation, this spacing is equal to that between longi-tudes at the equator: L1 = 21Ta/(3N + 1), with a theradius of the earth. Hence, L1 = 13.3/N in units ofthousands of kilometers; for a T31 model, L1 = 426 km.This estimate of resolution is overly optimistic becausethe dimensions of the transform grid are chosen toallow calculation of quadratic terms without aliasing ofthe resolved spectral fields, and hence the transformgrid is finer than required by the information content ofthe corresponding spectral series.A more realistic estimate of resolution is given bythe size of half a wavelength of the shortest resolvedzonal wave at the equator: L2 = 1Ta/N = 20/N in units ofthousands of kilometers. Hence, a T31 model wouldhave a resolution of L2 = 646 km, according to thismeasure. Triangular truncation provides an isotropicand uniform resolution on a sphere. The shortestresolved zonal wave (Iml = N) used to determine L2corresponds to a mode with the gravest meridionalstructure, because modes that are very short in onedirection must be elongated in the other direction:sectorial spherical harmonics (Iml = n ) have modalstructures shaped as orange segments and have theirlargest amplitude in the tropics, hardly an adequatemeasure of resolution for general circulation models.An alternative way to estimate the resolution ofspectral models is as follows. Consider that the area ofthe earth's surface is given by 47TB2; there are (N + 1)2real coefficients to a spherical harmonic series attriangular truncation with maximum index N, that is,N(N + 1 )/2 complex coefficients for the modes 1 :SIml :s N, plus (N + 1) real coefficients for the modeswith m = O. If an equal area on the surface of the earthis assigned to every piece of information contained inthe series, this gives a footprint of surface area equalto 41Ta2/(N + 1)2 for every real coefficient. Resolutionin a spectral model could be defined as the width L3 ofa flat, rectangular tile of the same surface area: L3 =(41T)1/2a/(N + 1) = 22.6/N in units of thousands ofkilometers. Hence, a T31 model would have a resolu-tion of L3 = 728 km, according to this measure.Yet another definition of resolution for spectralmodels would be to consider the representative spa-tial dimension of high-ordertesseral harmonics (0 < 1m I< n = N). The eigenvalue of the Laplacian operatorapplied on a spherical harmonics V':; is -K2 = -n(n +1 )/ a2. Equating the eigenvalue of the highest resolvedmode with the corresponding eigenvalue of Fouriermodes in Cartesian geometry for the purpose ofestimating resolution gives: K2 = N(N + 1 )/a2 = kx2 + ky2.Considering modes with unity aspect ratio, kx2 = k 2 =k2, that is, with checkerboard-like modal structOre,givesk2 = N(N + 1)/(2a2). An alternative measure ofresolution would be one-half of the correspondingwave-length: L4 = 1T/k = 21/21Ta/N = 28.3/N in units ofthousands of kilometers. So for a T31 model, L4 =899 km.It is noteworthy that the estimates of resolutiongiven by L2, L3' and L4 are all coarser than the simple-

On Differences in Radiosonde Humidity-Reporting Practices and Their Implications for Numerical Weather Prediction and Remote Sensing

Abstract: Radiosonde humidity distributions over the United States, Canada, and Europe are discussed. Striking dry-end and wet-end differences are caused by the lack of international standards in the transformation of relative humidity observations to dewpoint depression and in differing ways of calibrating data taken from the same type of instrument. Differences in sondes used in these regions are also discussed and an example of a dual ascent is shown. Some implications for remote sensing and weather prediction are highlighted.

African Rainfall as a Precursor of Hurricane-Related Destruction on the U.S. East Coast

Abstract: This paper describes a predictive relationship between West African rainfall and U.S. hurricane-spawned destruction, which is based on information for the 42-yr period 1949–90. It is shown that above-average rainfall during the previous year along the Gulf of Guinea, in combination with above-average rainfall in the western Sahel during June and July, is linked to hurricane-spawned destruction along the U.S. East Coast occurring after 1 August, which is 10–20 times greater than in years when pre-1 August precipitation for these West African regions is below average. Similar hurricane-spawned damage along the U.S. Gulf Coast shows only a negligible relationship with African rainfall. Hurricane-caused deaths for both U.S. coastal regions also show a similar association with West African rainfall.

The boardman regional flux experiment

Abstract: A field campaign was carried out near Boardman, Oregon, to study the effects of subgrid-scale variability of sensible- and latent-heat fluxes on surface boundary-layer properties. The experiment involved three U.S. Department of Energy laboratories, one National Oceanic and Atmospheric Administration laboratory, and several universities. The experiment was conducted in a region of severe contrasts in adjacent surface types that accentuated the response of the atmosphere to variable surface forcing. Large values of sensible-heat flux and low values of latent-heat flux characterized a sagebrush steppe area; significantly smaller sensible-heat fluxes and much larger latent-heat fluxes were associated with extensive tracts of irrigated farmland to the north, east, and west of the steppe. Data were obtained from an array of surface flux stations, remote-sensing devices, an instrumented aircraft, and soil and vegetation measurements. The data will be used to address the problem of extrapolating from a limited n...

Nonfederal automated weather stations and networks in the United States and Canada : a preliminary survey

Abstract: Not all weather data are collected by federal agencies. Fueled by the need for more specific meteorological data in real or near-real time, the number of automated weather stations (AWSs) and AWS n...

