Vertical wind distribution in and around upper tropospheric cirriform clouds

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1 Vertical wind distribution in and around upper tropospheric cirriform clouds NISHI Noriyuki (Graduate School of Science, Kyoto University) Rart I. FINE VERTICAL STRUCTURE OF THE HORIZONTAL DIVERGENCE OVER THE ASIAN SUMMER MONSOON REGION

Vertical fine structure in the upper troposphere Horizontal divergence in climatological July (NCEP Reanalysis Ver.1) In most of the region, 150hPa and 300hPa have same sign.

2 Vertical fine structure in the upper troposphere Horizontal divergence in climatological July (NCEP Reanalysis Ver.1) In most of the region, 150hPa and 300hPa have same sign. 150hPa(14.5km) Divergence 300hPa(9km) Convergence However, particularly in the Asian Monsoon Region, positive divergence is detected at 150hPa, while negative divergence at 300hPa.

Jun1998 10N (ECMWF) Divergence region extending leeward in the upper troposphere

3 Jun N (ECMWF) Divergence region extending leeward in the upper troposphere even in monthly mean field 100E Divergence Convergence Strong Easterly W E Westrly

Upper tropospheric cirriform clouds extend with a scale of 1000km in Asian summer monsoon region Cirriform clouds out of cumulus clusters -- extending leeward [GMS] due to very strong east or

4 Upper tropospheric cirriform clouds extend with a scale of 1000km in Asian summer monsoon region Cirriform clouds out of cumulus clusters -- extending leeward [GMS] due to very strong east or northeast wind. Horizontal divergence in the upper part of cumulus clusters -- also extending leeward [global analyses] Can the extension of divergence leeward be explained with a process in the cirriform clouds in the upper troposphere? Divergence Convergence W E

Monthly mean horizontal divergence at 200hPa in 1998Jun Horizontal Divergence at 200hPa averaged in June 1998 EC operation NCEP Reanalysis2 JMA GAME reanalysis ERA40

5 Monthly mean horizontal divergence at 200hPa in 1998Jun Horizontal Divergence at 200hPa averaged in June 1998 EC operation NCEP Reanalysis2 JMA GAME reanalysis ERA40 Strategy Finding interesting divergence patterns in global analyses For the patterns, analyzing more direct observation data in order to detect the supporting evidence

6 Case in Jun 1998 :Upward motion confined in the upper layer was observed in the central Bay of Bengal Upward in almost whole troposphere at 87.5E; confined in the upper layer at more western longitudes. Wind: 15m/s westerly in the lower layer; maximum 50m/s easterly in the upper layer 10N 6/16-26,1998 ECMWF Upward hpa Downward June, E 85E 82.5E 87.5E

7 Gap between precipitation area and upper cirriform cloud Comparing precipitation area (convective part and very thick anvil part) and upper tropospheric cirriform cloud area TRMM VIRS Ch4 TRMM TMI Surface Rain [warm color: High cloud top] 10N Eastern edge of precipitation area is close to the eastern edge of upper cloud Western edge of upper cloud is km west from western edge of precipitation area 80E 90E 0N Contour: Rainy in TMI(left) 08Z 18 Jun 1998 south west part of Bay of Bengal (80-90E 0N- 10N) 10mm

8 Example of cluster (GMS IR) (18Jun Z) Cluster itself moved eastward (10m/s almost same as wind speed in the lower layer) Upper cirriform clouds extended westward( 20-30m/s almost same as wind speed in the upper layer) Lifetime of cluster (region with Tbb less than 220K) is several hours 1hour km leeward extension of upper cirriform cloud in each cluster

9 Part.I Summary Purpose Getting supporting evidence Leeward extension of upward motion in the upper troposphere -- Even in monthly mean ECMWF data in June Data analysis with TRMM, GMS -- some cumulus clusters in Central Bay of Bengal in June Western edge of cumulus active region clear Each cluster Strong easterly confined in the upper troposphere Upper cirriform clouds spreading leeward with 20-30m/s speed Lifetime of cluster -- several hours As a result, upper cirriform cloud has km extension to the west of cumulus region. These process repeatedly happen in almost same longitude. Confined (tilted) upward motion (or thin convergence and divergence pair) in the upper troposphere even in monthly mean field. In the magnitude of vertical wind in the objective analysis (10-20cm/s) observed in the real upper cirriform clouds with 1000km scale?

