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Jeffrey Hawkins and Christopher Velden

Atmospheric and oceanographic field experiments are an important part of research programs aimed at enhancing observational analyses of meteorological and oceanic phenomena, validating new datasets, and/or supporting hypotheses. The Bulletin of the American Meteorological Society (BAMS) has chronicled many field programs, with a primary focus on the enhanced observational assets that were assembled to enable the projects' investigations. However, these field program summaries often overlook the multiple roles that satellite digital data, multispectral imagery, and derived products can play in premission planning, real-time forecasting and mission guidance, and extensive post–field phase analysis. In turn, these intensive observing periods often serve as crucial validation datasets for remotely sensed products and derived fields.

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Christopher S. Velden

Satellite imagery from the VISSR (Visible Infrared Spin Scan Radiometer) Atmospheric Sounder (VAS) 6.7-μm water-vapor absorption band is normally available to the National Hurricane Center (NHC) in real time (half-hourly intervals, 16 hours a day) through a remote Man-computer Interactive Data Access System (McIDAS) workstation located in the forecast center. Synoptic features that are not readily apparent in “visible” imagery or “11-μm-infrared” imagery are often well defined in the VAS “water-vapor” imagery with the help of special enhancement software that exists on McIDAS. A good example is Hurricane Elena (1985). Its erratic path in the Gulf of Mexico was responsible for the evacuation of nearly a million people in low-lying coastal areas during a three-day period. Imagery from the VAS 6.7-μm water-vapor channel clearly shows the interaction of a midlatitude trough with the hurricane, and supports other evidence that suggests this was responsible for altering Elena's course.

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Anthony J. Wimmers and Christopher S. Velden

Satellite-based passive microwave imagery of tropical cyclones (TCs) is an invaluable resource for assessing the organization and evolution of convective structures in TCs when often no other comparable observations exist. However, the current constellation of low-Earth-orbiting environmental satellites that can effectively image TCs in the microwave range make only semirandom passes over TC targets, roughly every 3 - 6 h, but vary from less than 30 min to more than 25 h between passes. These irregular time gaps hamper the ability of analysts/forecasters to easily incorporate these data into a diagnosis of the state of the TC. To address this issue, we have developed a family of algorithms called Morphed Integrated Microwave Imagery at the Cooperative Institute for Meteorological Satellite Studies (MIMIC) to create synthetic “morphed” images that utilize the observed imagery to fill in the time gaps and present time-continuous animations of tropical cyclones and their environment. MIMIC-TC is a product that presents a storm-centered 15-min-resolution animation of microwave imagery in the ice-scattering range (85–92 GHz), which can be interpreted very much like a ground-based radar animation. A second product, MIMIC-IR, animates a tropical cyclone-retrieved precipitation field layered over geostationary infrared imagery. These tools allow forecasters and analysts to use microwave imagery to follow trends in a tropical cyclone's structure more efficiently and effectively, which can result in higher-confidence short-term intensity forecasts.

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Jason P. Dunion and Christopher S. Velden

A deep well-mixed, dry adiabatic layer forms over the Sahara Desert and Shale regions of North Africa during the late spring, summer, and early fall. As this air mass advances westward and emerges from the northwest African coast, it is undercut by cool, moist low-level air and becomes the Saharan air layer (SAL). The SAL contains very dry air and substantial mineral dust lifted from the arid desert surface over North Africa, and is often associated with a midlevel easterly jet. A temperature inversion occurs at the base of the SAL where very warm Saharan air overlies relatively cooler air above the ocean surface. Recently developed multispectral Geostationary Operational Environmental Satellite (GOES) infrared imagery detects the SAL's entrained dust and dry air as it moves westward over the tropical Atlantic. This imagery reveals that when the SAL engulfs tropical waves, tropical disturbances, or preexisting tropical cyclones (TCs), its dry air, temperature inversion, and strong vertical wind shear (associated with the midlevel easterly jet) can inhibit their ability to strengthen. The SAL's influence on TCs may be a factor in the TC intensity forecast problem in the Atlantic and may also contribute to this ocean basin's relatively reduced level of TC activity.

