Search Results

You are looking at 1 - 4 of 4 items for

  • Author or Editor: Glenn Gordon x
  • Refine by Access: All Content x
Clear All Modify Search
Glenn L. Gordon
and
John D. Martwitz

Abstract

Hydrometeor distributions were measured in two rainbands that passed over the California Valley. The ground radar was used to vector the University of Wyoming's instrumented King Air aircraft to the top of the rainband at which time an onboard computer algorithm was used to make multiple penetrations of an ensemble of ice particles that were assumed to descend at 1 or 2 m s−1 while drifting downwind. Distribution parameters were calculated for each penetration and the changes in these parameters were used to infer the different modes of growth that the particles undergo. It was found that there were five distinct regions of particle growth. Nucleation and depositional growth were the dominant processes near the top of the rainband. The hydrometeors then fell through a region of aggregation from the −20°C level to the − 10°C level. Ice crystal multiplication was the dominant process from the −10°C level to the −4° level. From −4 to O°C, aggregation was again the dominant processes. Below the 0°C level, melting and collisional coalescence were the main processes.

Bulk ire densities were calculated by comparing radar reflectivities and reflectivites calculated store the hydrometeor distributions. Bulk ice densities were very low, reaching only 0.1 g cm−3 just above the melting layer.

Full access
Glenn L. Gordon
and
John D. Marwitz

Abstract

The 1977–78 Sierra Cooperative Pilot Project (SCPP) field season offered an opportunity for comparing several Particle Measuring Systems (PMS) probes. During that winter the University of Wyoming's King Air aircraft was instrumented with 1D cloud, 2D cloud and 2D precipitation probes. Data from the three probes were analyzed from several flights in stable oregraphic storms. Various temperature levels (and hence, hydrometeor habits) above and below 0°C were flown in order to compare the data for water drops and for different ice crystal habits. It was found that all three probes agree quite well when sampling water drops of any size; however, when sampling ice crystals the probes agreed only at sizes larger than about 1 mm.

Full access
William L. Woodley
,
Thomas J. Henderson
,
Bernard Vonnegut
,
Glenn Gordon
,
Robert Breidenthal
, and
Shirley M. Holle

Abstract

This paper presents the results of studies of aircraft-produced ice particles (APIPs) in supercooled fog over Mono Lake, California. The King Air 200T cloud physics aircraft of the University of Wyoming and three other aircraft (a Piper Aztec, a Cessna 421-C, and a T-28) were involved in the tests. The King Air served as the monitoring aircraft when the other aircraft were tested and as both the test and monitoring aircraft when it was tested.

The studies demonstrated that the King Air produces APIPs. The ice crystals, in concentrations up to several hundred per liter, are initially quite small and of almost uniform size, and they grow to larger nearly uniform sizes with time. APIPs production is most likely at low ambient temperatures and high power settings, and when the gear and flaps are extended.

APIPs were not detected from the other aircraft. The Piper Aztec and Cessna 421 aircraft were tested on days on which an APIPs signature was produced by the King Air. The T-28 aircraft was tested when the fog-top temperature was greater than − 6°C and neither the T-28 nor the King Air produced APIPs under these conditions.

Homogeneous nucleation appears to be responsible for the observed APIPs signature, although the exact mechanism for nucleation is not known. In addition, there is the suggestion that a weaker APIPs signature may be generated by heterogeneous nucleation, when the cooling in the prop-tip vortex falls short of that thought necessary for homogeneous nucleation (i.e., ∼ − 39°C).

Full access
William L. Woodley
,
Glenn Gordon
,
Thomas J. Henderson
,
Bernard Vonnegut
,
Daniel Rosenfeld
, and
Andrew Detwiler

Abstract

This paper presents new results from studies of aircraft-produced ice particles (APIPs) in supercooled fog and clouds. Nine aircraft, including a Beech King Air 200T cloud physics aircraft, a Piper Aztec, a Cessna 421-C, two North American T-28s, an Aero Commander, a Piper Navajo, a Beech Turbo Baron, and a second four-bladed King Air were involved in the tests. The instrumented King Air served as the monitoring aircraft for trails of ice particles created, or not created, when the other aircraft were flown through clouds at various temperatures and served as both the test and monitoring aircraft when it itself was tested. In some cases sulfur hexafluoride (SF6) gas was released by the test aircraft during its test run and was detected by the King Air during its monitoring passes to confirm the location of the test aircraft wake. Ambient temperatures for the tests ranged between −5° and −12°C. The results confirm earlier published results and provide further insights into the APIPs phenomenon. The King Air at ambient temperatures less than −8°C can produce APIPs readily. The Piper Aztec and the Aero Commander also produced APIPs under the test conditions in which they were flown. The Cessna 421, Piper Navajo, and Beech Turbo Baron did not. The APIPs production potential of a T-28 is still indeterminate because a limited range of conditions was tested. Homogeneous nucleation in the adiabatically cooled regions where air is expanding around the rapidly rotating propeller tips is the cause of APIPs. An equation involving the propeller efficiency, engine thrust, and true airspeed of the aircraft is used along with the published thrust characteristics of the propellers to predict when the aircraft will produce APIPs. In most cases the predictions agree well with the field tests. Of all of the aircraft tested, the Piper Aztec, despite its small size and low horsepower, was predicted to be the most prolific producer of APIPs, and this was confirmed in field tests. The APIPs, when they are created, appear in aircraft wakes in concentrations up to several hundred per liter, which are initially very small and almost uniform in size but grow to larger nearly uniform sizes with time. APIPs production is most likely at low ambient temperatures when an aircraft is flown at maximum power with the gear and flaps extended, resulting in a relatively low airspeed under high-drag conditions. It is predicted that APIPs production of an aircraft can be decreased or eliminated altogether by using a propeller with a larger number of propeller blades, such that the engine thrust is distributed over more blades, thereby decreasing the cooling on each blade. Plans to test this hypothesis using three- and four-bladed King Airs as the test aircraft never came to fruition because of unsatisfactory weather conditions. It is likely that APIPs have confounded the results of some past cloud microphysical investigations, especially those in which repeat passes were made through individual clouds under heavy icing conditions by aircraft known now to be APIPs producers. Aircraft flying under such conditions are forced to use high power settings to overcome the drag of a heavy ice load. These are the conditions that field tests demonstrate are most conducive to the production of APIPs. In these situations, APIPs may have led investigators to conclude that there was more rapid development of ice, and higher concentrations of ice particles in clouds, than actually was the case.

Full access