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At least 613 records · Page 34
All sourcesNASA NTRSDOE OSTI
NASA NTRS1988

On the dynamic estimation of relative weights for observation and forecast in numerical weather prediction

The problem of merging direct and remotely sensed (indirect) data with forecast data to get an estimate of the present state of the atmosphere for the purpose of numerical weather prediction is examined. To carry out this merging optimally, it is necessary to provide an estimate of the relative weights to be given to the observations and forecast. It is possible to do this dynamically from the information to be merged, if the correlation structure of the errors from the various sources is sufficiently different. Some new statistical approaches to doing this are described, and conditions quantified in which such estimates are likely to be good.

Wahba, Grace↗
NASA NTRS1987

Error growth and predictability in operational ECMWF forecasts

The forecast error growth in the 100-day ECMWF data set of 10-day forecasts previously utilized by Lorenz (1982) is studied, separating the square of the error into systematic and random components. The nature of the errors is analyzed in the spherical harmonics wavenumber domain, and a new parametrization and its application to global errors are presented. The wavenumber dependence of the error growth is studied.

Dalcher, Amnon↗
NASA NTRS1987

Forecast experiments with the NASA/GLA stratospheric/tropospheric data assimilation system

For the first time, a four-dimensional stratospheric/tropospheric data assimilation system with a top analysis level at 0.4 mb has been developed and used to produce physically consistent gridded analyses for the stratosphere as well as the troposphere for a period during the First GARP Global Experiment (FGGE) and Limb Infrared Monitor of the Stratosphere (LIMS) (November 1978-May 1979). The system consists of a two-dimensional optimum interpolation analysis with 18 mandatory pressure levels and a 19-level fourth order stratospheric/tropospheric general circulation model with a horizontal resolution of 4 (latitude) by 5 deg (longitude) and a top at 0.3 mb. The system allows the utilization of stratospheric data including LIMS, Tiros-N retrievals, rocketsondes and vertical temperature profile radiometer soundings in addition to the other FGGE level 2b data. These data are analyzed every six hours. In order to examine the quality of the analyzed data, forecast experiments starting from different analyses are performed for the period of the stratospheric sudden warming of late February 1979. The results indicate that by employing the present four-dimensional assimilation approach, the medium-range forecast skill for this event is improved.

Takano, Kenji↗
NASA NTRS1990

Simulated forecast error and climate drift resulting from the omission of the upper stratosphere in numerical models

Using an NCAR community climate model, Version I, the forecast error growth and the climate drift resulting from the omission of the upper stratosphere are investigated. In the experiment, the control simulation is a seasonal integration of a medium horizontal general circulation model with 30 levels extending from the surface to the upper mesosphere, while the main experiment uses an identical model, except that only the bottom 15 levels (below 10 mb) are retained. It is shown that both random and systematic errors develop rapidly in the lower stratosphere with some local propagation into the troposphere in the 10-30-day time range. The random growth rate in the troposphere in the case of the altered upper boundary was found to be slightly faster than that for the initial-condition uncertainty alone. However, this is not likely to make a significant impact in operational forecast models, because the initial-condition uncertainty is very large.

Boville, Byron A.↗
NASA NTRS1990

Systematic errors in the annual and intraseasonal variations of the planetary-scale divergent circulation in NMC medium-range forecasts

The systematic error in the National Meteorological Center's (NMC) medium-range operational forecasts of the global divergence during 1987 and 1988 is examined in this study. As in other operational NWP models the NMC model has too weak an annual mean, annual cycle, and 30-60 day oscillation. This weakness shows up after only a few days, especially over the monsoon region and tropical areas. When the intraseasonal oscillation amplitude is large the model predictive skill is improved. The eastward propagation of the low-frequency mode is well predicted throughout the 10-day forecast period. The north-south migration of the tropical Hadley circulation, depicted primarily by the annual-cycle mode, is also weaker although the phase pattern predicted by the MRF is consistent with analyses.

Chen, Tsing-Chang↗
NASA NTRS1991

Dynamo-based scheme for forecasting the magnitude of solar activity cycles

This paper presents a general framework for forecasting the smoothed maximum level of solar activity in a given cycle, based on a simple understanding of the solar dynamo. This type of forecasting requires knowledge of the sun's polar magnetic field strength at the preceding activity minimum. Because direct measurements of this quantity are difficult to obtain, the quality of a number of proxy indicators already used by other authors is evaluated, which are physically related to the sun's polar field. These indicators are subjected to a rigorous statistical analysis, and the analysis technique for each indicator is specified in detail in order to simplify and systematize reanalysis for future use. It is found that several of these proxies are in fact poorly correlated or uncorrelated with solar activity, and thus are of little value for predicting activity maxima. Also presented is a scheme in which the predictions of the individual proxies are combined via an appropriately weighted mean to produce a compound prediction. The scheme is then applied to the current cycle 22, and a maximum smoothed international sunspot number of 171 + or - 26 is estimated.

