Robert M. Aune

Application of GOES-8/9 Soundings to Weather Forecasting and Nowcasting

Abstract Since April 1994 a new generation of geostationary sounders has been measuring atmospheric radiances in 18 infrared spectral bands and thus providing the capability for investigating oceanographic and meteorological phenomena that far exceed those available from the previous generation of Geostationary Operational Environmental Satellites (GOES). Menzel and Purdom foreshadowed many of the anticipated improvements from the GOES-8/9 sounders. This article presents some of the realizations; it details the in-flight performance of the sounder, presents both validated operational as well as routinely available experimental products, and shows the impact on nowcasting and forecasting activities. For the first time operational hourly sounding products over North America and adjacent oceans are now possible with the GOES-8/9 sounders. The GOES-8/9 sounders are making significant contributions by depicting moisture changes for numerical weather prediction models over the continental United States, monitor...

Improved Precipitation Forecasts Using Parameterized Precipitation Drag in a Hydrostatic Forecast Model

Abstract An empirical Rayleigh drag parameterization of the nonhydrostatic mechanisms of precipitation drag and small-scale diabatically induced mixing is introduced into a hydrostatic regional forecast model to curb excessive grid-scale precipitation production. To get the needed damping, the coefficient in the Rayleigh drag is set proportional to the predicted liquid water, similar in form to the precipitation drag exhibited in nonhydrostatic calculations. The Rayleigh drag parameterization is found to be greatly superior to using the full nonhydrostatic precipitation drag term that produces a damping that is much too large in magnitude for use in a hydrostatic model. Even a rescaling of this nonhydrostatic term is found to be unsatisfactory since it lacks the sensitivity needed for hydrostatic calculations, resulting in an inability to control excessive precipitation. To incorporate nonhydrostatic vertical acceleration effects into a hydrostatic model, a modified version of the quasi-hydrostatic approx...

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

The synoptic-scale weather conditions preceding and following the ill-fated Space Shuttle Challenger launch are documented, with particular emphasis on the upper-level winds for central and northern Florida. Operational radiosonde data collected by the National Weather Service, visible and infrared imagery from the Geostationary Operational Environmental Satellite, and water-vapor imagery from the VISSR (Visible Infrared Spin Scan Radiometer) Atmospheric Sounder, ozone data collected by the Total Ozone Mapping Spectrometer aboard the Nimbus-7, and soundings collected at Cape Canaveral (XMR) are described. Analyses derived from these data sets point to the juxtaposition of two distinct jet-stream systems (a polar-front jet [PFJ] and a subtropical jet [STJ]) over north-central Florida on the morning of the launch. Both jets were characterized by regions of significant vertical wind shear, which was especially strong above and below the core of the STJ. Data from a radiosonde released at Cape Canaveral 10 mi...

A VAS-numerical model impact study using the Gal-Chen variational approach

Abstract Numerical experiments are conducted to assess the impact of incorporating temperature data from the VISSR Atmospheric Sounder (VAS) into a regional-scale numerical model using an assimilation technique developed by Gal-Chen. The technique uses a three-dimensional variational approach to combine the VAS observations with model temperature fields during the numerical integration. A nudging technique is also tested, whereby the model temperature field is constrained toward the VAS “updated” values during the assimilation cycle. Results of the experiments indicate that the Gal-Chen assimilation technique successfully combines actual VAS temperature observations with the dynamically balanced model fields without destabilizing the model during the assimilation cycle. Furthermore, increasing the temporal frequency of VAS temperature insertions during the assimilation cycle enhances the impact on the model forecast through successively longer forecast periods. These results support the conclusions of ear...

