Showing papers in "Bulletin of the American Meteorological Society in 1991"

ISCCP Cloud Data Products

Abstract: The operational data collection phase of the International Satellite Cloud Climatology Project (ISCCP) began in July 1983. Since then, visible and infrared images from an international network of weather satellites have been routinely processed to produce a global cloud climatology. This report outlines the key steps in the data processing, describes the main features of the data products, and indicates how to obtain these data. We illustrate some early results of this analysis.

The Polarization Lidar Technique for Cloud Research: A Review and Current Assessment

Abstract: The development of the polarization lidar technique is reviewed, and the current capabilities and limitations of the technique for the cloud research are discussed. At present, polarization lidar is a key component of climate-research programs designed to characterize the properties of cirrus clouds and is an integral part of multiple remote-sensor studies of mixed-phase cloud systems such as winter mountain storms, making it possible to discriminate between cloud phases and to identify some particle types and orientations. Recent theoretical approaches involving ice crystal ray-tracing and cloud microphysical-model simulations are expected to increase the utility of the polarization lidar technique.

On the Utility of Radiosonde Humidity Archives for climate studies

Abstract: This paper considers the use of upper-air data from radiosondes in long-term climate studies. The accuracy and precision of radiosonde humidity measurements, including temperature and pressure measurements used in calculating them, and their effects on the precision of reported and derived variables are estimated. Focusing on the U.S. radiosonde system, we outline the history of changes in instruments and reporting practices and attempt to assess the implications of such changes for studies of temporal variations in lower-tropospheric water vapor. Changes in biases in the data are highlighted, as these can lead to misinterpretation of climate change. We conclude that the upper-air data record for the United States is not homogeneous, especially before 1973. Because of problems with the humidity data in cold, dry conditions, the water vapor climatology in the upper troposphere, nominally above the 500-mb level, is not well known.

TOGA-TAO: A Moored Array for Real-time Measurements in the Tropical Pacific Ocean

Abstract: The importance of the EI Nino-Southern Oscillation phenomenon in year-to-year fluctuations of the global climate has led to efforts to improve the real-time ocean observing system in the tropical Pacific. One element of this improved system is the TOGA-TAO (Tropical Atmosphere-Ocean) Array of wind and upper ocean thermistor chain moorings. This array, the result of an international effort, has I already provided the rudiments of a basin-wide, real-time observing system and plans call for a major enhancement during the second half of the TOGA decade. The development of the TAO array is discussed, recent results from the pilot measurements are described, and plans for the expanded array are presented.

Overcoming Biases of Precipitation Measurement: A History of the USSR Experience

Abstract: Documenting the instrumentally observed precipitation climate record presents many challenges because scientists must rely on data from stations that undergo many changes in the course of their operation. Detecting changes from such networks is essential for adequate understanding of climate and global change. As an illustrative example, we review the history of the instrumentally observed precipitation in the USSR. In the USSR, similar to other countries, numerous problems must be addressed before reliable estimates of precipitation can be made. The types of problems range from inadequate and changing exposures of raingages to varying sampling periods used to measure precipitation. Using information about measurement procedures, instrument intercomparisons, and field studies, various methods have been devised to overcome biases in the measurements.

Effects of Recent Thermometer Changes in the Cooperative Station Network

Abstract: During the past five years, the National Weather Service (NWS) has replaced over half of its liquid-in-glass maximum and minimum thermometers in wooden Cotton Region Shelters (CRSs) with thermistor-based Maximum–Minimum Temperature Systems (MMTSs) housed in smaller plastic shelters. Analyses of data from 424 (of the 3300) MMTS stations and 675 CRS stations show that a mean daily minimum temperature change of roughly +0.3°C, a mean daily maximum temperature change of−0.4°C, and a change in average temperature of −0.1 °C were introduced as a result of the new instrumentation. The change of −0.7°C in daily temperature range is particularly significant for climate change studies that use this element as an independent variable. Although troublesome for climatologists, there is reason to believe that this change (relative to older records) represents an improvement in absolute accuracy. The bias appears to be rather sharp and well defined. Since the National Climatic Data Center (NCDC) station history database...