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Steven J. Nieman, W. Paul Menzei, Christopher M. Hayden, Donald Gray, Steven T. Wanzong, Christopher S. Velden, and Jaime Daniels

Cloud-drift winds have been produced from geostationary satellite data in the Western Hemisphere since the early 1970s. During the early years, winds were used as an aid for the short-term forecaster in an era when numerical forecasts were often of questionable quality, especially over oceanic regions. Increased computing resources over the last two decades have led to significant advances in the performance of numerical forecast models. As a result, continental forecasts now stand to gain little from the inspection or assimilation of cloud-drift wind fields. However, the oceanic data void remains, and although numerical forecasts in such areas have improved, they still suffer from a lack of in situ observations. During the same two decades, the quality of geostationary satellite data has improved considerably, and the cloud-drift wind production process has also benefited from increased computing power. As a result, fully automated wind production is now possible, yielding cloud-drift winds whose quality and quantity is sufficient to add useful information to numerical model forecasts in oceanic and coastal regions. This article will detail the automated cloud-drift wind production process, as operated by the National Environmental Satellite Data and Information Service within the National Oceanic and Atmospheric Administration.

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Christopher S. Velden, Christopher M. Hayden, Steven J W. Nieman, W. Paul Menzel, Steven Wanzong, and James S. Goerss

The coverage and quality of remotely sensed upper-tropospheric moisture parameters have improved considerably with the deployment of a new generation of operational geostationary meteorological satellites: GOES-8/9 and GMS-5. The GOES-8/9 water vapor imaging capabilities have increased as a result of improved radiometric sensitivity and higher spatial resolution. The addition of a water vapor sensing channel on the latest GMS permits nearly global viewing of upper-tropospheric water vapor (when joined with GOES and Meteosat) and enhances the commonality of geostationary meteorological satellite observing capabilities. Upper-tropospheric motions derived from sequential water vapor imagery provided by these satellites can be objectively extracted by automated techniques. Wind fields can be deduced in both cloudy and cloud-free environments. In addition to the spatially coherent nature of these vector fields, the GOES-8/9 multispectral water vapor sensing capabilities allow for determination of wind fields over multiple tropospheric layers in cloud-free environments. This article provides an update on the latest efforts to extract water vapor motion displacements over meteorological scales ranging from subsynoptic to global. The potential applications of these data to impact operations, numerical assimilation and prediction, and research studies are discussed.

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Christopher S. Velden, William L. Smith, and Max Mayfield

Initial results are presented on research designed to evaluate the usefulness of Visible Infrared Spin Scan Radiometer Atmospheric Sounder (VAS) data in tropical cyclone applications. It is part of the National Aeronautics and Space Administration funded VAS demonstration, and the A/ational Oceanic and Atmospheric Administration (NOAA) Operational FAS Assessment (NOVA) program. The University of Wisconsin (UW) Space Science and Engineering Center (SSEC) and the National Environmental Satellite, Data, and Information Service (NESDIS) Development Laboratory at the SSEC have been working with the National Hurricane Center (NHC), and the NOAA/Environmental Research Laboratories Atlantic Oceanographic and Meteorological Laboratory—Hurricane Research Division (HRD) to explore the different uses of geostationary satellite VAS data in tropical cyclone analysis and forecasting. Because of the cloud-penetrating capability of the microwave component of the TIROS Operational Vertical Sounder (TOVS), polar orbiting satellite TOVS soundings in cloudy regions are used in some cases to enhance the VAS products along with cloud drift and water vapor motion winds derived from VAS imagery. This report describes some of the VAS/TOVS products being generated and evaluated on the Man-computer Interactive Data Access System (McIDAS) at the UW-SSEC and the NHC.

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Christopher Velden, Jaime Daniels, David Stettner, David Santek, Jeff Key, Jason Dunion, Kenneth Holmlund, Gail Dengel, Wayne Bresky, and Paul Menzel

The evolving constellation of environmental/meteorological satellites and their associated sensor technology is rapidly advancing. This is providing opportunities for creatively improving satellite-derived products used in weather analysis and forecasting. For example, the retrieval methods for deriving atmospheric motion vectors (AMVs) from satellites have been expanding and evolving since the early 1970s. Contemporary AMV processing methods are continuously being updated and advanced through the exploitation of new sensor technologies and innovative new approaches. It is incumbent upon the research community working in AMV extraction techniques to ensure that the quality of the current operational products meets or exceeds the needs of the user community. In particular, the advances in data assimilation and numerical weather prediction in recent years have placed an increasing demand on data quality.

