Promises and Prospects for Predicting the South Asian Monsoon

Jim Kinter

COLAGeorge Mason University

Special Symposium on the South Asia MonsoonAmerican Meteorological Society Annual Meeting

Phoenix, Arizona :: 8 January 2015

Many Thanks To: Rodrigo Bombardi, Paul Dirmeyer, Mike Fennessy, Bohua Huang,

Subhadeep Halder, Ed Schneider, J. Shukla, Chul-Su Shin, Bohar Singh

Figure credit: National Geographic © 2002

Special Symposium on the South Asia Monsoon :: AMS :: Phoenix, AZ :: January 2015

South Asian Monsoon

– One of largest variations of seasonal to interannual climate observed on Earth

– Affects lives, property and (largely agrarian) economies

of countries inhabited by nearly 25% of human population …

– Current state of the science• Rudimentary understanding of monsoon dynamics• Extremely limited ability to predict monsoon variations

South Asian Monsoon

– One of largest variations seasonal to interannual climate observed on Earth

– Rudimentary understanding of the monsoon remains

– Extremely limited ability to predict monsoon variations

– Affects lives, property and (largely agrarian) economies of countries inhabited by nearly 20% of human population

… either by monsoon flood …

…or by monsoon drought

Special Symposium on the South Asia Monsoon :: AMS :: Phoenix, AZ :: January 2015

South Asian Monsoon

– One of largest variations seasonal to interannual climate observed on Earth

– Affects lives, property and (largely agrarian) economies

of countries inhabited by nearly 25% of human population

– Current state of the science• Rudimentary understanding of monsoon dynamics• Demonstrable predictability of monsoon seasonal rainfall• Limited ability to actually predict monsoon variations

Special Symposium on the South Asia Monsoon :: AMS :: Phoenix, AZ :: January 2015

F-values for JJAS precip. based on DEMETER data. Gray color indicates not statistically significant at 95% confidence interval (F < 1.4).

Thanks to J. Shukla & M. Fennessy

F as a Measure of Predictability in DEMETER

(5 CGCMs, 9 members, 46 years)

Monsoon Rainfall is Predictable

Special Symposium on the South Asia Monsoon :: AMS :: Phoenix, AZ :: January 2015

CFSv2 Reforecasts of JJAS EIMR Precip

February IC:

Ensemble Mean (24)Bias = -1.48 mm/dACC = 0.52RMSE = 0.33 mm/d

May IC:

Ensemble Mean (24)Bias = -0.78 mm/dACC = 0.62RMSE = 0.30 mm/d

Monsoon Rainfall Prediction: Only Moderate Skill

Special Symposium on the South Asia Monsoon :: AMS :: Phoenix, AZ :: January 2015

National Monsoon Mission of India and COLA Joint Research to Enhance Monsoon Prediction

Ocean-Land-Atmosphere Coupling and Initialization Strategies to Improve CFSv2 and Monsoon Prediction– Sponsored by Ministry of Earth Sciences, Government of India– Improve the coupled ocean-land-atmosphere model (CFSv2)

performance.– Improve initialization of ocean and land states in the pre-

monsoon season to improve forecasts of onset, monsoon season precipitation.

– Improve representation of land-atmosphere feedback in monsoon-dominated regions

– Focus on CFSv2 as baseline model

Special Symposium on the South Asia Monsoon :: AMS :: Phoenix, AZ :: January 2015

Climate Forecast System version 2 (CFSv2)

• Global coupled model: Atmosphere, Ocean, Land Surface, Sea Ice

• Atmosphere: based on the NCEP Global Forecast System (GFS) used for global numerical weather prediction– spectral discretization at T126 resolution (about 100 km grid spacing)– 64 levels in the vertical

• Ocean: Geophysical Fluid Dynamics Laboratory (GFDL) Modular Ocean Model version 4 (MOM4) – 1/2° horizontal grid spacing; 1/4° meridional grid spacing in the tropics– 40 vertical levels

• Land Surface: Noah (GFS grid)

• Sea Ice: a modified version of the GFDL Sea Ice Simulator (MOM4 grid)

Special Symposium on the South Asia Monsoon :: AMS :: Phoenix, AZ :: January 2015

ROLE OF ATMOSPHERIC CONVECTION

Special Symposium on the South Asia Monsoon :: AMS :: Phoenix, AZ :: January 2015

Convective Cloud Parameterization:The Simplified Arakawa-Schubert (SAS) Scheme

Deep ConvectionTrigger Mechanism:

Level of free convection (LFC) [for parcel with no sub-cloud level entrainment] being within 150-hPa of convection starting pointSource: MetEd

http://www.meted.ucar.edu/nwp/pcu2/avncp1.htm

Special Symposium on the South Asia Monsoon :: AMS :: Phoenix, AZ :: January 2015

Evap Sensible

Heated Condensation Framework (HCF)

• Quantifies how close atmosphere is to moist convection• Does not require parcel selection

• Uses typically measured quantities (needs only q and θ profiles)

• Is “conserved” diurnally• Can be used any time of year or any time of day and interpretation

stays the same

(Tawfik and Dirmeyer 2014 GRL)

Special Symposium on the South Asia Monsoon :: AMS :: Phoenix, AZ :: January 2015

Evap Sensible

Threshold Variables:

BCL = Buoyant Condensation Level [m]θBM = Buoyant mixing temperature [K]

Heated Condensation Framework

(Tawfik and Dirmeyer 2014 GRL)

Convection is initiated when:PBL intersects BCL

θ2m reaches θBM

New trigger mechanism for deep convection

Original SAS criterion (150-hPa pressure difference).OR.

