"POLARIMETRIC SIGNATURES FROM ICE CRYSTALS OBSERVED AT 95GHz IN WINTER CLOUDS. PARTS I AND II."

M. Wolde and G. Vali

(Preprints of papers accepted for publication in the Journal of Atmospheric Science.)

"Polarimetric signatures from ice crystals observed at 95 GHz in winter couds. Part I. Dependence on crystal form.


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   Table 1.   Summary of polarimetric observations for different crystal types.

    Figure 1.  (a) Variation of ZDR and LDRHV with radar beam incidence angle, alpha, in cloud regions of hexagonal plate (P1a) and/or stellar (P1d) crystals listed in lines 1-5 and 22-24 of Table 1. Means and standard deviations are indicated. Number of data points per alpha-interval varies between a minimum of 20 and many thousands, depending on the flight pattern during data collection. (b) Sample 2D-C images of the types of crystals included in this graph. The widths of the image strips is 800 micrometer.

    Figure 2.   (a) Same as Fig. 1, except for dendrite crystals listed in lines 8, 9 and 25 of Table 1. A - lightly rimed, P1e; B - moderately rimed, R1d; and C - densely rimed crystals, R2d. (b) Samples of 2D-P images. The width of each strip represents 6.4 mm.

   Figure 3.  (a) same as Fig. 1, except for lightly rimed needle crystals (R1a) listed in lines 10-11 and 26-27 of Table 1. (b) Sample 2D-C images with 800 micrometer wide limage strips.

   Figure 4.  (a) same as Fig. 1, except for obeservations taken within the melting layer, as listed in lines 18-19 and 33-34 of Table 1. (b) Sample 2D-C images with 800 micrometer wide limage strips.

   Figure 5.  (a) same as Fig. 1, except for special graupel' situations listed in lines 20-21 and 35-36 of Table 1. (b) Sample 2D-C images with 800 micrometer wide limage strips. (c) Size distribution for data segment of line 21, Table 1.

   Figure 6.  Summary of observations reported in this paper in terms of ZDR and LDR signatires of different ice crystal types for near-horizontal (lef-hand panel) andnear-vertical (right-hand panel) radar elevation angles. LDR < -22 dB represents the detection limit achieved.

"Polarimetric signatures from ice crystals observed at 95 GHz in winter couds. Part II.Frequencies of occurence.


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   Table 1.  Frequencies of occurrence (%) of ZDR and LDR values exceeding indicated thresholds at different incidence angles (alpha).

    Figure 1. Frequencies of occurrence (%) of ZDR > 3 dB and > 5 dB at different temperatures and radar incidence angles (alpha). Frequencies in the left-hand panels are with respect to the total number of valid observations within the given T-alpha interval. Histograms in the right-hand panels show the relative frequencies of ZDR > 3 dB or > 5 dB for alpha < 45 degrees; the number of points included is given by N. Temperature and alpha intervals with less than 1000 data points are denoted by "ND".

    Figure 2.   Frequencies of observations of LDR>-18 and -16 dB. Format is as described for Fig. 1.

   Figure 3.   Frequencies of occurrence (%) of ZDR > 3 dB and LDR > -18 dB for observations in altocumulus on February 18, 1997. Note the the contour intervals are much higher than those of Fig. 1 and 2.

   Figure 4. .Frequencies of occurrence (%) of ZDR > 3 dB and LDR > -18 dB for observations in nimbostratus on February 11, 1997. Format is as described for Fig. 1, except that the histogram in the right-hand panel is for alpha > 45 degrees.

   Figure 5.  Frequencies of occurrence (%) of ZDR > 3 dB and LDR > -18 dB for observations in cumulus congestus on April 4, 1997. Format is as described for Fig. 1.