To keep pace with these demands, innovative research toward improving methods of deriving winds from satellites has been a focus of the World Meteorological Organization and Coordination Group for Meteorological Satellites (CGMS) cosponsored International Winds Workshops (IWWs). The IWWs are held every 2 yr, and bring together AMV researchers from around the world to present new ideas on AMV extraction techniques, interpretation, and applications. The NWP community is always well represented at these workshops, which provide an important exchange of information on the latest in data assimilation issues. This article draws from recent IWWs, and describes several new advances in satellite-produced wind technologies, derivation methodologies, and products. Examples include AMVs derived from Geostationary Operational Environmental Satellite (GOES) rapid scans and the shortwave IR channel, AMVs over the polar regions from the Moderate Resolution Imaging Spectroradiometer (MODIS), improved AMV products from the new Meteosat Second Generation satellite, and new processing approaches for deriving AMVs. The article also provides a glimpse into the pending opportunities that will be afforded with emerging/anticipated new sensor technologies.

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Kerry Emanuel, Eugenia Kalnay, Craig Bishop, Russell Elsberry, Ronald Gelaro, Daniel Keyser, Steven Lord, David Rogers, Melvyn Shapiro, Christopher Snyder, and Christopher Velden

One of the most significant impediments to progress in forecasting weather over North America is the relative paucity of routine observations over data-sparse regions adjacent to the United States. Prospectus Development Team Seven was convened to consider ways to promote research that seeks to determine implementations of observing systems that are optimal for weather prediction in the United States. An “optimal” measurement system is considered to be one that maximizes the ratio of societal benefit to overall cost. The thrust of the conclusions is that existing means of estimating the value of current observing systems and the potential benefits of new or proposed observing systems are underutilized. At the same time, no rational way exists for comparing the cost of observations across the spectrum of federal agencies responsible for measuring the atmosphere and ocean. The authors suggest that a rational procedure for configuring an observation system that is optimal for weather prediction would consist of the following steps.

The authors believe that a rational approach to atmospheric measurement is critical to further improvements in weather prediction and that such improvements might very well be made within the current budget of routine observations, integrated across all of the responsible federal agencies. This document outlines a proposed strategy for rationalizing atmosphere observations in aid of weather prediction in the United States. The paper begins with a summary of recommendations.

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Johannes Schmetz, W. Paul Menzel, Christopher Velden, Xiangqian Wu, Leo van de Berg, Steve Nieman, Christopher Hayden, Kenneth Holmlund, and Carlos Geijo

This paper describes the results from a collaborative study between the European Space Operations Center, the European Organization for the Exploitation of Meteorological Satellites, the National Oceanic and Atmospheric Administration, and the Cooperative Institute for Meteorological Satellite Studies investigating the relationship between satellite-derived monthly mean fields of wind and humidity in the upper troposphere for March 1994. Three geostationary meteorological satellites GOES-7, Meteosat-3, and Meteosat-5 are used to cover an area from roughly 160°W to 50°E. The wind fields are derived from tracking features in successive images of upper-tropospheric water vapor (WV) as depicted in the 6.5-μ absorption band. The upper-tropospheric relative humidity (UTH) is inferred from measured water vapor radiances with a physical retrieval scheme based on radiative forward calculations.

Quantitative information on large-scale circulation patterns in the upper troposphere is possible with the dense spatial coverage of the WV wind vectors. The monthly mean wind field is used to estimate the large-scale divergence; values range between about −5 × 10−6 and 5 × 10−6 sec−1 when averaged over a scale length of about 1000–2000 km. The spatial patterns of the UTH field and the divergence of the wind field closely resemble one another, suggesting that UTH patterns are principally determined by the large-scale circulation.

Since the upper-tropospheric humidity absorbs upwelling radiation from lower-tropospheric levels and therefore contributes significantly to the atmospheric greenhouse effect, this work implies that studies on the climate relevance of water vapor should include threedimensional modeling of the atmospheric dynamics. The fields of UTH and WV winds are useful parameters for a climate-monitoring system based on satellite data. The results from this 1-month analysis suggest the desirability of further GOES and Meteosat studies to characterize the changes in the upper-tropospheric moisture sources and sinks over the past decade.

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