Bulletin of the American Meteorological Society

Published by American Meteorological Society

Online ISSN: 1520-0477


Print ISSN: 0003-0007


Research status and recommendations from the Alaska Workshop on Gravity Waves and Turbulence in the Middle Atmosphere, Fairbanks, Alaska, 18-22 July 1983
  • Article

March 1984


27 Reads






The Alaska Workshop on Gravity Waves and Turbulence in the Middle Atmosphere had as its purpose the assessment of current theoretical understanding and observational capabilities in this field, as well as to suggest what additional studies would further knowledge of these processes and their effects on the large scale circulation of the middle atmosphere. While it is judged that current understanding is primitive, theoretical and modelling studies are held to be able to contribute important quantitative data on gravity wave excitation, propagation, and dissipation mechanisms and effects. The combination of several observational systems is considered capable of expanding the present knowledge of gravity wave and turbulence morphology, parameters, and processes.

A video atlas of TOMS ozone data, 1978-88

January 1990


23 Reads

The Total Ozone Mapping Spectrometer (TOMS), on-board NASA's Nimbus-7 weather satellite, has been observing ozone over the earth once daily for the last 10 yr. A time-lapse atlas of 3440 color-coded images drawn from the TOMS archive from 1978 to 1988 has been visualized on a standard VHS videotape that is now available from NASA. The rapid and complex ozone variations presented demonstrate the difficulty of separating man-induced climate changes from natural variability. This article presents a few images from the atlas and describes interesting features in the animation, such as the correlation between ozone and 'the weather', and the recent deepening of the annual ozone hole over the South Pole. Originally intended as a browsing tool for the TOMS digital database, the videotape is a vivid presentation of the earth's atmospheric dynamics and chemistry that is recommended for scientists, educators, policy makers, and citizens concerned about the global environment.

Cloud-top Structure of Tornadic Storms on 10 April 1979 from Rapid Scan and Stereo Satellite Observations

November 1982


32 Reads

The cloud top structure of the Wichita Falls tornadic storm of 10 April 1979 (and other severe storms on this day) is studied using remotely-sensed observations from radar and satellite. A comprehensive data set included 3 min interval visible (0.6 μm) and infrared (11 μm) radiances from the eastern GOES and similar 30 min interval data from the western GOES. The near synchronization of these two satellites allowed for the stereoscopic determination of cloud top heights. In addition, at 2048 GMT, TIROS-N scanned the storms within one minute of the geosynchronous stereo and provided 1 km resolution infrared blackbody temperatures. Because internal storm dynamics are hidden from the view of the satellite, storm updraft intensity must be inferred from cloud-top minimum temperature and its rate of change. The Wichita Falls, Tex. tornadic storm could be defined in the satellite data by a point of minimum temperature which displayed temporal continuity and achieved a temperature of 208 K. A cloud-top cooling rate above the tropopause of 7 K/21 min preceded tornadogenesis. An adjacent warm area (221 K) developed downwind and was surrounded by a “V”-shaped pattern of lower temperatures. The warm area is postulated as due to subsidence in the lee of an ascending tower. The measured stereo height of the Wichita Falls storm was 15.6 km at 2349 GMT, 1.5 km higher than severe storms 150 km downwind, although its minimum blackbody temperature was 9 K higher than that of these downwind storms. In addition, unrealistic fluctuations in the time sequence of temperature 30 min prior to the Wichita Falls tornado indicate that the IR measurements are affected by sensor response and/or field of view limitations, at least close to the anvil edge. Cross sections of stereo heights, IR temperature, and radar reflectivity at 2349 GMT demonstrate that while there is, in general, a co-location of high tops, low temperatures, and high low-level radar reflectivity, significant variations can exist in height/rainfall relationships. A comparison of data sets at 2048 GMT between stereo height measurements and IR temperatures from GOES-East and TIROS-N revealed that anvil top features can be up to 10 K warmer in the GOES field of view (100 km2) than from TIROS-N (1 km2), and that this difference can reach 20 K for young thunderstorms, with perhaps 4 K explained by calibration differences. The lapse rate for tops penetrating the tropopause was substantially closer to the adiabatic lapse rate when TIROS-N temperature minima, rather than GOES minima, were plotted as a function of stereo determined height.

