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William H. Raymond, Gary S. Wade, and Tom H. Zapotocny

Abstract

Imager channel 3 (at 6.7 μm) on the Geostationary Operational Environmental Satellite (GOES) is particularly sensitive to water vapor in the atmosphere. Channel-3 data from both clear and cloudy regions are used in a new assimilation scheme to improve the initial upper-tropospheric moisture fields for modeling and numerical weather prediction purposes. In this assimilation, the navigated and calibrated radiance (brightness temperature) observations from GOES are used in combination with a forward radiative transmittance model and a numerical optimization procedure to produce modifications to the upper-tropospheric moisture field. All modifications are made proportional to the contribution weighting function, which is associated with the forward radiative model. Cloudy regions are given special consideration. When processed by a forward radiative transfer model, the assimilated moisture fields are shown to correlate better with GOES observations both initially and in 24- and 48-h forecasts. Additional merits of the proposed assimilation technique, which does not require an adjoint or linearization, are discussed.

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Christopher M. Hayden, Gary S. Wade, and Timothy J. Schmit

Abstract

Derived product imagery (DPI) is a method of presenting quantitative meteorological information, derived from satellite measurements, as a color-coded image at single-pixel resolution. Its intended use is as animated sequences to observe trends in the displayed quantities, which for the GOES-8 are total precipitable water, lifted index, and surface skin temperature. Those products are produced once per hour, over the continental United States and the Gulf of Mexico. This paper reviews the development of the DPI and details the algorithm used for GOES-8. The quality of the products is discussed, and an example is given. The greatest value of the DPI probably lies in comparing a sequence of the satellite product with a sequence derived from a numerical forecast. In this way, deviation of the forecast from reality is readily exposed.

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William H. Raymond, Gary S. Wade, and Tom H. Zapotocny

Abstract

An unsolved problem with water vapor wind estimates from the upper-tropospheric 6.7-μm water vapor band on the Geostationary Operational Environmental Satellite (GOES) Imager (channel 3) is its exact placement in the vertical column. Satellite water vapor observations are known to be depth-averaged assessments of the upper-tropospheric moisture. Details about the effective averaging of upper-tropospheric observations, valid for GOES or those of other satellite platforms, are not retrieved as part of the observation. However, details about the vertical placement can be accurately estimated from forward radiative models that mimic the instrument spectral characteristics. A new method has been developed to assimilate satellite radiances or brightness temperatures directly into a numerical forecast model. A by-product of the new scheme is knowledge of the weighting functions that describe the assignment value given to each vertical layer. As a consequence, given water vapor wind data, these weighting functions allow the guessed wind field to be “intelligently” modified. In this study the vertical and horizontal characteristics of these weighting functions are examined. Statistics for a 16-day period are presented that show how weighted average wind components from the initial model forecast fields, computed using the weighting functions, compare with GOES water vapor wind observations.

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William H. Raymond, Robert M. Rabin, and Gary S. Wade

The Mississippi River floodplain in the states of Arkansas, Tennessee, Mississippi, and Louisiana presents a readily discernible feature in weather satellite images. This floodplain appears in the spring and early summer as a daytime warm anomaly at infrared (IR) wavelengths and as a bright reflective area at visible wavelengths. Remnants of this feature can occasionally be identified at nighttime in the IR satellite images. During June the normalized difference vegetation index identifies major contrasts between this intense agricultural region and the surrounding mixed-forest region. This distinction and the homogeneity of the floodplain, with its alluvial soil, contrast with the encircling region, creating an agricultural region containing heat island features. Thirty years of climatological surface station data for the month of June reveal that the surface air temperatures in the floodplain experience less diurnal variation than those in the surrounding regions. This is primarily because nighttime minimums are warmer in the Mississippi River floodplain.

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Xiangqian Wu, W. Paul Menzel, and Gary S. Wade

Sea surface temperatures (SSTs) are derived using measurements from the new generation of imaging instruments on the Geostationary Operational Environmental Satellites (GOES). The National Environmental Satellite, Data and Information Service has been producing hourly GOES SST estimates since December 1998. This paper presents the algorithm for cloud detection and atmospheric moisture correction and shows some initial results. Several advantages of GOES SST are evident in comparison with SST from polar orbiting satellites. Frequent sampling by GOES imagers results in a more complete map of SST as clouds move away. Changes in scene temperature over a short period of time help to detect the presence of clouds. The abundance of GOES observations enables stringent screening for cloud-free observations while maintaining good spatial coverage of clear-sky inferences of SST. Diurnal variations of SST over large areas are observed for the first time and their implications for numerical weather prediction and climate monitoring are discussed.

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John J. Bates, William L. Smith, Gary S. Wade, and Harold M. Woolf

A technique for interactively producing sea-surface temperatures (SST) from VAS multispectral radiance observations and displaying the derived field is outlined. High-resolution composite images using data from several times per day and over a several-day period are shown to illustrate how the technique is applied. The cloud-screening procedures are interactive so that they can be optimized to eliminate the effects of small clouds while still retrieving a sufficient number of SSTs to permit analysis of mesoscale flow features. SST-image products have been produced in real time at the University of Wisconsin as part of the genesis of Atlantic lows experiment (GALE) and as part of the NOAA operational VAS assessment (NOVA) program.

