Mechanisms of land rainfall anomalies Mechanisms of land rainfall anomalies associated with tropical Atlantic variabilityassociated with tropical Atlantic variability

• Seek mechanisms for SST to land impacts examined by e.g., Hastenrath and Heller 1977, Moura & Shukla, 1981; …Enfield, 1996; … Saravanan & Chang 2000, Paegle & Mo, 2002; here focus on S. Trop. Atlantic impacts on NE Brazil • Intermediate atm/land model QTCM simulations; moist static energy diagnostics; intervention experiments, used on other teleconnection pbs. (e.g. Su and Neelin 2002, 2003)

Climate Systems Interactions group (CSI) http://www.atmos.ucla.edu/~csi

J. David Neelin and Hui Su,U.C.L.A

NCEP BrazilNCEP BrazilPrecip vs. SSTPrecip vs. SST

•SST regression on Brazil rainfall index (box)•NCEP precip (MAM)•nino3.4 effects removed•1982-98; K/(mm/day)•90% confidence stippled

•NCEP precip regression on S. Atl. SST (30S - 5N) MAM•nino3.4 effects removed•(mm/day)/K•90% confidence stippled

See also Paegle & Mo 2002

SST on Northern SST on Northern Nordeste Brazil PrecipNordeste Brazil Precip

•TAGA QTCM (MAM)•95% confidence shaded •1950-2000 ensemble of 10•(K/(mm/day))

•GOGA QTCM (MAM)•nino3.4 effects removed•90% confidence shaded •1950-2000 ensemble of 10

SST regression on Brazil rainfall index (box)

See also Saravanan & Chang 2000

Precip. regression on S. Precip. regression on S. Atl SST (30S-5N) MAMAtl SST (30S-5N) MAM

•TAGA QTCM• (90%) confidence stippled• 1982-98 ensemble of 10

•GOGA QTCM• nino3.4 effects removed• (90%) confidence stippled• 1982-98 ensemble of 10• (mm/day)/K

CMAP Precip regression on S. Atl. SST (30S-5N) MAM

• nino3.4 linear effects removed• 90% confidence stippled• 1982-98• (mm/day)/K

NCEP regression on S. NCEP regression on S. Atl. SST (30S-5N) MAMAtl. SST (30S-5N) MAM•Temperature (1000-

200mb avg) • nino3.4 effects removed• 90% confidence stippled• 1982-98• (K/K)

•Moisture (1000-850 mb avg) • nino3.4 effects removed• 90% confidence stippled• 1982-98• (g/kg)/K

Obs SST/GOGA Ts regression on S. Atl. SST index(30S-5n) MAM

• nino3.4 linear effects removed • 90% confidence stippled• 1982-98• (K/K)

GOGA QTCM GOGA QTCM regression on regression on

S. Atl. SST (30S-5N) S. Atl. SST (30S-5N) •Tropospheric temp. (1000-200 mb avg) •nino3.4 effects removed•90% confidence stippled•(K/K)

•Moisture (vert. avg)•nino3.4 effects removed•90% confidence stippled•1982-98 ensemble of 10•(g/kg)/K

GOGA (vGOGA (v··q)q)´ regression on S. Atl. SST (30S-5N) MAM regression on S. Atl. SST (30S-5N) MAM

• nino3.4 effects removed• 90% confidence stippled• 1982-98 ensemble of 10• (W/m2)

TAGA QTCM temperature (1000-200 mb avg) regression TAGA QTCM temperature (1000-200 mb avg) regression on S. Atl. SST (30S-5N) MAMon S. Atl. SST (30S-5N) MAM

• 90% confidence stippled• 1982-98 ensemble of 10• (K/K)

S. Atl. SST (30S-5N) S. Atl. SST (30S-5N) STAGA STAGA

(MAM98) – Clim(MAM98) – Clim

•Obs SST/QTCM Ts

• (K)

•QTCM Precip.• ensemble of 10• (mm/day)

STAGASTAGA(MAM98) - Clim(MAM98) - Clim

•Temperature (1000-200 mb avg) anom.

• (K)

•Moisture (vert. avg) anom.• (g/kg)

STAGASTAGAQTCM anomaliesQTCM anomalies(MAM98) - Clim(MAM98) - Clim

•Moisture advection v·q (vert. avg)• contour 3 W/m2

•Moisture convergence by divergent wind component Mq·v (vert. avg)• contour 20 W/m2

STAGA Prec – Clim STAGA Prec – Clim MAM98MAM98

•Control Precip. anom.• (mm/day)

•Experiment testing importance of advection: (v·q) anomalies suppressed• Precip. anom. • (mm/day)

S. Trop. Atl. SST on northeastern Brazil rain: S. Trop. Atl. SST on northeastern Brazil rain: Hypothesized mechanismHypothesized mechanism

• Warm SST higher moisture over ocean

• Advection raises moisture over downwind land [little effect where convectively stable]

• In & near clim. convection zone, (v·q)´, incr. P´ slightly. Main effect: balanced by moist static energy divergence M·v´. Implies low level moisture convergence Mq·v´ so

P´ =(Mq/M + 1) (v·q)´

• Mq/M large amplifies effect of (v·q)´

Paegle and Mo (2002)Paegle and Mo (2002)

DJF Precip. (merged Hulme/Xie-Arkin data) Correlation between seasonal

mean SSTAs and RPC1,2 for DJF

Correlation between SSTAs and RPC2

for SON and MAM

Saravanan & Chang (2000), [1]Saravanan & Chang (2000), [1]

• Regression Obs SST on Nino-3 (C)• Correlation higher in west• See also Enfield & Mayer (1997)

Saravanan & Chang Saravanan & Chang (2000), [2](2000), [2]

•CCM3 AGCM with obs SST 1950-1994• Squared correlation of SST to

Northern Nordeste Brazil precipitation index (box) (11-3S,46-38W)•MAM season

Saravanan & Chang (2000), [3]Saravanan & Chang (2000), [3]• MAM Precip regression (a) NINO3 (b)NTA SST index

(4N-20N, approx 15W-78W)