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Title: The role of the Southern Hemisphere semiannual oscillation in the development of a precursor to central and eastern Pacific Southern Oscillation warm events

The semiannual oscillation (SAO) is a twice-yearly northward movement (in May-June-July (MJJ) and November-December-January (NDJ)) of the circumpolar trough of sea level pressure (SLP) in the Southern Hemisphere with effects throughout the troposphere. During MJJ the second harmonic of SLP, describing the SAO, has low values of SLP north of 50°S in the subtropical South Pacific, while the first harmonic, which is dominant over the Australian sector, increases to its peak. This once-a-year peak in negative SLP gradients (decreasing to the east) between Australia and the ocean to its east extends to the equatorial Pacific. Southern Oscillation warm events since 1950, with an intensification of this seasonal cycle, have had larger-amplitude SST anomalies in the eastern equatorial Pacific in MJJ and during the following mature phase in NDJ. Weak amplification of the seasonal cycle in MJJ tends to be followed by larger-amplitude SST anomalies in the central equatorial Pacific during NDJ.
ORCiD logo [1] ;  [1] ; ORCiD logo [2]
  1. National Center for Atmospheric Research (NCAR), Boulder, CO (United States)
  2. National Center for Atmospheric Research (NCAR), Boulder, CO (United States); Monash Univ., Melbourne, VIC (Australia). School of Earth, Atmosphere and Environment
Publication Date:
Grant/Contract Number:
Accepted Manuscript
Journal Name:
Geophysical Research Letters
Additional Journal Information:
Journal Volume: 44; Journal Issue: 13; Journal ID: ISSN 0094-8276
American Geophysical Union
Research Org:
National Center for Atmospheric Research (NCAR), Boulder, CO (United States)
Sponsoring Org:
USDOE Office of Science (SC), Biological and Environmental Research (BER) (SC-23). Climate and Environmental Sciences Division; National Science Foundation (NSF)
Contributing Orgs:
National Oceanic and Atmospheric Administration (NOAA), Boulder, CO (United States)
Country of Publication:
United States
54 ENVIRONMENTAL SCIENCES; semiannual oscillation; El Nino; seasonal cycle
OSTI Identifier: