Secondary Experiments

SECONDARY EXPERIMENTS

It is anticipated that there will be occasions when CONTROLLED seeding experiments on hailstorms will not be possible for a variety of reasons, such as, when a storm has no feeding line and therefore does not fit the conceptual model. During those occasions, useful and valuable observations can still be obtained through a series of "fall back" experiments. These experiments are:

A. General Thunderstorm Penetrations

B. Aircraft and Radar Data Inter comparison

C. Storm Inflow

D. Super Cell Storm Studies

A. General Thunderstorm Penetrations

Purpose

Determination of micro physical characteristics of feeder clouds associated with NATURAL and OPERATIONALLY SEEDED clouds. This is to be carried out when controlled seeding experiments are not possible.

Experimental Procedure

A variety of flight tracks are permitted and are to be chosen by the Aircraft Mission Scientist. Penetrations of feeder clouds at any level (-10&#176C preferred) and cloud base storm inflow studies will be performed.

B. Aircraft and Radar Data Intercomparison

Purpose

To compare polarization radar data with aircraft observations of precipitation. This is to be carried out when controlled seeding experiments are not possible.

Experiment Procedure

Any weather condition producing S-band radar echoes within the project area may be suitable for this study. The flight track on a given day will be decided by the Aircraft Mission Scientist in a coordinated effort with the radar meteorologist on duty.

C. Storm Inflow Experiment

Purpose

This experiment will attempt to locate the inflow near cloud base for several different storms. It is hypothesized that such inflow is mainly from the right front flank of the storms. Such considerations are important for positioning cloud base seeding aircraft.

D. Super Cell Storm Studies

Background

A hailstorm is recognized as being of the super cell type if it has a large, single and steady updraft area below a weak echo region, continuous storm propagation to the right of the mid-level winds, typically a hook shape low level PPI echo, and no line of feeding towering cumulus clouds. These storms are considered uncommon, though not rare. They most often produce extensive hail damage. No controlled seeding experiments are possible for this type of storm.

Several fall back experiments are possible in this case:

1. Research aircraft maps the inflow area making kinematic and thermodynamic measurements,

2. Research seeder dispenses radar chaff in a line orthogonal to the inflow and about 10 miles from the storm,

3. Research aircraft penetrates weak echo regions over a range of temperatures from cloud base to -15&#176C making thermodynamic, micro physical and kinematic measurements,

4. Similar to 3, but add cloud base seeding by the research seeder close enough to storm to ensure delivery. The research aircraft would continue making repeated penetrations at -10&#176C to -15&#176C to monitor the changes which accompany seeding. The T-28 penetrates more storm near -20&#176C level in region where reflectivity is less than 45 dBZ to monitor seeding signature at higher levels.

Particular circumstances will identify which of these experiments would be most useful. The identification of this storm type and the decision of which experiments to pursue should rest jointly with the Research Director, the Aircraft Mission Scientist, and the Science Radar Monitor. If the storm changes character to one which allows controlled seeding experiments, then the fall back experiment should be concluded quickly so a controlled seeding experiment can commence.