Tuesday, 11 January 2005: 9:00 AM
ENSO influence on Atlantic hurricanes via tropospheric warming
A new pathway for the impact of ENSO on North Atlantic tropical cyclone activity is examined empirically. Anomalous free tropospheric temperatures communicated from the Pacific by equatorial wave dynamics are hypothesized to be unfavorable to tropical cyclone development when tropospheric temperatures are warmer than the equilibrium relationship to sea surface temperature (SST) in the tropical North Atlantic (NATL). This combines recent teleconnection theory with the role of tropospheric temperature-SST differences in hurricane intensity theory. Most of the variance of hurricane season (June-November) NATL averages of tropospheric temperature and SST is captured in a principle component (PC) in which tropospheric temperature and SST covary, termed the equilibrium PC (EQ PC), while departures from this are measured by a disequilibrium PC (DEQ PC). DEQ PC correlates highly with hurricane season indices for storm frequency and intensity and exceeds NATL SST correlations. Additionally, DEQ PC is closely related to ENSO SST just prior to and within the hurricane season, consistent with NATL SST not having had time to adjust to the teleconnected tropospheric warming. This relationship continues through the following winter, indicating a role for onsetting ENSO events. The EQ PC has a strong relationship with prior winter ENSO SST, consistent with NATL SST having adjusted to equilibrium with the troposphere via convection and surface heat fluxes.