From El Nino to Atlantic Nino: pathways as seen in the QuikScat winds Rong Fu 1, Lei Huang 1, Hui Wang 2 Presented by Nicole Smith-Downey 1 1 Jackson School of Geosciences, The University of Texas at Austin 2 NOAA CPC The NASA OVWST 2008 Meeting, Seattle, November, 19-21 2008
First a disclaimer
) What control the climate variability of the Atlantic Niños? Lagged regression of boreal spring SST anomalies in the tropical Atlantic (March- June) with Nino3 Index of the previous winter (December-January) Chang et al. 2006 Atlantic Nino region Zebiak 1993: The tropical Atlantic differs from the tropical Pacific in that it has proportionally more variability not attributable to the equatorial coupled mode. One aspect of this is the lower frequency, tropical basin-scale patterns. Additional contributors may be land surface interaction and global-scale forcing related to ENSO. Chang et al. 2006: It is unclear what causes the winds in the western equatorial Atlantic to respond strongly to some El Niños, but not others. The state of tropical Atlantic determines the ENSO influence.
What process might bridge the temporal gap between ENSO influence and Atlantic Niños on seasonal scale ENSO influence peaks in boreal winter, whereas Atlantic Nino peaks in boreal summer. Okumura & Xie 2006: the meridional mode of Atlantic SST anomalies. Peak of Equatorial Amazon rainfall Atlantic Nino Meridional mode Okumura and Xie 2006
Is the meridional mode the only pathway for ENSO influence on Atlantic Nino? The SSTA in the N. tropical Atlantic is better correlated with river flow in the S. America than with ENSO index. Are there other pathways, esp. through change of S. American rainfall, for ENSO to influence Atlantic Nino? Columbia Rivers vs. Atlantic SST Meridional mode Atlantic Nino Nino3 vs. Atlantic SST?? Kalney et al. 1988 Poveda & Mesa 1997: Atlantic SST anomalies, anomalies of Columbia River flow, Niño3 (1946-95).
Data Sets : QuikScat daily surface wind: daily ocean surface wind at 1 lat/lon resolution, 1999-2007; DT-MSLA merged altimeter data: 7-day running mean of sea-level height anomalies at 1/3 resolution. A merged product of Topex/Poseidon, Jason-1, and European Research Satellite (ERS) altimeter data produced by the French Archiving, Validation, and Interpolation of Satellite Oceanographic Data (AVISO) project; TRMM daily rainrate data (3B42): 1 lat/lon resolution. NCEP Reanalysis: Sea surface Temperature (SST), winds above the surface, 6 hrs, 2.5 lat/lon resolution The Prediction and Research Moored Array in the Atlantic (PIRATA) buoys: Thermocline depth
Mar SST Composite 11 warm events 1948 2005 Atlantic Niño starts during March-May season: Apr Composite: Atlantic Niño Index 6 o S 2 o N, 20 o W 5 o E May o C Jun J F M A M J J Peak A S O N D J F M A M J J A Month Jul Composite: SSTA & Wind Anomaly (10 m) May o C Westerly Aug Northerly
Link between Changes in wet season ending in the Amazon and Atlantic Niño: Composite of SSTA MJJ Early ending (4 yrs) Amazon Wet season Early ending in spring Weak Kelvin wave Late ending in spring Strong Kelvin wave Atlantic Niño cold phase in summer warm phase in summer Normal ending (7 yrs) Late ending (4 yrs) Data: 1979 1997 Ending date: Marengo
What is the underlying physical process?
- The leading EOF mode capture the convective coupled Kelvin Wave: 1 st EOF of 00 to 04 TRMM Rain TRMM Rain 4.2000 Day -3 4.11.2000 Day -2 4.12.2000 Eastward propagating Phase speed: 15 m/s Day -1 4.13.2000 Zonal wavenumber 6 Period: 6 7 days Day 0 4.14.2000 - Kelvin wave captures the major feature of the ITCZ. Day 1 Day 2 4.15.2000 4.16.2000 mm/day Wang & Fu 2007 Day 3 4.17.2000 TRMM data 2000 2003
Atlantic Nino Index (6S 2N, 20W 5E) 2000 2004 2001 2005 2002 2006 2003 2007
Atlantic Nino Index (6S 2N, 20W 5E) SST Anomalies Jan Apr 2002 Feb May Mar Jun Cold to warm transition occurred in March.
How do convection coupled Kelvin waves trigger Atlantic Niño?
Kelvin wave originated westerly surface Oceanic Kelvin waves warmer SSTA from S. America wind anomalies increase SLH in E. Atlantic in the E. Atlantic TRMM Rainfall Anomalies S. America Atlantic Africa QuickSCAT wind anomalies Sea-level Height Anomalies SST Anomalies S. America Atlantic Africa S. America Atlantic Africa S. America Atlantic Africa Higher SLH In W. Atlantic warmer Day lower SLH In W. Atlantic Day More rainfall Westerly easterly colder Higher SLH In W. Atlantic m/s o C M/s o C
In situ buoy data show changes in E-W slope of the thermocline depth consistent with winds and SSTA: Anomalous thermocline depth from PIRATA Buoys QuickSCAT wind anomalies SST anomalies δh 0, 35W δh 0, 23W - + δh 6S,10W S. America Africa
What control the variability of the convective coupled Kelvin waves in the S. America? Liebmann et al. 2008: Convective Kelvin waves in the S. America are forced by Rosbby waves from two sources: The Central America and The extratropical S. America. 3 days ago 2 days ago 2 days ago Kelvin wave at Eq. S. America 2 days after 2 days after
Two pathways for ENSO to influence winds to influence Atlantic Nino through changes of S. American rainfall: 2002, March-May 2007, March-May 2007, March-May Lead correlation between rainfall anomalies in the pacific and S. America and zonal wind anomalies in the equatorial W. Atlantic ocean.
Summary: Our preliminary analysis suggests that the rainfall change in S. America may play an important role in bridge the ENSO influence on Atlantic Ninos; ENSO influences can be carried out through two additional pathways using S. America as a Previously identified pathway spring board. Meridional mode El Nino Atlantic Nino S. America Equator Two pathways through S. America