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<br /> <br />Azimuth. 3200 <br /> <br />10 <br /> <br />-- <br /> <br />00 <br /> <br /> <br />CasallIarca <br />I <br /> <br />200 km <br /> <br />8km <br /> <br />'TARGET <br /> <br />Azimuth . 1520 <br /> <br />200 <br /> <br />Figure 2. Terrain cross-sections along the 1520 ant! 3200 rD;dials from the <br />radar site at Khouribga. The curoature of the base Ime and h~s of constant <br />elevation represent the effective c~roD:tu/"e of .au: earth (assummg stan~ard <br />refraction of the radar beam). SOlld lmes radiatmg ou.t from the center zllus- <br />trate the field of view along the 00, 10, 20, and. 30 elevation angles. <br /> <br />The three main cloud classes observed are <br />as follows: <br /> <br />(1) Stratiform cloud system associated <br />with either westerly or northwesterly <br />flow, and possibly containing embedded <br />convection. This class is called C 1. <br /> <br />(2) Relatively isolated convective clouds <br />that are generally associated with post <br />frontal storm events and consist mainly of <br />cumulus congestus. This class is called <br />C2. <br /> <br />(3) Cloud systems associated with a tropi- <br />cal air mass moving over Morocco from the <br />south and consisting mainly of alto- <br />cumulus and altostratus. This class is <br />called C3. <br /> <br />3. RESULTS <br /> <br />Figure 3 shows the frequency distribu- <br />tions (histograms) for the liquid water content <br />(g m-3) and ice particle concentration (number <br />of particles per 10 liters of air) for each of the <br />three cloud categories. In each case, the <br />ordinate indicates the number of one second <br />observations that fall into a given category. <br />All measurements in this data set were ob- <br />tained in-cloud at heights corresponding to <br />temperatures between _10 and -160C, so the <br />water contents represent a measure of the <br />available supercooled water. <br /> <br />This figure shows that the three cloud <br />classifications are microphysically distinct. <br />For instance, the supercooled liquid water <br />frequency distribution for class C2 indicates <br />that these clouds often contain relatively high <br />concentrations of supercooled water. Class C3 <br />clouds, on the other hand. were uniformly <br />found to contain little or no supercooled water. <br />The histogram for case Cl. has a more widely <br /> <br />distributed distribution of water contents, <br />with the most frequently measured levels <br />having. the lowest values, but occasionally <br />approaching the levels observed in class C2 <br />clouds. <br /> <br />As might be expected, the ice particle con- <br />centration (IPC) frequency distributions gen- <br />erally show an opposite trend as compared to <br />the liquid water plots. For example, the IPC <br />for class C2 is heavily skewed towards smaller <br />concentrations, while the liquid water plot <br />broadens out towards moderate or large <br />values. For class Cl and C3, the IPC distribu- <br />tion broadens towards larger values, with the <br />C3 category showing a secondary peak at high <br />concentrations. <br /> <br />4. TYPICAL STORM SEQUENCE <br /> <br />In order to understand the synoptic and <br />mesoscale conditions under which these cloud <br />types occur, we present below a brief discus- <br />sion of a typical storm sequence during which <br />a variety of cloud types were present. Data <br />used for this discussion are satellite photos, <br />radar data, rawinsonde data from the project <br />site at Beni Mellal, and observations from the <br />Moroccan cloud physics aircraft. <br /> <br />On January 16. 1988. a major storm sys- <br />tem entered Morocco producing a significant <br />period of clouds and precipitation. During <br />this storm, two cold fronts passed over <br />Morocco, in association with the southward <br />penetration of a polar air mass. A relatively <br />well organized cloud band was associated with <br />the main frontal passage at 00 Z on the 16th of <br />January. Although the radar echoes were <br />spatially quite extensive, they were rather <br />shallow, less than 4 km in most cases. After <br />the passage of this front. shallow isolated cu- <br />mulus clouds were present over the plains for <br />most of the day. During a research flight on <br />