The Radiative Effects of Clouds and their Impact on Climate

Abstract: Our knowledge of the direct role of clouds in long-term climate change is examined in an overview of key results published over the last 15 or 20 years, along with some relevant unpublished model studies. The focus is on 1) the impact of clouds on the incoming and outgoing radiation at the top of the atmosphere, and 2) the two-way interaction of clouds with other variables of the climate system—i.e., the cloud/climate feedback problem—as revealed by climate model simulations. A common framework is established for comparing results from different investigations. The total effect of clouds on radiative fluxes at the top of the atmosphere—specifically, the difference in flux between average conditions and cloud-free conditions, often called cloud forcing–has been derived from earth radiation budget measurements by several investigators using various data sources and methods. There is general agreement that the annual global mean effect of clouds is to cool the climate system, but there is significant disagre...

The Monsoon Year — A New Concept of the Climatic Year in the Tropics

Abstract: The concept of “monsoon year” is proposed as a unit year of climatic anomalies (i.e., the climatic year) in the tropics. This monsoon year is defined as one year starting just before the northern summer monsoon season. It is also argued that this climatic year in the tropics is physically based upon the characteristic nature of the coupled ocean/land/atmosphere system over the Asian monsoon/Pacific Ocean sector.

An Interdisciplinary Field Study of the Energy and Water Fluxes in the Atmosphere–Biosphere System over Semiarid Rangelands: Description and Some Preliminary Results

Abstract: Arid and semiarid rangelands comprise a significant portion of the earth's land surface. Yet little is known about the effects of temporal and spatial changes in surface soil moisture on the hydrologic cycle, energy balance, and the feedbacks to the atmosphere via thermal forcing over such environments. Understanding this interrelationship is crucial for evaluating the role of the hydrologic cycle in surface-atmosphere interactions. This study focuses on the utility of remote sensing to provide measurements of surface soil moisture, surface albedo, vegetation biomass, and temperature at different spatial and temporal scales. Remote-sensing measurements may provide the only practical means of estimating some of the more important factors controlling land surface processes over large areas. Consequently, the use of remotely sensed information in biophysical and geophysical models greatly enhances their ability to compute fluxes at catchment and regional scales on a routine basis. However, model cal...

Analysis of Global Cloud Imagery from Multiple Satellites

Abstract: Synoptic images of the global cloud field have been created from infrared measurements taken aboard tour geostationary and two polar-orbiting platforms simultaneously observing the earth. A series of spatial and temporal interpolations together with data reliability criteria are used to composite data from the individual satellites into synoptic images of the global cloud pattern. The composite Global Cloud Imagery (GCI) have a horizontal resolution of about half a degree and a temporal resolution of 3 h, providing an unprecedented view of the earth's cloud field. Each composite image represents a nearly instantaneous snapshot of the global cloud pattern. Collectively, the composite imagery resolve, on a global basis, most of the variability associated with organized convection, including several harmonies of the diurnal cycle. The dense and 3-dimensional nature of the GCI make them a formidable volume of information to treat in a practical and efficient manner. To facilitate analysis of global c...

Static Stability—An Update

Abstract: Static stability should not be evaluated from the local lapse rate. There is a growing body of observations, such as within portions of mixed layers and forest canopies, showing that the whole sounding should be considered to evaluate stability. Air parcels can move across large vertical distances to create turbulence within regions that would otherwise have been considered stable or neutral according to classical local definitions. A nonlocal determination of static stability is presented that accounts for both the local lapse rate and for convective air parcels moving across finite distances. Such a method is necessary to properly estimate turbulence, dispersion, and vertical fluxes that affect our weather and climate forecasts. Teachers of introductory meteorology courses and textbook authors are encouraged to revise their static stability discussions to follow air parcel displacements from beginning to end.