Meso beta-scale thunderstorm/environment interactions during AVE-SESAME V (20-21 May 1979)

November 1983


21 Reads

Meso β-scale rawinsonde data from the Atmospheric Variability Experiment-Severe Environmental Storms and Mesoscale Experiment (AVE-SESAME) V period (20–21 May 1979) are used to diagnose atmospheric variability in the environment of a convective area. As the storms developed, temperatures increased in the upper stratosphere; however, cooling was observed nearer to the surface and in the lower stratosphere. Height rises above 400 mb produced a mesohigh over the convective area that was most pronounced near 200 mb. Weaker height falls occurred in the lower troposphere. Wind patterns underwent especially interesting fluctuations. North of the convective area, upper-level winds increased significantly during storm development. Southeast of the convection, however, winds near 200 mb decreased approximately 50% during a 3 h period coinciding with the most active storms. On the other hand, winds at 400 mb almost doubled during the same 3 h period. Strong low-level convergence, upper-level divergence, and ascending motion developed after storm initiation. Much more detailed study is required to understand this fascinating case. However, many of the current findings about the meso β-scale storm environment are consistent with those previously attributed to feedback mechanisms from severe thunderstorms.

Earth Radiation Budget Experiment (ERBE) Archival and April 1985 Results

November 1989


27 Reads

This paper describes the Earth Radiation Budget Experiment (ERBE) data products being made available to the community. The Science Team used ten validation criteria to judge the acceptability of the data for archival. These criteria are listed, and uncertainty estimates based on them for four typical data products are presented. A brief description of the radiation budget for April 1985 from the combined data of ERBE and NOAA-9 concludes this paper.

The field project CLEOPATRA, May-July 1992 in southern Germany
  • Article
  • Full-text available

March 1993


37 Reads

CLEOPATRA (Cloud Experiment Oberpfaffenhofen and Transports) is described. This field program was performed in southern Germany 50 km north of the Alpine foothills, an area of known enhanced thunderstorm activity. The general goal is to quantify elements of the hydrological cycle on a regional scale in dependence upon precipitation events and the vegetation state. Embedded goals are to describe the mechanisms that force organizations of deep convective systems, to compare theories and observations of atmospheric depositions, and to test and compare observational methods from ground, aircraft, and space. The observational setup, including 10 research aircraft, four radar systems, and different ground-based networks, was operational from 11 May until 31 July 1992 to cover an essential period of the growing season.

Remote Sensing of Flooding in the U.S. Upper Midwest during the Summer of 1993

July 1995


21 Reads

The U.S. upper Midwest was subjected to severe flooding during the summer of 1993. Heavy rainfall in the Mississippi River basin from April through July caused flooding on many Midwest rivers, including the Mississippi, Illinois, Missouri, and Kansas Rivers. The flood crest of 15.1 m at St. Louis, Missouri, on 1 August 1993 was the highest ever measured, surpassing the previous record of 13.2 m set on 28 April 1973. Damage estimates include at least 47 flood-related deaths and a total damage cost of $12 billion. Remotely sensed imagery of severe flooding in the U.S. Midwest was obtained under cloud-free skies on 29 July 1993 by the MODIS (Moderate Resolution Imaging Spectroradiometer) Airborne Simulator (MAS). The MAS is a newly developed scanning spectrometer with 50 spectral bands in the wavelength range 0.55-14.3 micrometers. Estimation of the total flooded area in the MAS scene acquired near St. Louis was accomplished by comparing the MAS scene to a Landsat-5 thematic mapper (TM) scene of the same area acquired on 14 April 1984 in nonflood conditions. For comparison, the MAS band centered at 0.94 micrometers and the TM band centered at 1.65 micrometers were selected because of the high contrast seen in these bands between land and water-covered surfaces. An estimate of the area covered by water in the MAS and TM scenes was obtained by developing land/water brightness thresholds from histograms of the MAS and TM digital image data. Afetr applying the thresholds, the difference between the area covered by water in the MAS and TM scenes, and hence the flooded area in the MAS scene, was found to be about 396 sq km, or about 153 square miles.

The Amazon Boundary-Layer Experiment (ABLE 2B) - A meteorological perspective

February 1990


180 Reads

The Amazon Boundary-Layer Experiments (ABLE) 2A and 2B, which were performed near Manaus, Brazil in July-August, 1985, and April-May, 1987 are discussed. The experiments were performed to study the sources, sinks, concentrations, and transports of trace gases and aerosols in rain forest soils, wetlands, and vegetation. Consideration is given the design and preliminary results of the experiment, focusing on the relationships between meteorological scales of motion and the flux, transports, and reactions of chemical species and aerosols embedded in the atmospheric fluid. Meteorological results are presented and the role of the meteorological results in the atmospheric chemistry experiment is examined.

