HR: 1340h
AN: A43A-0039    [Abstracts]
TI: An Investigation of the Role of Internal Atmospheric Variability in ENSO
AU: * Zhang, L
EM: zli@ocean.tamu.edu
AF: Department of Oceanography, Texas A&M University, College Station, TX 77843
AU: Chang, P
EM: ping@ocean.tamu.edu
AF: Department of Oceanography, Texas A&M University, College Station, TX 77843
AU: Tippett, M
EM: tippett@iri.columbia.edu
AF: International research institude for climate prediction, The Earth Institude of Columbia University, Plisades, NY 10964
AU: Fluegel, M
EM: mfluegel@ocean.tamu.edu
AF: Department of Oceanography, Texas A&M University, College Station, TX 77843
AU: Ji, L
EM: link@ocean.tamu.edu
AF: Department of Oceanography, Texas A&M University, College Station, TX 77843
AB: The NCAR atmospheric general circulation model (CCM3) is coupled to a Zebiak-Cane type of reduced gravity ocean model (RGO) to study the role of atmospheric internal variability in ENSO. A novel noise- filter is developed and applied to the coupled model simulations. The filter effectively reduces the impact of the internal atmospheric variability on coupled ENSO dynamics, and thus allows a systematic examination of the effect of internal atmospheric variability on coupled ENSO dynamics. A set of numerical experiments was conducted with and without the noise filter. First, in a long control simulation where the filter is not employed we show that the coupled CCM3-RGO model generates ENSO variability that has many statistical properties similar to the observed one, including the power spectrum and seasonal phase locking. We then conducted a set of experiments where the filter is applied to surface wind stresses and surface heat fluxes jointly and separately. These experiments allow a closer look at the relative importance of dynamic vs. thermodynamic stochastic forcing in coupled ENSO dynamics, and provide a means to test various stochastic forcing mechanisms, such as the seasonal footprinting mechanism. The results show that the internal atmospheric variability plays a crucial role in maintaining ENSO variability. Without the presence of the internal atmospheric variability, not only is the variance of the ENSO substantially reduced, but also its statistical characteristics are altered. The physical mechanisms of how the atmospheric internal variability affects ENSO evolution are explored and will be discussed in some detail.
DE: 3339 Ocean/atmosphere interactions (0312, 4504)
DE: 4215 Climate and interannual variability (3309)
DE: 4522 El Ni¤o
DE: 1620 Climate dynamics (3309)
SC: Atmospheric Sciences [A]
MN: 2004 AGU Fall Meeting