10 Vertical wind speed in large vertical shear condition over Bay of Bengal Above Sumatra Island, the shear is not so small We tried to examine vertical wind with EAR (Equatorial Atmospheric Radar) m/s Magnitude of shear vector ( hPa)(NCEP reanalysis Ver.2)

11 Part II: Vertical circulation around tropical upper-tropospheric cirriform clouds observed by EAR (Equatorial Atmospheric Radar) NISHI Noriyuki 1, YAMAMOTO Masayuki 2,HAMADA Atsushi 1, HASHIGUCHI Hiroyuki 2, FUKAO Shio-Ichiro 2 ( 1 Graduate School of Science, Kyoto University) ( 2 Research Institute of Sustainable Humanosphere, Kyoto University) divergence convergence Observing vertical wind in the tropiacal upper troposphere (11-15km) -- difficlut Meteorological radar Only rainy or snowy area, Rawinsonde network Only larger scale, Lidar Distinguishing wind signal and snowfall is difficult Interesting events were reported in the circulation around upper tropospheric cirriform clouds ( anvil, cirrus) Case over the Bay of Bengal: reported at the last autumn meeting upward motion confined in the upper troposphre, it was located several hundred km west of cluster center and it may be formed by strong easterly wind in the upper troposphere We tried to observe vertical wind with scale of hours and vertical scale of 0.5-4km with using EAR (VHF radar) We could not get enough data through routine mode in this height range. We tried to establish the new observation and analysis mode for investigating upper tropospheric cirriform clouds.

12 Previous observational results of upper cirriform clouds by VHF radars in the world Houze(1989,QJRMS) In every campaign, upward motion in the cirriform clouds is 10-20cm/s Balsley et al.(1988,jas) Showing statistical results of VHF radar at Ponape. The error bar around 14-16km is fairly large Large error in this height range mm/hr Stratiform region 10cm/s Bay of Bengal Optically thick clouds with almost no rain extends several hundred km. Meteorological radar cannot always catch vertical motion.

Problems in analysis of vertical wind around upper tropospheric cirriform clouds (1) Weak echo around 12-14km low stability, interference Weak in even in the cloudy hours ( or worse ) by GMS image

13 Problems in analysis of vertical wind around upper tropospheric cirriform clouds (1) Weak echo around 12-14km low stability, interference Weak in even in the cloudy hours ( or worse ) by GMS image (2) Expected vertical wind speed is equal or less than 20cm/s: detectable minimum scale of routine observation Special mode (November 2003) Only vertical beam in continuous 90s Incoherent integration Using four sequence of 90s for 30 min scale event in the upper clouds Quality control by manual operation * All values got by automatic routine were again checked manually. Almost all troposphere can be observed during period with less interference Upper limit of upward motion in the upper cirriform clouds ROUTINE Vertical mode(90s) Vertical wind (3min) in 8 Nov Smoothing was conducted for each 9min, 450m height. If only one observation in the time-height grid, the data are plotted. Vertical axis shows the height from surface( 865m from sea level)

14 Vertical standing mode with the period of min :00 13:00 14:

Spectrum of vertical standing oscillation Dominant period range large day to day variability Peak is at 10-15min in the central troposphere and 15-60min in the

10m 6m Log of vertical wind spectrum averaged in each 6 hours. Showing spectrum averaged around 5-8km from surface.

