Vertical motion in the stratiform precipitation region observed with Equatorial Atmospheric Radar (EAR)

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1 Vertical motion in the stratiform precipitation region observed with Equatorial Atmospheric Radar (EAR) NISHI Noriyuki (Kyoto Univ.) with: M.K. Yamamoto, T. Shimomai, S. Mori, A. Hamada, S. Fukao SOWER 2006/07/19

2 Purpose observing the fine structure in various upper and middle troposphere clouds Cirriform clouds, Altostratus, Nimbostratus In this study, we present the fine structure in the nimbostratus with larger.

3 Group of cumulonimbus The understanding of the nimbostratus (anvil) is important also for the generation of cirriform clouds. Cumulo nimbus Nimbo stratus Cirrus

4 Mesoscale system convective part and stratosphere part

5 Vertical motion in the stratiform region Average 10-20cm/s Few exceptions W in stratiform precipitation region by sonde, weather radar and VHF radar etc. (m/s). Houze(1989,QJRMS) Line shape system LAYER ASCENT

6 W in stratiform region Few study on fine W structure Cifelli and Rutledge(1994, JAS): Two cases in monsoon and break periods in N. Australia Line-type system in break monsoon Z W(contour 50cm/s) Rain

7 Fine W structure in nimbostratus Observation of W with 10cm/s and 10-min scale in the upper troposphere -- difficult Comparison of instruments radiosonde Low time resolution Weather radar Problem in boundary condition when integrating horizontal divergence vertically Lidar etc. Need hypothesis VHF radar Possible,but VHF radar(e.g. Equatorial Atmospheric Radar: EAR) In upper troposphere Even EAR, difficult weak Bragg scattering and weak partial reflection Special vertical mode (only vertical beam) alternately operated with normal standard mode (5 beams) Intensified quality control of Doppler spectral data

8 Method and data EAR special obs. with vertical wind mode (Nov2003) Resolution resolution 3min 150m(Z) Accuracy 2.6cm/s Weather radar (λ= 3cm) Not directed vertical direction Average at circle with 29.5 elevation angle (dbz) and the ratio of above-noise-level data (%) Other datasets GOES9 Tbb Calculating estimated cloud top height with temperature in NCEP reanalysis Version 2. [In most cases, lower values are calculated than actual top] Optical raingauge (averaged in 10 minutes)

9 Typical case(6 Nov 2003) Almost isolated cloud cluster passes over EAR from SE to NW Movement of cluster (GOES-9 Tbb: K)

10 Conv./Strat. By Weather radar Convective 1200 UTC 06Nob2003 Stratiform 1647 UTC 06Nob2003

11 Gentle upward motion in the later stage of stratiform region Stratiform precipitation region identified by the presence of bright band When Bright Band is present, stratiform. The reverse is not always true (Steiner et al., 1995, JAM) 14 3 W(cm/s) Z (dbz) Stratiform

12 Downward motion and strong upward motion during earlier stage of stratiform period During later stage, only weak upward motion (0-40cm/s) two to three hours, 3-5km thickness in height 14 3

13 Gentle upward motion in the later stage of stratiform region 8-11km 平均 Fluctuation component is small Particularly in the vertical direction 12-min average Confirmation with 3min data Not available in the upper part 3km horizontal resolution (when 15m/s speed) No prominent small-scale structure even in 3-min data 3-min average

14 8 and 20 Nov case W(cm/s) 8 Nov case Gentle upward motion in the later stratiform period Z(dBZ) 14 3 Stratiform

15 W(cm/s) 20 Nov case A little stronger, but similar gentle upward motion Z(dBZ) 14 3 Stratiform

16 Comparison of 3 cases Histogram in 8-11km height range with 12 min and ΔZ=150m resolution In all cases, high rate of 0-40cm/s upward motion detected Similar gentle upward motion region in 2 and 15 Nov Down +40cm/s< +0~40cm/s

17 Cause of gentle upward motion Two factors 1. Generation of gentle uniform upward motion 2. Suppression of strong upward motion and short-period variabilities 1. Generation of gentle upward motion a)deposition Saturated with ice, but no with wate Latent heat by deposition of vapor to ice Mesoscale low pressure This process can product the uniform upward motion if it occurs in deep range Houze (1989, QJRMS)

18 b) Gravity wave (slow) The total effect of cumulonimbi in the convective region Slow gravity wave Upward motion phase is placed to the nimbostratus Pandya and Durran (1996,JAS)

19 2. Suppression of strong upward motion and short-period variability Processes that make small scale convective motions Old cells generated in the convective part New convective motions by instability Riming (seeder-feeder), which brings latent heat only in the lower part of nimbostratus (deposition, if it happens only in the lower part) Gravity wave with short time scale Generated in mainly convective region We hope the present results are referred for understanding dynamical and physical processes in nimbostratus and cirriform clouds through theoretical and modeling approach

20 Summary 3 cloud clusters during November 2003 Fine structure with 3min 150m(z) resolution data Gentle upward motion with small fluctuation during the later stage of stratiform precipitation region 0-40cm/s, thickness3-5km, 2-3 hours No predominance of waves and convective cells Although the representative value of W in stratiform region is 10-20cm/s, the fine structure has not been so well-examined Deposition and gravity wave may be possibly causes of this gentle upward motion