SE eb ead on ital Fate kanaRentol Pella EAE tliat8s lt, 143 Five separate types of experiments are planned by TABLE 59. the cooperating groups. For the most part, these are being done jointly by two or more investigators. Some Progecr ITREX ExpertmMents ann PanrticrPATING GROUPS Experiment Groups participating”) cooperating groups are listed in Table 59. In experiment 1, several hundred grams of indium 1. Indium tracer budget 2. Indium, lithium, silver tracer comparison | 3. Chemical analysis of serial rain samples | UM, SWs SWS, UM ANL, UM an aircraft flying below the cloud base in a thunder- 4. Sulfur hexafluoride downdraft tracing 5. Pollutant scavenging efficieney ANL, SWS ANL, SWS of the experiments have definite goals; others are pilot, or exploratory in nature. The experiments and the will be released from a burning pyrotechnic flare by storm updraft. Rain from that storm will be collected by the network of samplers on the ground and ana- lyzed for the tracer by neutron activation. Total depo- sition of indium by the storm over the network will be ealeulated and divided by the known amount of indiumreleased to obtain the removal efficiency. Survey; ANL, Argonne National Laboratory. TABLE 60. SerraL Rain WaTeR SAMPLE COLLECTION AND ANALYSIS, PRoject ITREN | Experiment 2 has similar objectives, but in addi- tion will compare results between tracers to see if the different materials are removed at different rates. Tracer material elements present in rain were once borne by one or Lead, lead-210 Oxygen-18, deuterium Ice nuclei Several elements by atomic absorption | Pollens, beta radioactivity Experiment 3 is based on the recognition that the more of the following: soluble particles, insoluble particles, large particles, small particles, condensation nuclei, and ice nuclei. Besides, oxygen and hydrogen isotopes are present in rain water. These different particles and water tracers may follow different pathways through the precipitation process, depending on their size and chemical nature. Sometimes different pathways result in different concentration-versustime curves (concentration ‘‘profiles”) between two tracers observed at the same station. For example, we know (Dingle and Gatz‘) that gross airborne dust, artificial radioactivity, and plant pollen concentra- tions In rain usually have an inverse relationship to rainfall rate, whereas ice nuclei (Vali'”)} usually have a direct relationship. We want to see if a number of different character- istic profiles occur, and whether each can be identified with a particular pathway through the precipitation process. If so, one could tell how precipitation scavenges a given particle or element (i.e., what its pathway is) by observing its concentration profile in rain. In this experiment we will look for different tracer profiles in two series of rain samples from the same storm at two stations 2km apart. The tracer mate- rials, rain collection sites, and analyst groups are listed in Table 60. Some analyses will be done by cooperating specialists at the U. S. Geological Survey, Denver, Colorado, and The University of Wyoming, Laramie. Experiment 4 is an attempt to trace thunderstorm downdrafts from their theoretical middle-level (3-6 km) origin to ground level, using gaseous SF,first developed for air pollution tracing. Such deep down- drafts could be important transport mechanisms for 1 ‘) UM, University of Michigan; SWS, Hlinois State Water Collection te Analyst group UM | ANL x xX xX | , xX | x X X xX | ANL, UM ANL, USGS | UW ANL | UM ‘) UM, University of Michigan; SWS, Illinois State Water Survey; ANL, Argonne National Laboratory; USGS, U. 8. Geological Survey; UW, University of Wyoming. bringing bomb-debris radioactivity from aloft to the surface, Experiment 4 is similar to the first experiment, but uses tracers that are naturally available instead of introduced. In this ease, the tracer input to the storm 18 not controlled and must be measured. This is done by taking a filter sample of the aerosols entering the storm from a plane flying in the updraft. The air and moisture inputs are measured at the same time. Depo- sition is measured over a network of rain collectors and divided by input to find the removalefficiency for each storm sampled. In summary, Project ITREX is a cooperative study to learn more about the mechanisms and efficiencies of aerosol scavenging by rain, using natural and artifi- cial tracers. We are also using techniques of trace analysis to understand the basic circulations, microphysics, and chemistry of convective storm precipitation. REFERENCES 1. Dingle, A. N., and Gatz, D. F. Air cleansing by convective rains. /. Appl. Meteorol. 6(2), 160-168 (1966). 2. Vali, G. Freezing-nucleus content of hail and rain in Alherta. Preprints of papers presented at the Sixth Conference of Severe Local Storms, Chicago, Hlinois, 8-10 April, 1969, pp. 270-274 (unpublished).