A Report on the Upper-Level Wind Conditions Preceding and During the Shuttle Challenger (STS 51L) Explosion

November 1986


60 Reads

The prelaunch, launch, and postlaunch synoptic-scale weather conditions on January 28, 1986 are described. Particular consideration is given to upper-level jet streams, vertical wind shear, and the possible effect of shear-induced turbulence on Cape Canaveral at the time of the Shuttle launch. General data revealing the relations between wind shear and turbulence and jet streams are discussed. The NWS operational and surface radiosonde data, visible and IR GOES imagery, and total ozone data obtained from TOMS on Nimbus-7 are analyzed. Numerical simulations of the weather conditions were conducted. The simulations and observational data are compared, and the data reveal the juxtaposition of two distinct jet-stream systems (a polar front jet and a subtropical jet) over north-central Florida the morning of the launch. Recommendations for improving the observing system at Cape Canaveral are discussed.

Meteorological applications of the Nimbus 4 Temperature-Humidity Infrared Radiometer, 6.7 Micron Channel Data

July 1972


39 Reads

Midtropospheric circulation features under essentially clear sky conditions have been noted in the data of the 6.7-micron channel of the Nimbus 4 temperature-humidity infrared radiometer (THIR), while at the same time these features were undetected by the 11.5-micron channel of the same instrument. The characteristic response of the 6.7-micron channel to atmospheric water vapor emission is primarily from the 250-mb (10.5 km) to 500-mb (5.5 km) levels with a peak contribution at 350 mb (8 km). Dry and moist patterns seen in the 6.7-micron data on Feb. 21, 1971, have been integrated into a 400-mb moisture analysis over the United States. This analysis provided more detailed and timely information than was conventionally available about the advection of dry air aloft prior to development of the Mississippi Tornado of February 1971.

A synoptic analysis of the first AVE-SESAME '79 period ( Texas).

December 1981


22 Reads

Fields of divergence, vertical motion, stability, and surface pressure tendency are examined at 3 h intervals for the first regional scale AVE-SESAME '79 (Atmospheric Variability Experiment—Severe Environmental Storms and Mesoscale Experiment) day. Two areas of severe storms formed during the period from 1200 GMT 10 April through 1200 GMT 11 April. The Red River Valley outbreak began during the afternoon of 10 April, while a second area formed in southwestern Texas during the early evening hours. Results show the rapid changes in environmental conditions associated with these two storm areas. The propagation of an upper level jet streak into the region was a major factor in producing the Red River Valley outbreak. This streak was associated with the formation of a strong low-level jet and a small-scale surface pressure perturbation. The sudden development of a strong upper tropospheric wind maximum over Oklahoma and Kansas corresponded with major changes in kinematic parameters at that level. Instability over the Red River Valley was released by strong upward motion producing intense convection. Similar features were responsible for the storms in southwestern Texas. Although this area was quite unstable, forcing mechanisms appear somewhat weaker than in the earlier outbreak.

NASA's participation in the AVE-SESAME '79 program

December 1979


10 Reads

NASA's Marshall Space Flight Center participated with its AVE (Atmospheric Variability Experiment) in a large interagency mesoscale and severe storms experiment identified herein as AVE-SESAME '79 (Atmospheric Variability Experiment-Severe Environmental Storms and Mesoscale Experiment 1979). A primary objective of NASA was to support an effort to acquire carefully edited sets of rawinsonde data during selected severe weather events for use in correlative and diagnostic studies with satellite and radar data obtained at approximately the same times. Data were acquired during six individual 24-h experiments on both the regional and storm scales over a network in the central United States that utilized approximately 20 supplemental rawinsonde sites meshed among 23 standard National Weather Service sites. Included among the six experiments are data obtained between 1200 GMT on April 10 and 1200 GMT on April 11, encompassing the formation and development period for the tornado-producing systems that devastated Wichita Falls, Texas, and other sections of Oklahoma and Texas. The other dates for which data sets are available are April 19-20 and 25-26, May 9-10 and 20-21, and June 7-8, 1979.

