In order to determine the utility of the coverage obtained by these centers visits were made to each location during periods of precipitation in the Mount Rose and Elko areas.

In addition a visit was made to the WSR-57 installation in Sacramento to compare its performance to the FAA system.

The visits verified the conclusions of the above-noted studies; i.e., the network has excellent precipitation detection capabilities, approximately equal to that of the WSR-57. One advantage that the FAA system has for our application is that in the mountainous areas of the West the ground clutter is very severe and unless eliminated by special circuitry such as the FAA radars possess can obscure many details of the precipitation patterns that are of interest. During the visit to the Salt Lake Center photographs were obtained of scattered precipitation over Elko and of a major storm in the Upper Colorado Basin. This data, taken by Weather Bureau research station personnel stationed at the ARTCC for tetroon tracking purposes will be reported on in the next report period. Two features of the FAA system should be noted at this time. The first is that the radars possess circular polarization. This feature is sometimes used to minimize, but not completely eliminate, the precipitation return. This is a disadvantage for our purposes. The second factor is that the FAA has instituted an experimental program to simultaneously provide both circular and noncircular return in an overlay and isoecho contoured manner. If implemented on a nationwide basis this would be of extreme value to this program.

During the next report period it is planned to utilize the FAA network to track tetroons from the coast, over the Sierra Nevada Mountains. In addition discussions have been initiated with WBRS, Las Vegas, on their study of economically remoting the ARTCC displays over telephone lines, to determine if their techniques can be utilized to remote the Salt Lake and Fremont ARTCC displays to Reno.

Work plan D. Study the physics and dynamics of orographic and convective cloud systems

(1) Several tetroon runs to study the airflow patterns over the Mount Rose area have been made during this report period. The data is being reduced and will be presented in the next report.

(2) Numerous aircraft flights, in conjunction with ground radar tracking, and ground radar observations of precipitation have been made during this period.

LETTER PROGRESS REPORT No. 4, APRIL 30, 1965-BUREAU OF RECLAMATION CONTRACT No. 14-06-D-5410; NATIONAL SCIENCE FOUNDATION GRANT No. GP 941

(Submitted by the Desert Research Institute of the University of Nevada)

INTRODUCTION

This is the fourth of a series of monthly letter progress reports outlining the activities of the Desert Research Institute on the above noted Bureau of Reclamation contract and National Science Foundation grant.

These monthly letter reports will be supplemented at various intervals by technical reports detailing a specific aspect of the program.

The format of these letter reports coincides with the work plan accepted by the Bureau.

Work plan A. Acquisition of meteorological and hydrological data

The GMD 1-A radiosonde set located at the Truckee-Tahoe Airport has been used for seven releases during the month of April. An additional x band M-33 radar has been placed in operation in the Reno area, east of Mount Rose. The computer program to reduce the GMD data numercially was completed and is being used operationally.

During the month of April three flights, April 6, 7, and 28 were made in the aircraft for the purposes of gathering data with respect to cloud systems over the Mount Rose complex.

New engines with a 12-1 blower ratio have been installed in the Twin Beach test aircraft. A test flight to 24,000 feet with this new configuration has been

achieved, as contrasted to the previous altitude performance of 19,000 feet. This greater altitude capability permits us to utilize the majority of the wave clouds that frequently occur over the Mount Rose area. These wave clouds provide ideal "atmospheric laboratory" conditions due to their stationary configuration in space.

Work plan B. Perform field experiments in cloud nucleation in the Elko and Reno area Elko. The existing cloud-seeding program is continuing in the Elko area. No significant design changes have occurred in this program during the reporting interval. The radiosonde has been installed at Elko. This will greatly aid in the statistical analysis of seeding results.

Mount Rose. No seeding experiments have been conducted.

Work plan C. Investigate the feasibility of a weather surveillance radar network in the Western United States

As noted in Letter Progress Report No. 3, personnel of the Weather Bureau Research Station, Las Vegas, Nev., obtained information on precipitation in the Elko area by photographing a PPI presentation of the FAA Battle Mountain radar. The actual photographing was done in the Salt Lake ARTCC Center since the output of the Battle Mountain radar is microwaved to Salt Lake.

The data was obtained by using a Polaroid camera to photograph a Bright Display. A Bright Display is a TV-type presentation of radar data stored on a storage tube. The technique is as follows:

The radar output is read into one side of a storage tube and stored there for a period up to 6 minutes (as determined by the operator). The stored data is scanned and displayed on what are essentially conventional TV receivers.

As noted previously one of the major advantages of the FAA system is the use of MTI (moving target indication) to eliminate ground clutter. This is especially advantageous in the mountainous areas of the West.

A second advantage of the FAA system is the use of video mapping. This presents easy identification of the areas of interest by correlating the video maps with airways charts.

Both the above features, the use of MTI and video mapping can be noted in the enclosed photographs figures A through F.

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