Coupling Strength between Soil Moisture and Precipitation Tunings and the Land-Surface Database Ecoclimap Experiment design:Two 10-member ensembles - Period November 1992 – March 1993

Ensemble W: the soil moisture is calculated by the model at each time step - the soil is interactive with the atmosphere

Ensemble S: All ensemble members are forced, at each time step, to maintain the same space-time varying series of soil moisture. The soil moisture field is a boundary condition for the atmosphere - the atmosphere does not feed back upon the soil moisture.

)()( WSCS vvv Coupling Strength CS:

Since soil moisture is a boundary condition for ensemble S but not for

ensemble W, the difference Ω(S) – Ω(W) isolates the fraction of

atmospheric variability that is explained by the soil moisture and

is used as a measure of the coupling strength.

2

22

)1( v

vvv

m

m

Similarity parameter Ωv:

Variance of the mean

time series of all

ensemble members

ensemble inter-

member variance

Number of ensemble members

Ω is the ratio of the variance of the variable v

that is explained by (all) boundary

conditions in relation to total

variance.

Results:We present the coupling strength between soil moisture and evaporation and soil moisture and precipitation. The precipitation coupling strength depends to some (unknown) degree on the evapotranspiration coupling strength but also on e.g. model parameterizations of boundary layer and moist convection. The precipitation coupling strength is proposed by various authors (e.g. GLACE project) to be highest in transition zones – regions that are neither arid nor humid.

0.0 - 0.2 0.2 - 0.4 0.4 - 0.6 0.6 - 0.8 0.8 - 1.00

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0.18

0.2

SWA

Evaporation coupling strength binned

according to Soil Water Availability

(SWA)

CS

In arid regions the atmosphere is dry and

rainfall easily evaporates to the atmosphere.

High coupling strength

-0.2 -0.1 0 0.1 0.2 0.3

-0.2 -0.1 0 0.1 0.2 0.3

“HOT SPOTS”

Coupling Strength Soil Moisture –

EvapotranspirationJanuary -93

Coupling Strength Soil Moisture –

PrecipitationJanuary -93

0.0 - 0.2 0.2 - 0.4 0.4 - 0.6 0.6 - 0.8 0.8 - 1.00

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0.18

0.2

SWA

Precipitation coupling strength binned

according to Soil Water Availability

(SWA)

CS

In transition zones, the coupling to evapotranspiration is intermediate

AND the atmosphere can get unstable by a less amount of added

water vapor.Higher coupling strength

In humid regions, the air is wet and the soil is close

to field capacity, and 1. rainfall will not change the soil moisture to such a

high degree.2. The evapotranspiration will be limited by the wet

atmosphereLow coupling strength

In arid regions the atmosphere is too dry

to get unstable. Lower coupling

strength

t

t

Initialization dates

SOIL MOISTURE ENSEMBLE S

SOIL MOISTURE ENSEMBLE W

Annual cycle of Precipitation, Amazon region 2001-2002

Annual cycle of T2m, Amazon region 2001-2002

Annual cycle of Precipitation, La Plata Basin 2001-2002To increase the RCA3

performance in simulating the South American climate, the

land-surface database Ecoclimap was incorporated

and a set of tunings were performed.

The monsoon precipitation was improved for the

Amazon and Plata Basin regions although large

negative winter bias prevails.

Anna A. Sörensson (1), Claudio G. Menéndez (1), Ulf Hansson (2), Patrick Samuelsson (2), Ulrika Willén (2)(1) Centro de Investigaciones del Mar y la Atmósfera, CONICET/UBA, Buenos Aires, Argentina

(2) Rossby Centre, Swedish Meteorological and Hydrological Institute, Norrköping, Sweden

Anna A. Sörensson (1), Claudio G. Menéndez (1), Ulf Hansson (2), Patrick Samuelsson (2), Ulrika Willén (2)(1) Centro de Investigaciones del Mar y la Atmósfera, CONICET/UBA, Buenos Aires, Argentina

(2) Rossby Centre, Swedish Meteorological and Hydrological Institute, Norrköping, Sweden

Soil Moisture - Atmosphere Coupling in the Rossby Centre Regional Atmospheric Model

during the South American Monsoon

Soil Moisture - Atmosphere Coupling in the Rossby Centre Regional Atmospheric Model

during the South American Monsoon

Initial Soil Moisture – the effect of a dry/wet winter on SAMS

Initial soil moisture of ensemble “DRY”

Initial soil moisture of ensemble “WET”

Sm(xi,yj)

The soil moisture memory could influence on the intraseasonal variability of precipitation during the development of the South American Monsoon System (SAMS) and potentially contributes to atmospheric variability and seasonal predictability. We explore the interaction between soil moisture and atmosphere during the SAMS of 92-93 through a) calculating the coupling strength

and b) studying the effect of initial dry and wet soil moisture conditions, using the Rossby Centre regional atmospheric climate model (RCA3). The model has been adapted to the South American region through a series of tunings and by incorporating the surface database Ecoclimap.

Introduction

We explored the influence of anomalous soil moisture initial conditions on the intraseasonal development of the 1992-93 SAMS on a monthly timescale. Two ensembles of five members each were realized, one with anomalously dry and the other with anomalously wet land surface initial conditions over the whole domain. The simulated period is August 1992 – March 1993.

Precipitation Winds and temperature 850hPa

• The choice of land surface database and parameters like soil depth and leaf area index is important for the for the performance of RCA3 over South America. With the database Ecoclimap and a set of tunings to the atmosphere, the surface temperature and the summer precipitation was improved for important South American regions, including La Plata Basin.

• La Plata Basin seems to be a region where the precipitation is partly controlled by the soil moisture in January. Results were similar for other months. The coupling strength of evapotanspiration is very high for la Plata Region, which indicates that the soil probably is too dry in RCA3 in this region, perhaps due to the winter precipitation deficit.

• A very dry winter with a very dry soil in August, induced continental scale circulation changes through changed Bowen Ratio and deep convective areas. Moisture fluxes from the Atlantic increased and initiated the monsoon earlier than for a simulation with wet initial conditions.

Conclusions

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25

27

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31

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35

37

JAN FEB MAR APR MAY JUN JUL AGO SEP OCT NOV DEC

RCA3RCA3+ECOCL

RCA3+ECOCL+MP+ConvRCA3+ECOCL+MP+Conv+2mSDRCA3+ECOCL+MP+Conv+LAIoldERA

CRU

0

2

4

6

8

10

12

14

16

18

JAN FEB MAR APR MAY JUN JUL AGO SEP OCT NOV DEC0

2

4

6

8

JAN FEB MAR APR MAY JUN JUL AGO SEP OCT NOV DEC

The spring T2m bias of Amazon region

was removed by Ecoclimap.