Layden, A. C.↗
NASA NTRS1991

An assessment of VAS-derived retrievals and parameters used in thunderstorm forecasting

VAS satellite retrievals and derived parameters used in forecasting severe local storms were evaluated against corresponding radiosonde values. VAS products were also compared with the first-guess input to the retrieval algorithm. The evaluation methodology was to pair each radiosonde observation with the closest VAS retrieval within 50 km during a four-month period in 1986. VAS temperatures agreed closely with radiosonde values; dewpoints showed less agreement. Sounding differences were poorly correlated with the number of pixels from which the retrievals were prepared. VAS discrepancies usually were not well correlated with first-guess errors. Horizontal gradients of VAS products were stronger than those from radiosondes. VAS precipitable water agreed better with ground truth than did dewpoints at individual levels, but VAS thicknesses were not much improved. Results for severe storms forecasting parameters indicated that discrepancies increased with the amount of manipulation required during computation. The lifted index showed the best agreement; positive bouyant energy showed poor comparisons.

Fuelberg, Henry E.↗
NASA NTRS1991

The behavior of forecast error covariances for a Kalman filter in two dimensions

The behavior of forecast error covariances in a fairly realistic setting is demonstrated via a Kalman filter algorithm. It is used to assimilate simulated data from the existing radiosonde network, from the demonstration network of 31 Doppler wind profilers in the central U.S., and from hypothetical radiometers located at five of the profiler sites. Some theoretical justification of the hypothesis advanced by Phillips (1982), and the hypothesis is used to formulate the model error covariance matrix required by the Kalman filter. The results show that assimilating the profiler wind data leads to a large reduction of forecast/analysis error in heights as well as in winds, over the profiler region and also downstream, when compared with the results of assimilating the radiosonde data alone. The forecast error covariance matrices that the Kalman filter calculates to obtain this error reduction differ considerably from those prescribed by the optimal interpolation schemes that are employed for data assimilation at operational centers.

Cohn, Stephen E.↗
NASA NTRS1991

Future mission studies: Forecasting solar flux directly from its chaotic time series

The mathematical structure of the programs written to construct a nonlinear predictive model to forecast solar flux directly from its time series without reference to any underlying solar physics is presented. This method and the programs are written so that one could apply the same technique to forecast other chaotic time series, such as geomagnetic data, attitude and orbit data, and even financial indexes and stock market data. Perhaps the most important application of this technique to flight dynamics is to model Goddard Trajectory Determination System (GTDS) output of residues between observed position of spacecraft and calculated position with no drag (drag flag = off). This would result in a new model of drag working directly from observed data.

Ashrafi, S.↗
NASA NTRS1992

Impact of cumulus initialization on the spinup of precipitation forecasts in the tropics

To ameliorate the precipitation spinup problem, i.e., the prediction model's inability to produce realistic precipitation rates at the beginning of the forecast period, the impact of a tropical initialization procedure on precipitation forecasts is examined. Attention is focused on the examination of the time behavior of precipitation rates and the closely associated variables of horizontal divergence and moisture during the first 42 time steps corresponding to 10.5 h. It is determined that the originally analyzed tropical divergence fields have realistic geographical distributions but there intensities seem to be too low by a factor of two.

Kasahara, Akira↗
NASA NTRS1993

The importance of short-term forecasting of thunderstorms to launch operations at Cape Canaveral

The local meteorological events leading up to the launch of the space shuttle Atlantis on 2 August 1991 were captured in full-resolution GOES visible data being archived for the Convection and Precipitation/Electrification Experiment. The postponement of the launch on 1 August, and the successful lift-off on the following day provide a good example of the important role played by nowcasting and short-term forecasting at Cape Canaveral. In this brief article, we discuss the local weather conditions prior to, during, and after the launch and demonstrate the importance of short-term forecasting capabilities around the cape during launch operations.

Cooper, Harry J.↗
NASA NTRS1992

The Harang discontinuity and magnetospheric forecasting

This paper describes the physics of the Harang discontinuity and its application to forecasting of the magnetospheric environment. Gradient/curvature depletion of energetic ions from earthward drifting flux tubes results in upward Birkeland currents. Ionospheric closure rotates the dawn-dusk convection electric field resulting in the Harang reversal. This physical mechanism has been incorporated into the Rice Convection Model (RCM) and can serve as a fundamental part of the forecasting of the magnetospheric system. The inclusion of this physics within the RCM results in a physical picture of the Harang discontinuity which did not previously exist. Model results are close to observations and represent a significant improvement in predicted electric field and Birkeland current patterns.

