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<br />The abundance of available data is reflected in the treatment of missing data. <br />If any portion of a sounding which is used to calculate a parameter is missing, the <br />entire sounding is discarded from the analysis. Missing precipitation observations <br />are, however, carried through the analysis as missing rather than discarded. <br />The parameters derived from the soundings and made available for analysis are: <br />. wind component normal to the massif barrier at the 600 mb level <br />. stability index (e [500] - e [700]), where saturation is assumed <br />e e <br />. pressure at the nodal surface <br />. pressure, temperature, wind direction and speed at effective cloud top <br />. temperature at lifted cloud top <br />. temperature at the base of the effective cloud layer <br />. average normal wind component in the effective cloud layer <br />. height of the 500 mb level <br />. normal component of the wind at the height of the barrier crest <br />. mixing ratio at effective cloud base <br />. mixing ratio at effective cloud top <br />. difference of the above two quantities <br />. pressure at the base and top of each cloud layer detected in the sounding <br />Each sounding is first checked for valid winds. The procedure is to begin at <br />the height of the valley floor and step upward at even 50 mb increments until a <br />level is reached at which the component of wind nOTI!lal to the barrier is greater than <br />V . , an adjustable minimum generally set at 2 m see-I. This level is designated to <br />mln <br />be the top of the dead layer. If the dead layer is found to extend above the crest <br />height, the observation is discarded since no lifting would be indicated. Then the <br />winds at the levels required for the nodal surface calculation are checked to insure <br />a positive component normal to the barrier. If the co~ponent is negative (ie, winds <br />blowing the wrong direction over the barrier) or the wind is missing, the sounding <br />is discarded. Finally, the winds at all levels between the top of the dead layer and <br />the nodal surface are checked to insure positive components normal to the barrier. <br />The next step is to identify all cloud layers in the sounding. A layer is de- <br />fined as being cloudy if the dewpoint depression in that layer is less than an <br />assumed threshold value as described earlier. The threshold value used is a function- <br />of pressure varying linearly from 2C at 800 mb to 6C at 400 mb. At pressures greater \! <br />than 800 mb the threshold is held constant at 2C; at pressures less than 400 mb the III <br />threshold is held constant at 6C. With all cloud layers defined, it is then necessary \.1 <br />to determine which layers were effectively participating in the precipitation processes. ,i <br />I. <br />i <br />1-31 t <br />I' <br />I <br />I <br />