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M. Halem, E. Kalnay, W. E. Baker, and R. Atlas

This study investigates the degree to which data from the space-borne FGGE observing systems are able to determine the complete state of the atmosphere when incorporated into a global objective analysis cycle. Three data assimilation experiments are performed with the Goddard Laboratory for Atmospheric Sciences (GLAS) analysis/forecast system, using different combinations of the FGGE level II–b data collected during the first Special Observing Period (SOP-1), 5 January through 5 March 1979. The control experiment is an assimilation cycle with the complete FGGE II–b data. The other two assimilation/forecast experiments consist of i) the conventional system without the satellite data and special FGGE data sets; and ii) the FGGE II–b surface and satellite temperature soundings and cloud-track winds, aircraft data, and special FGGE data sets, but without the conventional rawinsonde/pilot balloon network.

From these experiments, we attempt to assess the accuracy of the inferred mass and motion fields over data-sparse regions, by examining their influence on analyses and forecasts over data-rich regions. The sensitivity of the analysis to the FGGE satellite data is shown by comparisons of the 6 h forecast error of the 300 mb geopotential height fields for these three experiments. It is found that large 6 h forecast errors downstream of data-sparse regions are reduced when the satellite observations are incorporated in the analysis. Forecast impact results from the initial states of these assimilation cycles show the geographical influence of the FGGE satellite observing system on short- to medium-range (two to five days) weather forecasting. Over North America and Europe, there is a small improvement in forecast skill from the use of the FGGE II–b data. Over Australia, as expected, the positive impact of satellite data is much larger. The number of skillful four- and five-day forecasts over North America and Europe has been increased substantially by the addition of the FGGE II–b data. Examples of useful eight-day forecasts, which occurred in periods of atmospheric blocking situations also are presented.

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G. K. Walker, Y. C. Sud, and R. Atlas

Numerical simulation experiments were conducted to delineate the influence of in situ deforestation data on episodic rainfall by comparing two ensembles of five 5-day integrations performed with a recent version of the Goddard Laboratory for Atmospheres GCM that has a simple biosphere model (SiB). The first set, called control cases, used the standard SiB vegetation cover (comprising 12 biomes) and assumed a fully forested Amazonia, while the second set, called deforestation cases, distinguished the partially deforested regions of Amazonia as savanna. Except for this difference, all other initial and prescribed boundary conditions were kept identical in both sets of integrations. The differential analyses of these five cases show the following local effects of deforestation.

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G. R. Gray, R. J. Serafin, D. Atlas, R. E. Rinehart, and J. J. Boyajian

Color enhancement of images has become a powerful tool in rapid evaluation of grey-scale information. Recent advances in semiconductor technology have made possible the construction of an inexpensive digital real-time color-enhanced (or false-color) display for meteorological radar information such as reflectivity and Doppler velocities. Variable magnification allows detailed analysis of selected areas of the radar coverage.

The display was interfaced to a Doppler/reflectivity processor on the NHRE S-band radar at Grover, Colorado, during the 1974 hail season. A preliminary meteorological analysis of the Doppler color displays of the storm of 7 August 1974 demonstrates a large variety of significant features which may be observed either in real-time or subsequently. These include the regions of convergence and vorticity, major inflow and outflow regions, and turbulence. Most importantly, it is shown that the updraft cores can be identified with the easterly-momentum air which has been transported upward with the drafts from the lower levels. In view of the slow eastward motion of the storm system, the very large Doppler components found at the leading edge of the higher-level echo pattern also indicate rapid evaporation of the particles as they move out into the clear, dry environmental air. It is the resulting evaporative cooling which is responsible for the downdrafts in this vicinity. Among the many real-time applications of the color Doppler display, perhaps the most important in the artificial modification of convective storms is the location of the major inflow and updraft regions. These determine where seeding should be focused. The use of the color display also permits the ready discrimination of storm echoes from ground clutter in which they are frequently obscured. Its applicability to the detection of tornado cyclones and hurricane velocity mapping is also self-evident.

