Transcript Document 7132322

Warm Season Diurnal Cycle Simulations Over North
America - Sensitivities to Model Resolution
Myong-In Lee1,2, Siegfried Schubert2, Max Suarez2, Julio Bacmeister2,
Phil Pegion2, Isaac Held3, Gabriel Lau3, Jeff Ploshay3, Arun Kumar4,
Jae Schemm4, Hyun-Kyung Kim4, and Soo-Hyun Yoo4
1 Goddard
Earth Science and Technology/ UMBC
2 Global Modeling and Assimilation Office, NASA/GSFC
3 Geophysical Fluid Dynamics Laboratory, NOAA
4 Climate Prediction Center, NCEP
The 30th Annual Climate Diagnostics & Prediction Workshop
The Pennsylvania State University
October 24-28, 2005
NOAA/OGP proposal: “An Assessment and
Analysis of the Warm Season Diurnal Cycle over
the Continental United States and Northern
Mexico in Global Atmospheric General
Circulation Models”
1) assess and analyze the diurnal cycle in the NASA,
NCEP and GFDL AGCMs
2) improve our understanding of the important physical
processes that drive the diurnal cycle
3) provide guidance for development of physical
parameterizations
http://janus.gsfc.nasa.gov/~milee/diurnal
Outline
1. Diurnal Cycle of Precip in 3 AGCMs
(in climate resolution)
2. Sensitivity to Horizontal Resolution
3. Cumulus Convection Scheme Test
4. Summary
Description of Models
GFDL
NCEP
NASA/
GMAO
Cumulus
Convection
Version
Resolution
AM2p12
Relaxed
ArakawaGrid-points
Schubert
2x2.5 L24
(Moorthi and
Suarez 1992)
GFS v2
Simplified
ArakawaSchubert
(Grell 1993,
Pan and Wu
1994)
NSIPP
v2
Spectral
T62 (~2 x
2) L64
Relaxed
ArakawaGrid-points
Schubert
2x2.5, L40
(Moorthi and
Suarez 1992)
Shallow
Convection
Large-scale
condensation
PBL
LSM
None
Prognostic
cloud, RH
saturation
Non-local
Lock et al.
(2001)
Anderson et
al. (2004)
Nonprecipitating
diffusion
(Tiedtke
1982)
Prognostic
cloud, RH
saturation
Local/nonlocal
Pan and
Hong and Mahrt (1987)
Pan (1996)
None
Prognostic
cloud, RH
saturation
Local
diffusion
Louis et al.
(1982)
Koster and
Suarez
(1996)
Experiments and Validation
• Ensembles of 5-Month Hindcasts
– 5 members with different IC, starting 1 May
– analyze warm season of Jun-Aug
– SST climatology (1983-2002) prescribed
• Validations
– NCEP Hourly Precipitation Data (HPD)
– NCEP North American Regional Reanalysis
(NARR) 3-hourly
JJA Precipitation and 925mb Winds: 2-Degree Resolution
Reanalysis
Phase (local time) of Maximum Precipitation (24-hour cycle)
Observations
local time
Sensitivity to Resolution
model
resolution
2 Deg.
1 Deg.
0.5 Deg.
GFDL
NCEP
NASA/
GMAO
5 runs
5 runs
(T62 L64)
5 runs
5 runs
5 runs
(T126 L42)
5 runs
5 runs
2 runs
(T170 L42)
2 runs
Local Time
Eastward Propagation?
Observations
GFDL
NCEP
NASA
6pm
6pm
6pm
6pm
9pm
9pm
9pm
9pm
12pm
12pm
12pm
12pm
Diurnal Cycle in GP Region
precip, wind 925 hPa
Diurnal Cycle in GP Region
precip, wind 925 hPa
Diurnal Cycle in GP Region
precip, wind 925 hPa
North American
Monsoon Region
Diurnal Cycle in NAME Region
precip, wind 925 hPa
Diurnal Cycle in NAME Region
precip, wind 925 hPa
Diurnal Cycle in NAME Region
precip, wind 925 hPa
Time-mean Precip and w925
(1/2 degree resolution)
NASA
m/s
GFDL
NCEP
mm/day
NARR
NSIPP
Diurnal Cycle from NERN Observation (Dave Gochis)
Phase of Diurnal Cycle
(1/2 degree resolution, p>0.1)
NASA
GFDL
NCEP
Description of Convection
Scheme
Cumulus
Convection
GFDL
RAS
(multiple
plumes)
NCEP
SAS
(single
plume)
NASA
/GMAO
RAS
(multiple
plume)
Quasi-equilibrium
CWF
calculation
Trigger
/inhibition
Others
Relaxed adjustment
(~2-12 hrs)
critical CWF~f (z)
LCL ~
neutral
Minimum
entrainment
(Tokioka <500 mb)
Rain reevaporation
Cumulus friction
Relaxed adjustment
Critical CWF~f(z, w at
cb)
LFC
~neutral
LFC within 150
hPa from starting
level
Rain reevaporation
Downdrft
Cumuls friction
Strapping
lowest
~neutral
RH trigger
Wind shear trigger
Minimum
entrainment (all
clouds)
Rain reevaporation
Cumlus friction
Relaxed adjustment
(~30 min)
Critical CWF~f(z)
Sensitivity to Treatment of
Convection Scheme
(NASA/GMAO Model)
Relaxation Time Scale
Sub-cloud Layer
Phase of Diurnal Cycle of Precipitation
TRMM
NASA
CNTL
NASA
with GFDL
parameters
Concluding Remarks
1. Diurnal cycles of precipitation are differently simulated among the models,
while the models have basically similar convective schemes (buoyancy
closures)
2. Increased resolution has mixed impact on the simulated diurnal cycle of
convection
• it resolves some of the key local features (e.g. land-sea breeze and
topographic impacts)
• it improves the initiation and propagation of precipitation over the
Rockies
• but, highest resolution tends to dry out the Great Plains
3. The major differences in diurnal cycle simulation appear to be in the
implementation details of the convection scheme and the interaction with
the boundary layer; this suggests the need for improvement in model
physics parameterizations
Thank you !!
LLJ Frequency Simulation (nighttime 06 Z + 12 Z Composite)
NARR (1995)
GFDL
NCEP
NASA
[mm/day]
Significant Test

