Anvil Characteristics Associated
With MCSs
Jian Yuan
Robert A. Houze
University of Washington, Dept. of Atmospheric Sciences, Cloud and Precipitation Seminar, 4 December 2008
Outline
•
Motivation
•
Methodology & Data
•
MCS definition & Global Mapping of MCS
•
Preliminary results of Anvil Cloud
Properties
•
Summary & Future Work
Motivation


Cirriform cloud has important impacts on global
radiation balance and much of them is from deep
convection. (Luo and Rossow 2004)
High cloud production is very sensitive to convection
parameterization in climate models (Clement and Soden
2005).

Latent heating profile associated with tropical
convective systems can affect the structure of the
large-scale circulation. (Houze, 1982; Hartmann et al. 1984;
Schumacher et al. 2004 etc.)

The associated radiative heating profile has not been
documented with observational study.
Motivation (continued)



In both the Tropics and warm middle latitudes much
of cirriform cloud produced by deep convection is
from MCSs.
Un-precipitated ice-phase hydrometeors injected into
the atmosphere by MCS are not well documented
and understood.
CloudSat now provides globally sampled cloud
vertical structure information.
Goal: Structure and composition
of MCS Anvils
ANVIL
AC
ANVIL
AS
Methodology
1. Objective Identification of MCSs.
–
Size, Coldness, intensity etc.
2. Associate anvils with MCSs.
3. Analyze MCS anvil clouds captured by
CloudSat cloud radar.
Data
• Rain Rate: AMSR-E
 Aqua L2B Global Swath Rain Rate (AE_Rain).
• Horizontal Cloud Structure: MODIS
 MODIS06/Aqua Cloud product V5
• Vertical Cloud Structure: CloudSat
 Products 2B-GEOPROF
Identification of High Cloud Features
MODIS Tb11 (KO)
Combined
AMSR Rain (mm/h)
Cloud Features
Precipitation from high cloud
systems
Percentages are contributions of total rainfall
from all high cloud systems within each region for
the whole 12 months of 2007.
PDF of Rainfall
77.5%
59.8%
73.1%
82.5%
67.8%
77.3%
2000km2
Identify Meso-scale Convective
Systems
• Rain area 2,000-250,000 km2
• Mean Tb11 <235 Ko
• Rain area with R>10 mm/h > 200km2
• Subdivided by the coldness
– Cold: Tb11min10%<208 K
– Warm: 208 Ko<Tb11min10%<220 Ko
Cold MCS (Biggest 30%)
MAM
Warm MCS (Biggest 30%)
MAM
Cold MCS (Smallest 30%)
MAM
Warm MCS (Smallest 30%)
MAM
Buoyancy profile (75th percentile; in
degrees Celsius) from NCEP reanalysis
Cetrone & Houze , QJR, 2008 (Figure 2)
PDF of Non-precipitating Clouds
Anvil Clouds
Color-map unit (Num/[.25km]2)
Non-precipitating: Ze_max(0~4km) <= -10dBZe
(according to Stehpens and Wood 2006).
PDF of the anvil cloud thickness
Normalized Histograms of Anvil Clouds
Cloud Top and base Distribution of Anvil
Clouds
Normalized Sample Size
CFAD of Anvil Clouds (WP)
CFAD of Anvil Clouds (AF)
Normalized Sample frequency as
function of Reflectivity
Summary

OBJECTIVE MODIS/AMSR-E METHODOLOGY CAPTURES
TROPICAL MCS CHARACTERISTICS
– Cloud tops of MCSs colder over Africa and West Pacific than over East
Pacific and tropical Atlantic
– Larger MCSs more frequent over ocean
– Smaller MCSs more frequent over land
– MJO AND South Asian monsoon favor larger, colder MCSs
– Etc.

PRELIMINARY CLOUDSAT RESULTS SHOW ANVIL
STRUCTURE FOR OBJECTIVELY IDENTIFIED MCSs
– Africa: Broad distribution of reflectivity, more stronger echo– stronger
convection and more anvils attached to convective area
– West Pacific: Narrow peaked distribution of reflectivity with values
increasing downward--suggests diffusion, aggregation processes,
relative weak convection and more anvils attached to stratiform area
Future Plan

Further analysis of anvil properties for different regions
and seasons—microphysics, frequency of occurrence,
water budget etc..

Understand and quantify the radiative heating associated
with anvil clouds—complete the heating structure
(LH+RH) associated with MCSs.
END
CFAD of Anvil Clouds (W. P.)
CFAD of Anvil Clouds (Africa)
Cold MCS (30~70%)
MAM
Warm MCS (30~70%)
MAM
Capturing MCSs
1. Isolating high cloud systems by finding the Tb11
isotherm associated with the maximum gradient
within TB11 patterns.
2. Identifying cold cloud center by finding local
minimum of Tb11 within each high cloud
system.
3. Identifying precipitating core by finding spatially
contiguous raining area with R>3mm/hr.
4. Associate anvils clouds with cloud cores.
Nominal Frequency
94 GHz
Pulse Width
3.3 µsec
PRF
4300 Hz
Minimum Detectable Z*
-26 dBZ
Data Window
0-25 km
Antenna Size
1.95 m
Dynamic Range
70 dB
Integration Time
0.3 sec
Vertical Resolution
500 m
Cross-track Resolution
1.4 km
Along-track Resolution
2.5 km
Data Rate
15 kbps
Missing data
Cloud structures