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R. Atlas, R. N. Hoffman, S. C. Bloom, J. C. Jusem, and J. Ardizzone

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

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R. E. Carbone, D. Atlas, P. Eccles, R. Fetter, and E. Mueller

Results of the first real-time dual wavelength radar hail detection are given. The fundamental theoretical basis for detection is briefly discussed and preliminary qualitative conclusions are drawn as to the physical significance of the measurements. The results show that hail signatures gradually become more likely in regions of increasing reflectivity. The data support the concept of water storage in severe convective storms, but suggest that such regions are not necessarily accompanied by the growth of large hail.

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A. L. Conaty, J. C. Jusem, L. Takacs, D. Keyser, and R. Atlas

The realism of extratropical cyclones, fronts, jet streams, and the tropopause in the Goddard Earth Observing System (GEOS) general circulation model (GCM), implemented in assimilation and simulation modes, is evaluated from climatological and case-study perspectives using the GEOS-1 reanalysis climatology and applicable conceptual models as benchmarks for comparison. The latitude-longitude grid spacing of the datasets derived from the GEOS GCM ranges from 2° × 2.5° to 0.5° × 0.5°. Frontal systems in the higher-resolution datasets are characterized by horizontal potential temperature gradients that are narrower in scale and larger in magnitude than their lower-resolution counterparts, and various structural features in the Shapiro–Keyser cyclone model are replicated with reasonable fidelity at 1° × 1° resolution. The remainder of the evaluation focuses on a 3-month Northern Hemisphere winter simulation of the GEOS GCM at 1° × 1° resolution. The simulation realistically reproduces various large-scale circulation features related to the North Pacific and Atlantic jet streams when compared with the GEOS-1 reanalysis climatology, and conforms closely to a conceptualization of the zonally averaged troposphere and stratosphere proposed originally by Napier Shaw and revised by Hoskins. An extratropical cyclone that developed over the North Atlantic Ocean in the simulation features surface and tropopause evolutions corresponding to the Norwegian cyclone model and to the LC2 life cycle proposed by Thorncroft et al., respectively. These evolutions are related to the position of the developing cyclone with respect to upper-level jets identified in the time-mean and instantaneous flow fields. This article concludes with the enumeration of several research opportunities that may be addressed through the use of state-of-the-art GCMs possessing sufficient resolution to represent mesoscale phenomena and processes explicitly.

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R. Atlas, R. N. Hoffman, S. M. Leidner, J. Sienkiewicz, T.-W. Yu, S. C. Bloom, E. Brin, J. Ardizzone, J. Terry, D. Bungato, and J. C. Jusem

Satellite scatterometer observations of the ocean surface wind speed and direction improve the depiction of storms at sea. Over the ocean, scatterometer surface winds are deduced from multiple measurements of reflected radar power made from several directions. In the nominal situation, the scattering mechanism is Bragg scattering from centimeter-scale waves, which are in equilibrium with the local wind. These data are especially valuable where observations are otherwise sparse—mostly in the Southern Hemisphere extratropics and Tropics, but also on occasion in the North Atlantic and North Pacific. The history of scatterometer winds research and its application to weather analysis and forecasting is reviewed here. Two types of data impact studies have been conducted to evaluate the effect of satellite data, including satellite scatterometer data, for NWP. These are simulation experiments (or observing system simulation experiments or OSSEs) designed primarily to assess the potential impact of planned satellite observing systems, and real data impact experiments (or observing system experiments or OSEs) to evaluate the actual impact of available space-based data. Both types of experiments have been applied to the series of satellite scatterometers carried on the Seasat, European Remote Sensing-1 and -2, and the Advanced Earth Observing System-1 satellites, and the NASA Quick Scatterometer. Several trends are evident: The amount of scatterometer data has been increasing. The ability of data assimilation systems and marine forecasters to use the data has improved substantially. The ability of simulation experiments to predict the utility of new sensors has also improved significantly.

