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<br />17 minutes after treatment, the aircraft will descend in approxi- <br />mately 600-m increments in about 2-min intervals to the +10 oel level, <br />further documenting the cloud water content and the precipitatfing ice <br />spectra and concentrations.* <br /> <br />F. Time of First Radar Echo <br /> <br />The time of first-echo formation (TFE) will be determined by the <br />first appearance of a 15-dBZ echo measured by the SWR-75 radar; at <br />Miles City. <br /> <br />G. Precipitation Response Variables Estimated From Aircraft <br />Measurements <br /> <br />e <br /> <br />After the King Air reaches the +10 oe level, it will make alternate <br />passes at about 3-min intervals along and across the shear vector <br />centered on the initial pointer. It will continue this procedure <br />until the case is terminated or the onboard radar detects an echo at <br />the aircraft's level within 8 km of the pointer. The King Air will <br />make repeated penetrations through any such echoes in an approximately <br />"X" pattern, with the most intense core of the rain shaft forming the <br />intersection of the flight paths. The onboard radar will be used to <br />guide the flight pattern and penetrations through the most intense <br />core. A third pointer will be set at the center of the rain shaft to <br />guide any penetrations made after the radar echoes disappear. I <br /> <br />The time to initial precipitation at the +10 oe level (TIPA) is <br />defined as the time of the first measurement of a rainfall rate in <br />excess of 1 mm/h averaged over a l-km distance at the +10 oe level. <br />The portion of the aircraft pass over which this measurement is made <br />must lie entirely within 8 km of the initial pointer location. <br /> <br />Aircraft-estimated rainfall (AER) is determined as follows: <br /> <br />1. The rainfall rate as measured by the 2D-P probe on board the <br />King Air is integrated along each path at the +10 oC level to <br />yi e 1 d . <br /> <br />Ti = fR(S) ds <br /> <br />,,", <br /> <br />'" <br /> <br />* If modifications to the instrumentation permit real-time determina- <br />tion of TFPI, the aircraft descent will begin after documenting TFPI, <br />or after the appearance of a first echo on the airborne radar,. or <br />17 minutes after treatment, whichever comes earliest. <br /> <br />20 <br />