The Cloud Population and Onset of the Madden-Julian Oscillation over the Indian Ocean during dynamo-amie



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Table 3: Maximum lagged cross-correlation coefficients (with lag in hours in parentheses) between 20 dBZ echo-top height, convective/stratiform areal coverage, and unfiltered, unsmoothed specific humidity anomalies for 1 October – 15 January using various smoothing periods. All correlation values that are bolded are statistically significant at the 95% level. Variables correlated are shown in columns 1 and 2. Positive lags indicate that Variable 1 comes first. (Conv = Convective areal coverage; Strat = Stratiform areal coverage).









Smoothing Interval

Var. 1

Var. 2

None

6 h

12 h

24 h

36 h

72 h

Conv

q'850

0.45 (0)

0.49 (0)

0.54 (0)

0.60 (0)

0.61 (0)

0.69 (0)

Conv

q'700

0.50 (+3)

0.53 (0)

0.58 (0)

0.66 (0)

0.70 (0)

0.80 (0)

Conv

q'500

0.49 (+6)

0.51 (+6)

0.54 (+12)

0.61 (+24)

0.61 (+36)

0.73 (+72)

Conv

q'300

0.44 (+9)

0.47 (+6)

0.51 (+12)

0.50 (0)

0.51 (+36)

0.59 (+72)

Strat

q'850

0.34 (-3)

0.37 (-6)

0.39 (-12)

0.42 (-24)

0.46 (-36)

0.54 (-72)

Strat

q'700

0.45 (-3)

0.47 (0)

0.50 (0)

0.55 (0)

0.61 (0)

0.77 (0)

Strat

q'500

0.55 (+3)

0.57 (0)

0.60 (0)

0.65 (0)

0.70 (0)

0.76 (0)

Strat

q'300

0.52 (+3)

0.56 (0)

0.61 (0)

0.66 (0)

0.68 (0)

0.74 (0)

Conv

Strat

0.81 (+3)

0.80 (+6)

0.76 (0)

0.80 (0)

0.82 (0)

0.81 (0)

Figure Captions

Figure 1: Location of the IOP in the Indian Ocean. Labeled dots represent rawinsonde launch locations within the IOP. Inset: Location of S-PolKa, SMART-R, and the ARM facility on Addu Atoll.


Figure 2: Radar-derived precipitation averaged over the entire observational domain of S-PolKa. The red and blue lines attribute the amounts of precipitation to clouds classified as either convective or stratiform, and the black line denotes the total precipitation. WH MJO phases are denoted along the top axis. Solid, black vertical lines are drawn at times of minimum rainfall before or after large-scale convective events, which are denoted by LCE1, LCE2, and LCE3.
Figure 3: Examples of isolated shallow cells (top left), small clusters of convection with limited stratiform (top right), a squall line with associated stratiform area (bottom left), and mesoscale convection with widespread stratiform coverage (bottom right). The boxes in each 2x2 table correspond to the percentage of rainfall that is convective (top left) and stratiform (bottom left) and the fraction of the radar domain covered by convective (top right) and stratiform (bottom right) echoes for each panel. Dates for each event are shown.
Figure 4: a) Mean fraction of radar domain occupied by either stratiform or convective precipitating clouds during each phase of the MJO as described by WH. b) Same as a), but composited in three day intervals relative to Day 0 instead of by WH MJO phase for stratiform echoes during each LCE and composited among the three LCEs. c) Same as b), but for convective echoes.
Figure 5: Joint probability density function, with respect to time and height, of 20 dBZ echotop heights observed by S-PolKa. The series is first smoothed to 3-hour intervals, then the PDF at each time is normalized to 1. White columns represent periods when the S-band was not operational. The dates denoted on the top axis represent the Day 0 associated with each large-scale convective event.
Figure 6: a) Probability distribution functions of 20 dBZ echo-top heights and b) number of 20 dBZ echo-tops at various heights observed by S-PolKa. Both are plotted as time-height diagrams. c) Probability distribution functions for 20 dBZ echo-top heights for "rainy periods" and "dry periods " and WH MJO phases 8-3 and 4-7.
Figure 7: Anomalies of zonal wind (u'), meridional wind (v'), and temperature (T'); and fractional difference of specific humidity from the mean (q*'). All are computed with rawinsonde data from soundings launched from Gan Island. All anomalies are calculated relative to the mean value from 1 October 2011 to 9 February 2012. Data have been interpolated temporally to fill in for missing soundings or bad data, and vertical resolution of the data after smoothing is 5 hPa. The dates denoted on the top axis represent the Day 0 associated with each large-scale convective event.
Figure 8: a) Same as Figure 5 but smoothed to 72-hour intervals. The solid red line follows the modal distribution of cloud echo-top height. b) Timeseries of q*' smoothed to 72 hour intervals. The Eulerian derivative of q*' is shown in gray contours only where positive. The solid black line is the same as the red line in a). The dates denoted on the top axis represent the Day 0 associated with each large-scale convective event.
Figure 9: Composite median relative humidity vertical profiles computed from rawinsonde data at Gan Island. The black solid (dashed) line is the relative humidity profile for MCS days during MJO active (inactive) phases 8-3 (4-7). The blue and red lines show the relative humidity profiles, respectively, for rainy periods and dry periods.
Figure A1: a) Same as Figure 6c, but using a precipitation threshold of 0.25 mm to separate rainy and dry periods (see text). b) Same as Figure 9, but using a precipitation threshold of 0.25 mm.

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