The Potential Impacts of Climate Change on the Great Lakes

Abstract: Global climate change could have a significant impact on the Great Lakes. A number of studies of the potential effects of climate change on the Great Lakes were commissioned by the U.S. Environmental Protection Agency, using common scenarios of global warming derived mainly from general circulation models. These studies found that a doubling of carbon dioxide concentrations in the atmosphere could eventually lower Great Lakes water levels by 0.5 to 2.5m; reduce ice cover by 1 to 2 ½ months; lengthen shipping seasons while increasing shipping and dredging costs; reduce dissolved oxygen levels in shallow lake basins; and increase fish productivity. Measures should be taken in the near future to anticipate many of these impacts and mitigate their effects or avoid costly political issues.

The development of impact-oriented climate scenarios

Abstract: Appropriate scenarios of future climate must be developed prior to any assessment of the impacts of climate change. Information needed was examined in consultation with those having experience in scenario use. Most assessors require regional scenarios with a temporal resolution of one day and a spatial resolution of around 100 km. Scenarios should contain one or more of: 1) general descriptive statistics of the major climate elements, 2) information about climatic anomalies such as drought, 3) statistics on the frequency and probability of events exceeding particular thresholds, and 4) general synoptic information. Techniques of climate analysis currently available were reviewed for their suitability to meet these scenario needs. The techniques were divided into a series of modules: groups of similar analysis techniques providing scientifically sound pieces of required information. A series of linked modules then provides the complete scenario. One set of modules emphasizes process models, anothe...

Riding the crest : a tale of two wave experiments

Abstract: This paper gives a general overview of two ocean wave experiments. The experimental goals of the Surface Wave Processes Program (SWAPP) and of the Surface Wave Dynamics Experiment (SWADE) are quite different but complementary. In general terms, SWAPP is focused on local processes: principally wave breaking, upper mixed layer dynamics, and microwave and acoustic signatures of wave breaking. SWADE, on the other hand, is concerned primarily with the evolution of the directional wave spectrum in both time and space, improved understanding of wind forcing and wave dissipation, the effect of waves on the air-sea coupling mechanisms, and the radar response of the surface. Both programs acknowledge that wave dissipation is the weakest link in our understanding of wave evolution on the ocean. SWAPP takes a closer look at wave dissipation processes directly, while SWADE, with the use of fully non-linear (third generation) wave models and carefully measured wind forcing, provides an opportunity to study the effect o...

North American Rawinsonde Observations: Problems, Concerns, and a Call to Action

Abstract: Meteorologists, like most scientists, often use observational data assuming the necessary steps have been taken to ensure that the quality of the data has been properly controlled. Experience developing an archive of upper-air observations from historical and real-time data suggests that some of the steps necessary to assure the basic scientific integrity of these data have not, in fact, been taken. This is especially so in recent years, since the introduction of automation into data observing and processing. Some of the problems and issues related to the observation, collection, and archiving of upper-air data are discussed. The intent of this paper is to stimulate dialogue within the upper-air-data-user community about these issues so that appropriate action can be formulated and implemented.

A Recommended Specific Definition of “Resolution”

