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Role of Antecedent Land Surface Conditions on North American Monsoon Rainfall Variability

Chunmei Zhu

Department of Civil and Environmental EngineeringUniversity of Washington

Sep, 2005

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North American Monsoon System (NAMS)

North American monsoon is experienced as a pronounced increase in rainfall from extremely dry May to rainy June.

North American Monsoon Experiment (NAME): Tier 1,2,3. (http://www.cpc.ncep.noaa.gov/products/precip/monsoon/NAME.html)( Comrie & Glenn, 1998 )

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The NAMS concept --- thermal contrast between land and adjacent oceanic regions

( http://www.ifm.uni-kiel.de )

The importance to explore possible links between NAMS and antecedent surface conditions.

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Study Domain

Monsoon regions are defined as in Comrie & Glenn (1998)

Monsoon West

Monsoon South

Monsoon North

Monsoon East

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Monsoon West

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15-year Moving Average Correlation of PI versus MW JJAS rainfall JFM Precipitation Index (PI)

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1950 1960 1970 1980 1990

Year

Pre

cipi

tatio

n (m

m)

JFM PI

Winter Precipitation –

Monsoon Relationship

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Winter Precipitation - Monsoon Rainfall

feedback hypothesis

Higher (lower) winter precipitation & spring snowpack

More (less) spring & early summer soil moisture

Weak (strong) monsoon Lower (higher) spring & early summer surface temperature

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JFM Precipitation in extreme monsoon

years

DRY WET

DRY WET

Apr-May Soil Moisture in extreme monsoon years

Dry MonsoonWet Monsoon

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Soil moisture anomalies persist from spring until June

Correlation of June Sm & JFM PI (1965-1999)

Correlation:June Sm & June Ts (No significant relationship in MW )

SW Sm has no significant relationship with Ts

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Z500 (m) anomalies June Ts anomalies

High

June

Low

Dry Monsoon

Low

June

High

Wet Monsoon

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Monsoon South

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Development of a Long-Term Land Surface Data Set for Mexico

SMN daily precipitation, surface air temperature data (pre-1940 – 2003 ) produced by SMN (Servicio MeterorolÓgico Nacional), over 5000 stations.

SMN daily precipitation data (1995 – near realtime) provided courtesy of Miguel Cortez Vázquez of SMN, around 1,000 stations.

NW Mexico NAME Event Raingage Network (NERN) precipitation daily data ( 2002 - ) provided courtesy of David Gochis, 86 station cross Sierra Madre Occidental

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Comparison of simulated and observed streamflowThe streamflow dataset is the

Mexico acronym BANDAS (CNA and IMTA).

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Study Domain

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The Monsoon South domain is divided into 2 sub-regions

(Higgins et al 1998, Hu & Song 2002, Englehart and Douglas, 2001)

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The long-term mean monthly precipitation 1950-1999

MSa MSb

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Standardized JJAS Rainfall

-1.5

-0.75

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2.25

1950 1955 1960 1965 1970 1975 1980 1985 1990 1995

Wet years

Dry years

1951 1969 1973 1979 1987 1995

1958 1966 1984 1986 1990

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1950 1955 1960 1965 1970 1975 1980 1985 1990 1995

Monsoon onset date anomaly

1972 1976 1977 1984 1996

Early years

Late years

1953 1957 1979 1989 1992

? monsoon magnitude or onset

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Winter Precipitation - Monsoon Rainfall feedback hypothesis

Higher (lower) winter precipitation & spring snowpack

More (less) spring & early summer soil moisture

Weak (strong) monsoon Lower (higher) spring & early summer surface temperature

From previous study on Southwestern US, we propose a similar …

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Winter Precipitation – Monsoon Onset

15-year Moving Average Correlation of PI versus monsoon onset

Correlation of JFM Precip and Monsoon Onset Date

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Winter Snow – Monsoon Onset

15-year Moving Average Correlation of JFM SWE index versus monsoon onset

The snow – monsoon onset relationship is only significant from 1960 to 1980

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Late

Early

Late Early

JFM Precipitation in extreme monsoon years

May Soil moisture in extreme monsoon years

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Winter precipitation – May soil moisture

Correlation of JFM Precip and May total column soil moisture

Correlation of JFM Precip and May first layer soil moisture

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May Sm in extreme monsoon years

May Ts in extreme monsoon years

Late Early

Late Early

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Correlation:May first layer Sm & May Ts

Correlation:May Ts & monsoon onset

May soil moisture plays some role in pre-monsoon seasonal surface thermal condition

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Late - early

Land – sea thermal contrast

Late Early

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Atmospheric Circulation effect?

May Ts anomalies

May Z500 anomalies

May Ts – Z500 correlation

Late Early

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Feedback to monsoon magnitude

Correlation:May first layer Sm & May Ts

Correlation:May Ts & monsoon magnitude

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Summary● MW monsoon is negatively related with Southwest

winter precipitation. NW Mexico summer monsoon onset date is positively related with Southwest winter precipitation and snow especially for extreme late and early years.

● Spring soil wetness conditions in the SW U.S. and northwestern Mexico are strongly determined by the previous winter’s precipitation, this land memory appears to play some role in the surface thermal condition, then influence the NW Mexico monsoon onset, but seems to contribute little to MW summer monsoon.

● May Z500 anomalies shows strong relationship with May Ts anomaly all over the North America continent, which suggesting that the atmospheric circulation condition may contribute more to the pre-monsoon Ts anomalies than land surface conditions.