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<br /><t. <br /> <br />.* <br /> <br />.. <br /> <br />I' <br /> <br />! "' <br />, <br /> <br />i. <br /> <br />~ . <br />i <br /> <br />, <br />to... <br /> <br />:. <br /> <br />em wavelength) radar, also operating in volume scan mode and located at Carolina. <br />Microphysical measurements were obtained using an instrumented Learjet. The Learjet <br />was equipped with a PMS FSSP probe measuring cloud droplet spectra and a PMS <br />two-dimensional cloud particle imaging probe (2D-C). A CSmO-King liquid water probe <br />was used to measure liquid water contents while a Lyman-alpha engine vapor technique <br />(Morgan et al.,1989) was used to measure the total water content in the clouds. An on- <br />board X-band (3-em wavelength) radar was used to measure in-cloud radar reflectivity in <br />the range bin 1800 m ahead of the aircraft. Other instrumentation on the aircraft pr~ded <br />measurements of temperature, humidity, static pressure, air speed and vertical air motions. <br /> <br />In both the BPRP and PAWS studies the aircraft also conducted soundings at the start <br />and end of each mission to obtain vertical profiles of temperature, dewpoint and pressure. <br />In addition to the aircraft soundings and the rawinsonde releases at Bethlehem, data from <br />rawiusonde releases at Pretoria, Bloemfontein and Durban by the South African Weather <br />Bureau were also used to reconstruct profiles to initialize the model in the modelling studies <br />described in chapter 4. <br /> <br />Regular checks and calibrations were performed on the instrumentation and data were <br />subject to quality control on a daily basis in order to assure reliable and accurate data <br />collection. <br /> <br />2.2 Numerical model <br /> <br />The objective with the modelling studies is to assess certain aspects of the physical <br />chain of events which might allow seeding to affect the surface precipitation. Physically <br />accurate dynamics is essential for the success of such a study since the dynamics to a <br />large extent drives the microphysics. The model has to be able to study the initiation, <br />organization and complete life cycle of convective and orographic clouds over complex <br />terrain. Thus the level of sophistication of the model must be chosen such that the overall <br />character of summertime convective and winter orographic clouds as well as the fields of <br />any embedc:led convective clouds are similar to those observed. In particular the temporal <br />and spatial structures of the clouds and the surrounding flow should be well reproduced, <br /> <br />26 <br />