An Analysis of the “Blizzard of '88”

December 1983


21 Reads

The analysis of the blizzard, an intense cyclone that was accompanied by unusually heavy snowfall, high winds, and cold temperatures, is carried out using a collection of detailed surface weather observations. It follows the cyclone from its genesis along a slow-moving frontal system through its rapid development and occlusion along the Middle Atlantic and southern New England coasts. Unusual aspects of the cyclone are discussed. Among these are the limited areal extent of heavy snow accumulations, the establishment of very cold air across western New England and the Middle Atlantic states, a persistent stationary front zone across central New England that separated frigid continental air from maritime air, and the slow movement and rapid warming associated with the decay of the storm.

FIG. 1. (top) Spatial distribution of the 12 133 ground flashes (red dots) that had no QA alerts, no TAC , 140, and no positive peak currents below 15 kA; the 4752 green dots are ground flashes that also passed these filters but were removed because they fell outside of the spatial mask. (bottom) There are 107 246 cloud flashes (red dots) that had no QA alerts and no TAC , 140; a total of 75 830 cloud flashes are outside the mask (green dots).
TABLE 1 . Summary of OTD data classification and filtering.
FIG. 2. The distributions of (top) flash radiance and (bottom) flash area for (left) ground flashes and (right) cloud flashes.
TABLE 2 . A summary of the mean, median, and standard deviation ratios.
FIG. 3. The distributions of flash duration for (left) ground flashes and (right) cloud flashes. (bottom) The results when the ''zero'' duration (single frame flashes) are removed; see the text for a discussion.


Observations of Optical Lighting Emissions from above Thunderstorms Using U-2 Aircraft

March 1983


224 Reads

In order to determine how to achieve orders of magnitude improvement in spatial and temporal resolution and in sensitivity of satellite lightning sensors, better quantitative measurements of the characteristics of the optical emissions from lightning as observed from above tops of thunderclouds are required. A number of sensors have been developed and integrated into an instrument package and flown aboard a NASA U-2 aircraft. The objectives have been to acquire optical lightning data needed for designing the lightning mapper sensor, and to study lightning physics and the correlation of lightning activity with storm characteristics. The instrumentation and observations of the program are reviewed and their significance for future research is discussed.

On-Line Access to Weather Satellite Imagery and Image Manipulation Software

July 1995


28 Reads

Advanced Very High Resolution Radiometer and Geostationary Operational Environmental Satellite Imagery, received by antennas located at the University of Colorado, are made available to the Internet users through an on-line data access system. Created as a 'test bed' data system for the National Aeronautics and Space Administration's future Earth Observing System Data and Information System, this test bed provides an opportunity to test both the technical requirements of an on-line data system and the different ways in which the general user community would employ such a system. Initiated in December 1991, the basic data system experienced four major evolutionary changes in response to user requests and requirements. Features added with these changes were the addition of on-line browse, user subsetting, and dynamic image processing/navigation. Over its lifetime the system has grown to a maximum of over 2500 registered users, and after losing many of these users due to hardware changes, the system is once again growing with its own independent mass storage system.

An Analysis of Three Weather-Related Aircraft Accidents

December 1977


72 Reads

Two aircraft accidents in 1975, one at John F. Kennedy International Airport in New York City on 24 June and the other at Stapleton International Airport in Denver on 7 August, were examined in detail. A third accident on 23 June 1976 at Philadelphia International Airport is being investigated. Amazingly, there was a spearhead echo just to the north of each accident site. The echoes formed from 5 to 50 min in advance of the accident and moved faster than other echoes in the vicinity. These echoes were photographed by National Weather Service radars, 130-205 km away. At closer ranges, however, one or more circular echoes were depicted by airborne and ground radars. These cells were only 3-5 km in diameter, but they were accompanied by downdrafts of extreme intensity, called downbursts. All accidents occurred as aircraft, either descending or climbing, lost altitude while experiencing strong wind shear inside downburst cells.

Omega windfinding system designed to meet accuracy requirements of GARP Atlantic Tropical Experiment

October 1973


9 Reads

Illustrations of high sferics content Omega data are presented and techniques for recovering the true Omega phase data are discussed. A description is given of the design and the operation of the hardware preprocessor developed to extract the true Omega phase data from the received signals. The software developed to compute upper-air winds from high sferics content data is discussed together with the program conducted to establish the validity of the system.