Abstract: 1991 b: Surface airtemperature response to increasing gJobal industrial productivity: A beneficial greenhouse effect? a: Effects of two and a half years of atmospheric CO2 enrichment on the root density distribution of three-year-oldsourorangetrees. 1991 b: Downward regulation of photosynthesis and growth at high CO2 levels: No evidehce for either phenomenon in three-year study of sour orange trees. a CO2\"fertilization effect of the terrestrial vegetation to the amplitude increase in atmospheric CO2 at Mauna Loa Ob-The annual variation of atmospheric CO2 concentration observed in the northern hemisphere. 1960: Accumulation of organic matter in a chronosequence of soils developed on wihd-blown sand in New Zealand. 1991: Root restriction as a factor in photosynthetic acclimation of cotton seedlings groWn in elevated carbon dioxide. The term, \"resolution,\" has been used in a wide variety of peer-reviewed publications to refer to the grid increment used in a model. For example, general circulation models (GCMs) are said to have a resolution of about 400 km by 400 km, when that scale more appropriately refers to the horizontal grid mesh. From sampling theory, it is well known, however, that at least two grid increments are required to represent data. Real information at scales smaller than two grid increments are erroneously aliased to larger scales. An illustration of this is presented in Pielke (1984, Fig. 10.7). Models such as GCMs, however, require additional grid resolution to adequately simulate meteorological processes as a result of serious computational inaccuracies at scales less than four grid increments (e.g., see Table 10.1, 10.2, and 10.3 in Pielke 1984). Some investigators suggest even more grid increments are needed for adequate simulations. Using these clarifications, resolution within a numerical model should refer to at least four times the grid interval. For instance, a GCM with 400 km by 400 km horizontal grid increments would have a resolution of no less than 1600 km by 1600 km. Diagnostic data (e.g., terrain) with sampling ata400-km interval would have a resolution of no better than 800 km.

The Equatorial Mesoscale Experiment (EMEX): An Overview

Abstract: During the Southern Hemisphere summer, an aircraft research program (EMEX: the Equatorial Monsoon Experiment) was conducted over the tropical ocean north of Australia to investigate the mesoscale convective systems in the monsoon flow. EMEX was conducted concurrently and in the same location as the Australian Monsoon Experiment (AMEX) and the Stratosphere-Troposphere Exchange Program (STEP). Airborne Doppler radar and other aircraft instrumentation were used to document the horizontal and vertical air motions in ten major cloud systems. The EMEX airborne platforms were supplemented by a surface Doppler radar and the enhanced AMEX upper-air sounding network. The data obtained should significantly enhance the knowledge of vertical motions in tropical clouds and thereby lead to a better understanding of how these clouds influence the large-scale tropical circulation and climate. An overview of the project is given in which the weather situations are reviewed and examples of the data are shown. Some ...

Canadian Atlantic Storms Program: Progress and Plans of the Meteorological Component

Abstract: The Canadian Atlantic Storms Program (CASP) field project was conducted from 15 January to 15 March 1986 over Atlantic Canada in conjunction with the American Genesis of Atlantic Lows Experiment (GALE). The goals of CASP were to begin the process of understanding and eventually better predicting the mesoscale structure of East Coast storms as well as the storms themselves. Conceptual models of the storms have been formulated, the nature of cyclogenesis and the structure of frontal surfaces have been investigated, and precipitation regions and precipitation type transitions have been studied. Numerical weather simulations have been used to better understand critical parameters affecting storm behavior and improvements in instrumentation have been made. Future research activities are needed to better understand the interaction of the storms with surface features such as coastlines and sea ice.

Synoptic Frontal Analysis: Time for a Reassessment?

Abstract: For over a half-century, the Bergen School conceptual model of cyclone structure and development has dominated the practice of synoptic meteorology, especially regarding the techniques by which surface synoptic charts are analyzed. Although the Norwegian paradigm captures some of the essential features of cyclone evolution, research and practical application over the last 60-odd years have revealed significant deficiencies, several of which are discussed in this paper. The Bergen model has also been applied in regions and under conditions quite unlike those for which the model was originally developed. Knowledge of these problems by many in the research and operational communities has had little impact on the manner in which synoptic charts are analyzed or the way the subject is described in many textbooks. Deficiencies In the underlying conceptual model of cyclone development have been compounded by a lack of consistent and well-defined procedures for defining fronts and for analyzing surface sy...

Research on Clouds and Precipitation: Past, Present and Future, Part II.

Abstract: It is now thirty-four years since the 1st International Conference on Cloud Physics was held in Switzerland. The 1988 conference marks the tenth in this series of conferences. On this occasion it is perhaps appropriate to glance back to our origins, to reflect on the current situation, and to look to the future.

Response to Skeptics of Global Warming.