15 Spectrum of vertical standing oscillation Dominant period range large day to day variability Peak is at 10-15min in the central troposphere and 15-60min in the upper troposphere In some days, no clear peak was observed Cause of day to day veriation not sure Local time 0h vaisala period 6hr 1hr 30m 15m 10m 6m Log of vertical wind spectrum averaged in each 6 hours. Showing spectrum averaged around 5-8km from surface Nov2003 Brunt-Vaisala Oscillation (Fukao et al., 1980, Radio Science) 6hr 1hr 30m 15m 10m 6m Log of vertical wind spectrum averaged 3km height range 05-11Z 07Nov2003, vertical axis shows the height from surface (km)

problem for rain amount EAR W(12 min average with 6 min

16 GMS Tbb IR1 (K) Period-I Period-II EAR W (One hour mean with 6 min shift) raingauge(mm/10min) Observational problem for rain amount EAR W(12 min average with 6 min shift) Vertical axis is height from sea level (km) The position of

17 Distribution of Vertical wind (W) in the upper troposphere Period-I(3-9Nov) is more quiet in 12-14km than Period-II (19-21Nov) The magnitude of W is less than 5cm/s regardless of cloud cover (by GMS) Even when active cumulus cluster passed, the upper limit of upward motion (5cm/s<) is around 12km Upward motion in the cirriform cloud in the cluster in Period-I See 14-15Z on 6 Nov Cloud top estimated by GMS is at leaset 14-15km Continuous upward motion (5cm<) is limited below11.5km; above that level downward motion range is a little larger than upward one Similar in 6Nov case Many previous studies show that downward motion after overshooting was observed above the top of cirriform cloud. In this case, upper 3km range inside the cirriform cloud is also downward or almost no vertical motion

Case of large cumulus cluster Typical cloud cluster Generated in the mountanious region to the

Convection part (12-14Z) and following cirriform part (14-18Z) Properties in cirriform part

In 14-15z, the cloud top is around 15km (see GMS).

18 Case of large cumulus cluster Typical cloud cluster Generated in the mountanious region to the east of EAR and moved westward slowly. The Shape is close to circle. Convection part (12-14Z) and following cirriform part (14-18Z) Properties in cirriform part Upward motion larger than 20cm/s continues 3-4hours. In 14-15z, the cloud top is around 15km (see GMS). But the upward motion (5cm/s<) is confined below 12km. Above that level, downward range is larger than upward range; it must be inside the cloud. GMS Tbb IR1 (K) Warm color shows high cloud top 12.5km 14.5km

cirriform clouds Depending of observational methods?

19 Upward motion around cirriform clouds Large scale cloud clusters in Period I In some previous papers, downward motion following overshoot was observed ABOVE top of cirriform clouds We need to make further analysis of vertical motion in the upper half of cirriform clouds Depending of observational methods? Little direct observation of W in the tropics What brings the difference between both Period I and II MJO phase? Wind shear ( Period I small shear, Period II Large easterly shear) Houze et al QJRMS Houze(1993) Text

20 Part II: Summary New observational mode and manual quality control enable us to get vertical wind data up to 13km ( height of upper cirriform clouds )with 5cm/s and 12min scale. Vertical wind in 12-13km height-range: During most of Period-I (3-9 Nov 2003), magnitude of W is below 5cm/s, while in Period-II (19-21Nov) rather large values of W were frequently observed. It does not depend on cloud coverage. During Period-I, active cloud clusters with top of around 15km passed EAR; the upper limit of upward motion (5cm<) is around 12km or lower. Vertically standing oscillation is the most dominant in middle troposphere; the amplitude reach 30cm/s even when upper cirriform cloud covered EAR. The events were possibly Brunt-Vaisala Oscillation. [Acknowledge] Rasiosonde data were offered by the following persons. Thank you so much. Dr YAMANAKA Manabu, Dr MORI Shu-ichi and Dr HAMADA Jun-Ichi

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

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