Sea Surface Winds—A Critical Input to Oceanic Models, but Are They Accurately Measured?

February 1995


8 Reads

Wind, driving oceans, and the links between them to the atmosphere compose a critical parameter for the world circulation model as well as for the evaluation of climate changes. Traditionally, wind velocities have been reported by ships of oppurtunity and recorded on a network of buoys; they have also recently been generated by numerical weather prediction models and mapped with spaceborne remote sensors. Wind speeds from buoy measurements, ship observations, and model computations are compared, using the globally available altimeter returns that they have in common. Large, systematic deviations are found among the results obtained with these techniques, cautioning against use of these wind speeds.

THE I3RC: Bringing Together the Most Advanced Radiative Transfer Tools for Cloudy Atmospheres

September 2005


525 Reads

The interaction of clouds with solar and terrestrial radiation is one of the most important topics of climate research. In recent years it has been recognized that only full three-dimensional (3D) treatment of this interaction can provide answers to many climate and remote sensing problems, leading to worldwide development of numerous 3D radiative transfer (RT) codes. The international "Intercomparison of 3-Dimensional Radiation Codes," or I3RC, described in this paper, sprung from the natural need to compare the performance of these 3D RT codes used in a variety of current scientific work in the atmospheric sciences. I3RC supports intercomparison and development of both exact and approximate 3D methods in its effort to (1) understand and document the errors/limits of 3D algorithms and their sources; (2) provide "baseline" cases for future code development for 3D radiation; (3) promote sharing and production of 3D radiative tools; (4) derive guidelines for 3D radiative tool selection; and (5) improve atmospheric science education in 3D RT. Results from the two completed phases of I3RC have been presented in two workshops and are expected to guide improvements in both remote sensing and radiative energy budget calculations in cloudy atmospheres.

FIG. 1. The role of water vapor in the earth's atmosphere.  
FIG. 2. Conceptual drawing of the DIAL principle.  
FIG. 5. Comparison of the vertical extent of WALES (top blue curve), AIRS (middle red curve), and radiosonde observations (RAOB; bottom green curve) based on simulations from a 90°S–90°N cross section valid 24 May 2001 at 0600 UTC.  
Major Advances Foreseen in Humidity Profiling from the Water Vapour Lidar Experiment in Space (WALES)

February 2004


532 Reads

The need for an absolute standard for water vapor observations, in the form of a global dataset with high accuracy and good spatial resolution, has long been recognized. The European Space Agency's Water Vapour Lidar Experiment in Space (WALES) mission aims to meet this need by providing high-quality water vapor profiles, globally and with good vertical resolution, using a differential absorption lidar (DIAL) system in a low earth-orbit satellite. WALES will be the first active system to measure humidity from space routinely. With launch envisaged in the 2008 2010 time frame and a minimum duration of two years, the primary mission goals are to (a) contribute to scientific research and (b) demonstrate the feasibility of longer-term operational missions. This paper assesses the benefits of the anticipated data to NWP through quantitative analysis of information content. Good vertical resolution and low random errors are shown to give substantial improvements in analysis error in one-dimensional variational data assimilation (1DVAR) comparisons with advanced infrared sounders. In addition, the vertical extent of the profiles is shown to reach 16.5 km or 100 hPa, well above the limit of radiance assimilation (13 km or 200 hPa). Also highlighted are important applications in atmospheric sciences and climate research that would benefit from the low bias promised by spaceborne DIAL data and their complemen-tarity to other types of humidity observations.

Design and Implementation of a Prototype Data System for Earth Radiation Budget, Cloud, Aerosol, and Chemistry Data

May 1993


36 Reads

Activities at the NASA Langley Research Center's distributed active archive centers (DAACs) intended to capitalize on existing centers of scientific expertise and to prevent a single point of failure are described. A Version 0 Langley DAAC, a prototype of an Earth Observing System Data and Information System, started archiving and distributing existing datasets on the earth's radiation budget, clouds, aerosols, and tropospheric chemistry in late 1992. The major goals of the LaRC Version 0 effort include to enhance scientific use of existing data; to develop institutional expertise in maintaining and distributing data; to encourage cooperative interagency and international involvement with datasets and research; and to use institutional capability for processing data from previous missions to prepare for processing the future EOS satellite data.

