Frederick H. Carr

A Prognostic Cloud Scheme for Operational NWP Models

Abstract An explicit cloud prediction model has been developed and incorporated into the Eta Model at the National Centers for Environmental Prediction. In this scheme, only one predictive variable, cloud mixing ratio, is added to the model’s prognostic equations to represent both cloud liquid water and cloud ice. Precipitation is diagnostically calculated from cloud mixing ratio. Extensive tests have been performed. The statistical results show a significant improvement in the model precipitation forecasts. Diagnostic studies suggest that the inclusion of cloud ice is important in transferring water vapor to precipitation and in the enhancement of latent heat release; the latter subsequently affects the vertical motion field significantly.

Verification of the Origins of Rotation in Tornadoes Experiment: VORTEX

Abstract This paper describes the Verification of the Origins of Rotation in Tornadoes Experiment planned for 1994 and 1995 to evaluate a set of hypotheses pertaining to tornadogenesis and tornado dynamics. Observations of state variables will be obtained from five mobile mesonet vehicles, four mobile ballooning laboratories, three movie photography teams, portable Doppler radar teams, two in situ tornado instruments deployment teams, and the T-28 and National Atmospheric and Oceanic Administration P-3 aircraft. In addition, extensive use will be made of the new generation of observing systems, including the WSR-88D Doppler radars, demonstration wind profiler network, and National Weather Service rawinsondes.

A Composite Study of Comma Clouds and their Association with Severe Weather over the Great Plains

Abstract Sixty-eight comma-cloud systems over the Great Plains during two spring seasons were examined using satellite imagery and rawinsonde data. Composite soundings were produced for each of ten distinct parts of the comma cloud in order to describe quantitatively the atmospheric structure associated with wave cyclones that produced 585 severe weather events. Composite sectionals and soundings document the different kinematic and thermodynamic environment of each part of the comma-cloud system. Relative-wind, isentropic analyses show air flow relative to the storm and provide additional evidence that the clear region intruding northward east of the cyclone center is an area of strong ascent of dry air with a previous history of subsidence. Stability computations from the mean soundings suggest that the most likely location for severe weather is near the central part of the comma tail, in agreement with the tabulated severe weather reports. A case study from 21–22 March 1981 is conducted to investigate ...

MULTIFUNCTIONAL MESOSCALE OBSERVING NETWORKS

Abstract More than 120 scientists, engineers, administrators, and users met on 8–10 December 2003 in a workshop format to discuss the needs for enhanced three-dimensional mesoscale observing networks. Improved networks are seen as being critical to advancing numerical and empirical modeling for a variety of mesoscale applications, including severe weather warnings and forecasts, hydrology, air-quality forecasting, chemical emergency response, transportation safety, energy management, and others. The participants shared a clear and common vision for the observing requirements: existing two-dimensional mesoscale measurement networks do not provide observations of the type, frequency, and density that are required to optimize mesoscale prediction and nowcasts. To be viable, mesoscale observing networks must serve multiple applications, and the public, private, and academic sectors must all actively participate in their design and implementation, as well as in the creation and delivery of value-added products...

A Case Study of Excessive Rainfall Centered Around Wellsville, New York, 20–21 June 1972

Abstract The pretropical storm Agnes rainstorm across western New York and Pennsylvania is analyzed using conventional surface and aerological data. Hourly precipitation maps and surface maps showed the north-eastward motion and intensification of a developing rain area over eastern Kentucky at 1200 GMT 20 June 1972. This area remained a separate entity from the main Agnes rainshield. Nonlinear balanced omega as well as kinematic omega computations suggest that a weak short wave in the mid and upper troposphere provided the initial triggering mechanism for the growth of the rain area. Plentiful moisture was available from the Agnes circulation to the south and the western Atlantic. Latent heat release then played a dominating role in modifying the resulting vertical velocity patterns. Finally, some possible general forecast considerations are suggested by these results.

Four-Dimensional Data Assimilation in the Monsoon Region. Part I: Experiments with Wind Data

Abstract A limited primitive equation model has been used to study the feasibility of four-dimensional data assimilation in the monsoon region and, further, to study the applicability of several assimilation techniques currently being employed in global models. The two fundamental objectives of this research are (i) to understand how the model atmosphere responds to the insertion of asynchronous data and its impact on the assimilation-prediction cycle, and (ii) to determine what assimilation strategies work best for limited-area models in the tropics. A sequence of ten assimilation experiments are performed using different update procedures; all insertions are carried out with only the wind observations. The model is initialized with the ECMWF FGGE level III-b data for the onset vortex case of 17 June 1979, and assimilations are carried out using the summer MONEX level II-b data during the first 12 hours. From these assimilated states, 24-h forecasts are then made. The results lend support to the premise ...

A Comparison of Two Objective Analysis Techniques for Profiler Time-Height Data

Abstract Two methods for objective analysis of wind profiler data in time-height space are proposed and compared. One is a straightforward adaptation of a procedure developed by Doswell for introducing time continuity into a sequence of spatial analyses. The second technique, named the correlation method, introduces a new rationale for selection of the Barnes filter parameter that is based on knowledge of the statistical structure of wind profiler data. The advantages and disadvantages of each method are discussed. It is noted that the correlation method, in principle, allows the deduction of consistent sampling intervals in time and space for the most dominant phenomena resolved by the data provided by a given atmospheric observing system. It is recommended that an objective analysis of wind profiler data be performed before single- or multiprofiler kinematic calculations are made. In addition, it is shown that the positions of extrema in kinematic quantities computed from profiler triangles are relative...

Cloud-to-Ground Lightning throughout the Lifetime of a Severe Storm System in Oklahoma

Cloud-to-ground (CG) lightning data are examined relative to digitized radar data for a storm system that occurred in Oklahoma on 26 May 1985. This system evolved through three stages: 1) two lines of cells, one near the dryline and the other 60 km ahead of it; 2) a supercell storm; and 3) a mesoscale convective system (MCS). The behavior of lightning in each stage was different. Initially no ground flashes were observed in either line until reflectivity increased to

A Diagnostic Evaluation of Rainfall Predictability for Tropical Storm Agnes, June 1972

46 dBZ and vertically integrated liquid (VIL) increased to

Summary of the 1998 Workshop on Mesoscale Model Verification

10 kg m22; then ground flash rates remained ,1.2 min21 for .1 h. Most ground flashes in the line of storms near the dryline were negative (18 2CG, 3 1CG), while most in the leading line were positive (11 1CG, 3 2CG), a pattern of polarity opposite to what usually has been observed. Approximately 3 h after radar detected the first storm, ground flash rates increased to .5 min21 and remained so for 6 h. A mesocyclone formed approximately 30 min after flash rates exceeded 5 min 21, and a few positive ground flashes occurred near it. Ground flash rates increased briefly to .20 min21 as the mesocyclone dissipated and then remained .10 min21 as a squall line formed along the outflow boundary from the dissipating supercell and produced a stratiform region. Most ground flashes in this MCS occurred in the convective line and had negative polarity. The few ground flashes in the stratiform region tended to be positive (42 1CG, 32 2CG during 3 h). Durin g1ho f theMCS, ground flash rates decreased and then increased again simultaneously in both the convective and stratiform regions, a previously undocumented behavior. It is possible that this was caused by updrafts in both the convective line and stratiform region changing at roughly the same time. It is also possible that most ground flashes in the stratiform region originated near the convective line, and so were influenced by the line. Overall trends in ground flash density, flash relative frequency, reflectivity, VIL, and severe hail reports appeared similar as the storm system evolved.