Abstract: The majority of the scientific community involved in climate research is convinced of the reality of a current and future global warming due to the greenhouse effect, a change that must be largely caused by human activities. However, a minority of scientists is still skeptical of the notion that mankind is significantly influencing the climate of the earth, and it therefore argues against taking certain measures to avert this alleged global warming. In recent years the media have given considerable coverage to the statements of these skeptics. Reasons for their statements range from a simple argument that we do not understand the earth's climate system well enough to predict the future, to more complex arguments involving negative feed-backs and changes of solar activity. They question whether the global temperature increase in this century of up to 0.6 K is primarily a result of worldwide burning of fossil fuels. The purpose of this article is to show that the statements of this skeptical school...

The Transition from the Present Radar Dissemination System to the NEXRAD Information Dissemination Service (NIDS)

Abstract: The National Weather Service (NWS) will begin replacing its current system of weather radars with Next Generation Weather Radars (NEXRAD) in late 1990. Presented is an overview of previous and current systems, and the replacement NEXRAD Information Dissemination Service (NIDS), for the dissemination of radar products to government and private users. The NIDS will be implemented and operated for the NWS by private sector data providers under a memorandum of agreement. The requirements of the NIDS, the suite of products to be provided, and its implementation milestones are described.

The Potential Impacts of Climate Change on the Great Lakes1

Abstract: Global climate change could have a significant impact on the Great Lakes. A number of studies of the potential effects of climate change on the Great Lakes were commissioned by the U.S. Environmental Protection Agency, using common scenarios of global warming derived mainly from general circulation models. These studies found that a doubling of carbon dioxide concentrations in the atmosphere could eventually lower Great Lakes water levels by 0.5 to 2.5m; reduce ice cover by 1 to 2 1/2 months; lengthen shipping seasons while increasing shipping and dredging costs; reduce dissolved oxygen levels in shallow lake basins; and increase fish productivity. Measures should be taken in the near future to anticipate many of these impacts and mitigate their effects or avoid costly political issues.

Assessment of the Role of Aircraft Reconnaissance on Tropical Cyclone Analysis and Forecasting

Abstract: The impact of aircraft reconnaissance on tropical cyclone (TC) observation and forecasting is assessed. The motivation for this assessment is the termination of Department of Defense (DOD) aircraft reconnaissance in the northwest Pacific in 1987 and the suggestion by some DOD officials that it may also be technically feasible to greatly reduce or similarly discontinue DOD aircraft reconnaissance in the Atlantic. In response thereto, the American Meteorological Society (AMS) Committee on Tropical Meteorology and Tropical Cyclones recommended that a specialized ad hoc group be formed to study the technical aspects of this issue. The resulting study presented here focuses on the issue of the extent to which reliable TC warnings can be continued along the United States hurricane-vulnerable coastline without observations from aerial reconnaissance and summarizes relevant information contained in recent studies prompted by the termination of reconnaissance in the western North Pacific. Primary attentio...

Multisensor Observation of an Atmospheric Undular Bore

Abstract: A detailed and unique multisensor observation of an undular bore is presented. The data include those from rawinsonde, satellite, two Doppler radars, and a tall instrumented tower. Noteworthy are Doppler radar images that resolve the wave's characteristics and capture a good part of its spatial extent. The basic parameters of the wave train are established from the observations.

Legacy of the Seasat mission for studies of the atmosphere and air-sea-ice interactions

Abstract: Studies of midlatitude and tropical cyclones and regional weather and climate analyses are examined. Consideration is also given to studies of long swell, sea ice, and continental ice sheets with Seasat data. Many of these results of the Seasat mission were serendipitous. In preparation for the major NASA initiative for the next decade, the Earth Observing Satellite program, it was thought timely to bring some of the Seasat experiences to the fore, since valuable lessons can be learned from the successes and the failures (or omissions) of the Seasat program. Data have been obtained about: (1) the synergistic value of integrated overlapping sampling by several instruments, (2) the invaluable contribution of carefully planned surface measurements, and (3) the importance of retaining flexibility in the system (enough data retention) to allow unexpected and innovative analysis techniques. 72 refs.