The Life Cycle of Stratospheric Aerosol Particles

August 1997


278 Reads

This paper describes the life cycle of the background (nonvolcanic) stratospheric sulfate aerosol. The authors assume the particles are formed by homogeneous nucleation near the tropical tropopause and are carried aloft into the stratosphere. The particles remain in the Tropics for most of their life, and during this period of time a size distribution is developed by a combination of coagulation, growth by heteromolecular condensation, and mixing with air parcels containing preexisting sulfate particles. The aerosol eventually migrates to higher latitudes and descends across isentropic surfaces to the lower stratosphere. The aerosol is removed from the stratosphere primarily at mid- and high latitudes through various processes, mainly by isentropic transport across the tropopause from the stratosphere into the troposphere.

Improving National Air Quality Forecasts with Satellite Aerosol Observations

October 2005


2,937 Reads

Accurate air quality forecasts can allow for mitigation of the health risks associated with high levels of air pollution. During September 2003, a team of NASA, NOAA, and EPA researchers demonstrated a prototype tool for improving fine particulate matter (PM(sub 2.5)) air quality forecasts using satellite aerosol observations. Daily forecast products were generated from a near-real-time fusion of multiple input data products, including aerosol optical depth (AOD) from the Moderate Resolution Imaging Spectroradiometer (MODIS)/Earth Observing System (EOS) instrument on the NASA Terra satellite, PM (sub 2.5) concentration from over 300 state/local/national surface monitoring stations, meteorological fields from the NOAA/NCEP Eta Model, and fire locations from the NOAA/National Environmental Satellite, Data, and Information Service (NESDIS) Geostationary Operational Environmental Satellite (GOES) Wildfire Automated Biomass Burning Algorithm (WF_ABBA) product. The products were disseminated via a Web interface to a small group of forecasters representing state and local air management agencies and the EPA. The MODIS data improved forecaster knowledge of synoptic-scale air pollution events, particularly over oceans and in regions devoid of surface monitors. Forecast trajectories initialized in regions of high AOD offered guidance for identifying potential episodes of poor air quality. The capability of this approach was illustrated with a case study showing that aerosol resulting from wildfires in the northwestern United States and southwestern Canada is transported across the continent to influence air quality in the Great Lakes region a few days later. The timing of this demonstration was selected to help improve the accuracy of the EPA's AIRNow (www.epa.gov/airnow/) next-day PM(sub 2.5) air quality index forecast, which began on 1 October 2003. Based on the positive response from air quality managers and forecasters, this prototype was expanded and transitioned to an operational provider during the summer of 2004. (copyright) 2005 American Meteorological Society.

Satellite Studies of the Stratospheric Aerosol

October 1979


29 Reads

The potential climatological and environmental importance of the stratospheric aerosol layer has prompted interest in measuring the properties of this aerosol. This paper reports on two recently deployed NASA satellite systems (SAM II and SAGE) that are monitoring the stratospheric aerosol. The satellite orbits obtain nearly global coverage. The instruments mounted in the spacecraft are sun photometers that measure solar intensity at specific wavelengths as it is moderated by atmospheric particulates and gases during each sunrise and sunset encountered by the satellites. Latitudinal, longitudinal, and temporal variations in the aerosol layer are evaluated. The satellite systems are being validated by a series of ground truth experiments using airborne and ground lidar, balloon-borne dustsondes, aircraft-mounted impactors, and other correlative sensors. The SAM II and SAGE satellite systems, instrument characteristics, and mode of operation are described; the methodology of the experiments is outlined; and the ground truth experiments are discussed. Preliminary results from these measurements are presented.

Quantifying and Minimizing Uncertainty of Climate Forcing by Anthropogenic Aerosols

April 1993


52 Reads

The clear-sky climate forcing by anthropogenic aerosols was shown to be of sufficient magnitude to mask the effects of anthropogenic greenhouse gases over large regions. Anthropogenic aerosols are composed of a variety of aerosol types including water-soluble inorganic species (e.g., sulfate, nitrate, ammonium), organic condensed species, elemental or black carbon, and mineral dust. Estimates of the clear-sky forcing by anthropogenic sulfate aerosols and by organic biomass-burning aerosols were published previously. The uncertainty in the forcing by these aerosol types is estimated. Estimates of the clear-sky forcing by other anthropogenic aerosol types do not even exist though the forcing by these aerosol types is thought to be smaller than that by sulfate and biomass burning aerosols.

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