Erickson, G. M.↗
NASA NTRS1993

The application of VAS satellite imagery to thunderstorm forecasting at Cape Canaveral

The Final Report on the application of VAS satellite imagery to thunderstorm forecasting at Cape Canaveral is presented. The objective of this research was to investigate whether satellite-derived imagery and derived products could be used advantageously in forecasting thunderstorms in the Cape Canaveral area. Specifically, data from the VISSR Atmospheric Sounder that is housed on the current series of GOES geostationary meteorological satellites was used. These satellite data were used extensively in the middle latitudes, but their utility over central Florida where the climate is more tropical had not been examined.

Fuelberg, Henry E.↗
NASA NTRS1992

Weather forecasting support for AASE-2

The AFEAS Contract and NASA Grant were awarded to Penn State in order to obtain real-time weather forecasting support for the NASA AASE-II Project, which was conducted between October 1991 and March 1992. Because of the special weather sensitivities of the NASA ER-2 aircraft, AASE-II planners felt that public weather forecasts issued by the National Weather Service would not be adequate for mission planning purposes. A likely consequence of resorting to that medium would have been that scientists would have had to be at work by 4 AM day after day in the hope that the aircraft could fly, only to be frustrated by a great number of 'scrubbed' missions. Thus, the Pennsylvania State University was contracted to provide real-time weather support to the AASE-II mission.

Forbes, Gregory S.↗
NASA NTRS1993

FASTER - A tool for DSN forecasting and scheduling

FASTER (Forecasting And Scheduling Tool for Earth-based Resources) is a suite of tools designed for forecasting and scheduling JPL's Deep Space Network (DSN). The DSN is a set of antennas and other associated resources that must be scheduled for satellite communications, astronomy, maintenance, and testing. FASTER consists of MS-Windows based programs that replace two existing programs (RALPH and PC4CAST). FASTER was designed to be more flexible, maintainable, and user friendly. FASTER makes heavy use of commercial software to allow for customization by users. FASTER implements scheduling as a two pass process: the first pass calculates a predictive profile of resource utilization; the second pass uses this information to calculate a cost function used in a dynamic programming optimization step. This information allows the scheduler to 'look ahead' at activities that are not as yet scheduled. FASTER has succeeded in allowing wider access to data and tools, reducing the amount of effort expended and increasing the quality of analysis.

Werntz, David↗
NASA NTRS1995

Acquisition forecast: Fiscal year 1995

This volume includes projections of all anticipated FY95, and beyond, NASA contract actions above $25,000 that small and small disadvantaged businesses may be able to perform under direct contract with the government or as subcontractors. The forecast consolidates anticipated procurements at each NASA center into an agencywide report, with the aim of increasing industries' advance knowledge of NASA requirements and enhancing competition in contracting. Each center forecast report is divided into three principal categories of procurement: research and development, services, and supplies and equipment.

Source record↗
NASA NTRS1994

An algorithm for forecasting mountain wave-related turbulence in the stratosphere

A global mountain wave parameterization for prediction of wave-related displacements and turbulence is described. The parameterization is used with input from National Meteorological Center (NMC) analyses of wind and temperature to examine small-scale disturbances encountered by the National Aeronautics and Space Administration high-altitude ER-2 during the Second Airborne Arctic Stratosphere Experiment (AASE-II). The magnitude and location of observed large wave events are well reproduced. A strong correlation is suggested between patches of moderate turbulence encountered by the ER-2 and locations where breaking mountain waves are predicted by the parameterization. These facts suggest that useful forecasts of global mountain wave activity, including wave-related clear-air turbulence, can be made quickly and inexpensively using our mountain wave parameterization with input from current numerical forecast models.

Bacmeister, Julio T.↗
NASA NTRS1993

Tracking motions from satellite water vapor imagery: Quantitative applications to hurricane track forecasting

Water vapor imagery from GOES satellites has been available for over a decade. These data are used extensively, mainly in a qualitative mode, by forecasters in the United States (Weldon and Holmes, 1991). Some attempts have been made at quantifying the data by tracking features in time sequences of the imagery (Stewart et al., 1985; Hayden and Stewart, 1987). For a variety of reasons, applications of this approach have produced marginal results (Velden, 1990). Recently, METEOSAT-3 (M-3) was repositioned at 50W by the European Space Agency, in order to provide complete coverage of the Atlantic Ocean. Data from this satellite are being transmitted to the U.S. for operational use. Compared with the GOES satellite, the M-3 has a superior resolution and signal-to-noise ratio in its water vapor channel, which translates into improved automated tracking capabilities. During a period in 1992 which included the Atlantic hurricane season, water vapor tracking algorithms were applied to the M-3 data in order to evaluate the coverage, accuracy and model impact of the derived vectors. Data sets were produced during several tropical cyclone cases, including Hurricane Andrew. In this paper, the M-3 water vapor wind sets are assessed, and their impact on a hurricane track forecast model is examined.

Velden, Christopher↗