Aerial Rivers and Lake, Subtropical Rainfall and

soil EvaporationJosefina Moraes Arraut,

C. Nobre, H.M.J. Barbosa, A. Marengo,

CCST - INPEEGU General Assembly, April 5

2011

Moisture Transport over South America

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Wet season Dryseason

GPCP monthly means and ERA-Interim (we also use ERA40)

Aerial

Rivers

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Aerial Rivers

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W =1

gqdp

0

ps

∫

Precipitable water:

is analogous to the height of a column of liquid,multiplied by an equivalent column speed it gives the column discharge.

A Lake of Moisture over Amazonia

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Aerial Rivers and Lake (wet season)

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Questions we’ve been asking ourselves :

Is Amazonia a source of moisture for the atmosphere? When? Where? – There has been much speculation on this issue because of measurements showing a moister atmosphere over the

forest than over the ocean.

What is the total aerial river discharge into the subtropical rainfall areas?

What’s the importance of moisture from Amazonia to this flow?

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Amazonia, source of moisture?

The basin cannot be systematically a source of moisture or it would dry out.

For the whole basin RT>0 always.

If then and if , then

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P − E = RT + S

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P − E < 0

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S < −RT < 0

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S > 0

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P − E > RT > 0

When soil moisture is increasing in the basin as whole we expect it to be a sink of moisture. (There could be variability in space)

It is worth investigating if, in the drier season, or in the months following it the basin acts as a source of moisture.

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One option is to use the balance equation for atmospheric water vapor as put by Peixoto & Oort 1992.

Time variation of precipitable water is being dismissed as small.

But the divergence field requires validation.

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P − E = −∇(QV )

Rainfall and Divergence

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Divergence of the vertically integrated moisture transport for ERA40 (left, 1980-2001) and ERA-Interim (right, 1989-

2008) data.

Interim

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ERA40

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Summary

Both data sets show flow from Amazonia and from the Atlantic to be similar in mean magnitude.

Flow from Amazonia has larger spread and therefore a larger effect over the variability of the aerial river discharge.

The contribution from soil evaporation follows closely in intensity. -> ”Only” moistens the air. April 3-8 2011 15

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Summary

It would be very interesting to compare with evaporation data.

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Danke Schön