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Robert M. Rabin, Lynn A. McMurdie, Christopher M. Hayden, and Gary S. Wade

Abstract

Spatial and temporal changes of atmospheric water vapor and surface wind speeds are investigated for a period following an intrusion of cold continental air over the Gulf of Mexico, during the Gulf of Mexico Experiment (GUFMEX) in March 1988. Microwave and infrared satellite measurements from the Special Sensor Microwave/Imager (SSM/I) instrument aboard the Defense Meteorological Satellite Project (DMSP) F8 satellite and from the GOES VISSR Atmospheric Sounder (VAS) are used to augment the sparse coverage of rawinsonde sites and surface reports in the vicinity of the Gulf of Mexico. Total precipitable water is derived from both instruments and from rawinsonde measurements at coastal locations and auxiliary sites on ships and platforms over the Gulf. Accuracies of the precipitable water derived from SSM/I and GOES are comparable, though microwave data provide more uniform coverage, when they are available, than VAS since they are relatively free from contamination by most clouds. Also, the moisture fields derived from microwave data appear to be less noisy than those derived from the infrared. To illustrate possible use of satellite data in the forecast office, moisture fields from both SSM/I and VAS are blended together into imagery, which are compared to analyses from an operational model. Surface wind speeds are also obtained from the microwave data and are compared to the surface observations. Analyses from satellite data appear to add considerable information to the moisture and wind analysis over the Gulf of Mexico and should help in forecasting moisture changes, particularly moisture return near the surrounding coastal areas.

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William L. Smith, Gary S. Wade, and Harold M. Woolf

A method for displaying sounding and cloud information in a composite image is described. Examples are shown to illustrate how a forecaster may use a time sequence of these images to monitor changes in atmospheric moisture and stability antecedent to convective weather and at the same time monitor the cloud developments resulting from these atmospheric moisture and stability tendencies. The image products are now being produced in real time at the University of Wisconsin for an assessment of their operational utility as a part of the NOAA Operational VAS Assessment (NOVA) program. It is likely that the sounding/cloud imagery product will be available to all forecast centers in 1986, after the VAS data acquisition and processing system becomes fully operational.

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Robert M. Rabin, Lynn A. McMurdie, Christopher M. Hayden, and Gary S. Wade

Abstract

Spatial and temporal changes in the vertical distribution of atmospheric water vapor are investigated during a period following the intrusion of cold continental air over the Gulf of Mexico, during the Gulf of Mexico Experiment (GUFMEX) in February-March 1988. Infrared satellite measurements from the GOES (Geostationary Operational Environmental Satellite) VISSR (Visible-Infrared Spin Scan Radiometer) Atmospheric Sounder (VAS) are used to augment the sparse coverage of rawinsonde sites in the vicinity of the Gulf of Mexico. Precipitable water from two vertical layers, surface-850 and 850–250 mb, are estimated from the VAS and compared to those from rawinsonde observations. The accuracy of precipitable-water estimates in each vertical layer is less than that for the total precipitable water. However, improvements in the estimate of precipitable water for each layer are observed with respect to the profiles used in initializing the retrieval process. A consistent horizontal and temporal pattern of the vertical partition of water vapor between the lower and middle to upper troposphere is obtained from the analysis in both layers. A band of moist air that develops with return to southerly flow is common to both layers; however, the width of the band is more extensive in the lower layer. Drying to the rear of the band predominates in the upper layer while the lower layer remains quite moist.

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Robert M. Rabin, Lynn A. McMurdie, Christopher M. Hayden, and Gary S. Wade

Abstract

The atmospheric water budget is examined for a 12-day period following an intense cold-air outbreak over the Gulf of Mexico. Budget terms are compared using analyses from the U.S. National Meteorological Center's operational Nested Grid Model (NGM) and using precipitable water and surface wind speed estimated from the Special Sensor Microwave/Imager (SSM/I) instrument aboard the defense meteorological satellite F8. The atmospheric-storage term, determined from the areal-averaged total precipitable water, does not differ significantly between that obtained from the NGM and that obtained from SSM/I data. The storage increases by a factor of more than 3 during the initial five days following the passage of the surface high over the Gulf. Horizontal flux divergence of water vapor computed from the full vertical structure in the NGM output is well approximated by the substitution of the surface-700-mb mean wind and the total precipitable water for the vertical profiles along the boundaries of the atmospheric volume. Evaporation from the sea surface is determined using GOES surface temperatures and NGM surface air conditions. The impact of satellite-derived surface winds on the areal-average evaporation is determined by replacing NGM wind speeds with those estimated from the SSM/I data. The relative importance of precipitation on the water budget is assessed from model estimates. During the onset of airmass modification, evaporation appears to be the dominant mechanism in producing the observed atmospheric moistening. As evaporation diminishes after one to two days, evaporation and flux convergence are of similar magnitude. Together, these terms underestimate the amount of moistening observed during the first five days.

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