In Situ Meteorological Sounding Archives for Arctic Studies

Abstract: Two new databases containing Arctic in situ meteorological soundings have been constructed and are now available for distribution to interested researchers. The Historical Arctic Rawinsonde Archive is a comprehensive collection of over l.2 million rawinsonde soundings north of 65°N.For most stations the record begins in l958 and extends to 1987; however, for some stations the record begins as early as 1948. The Ptarmigan Dropsonde Archive contains more than 10000 lower-tropospheric soundings over the Beaufort Sea and western Arctic Ocean during the period 1950– 1961.

How Agribusiness Uses Climate Predictions: Implications for Climate Research and Provision of Predictions

Abstract: The paper presents an analysis of climate prediction needs and uses within six important subsegments of the agribusiness sector. Results are based on a mail survey of 114 managers. Although nearly 70% of the respondents indicated some use of climate predictions in the last year, only 1 in 8 of the respondents used that information in a specific decision. Lack of sufficient accuracy and prediction lead time were identified as two important impediments to current use of climate predictions. Estimates of necessary accuracy levels and lead time are reported both for the group average and by segments of need. Recommendations are offered regarding research needs to enhance climate prediction and activities of the government and the private sector to improve use of climate predictions.

Is There Any Hope for Tropical Cyclone Intensity Prediction?—A Panel Discussion

Abstract: The outlook for tropical cyclone intensity forecasts from operational and from research perspectives was discussed during a panel discussion at the 19th Conference on Hurricanes and Tropical Meteorology. Whereas the operational requirement at the National Hurricane Center is to predict maximum 1-min sustained wind speeds at specific locations, the research community is addressing the prediction of the maximum wind or minimum sea level pressure in the storm. Commonality was found in the forecast strategies for subjectively predicting storm intensity. The panelists suggested improvements may be gained from additional observations, better conceptual and theoretical models of storm structure and behavior, and enhancements in statistical and numerical models. The discussion period brought out opposing viewpoints on a number of topics. Both new observations and better use of the existing observations were believed to be necessary. The limitations and advantages of remotely sensed data for this problem were rais...

Recent great lakes ice trends

Abstract: Analysis of ice observations made by cooperative observers from shoreline stations reveals significant changes in the ice season on the North American Great Lakes over the past 35 years. Although the dataset is highly inhomogeneous and year-to-year variability is also quite large, there is a statistically significant indication that the end of the ice season (as defined by the time at which ice departs from the observer stations in spring) has come increasingly early at a number of locations. The earlier ice departure is reflected in a somewhat earlier spring runoff through the St. Lawrence River over the same time period and correlates with increases in springtime temperatures at stations in the region. This example of a trend toward warmer, earlier springs in the upper Midwest is consistent with results from a number of other regional datasets. Because the ice observations began in the mid-1950s, other analyses, including comparisons with modern satellite datasets, could provide a useful tool for monito...

Preparing for the AMSU

Abstract: The Advanced Microwave Sounding Unit (AMSU) is a 20-channel microwave satellite remote-sensing system comprising two separate radiometers, which is slated to be launched on NOAA polar-orbiting satellites beginning in 1994. With the AMSU will come improvements in remote sounding of the atmosphere and estimation of atmospheric and surface physical characteristics (rain and cloud water, snow and ice cover, etc.) gained through application of the dramatic improvements in microwave technology that have taken place in the past 20 years. In this work we describe prelaunch work designed to evaluate the remote-sensing information that will be available with the launch of the AMSU.

The North Dakota Thunderstorm Project: A Cooperative Study of High Plains Thunderstorms

Abstract: The North Dakota Thunderstorm Project was conducted in the Bismarck, North Dakota, area from 12 June through 22 July 1989. The project deployed Doppler radars, cloud physics aircraft, and supporting instrumentation to study a variety of aspects of convective clouds. These included transport and dispersion; entrainment; cloud-ice initiation and evolution; storm structure, dynamics, and kinematics; atmospheric chemistry; and electrification. Of primary interest were tracer experiment that identified and tracked specific regions within evolving clouds as a means of investigating the transport, dispersion, and activation of ice-nucleating agents as well as studying basic transport and entrainment processes. Tracers included sulfur hexafluoride (SF6), carbon monoxide, ozone, radar chaff, and silver iodide. Doppler radars were used to perform studies of all scales of convection, from first-echo cases to a mesoscale convective system. An especially interesting dual-Doppler study of two splitting thunder...

An Examination of Four-Dimensional Data-Assimilation Techniques for Numerical Weather Prediction

Abstract: Four-dimensional data-assimilation methods, along with the most commonly used objective analysis and initialization techniques, are examined from a historical perspective. Operational techniques, including intermittent data assimilation and Newtonian nudging, and next-generation methods (Kalman–Bucy filtering and the adjoint method) are briefly described. Several methods are compared, with primary emphasis being placed on recent papers dealing with the operational assimilation techniques. Ongoing and future research is outlined, and some important implications of this research are discussed.

Global warming - A reduced threat

Abstract: Issues associated with global warming are analyzed focusing on global and hemispheric temperature histories and trace gas concentrations; artificial warming from urban heat islands; high-latitude and diurnal temperatures; recent climate models; direct effects on vegetation of an increase in carbon dioxide; and compensatory cooling from other industrial products. Data obtained indicate that anthropogenerated sulfate emissions are mitigating some of the warming, and that increased cloudiness as a result of these emissions will further enhance night, rather than day, warming. It is noted that the sulfate emissions are not sufficient to explain all of the night warming. The sensitivity of climate to anthropogenerated aerosols, and the general lack of previously predicted warming, could drastically alter the debate on global warming in favor of less expensive policies. 61 refs.