Characteristic differences between the heaviest rainfall and the tallest storms
Atsushi Hamada1, Yukari N. Takayabu1, Katsuhiro Nakagawa2, Toshio Iguchi2,
Chuntao Liu3, and Edward J. Zipser4
1
Atmosphere and Ocean Research Institute, the University of Tokyo, Japan; 2 National Institute of Information and Communications Technology, Japan;
3 Texas A&M University-Corpus Christi; 4 University of Utah
Data
Introduction

TRMM PR 2A25 version 7
- A removal filter for false-extreme was applied (Hamada and Takayabu 2014, JAMC)
 ERA-interim: monthly and 6-hourly, 1.5˚ in lon/lat
 Analysis period: Sep 2001–Aug 2012 (11 yrs)
Tallest convection ≠ Heaviest rainfall

Zipser et al. (2006)
The world’s most intense
convections from TRMM PR/TMI
Definition of regional extreme rainfall events
Murayama (2011)
Regional (2.5°°x2.5°) extreme
rainfall from TRMM PR
Construct a rain event database
• Rain event: A set of contiguous pixels of PR_2A25 near-surface rain rate (NSR)
> 0.5mm/h (~17dBZ)
2. Determine regional extreme events on each 2.5° x 2.5° grid cell
• Extreme rain event: Rain events in which max. NSR is within uppermost 0.1%
• Extreme convection event: In the same way but using max. 40-dBZ ETH
3. Categorize extreme events into 3 types
• R-only extreme: Extreme events that is determined as an extreme rain event,
but not as an extreme convection event
• H-only extreme: An extreme convection event, but not an extreme rain event
• RH extreme: Determined as both extreme rain and convection events
- Rain type (conv/strat) is not considered, since >95% are convective
1.
There have been several regional studies on the differences between heavy
rainfall and intense convection (e.g., Smith et al. 1996; McCollum et al. 2000;
Sohn et al. 2013; Shige et al. 2013)
 What is the global aspect?
 Physical interpretation?

Questions to be answered
To what extent is extreme rain linked with extreme convection?
 Any difference between rain and convection extreme events?
- Rain characteristics
- Preferred environment
 Any regional dependence of extreme event characteristics/environments?

Example of rain events
max. 40-dBZ echo-top
max. near-surf. rain rate
Robust difference between R/H extremes irrespective of region
Ocean
Land
R-only
Color: No. of profiles at extreme pixels w/ (solid) mean & (dashed) ±1σ
Along right axes: Histogram of (solid) rain-top height, (dashed) 0°C level
H-only
R-only
H-only
Amazon (land)
Eq. Africa (land)
US (land)
Eq. W. Pacific
Japan (ocean)
RH
RH + Ronly
Weak linkage between extreme rain and extreme convection
 Clear differences in R-only and H-only extremes, both over land and over ocean
 R-only:
 Low RTH ~8 km (30dBZ ~7 km)
 Downward increase of Ze below 0°C level
 Land-ocean differences of the ‘shape’ of Ze profiles: basically little for both extreme types

Precipitation system characteristics and environmental conditions
No. of events
Max. rain-top
Stratiform rain
area fraction
Even in regions where severe convective storms are representative
extreme weather events, the heaviest rainfall events are mostly
associated with less intense convection
Evaluation by ground-base radar observations
Area
Blue: R-only; Red: H-only extremes
Error bars: 95% confidence interval of the mean
No. of extreme events:
 R-only extremes: Almost in phase with monthly rainfall
 H-only extremes: Short-period peak different from the rainiest season
 Rain system characteristics
 R-only: much lower rain-top (partly by definition); Larger in size; Higher strat. fraction
 Little seasonal variation for both extreme types

Moist static
energy
Temperature
Relative
humidity

Environments related with R-only extreme:
 Less convectively/statically unstable; Wetter in the low-middle troposphere;
Larger moisture convergence in the lower troposphere
R-only
H-only
Time diff. [min]
Time diff. [min]
5-yr RHI observations from a C-band radar at Okinawa Is. in Baiu season
 Quite similar structures obtained  Attenuation issue at Ku-band is qualitatively little
 Different life cycles of prec. systems  Not looking at the different stages

Moisture flux
convergence
Env. difference
(Ronly – Honly;
ERA-int nearest)
TRMM/PR top0.1%
R-only
H-only
Height [km]
COBRA top-50 events
R-only
H-only
Summary and discussions
Only weak linkage between extreme rainfall and tallest storms, even in the regions where
severe convective storms are dominant
 Robust differences in echo profiles, rain system characteristics, and environmental
conditions, irrespective of region/season
 R-only extremes: Lower rain-top; Downward Ze increase below 0°C level; Less
convectively unstable; Higher RH in low-mid troposphere
 Implies a dominance of warm-rain processes (Cold-rain processes may also play some role)