Rainfall (R) in each grid point is assumed to sinusoidal
harmonics in a day
R(t )  r0  r1 cos[1 (t  1 )]  r2 cos[2 (t   2 )]
1
 2 / 24h
2
 2 / 12h

Coefficients of amplitude (r) in daily are tested with the 90
% confidence level (p < 0.1)
Eastward Propagation?
Observations
GFDL
NCEP
NASA
6pm
6pm
6pm
6pm
9pm
9pm
9pm
9pm
12pm
12pm
12pm
12pm
1- Degree Runs in Three AGCMs
GFDL
NCEP
NASA
6pm
6pm
6pm
9pm
9pm
9pm
12pm
12pm
12pm
Small hint of eastward propagation but suppressed over the GP region
Phase of Diurnal Cycle- NASA
(p>0.1)
Phase of Diurnal Cycle- NCEP
(p>0.1)
Phase of Diurnal Cycle- GFDL
(p>0.1)
Diurnal Cycle of NASA/GMAO AGCM
(compared with TRMM)




Six years (1998–2003) of TRMM Microwave
Instrument (TMI) rain retrievals at 2.5°x2.5° grid box
(Tom Bell 2004)
Model AMIP simulation for the same period at 2.5°x2°
horizontal resolution
Seasonal statistics (e.g., JJA)
Rainfall (R) in each grid point is fit to sinusoidal
harmonics
TRMM
MODEL
Diurnal Cycle Simulation in the NCAR CCSM2 (CAM2 AGCM)
From Dai and
Trenberth (2004)
Diurnal Cycle of PBL
(Temperature, JJA, Great Plains, U.S.)
OBS
Model
1. Strapping Process (defining sub-cloud layers)
cloud base
Levels up

ground
Low-Strapping
Case

strapping levels
Determine
cloud base
properties
averaged
profiles
High-Strapping
Case
2. Relaxation Time Scale Tests
Rather than “quasi-equilibrium” achieved at each time step,
only the fraction of the cumulus mass flux relaxes the state toward equilibrium
(RAS), assuming certain time-scale.
Current: 30 minutes for all cloud types
Sensitivity runs: vertically increasing function from 2 - 12 hrs
Sensitivity Experiments with
NASA/NSIPP AGCM
• Climate SST Run
• Single summer (JJA)
RUN
CTRL
Description
Control
Strapping
levels
Relaxation
time
2
0.5 hr
0.5 hr
CEXP1
Strapping Test
10
(~sig=0.85)
CEXP2
Relaxation Test
2
2hr -12hr
CEXP3
Strapping and
Relaxation
10
2hr -12hr
Phase Changes in Land Convection ?
Strapping Effects
Critical CWF
Delaying
t
Increasing Relaxation Time
Maintaining
t
Boundary layer averaged T,q
(more sensitive in upper PBL,
rather than near ground)
-> reduced the CWF and delay
the phase
-> inhibit convection until CWFCWFcrit >0 should be met
Partial adjustment of large-scale
instability
-> initially reduced adjustment
and rainfall
-> maintaining convection with
extended hours
-> transition to the deep
convection ? (nighttime reboost)
TRMM
exp1
exp2
Control
exp3
Phase of Diurnal Cycle of Precipitation