Condensation due to mixing (HCF)

Special Symposium on the South Asia Monsoon :: AMS :: Phoenix, AZ :: January 2015

Experiments:

• Seasonal hindcasts

• Four member per year (1998 – 2010)

• From April to October starting on April 1,2,3, and 4

• With (HCF) and without (CTRL) the new trigger

Thanks to Rodrigo BombardiMonthly Accumulated Precip. (mm)

OBS

CTL

Thanks to Rodrigo Bombardi

JJASPrecipitation

Special Symposium on the South Asia Monsoon :: AMS :: Phoenix, AZ :: January 2015

JJAS Seasonal Precipitation

Thanks to Rodrigo Bombardi

Mean StDev

Improvement of seasonal variability

Small but significant improvementof seasonal total

Special Symposium on the South Asia Monsoon :: AMS :: Phoenix, AZ :: January 2015

Rainy Season

Improved seasonal cycle of precipitation

Improved rainy season onset dates.

Thanks to Rodrigo Bombardi

Special Symposium on the South Asia Monsoon :: AMS :: Phoenix, AZ :: January 2015

Mechanisms

The new trigger is an alternative condition

• Better representation of the background state of convection

• SAS triggers more frequently

Small improvement in the right direction

Central India: 16.5-26.5oN, 74.5-86.5oE Thanks to Rodrigo Bombardi

Special Symposium on the South Asia Monsoon :: AMS :: Phoenix, AZ :: January 2015

OCEAN INITIALIZATION

Special Symposium on the South Asia Monsoon :: AMS :: Phoenix, AZ :: January 2015

Multiple Ocean Initial Conditions (OICs) for CFSv2

1. Four different ocean data sets• ECMWF Combine-NV (NEMO)

• NCEP CFSR (Climate Forecast System Reanalysis)

• ECMWF ORA-S3 (Ocean Reanalysis System3)

• NCEP GODAS (Global Ocean data Assimilation System)

2. Variables • Monthly mean potential temperature[°C], salinity[g/kg], u[m/s], v[m/s]

3. Pre-Processing• Filling up (extrapolation) the land mass to make up potential gaps due to

different land-sea masks between each ocean analysis and MOM4 (Note that zonal mean of each variable is initially assigned to grids over the land as an initial guess.)

4. Period: 1979-2009 (Jan. – May)

Special Symposium on the South Asia Monsoon :: AMS :: Phoenix, AZ :: January 2015

OICs

Initial monthNEMO

(4mem*30yrs)CFSR

(4mem*31yrs)ORA-S3

(4mem*31yrs)GODAS

(4mem*31yrs)

May(5-month lead)

April(6-month lead)

March(7-month lead)

February(8-month lead)

January(9-month lead)

* 4 members : 1st 4 days (00Z) of each month using the atmosphere/land surface conditions from CFSR

600 runs completed

620 runscompleted

620 runscompleted

620 runs completed

CFSv2 Retrospective Forecasts with 4 OICs

Special Symposium on the South Asia Monsoon :: AMS :: Phoenix, AZ :: January 2015

NEMOCFSR

ORA-S3GODAS

ES_MEAN

JAN ICs FEB ICs MAR ICs

CFSv2 Prediction Skill of NINO3.4 (1982-2008) vs. OISST

Special Symposium on the South Asia Monsoon :: AMS :: Phoenix, AZ :: January 2015

NEMOCFSR

ORA-S3GODAS

ES_MEAN

APR ICs MAY ICs

CFSv2 Prediction Skill of NINO3.4 (1982-2008) vs. OISST

Special Symposium on the South Asia Monsoon :: AMS :: Phoenix, AZ :: January 2015

Multiple Ocean Analyses Ensemble Mean

CFSv2 Prediction Skill of NINO3.4 (1982-2008) vs. OISST

Special Symposium on the South Asia Monsoon :: AMS :: Phoenix, AZ :: January 2015

corresponds to ENSO onset years

corresponds to ENSO decay years

(1979 – 2008; linear trend removed)

2 Dominant Modes of JJAS mean Precip

CFSv2

CMAP

1st EOF Mode

Correlation (1979-2008)

lead month

NEMOCFSR

ORA-S3GODAS

ES_MEAN

CFSv2

CMAP

2nd EOF Mode

Correlation (1979-2008)

lead month

NEMOCFSR

ORA-S3GODAS

ES_MEAN

Special Symposium on the South Asia Monsoon :: AMS :: Phoenix, AZ :: January 2015

Conclusions• ROLE OF CONVECTION

– HCF - alternative condition to whether or not deep convection should be initiated - was implemented into the Simplified Arakawa-Schubert scheme in the CFSv2.

• Better representation of background state of convection• Increased frequency at which convective scheme is activated

– HCF improves representation of monsoon in CFSv2:• Better daily and seasonal precipitation, mean & variability• Better seasonal cycle of precipitation, including onset dates

• ROLE OF OCEAN ICs• Substantial dependence on ocean ICs of skill of monsoon rainfall forecasts• Multi-analysis initialization results in superior prediction, on average• Two main modes of monsoon variability, associated with onset and decay

phases of ENSO, are well reproduced and predicted in CFSv2 with most ocean IC data sets