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EXECUTIVE COMMITTEE, C. L. Hosler, W. A. Baum, D. Atlas, P. M. Austin, E. S. Epstein, R. L. Leep Jr., K. C. Spengler, and D. F. Landrigan
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Laura L. Pan, Kenneth P. Bowman, Elliot L. Atlas, Steve C. Wofsy, Fuqing Zhang, James F. Bresch, Brian A. Ridley, Jasna V. Pittman, Cameron R. Homeyer, Pavel Romashkin, and William A. Cooper

The Stratosphere–Troposphere Analyses of Regional Transport 2008 (START08) experiment investigated a number of important processes in the extratropical upper troposphere and lower stratosphere (UTLS) using the National Science Foundation (NSF)–NCAR Gulfstream V (GV) research aircraft. The main objective was to examine the chemical structure of the extratropical UTLS in relation to dynamical processes spanning a range of scales. The campaign was conducted during April–June 2008 from Broomfield, Colorado. A total of 18 research flights sampled an extensive geographical region of North America (25°–65°N, 80°–120°W) and a wide range of meteorological conditions. The airborne in situ instruments measured a comprehensive suite of chemical constituents and microphysical variables from the boundary layer to the lower stratosphere, with flights specifically designed to target key transport processes in the extratropical UTLS. The flights successfully investigated stratosphere–troposphere exchange (STE) processes, including the intrusion of tropospheric air into the stratosphere in association with the secondary tropopause and the intrusion of stratospheric air deep into the troposphere. The flights also sampled the influence of convective transport and lightning on the upper troposphere as well as the distribution of gravity waves associated with multiple sources, including fronts and topography. The aircraft observations are complemented by satellite observations and modeling. The measurements will be used to improve the representation of UTLS chemical gradients and transport in Chemistry–Climate models (CCMs). This article provides an overview of the experiment design and selected observational highlights.

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Wayman E. Baker, Robert Atlas, Carla Cardinali, Amy Clement, George D. Emmitt, Bruce M. Gentry, R. Michael Hardesty, Erland Källén, Michael J. Kavaya, Rolf Langland, Zaizhong Ma, Michiko Masutani, Will McCarty, R. Bradley Pierce, Zhaoxia Pu, Lars Peter Riishojgaard, James Ryan, Sara Tucker, Martin Weissmann, and James G. Yoe

The three-dimensional global wind field is the most important remaining measurement needed to accurately assess the dynamics of the atmosphere. Wind information in the tropics, high latitudes, and stratosphere is particularly deficient. Furthermore, only a small fraction of the atmosphere is sampled in terms of wind profiles. This limits our ability to optimally specify initial conditions for numerical weather prediction (NWP) models and our understanding of several key climate change issues.

Because of its extensive wind measurement heritage (since 1968) and especially the rapid recent technology advances, Doppler lidar has reached a level of maturity required for a space-based mission. The European Space Agency (ESA)'s Atmospheric Dynamics Mission Aeolus (ADM-Aeolus) Doppler wind lidar (DWL), now scheduled for launch in 2015, will be a major milestone.

This paper reviews the expected impact of DWL measurements on NWP and climate research, measurement concepts, and the recent advances in technology that will set the stage for space-based deployment. Forecast impact experiments with actual airborne DWL measurements collected over the North Atlantic in 2003 and assimilated into the European Centre for Medium-Range Weather Forecasts (ECMWF) operational model are a clear indication of the value of lidar-measured wind profiles. Airborne DWL measurements collected over the western Pacific in 2008 and assimilated into both the ECMWF and U.S. Navy operational models support the earlier findings.

These forecast impact experiments confirm observing system simulation experiments (OSSEs) conducted over the past 25–30 years. The addition of simulated DWL wind observations in recent OSSEs performed at the Joint Center for Satellite Data Assimilation (JCSDA) leads to a statistically significant increase in forecast skill.

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