Conservation of Moisture in a Hybrid Kuo-Type Cumulus Parameterization

Abstract The conservation of moisture requirement used in a hybrid Kuo-type cumulus parameterization scheme is generalized so that the source of moisture for the cumulus process originates from all layers below the level of condensation, including the subcloud layer(s). This conservation scheme is distinctly different than those used with the traditional Kuo-type cumulus parameterizations, which do not include convective-scale vertical transport involving the subcloud layer(s). Numerical forecasts with the modified conservation scheme are compared with those obtained using the conventional approach that extracts the moisture from the grid-scale moisture field at the level of condensation. Radiosonde observations and Geostationary Operational Environmental Satellite (GOES) observed brightness temperatures for water vapor channel 3 (6.7 μm) are used to verify the lower- and upper-tropospheric moisture fields, respectively. Forecast statistics, including precipitation as measured against rain gauge reports, ...

Many uses of the geostationary operational environmental satellite-10 sounder and imager during a high inclination state

Geostationary Operational Environmental Satellite (GOES)-10 was the National Oceanic and Atmospheric Administrations (NOAA) operational GOES-West satellite for approximately eight years until it was retired as an operational satellite due to an ever increasing inclination in its orbit. Since its retirement, GOES-10 has been used for a number of applications, such as, special 1-minute imagery over parts of North America during its move to 60° West longitude, routine imagery of the Southern Hemisphere, the first operational Sounder coverage over South America, initialization of regional numerical weather prediction models, and even temporary recalled as the operational GOES-East satellite during a major GOES-12 anomaly. Products from the GOES-10 Sounder and/or Imager include: imagery, cloud-top parameters, atmospheric stability indices, total precipitable water vapor, motion vector winds, volcanic ash detection, fire detection and characterization, and precipitation. As the mission of GOES-10 has continued beyond its retirement as an official operational US satellite, already lasting more than double its five-year life expectancy, many countries have been afforded the opportunity to benefit from on-going GOES-10 measurements. The purpose of this paper is to summarize the history of GOES-10, especially the unique situation of GOES-10 operating in support of central and South America after its operational use.

An objective nowcasting tool that optimizes the impact of satellite derive sounder products in very-short-range forecasts

Future instruments will improve atmospheric measurements in both time and space. Although these data are expected to advance traditional Numerical Weather Prediction (NWP) guidance at 48 hours and beyond, greater benefit may come from objective nowcasting systems that assist forecasters in identifying rapidly developing and isolated extreme weather events a few hours in advance. These systems should detect and retain extreme variations in the atmosphere and incorporate large volumes of high-resolution asynoptic data. Because they need to be extremely fast, they may use numerical approaches different from current NWP. A new objective nowcasting approach is presented that uses trajectories to optimize the impact and retention of satellite information. It is designed to detect and preserve intense vertical and horizontal variations observed over time. Real data tests have identified atmospheric details associated with the onset of significant weather events up to 6 hours in advance. Using full resolution moisture products from current GOES sounders to update and enhance current operational forecasts, the Lagrangian system captures and retains details (maxima, minima and extreme gradients) important to the development of convective instability, even after IR observations are no longer available due to cloud development. Examples of the issues and impact of using hyperspectral AIRS data are also discussed.

Observing atmospheric moisture from geostationary orbit: how many channels is enough?

Most of todays operational numerical weather prediction (NWP) models demonstrate measurable skill at predicting the onset and amount of precipitation from extratropical systems. This is somewhat surprising when you consider that atmospheric water vapor is the least measured parameter of all the dependent variables that collectively define a set of initial conditions. In many of todays operational models the moist dependent variable is often not conserved due to limitations in the moist parameterizations, missing components of the moisture budget, or due to the use of diffusion operators required for numerical stability. Forecasts of the moist dependent variable are rarely validated because of the lack of observations. Precipitation amounts, however, are routinely observed which allow modelers to subjectively tune the moist physical parameterizations that force precipitation. These same models often remain relatively insensitive to details in the initial moisture fields. As model resolution increases, so will the need for frequent high-resolution measurements of atmospheric moisture. At present there is an increasing emphasis being placed on the numerical prediction of water vapor and moisture-sensitive diagnostics such as visibility, clouds, aircraft icing potential, and convective potential. Models running at resolutions of 4 to 10 kilometers will require detailed moisture information to successfully predict these quantities. Instruments in geostationary orbit will play a key role in providing moisture observations at spatial and temporal resolutions required by future NWP models.