Showing papers by "Cooperative Institute for Research in the Atmosphere published in 1997"
TL;DR: In this article, the authors used a vertically pointing 8.6mm-wavelength Doppler radar for measuring drop size spectra in clouds and compared the amount of liquid residing in the cloud regime with that found in the precipitation regime where drop fall velocities are resolvable.
Abstract: This paper describes the use of a vertically pointing 8.6-mm-wavelength Doppler radar for measuring drop size spectra in clouds. The data used were collected in the Atlantic Stratocumulus Transition Experiment in 1992. This paper uses the full Doppler velocity spectrum from the time series of Doppler radial velocities to extract information farther into the small-drop regime than previously attempted. The amount of liquid residing in the cloud regime is compared with that found in the precipitation regime where drop fall velocities are resolvable. Total liquid is compared with that measured with a collocated three-channel microwave radiometer. Examples of number density spectra, liquid water spectra, and flux spectra are shown and compared with what is known of these quantities from various in situ measurements by aircraft in similar clouds. Error estimates and uncertainties are discussed. It is concluded that 8-mm Doppler radars have the potential for broader use in cloud and precipitation studi...
59 citations
TL;DR: In this article, the authors used a normalized polarization difference (NPD) of the brightness temperatures to estimate the surface emissivities of the clouds in clear sky regions from SSM/I measurements and window infrared measurements from the Visible and Infrared Spin Scan Radiometer on GOES-7.
Abstract: Refinements and improvements of an earlier technique to retrieve the cloud liquid water path (LWP) of nonprecipitating clouds over land surfaces using Special Sensor Microwave/Imager (SSM/I) 85.5-GHz measurements are presented. These techniques require estimates of the microwave surface emissivity, which are derived in clear-sky regions from SSM/I measurements and window infrared measurements from the Visible and Infrared Spin Scan Radiometer on GOES-7. A comparison of forward model calculations with SSM/I measurements in clear regions demonstrates that over a 7-day period the surface emissivities are stable. To overcome limitations in the single-channel retrieval method under certain situations, a new method is developed that uses a normalized polarization difference (NPD) of the brightness temperatures. This method has the advantages of providing estimates of the LWP for low clouds and being extremely insensitive to the surface skin temperature. Radiative transfer simulations also show that the...
38 citations
TL;DR: In this paper, it was shown that large spatial-scale gravity waves with amplitudes and periods of the pressure perturbations the same as the reduced system component of the solution can be generated by mesoscale storms.
Abstract: Pressure oscillations with amplitudes of the deviations from the horizontal mean and periods considerably less than those for the large-scale case have been observed in a number of summer and winter storms. However, there is conflicting evidence about the role of these waves in mesoscale storms. In the case of mesoscale heating that is a prescribed function of the independent variables, it has been proven that the dominant component of the corresponding slowly varying in time solution is accurately described by a simple dynamical (reduced) system in which gravity waves play no role. This paper proves that large spatial-scale gravity waves with amplitudes and periods of the pressure perturbations the same as the reduced system component of the solution can be generated by mesoscale storms. Because the amplitudes and the periods of the pressure perturbations for the two components of the solution are similar, it is difficult to distinguish between them using temporal plots of the pressure at a sing...
11 citations
TL;DR: In this article, the authors examined the meteorological setting and evolution that led to the severe weather on 4 July 1995 and found that small-scale outflow interactions may have played an important role in changing the nature of the convection already under way and were associated with the two most damaging tornadoes of the day.
Abstract: Tornadic storms that occurred over northeastern Kansas and northern Missouri on 4 July 1995 are examined by combining the latest in National Weather Service technology with more routine datasets. The analysis provides an insightful description of the meteorological setting and evolution that led to the severe weather on this day. Strong thunderstorms first formed where an outflow boundary intersected a cold front, then new activity was triggered along the outflow boundary itself. It was found that small-scale outflow interactions may have played an important role in changing the nature of the convection already under way and were associated with the two most damaging tornadoes of the day. The case is also used to showcase how several new “modernization” datasets can be used together in a quickly accessible manner to provide a valuable and precise overview of a rapidly evolving meteorological event.
7 citations
TL;DR: Results of a research project designed to develop an empirical model that could be used as a tool to predict human visual sensitivity to plumes are discussed and an example of the PROBDET algorithm is presented to demonstrate its potential usefulness for assessing how probability of detection estimates change as plume size and contrast parameters vary.
Abstract: This paper discusses results of a research project designed to develop an empirical model that could be used as a tool to predict human visual sensitivity to plumes The resultant probability of detection algorithm (PROBDET) allows one to estimate the probability of a plume of known size, shape and contrast being detected visually As a basis for the algorithm, a series of laboratory experiments using a high threshold signal detection procedure and computer generated images of plumes with Gaussian luminance distributions was conducted to measure human visual sensitivity to plumes Results of the laboratory experiments are compared with results of contrast sensitivity experiments that examined visual sensitivity to stimuli with square and sine wave luminance distributions An example of the PROBDET algorithm is presented to demonstrate its potential usefulness for assessing how probability of detection estimates change as plume size and contrast parameters vary Since this research was designed to build on existing knowledge, a discussion of that knowledge and how it relates to the research conducted is also presented The focus of this discussion is on the human visual system (HVS) and on how visual sensitivity is affected by factors such as the luminance of the stimulus and the surround, the luminance distribution of the stimulus, the size of the surround, and the size and spatial frequency characteristics of the stimulus
3 citations
TL;DR: A non-operational demonstration, evaluation and training program that allows for the receipt and analysis of digital GOES imagery and products has been placed at approximately 50 of National Weather Service field offices, addressing the successes of that program and its importance in assessing GOES digital imagery and nowcast products.