HR: 13:40h
AN: A33B-01 INVITED     [Abstracts]
TI: Moist Teleconnection Mechanisms
AU: * Neelin, J
EM: neelin@atmos.ucla.edu
AF: Dept. of Atmospheric Sciences and Inst. of Geophysics and Planetary Physics, University of California, Los Angeles, 405 Hilgard Ave., Los Angeles, CA 90095-1565 United States
AB: Teleconnections have traditionally been studied for the case of dry dynamical response to a given diabatic heat source. Important anomalies often occur within convective zones, for instance, in the observed remote response to El Ni\~no. The reduction of rainfall and teleconnection propagation in deep convective regions pose theoretical challenges because of the role of moist convective feedbacks. During El Ni\~no, large-scale negative precipitation anomalies often occur over equatorial South America and the Atlantic intertropical convergence zone (ITCZ), and in a horseshoe pattern around the central Pacific region of positive precipitation. Analysis of these in an intermediate complexity model is used to propose and review some general principals of teleconnections occurring in deep convective zones, contrasting land and ocean cases. Tropospheric temperature and wind anomalies are spread by wave dynamics modified by interaction with the moist convection zones. The traditional picture of gradual descent balanced by radiative damping misses the most important balances in the moist static energy (MSE) budget. A small ``zoo'' of mechanisms is active in producing strong regional descent and negative precipitation anomalies. Factors common to several mechanisms include the role of convective quasi-equilibrium (QE) in linking low-level moisture anomalies to free tropospheric temperature anomalies in a two-way interaction referred to as {\it QE mediation}. Convective heating feedbacks change the net static stability to a gross moist stability (GMS) $M$. The large cloud-radiative feedback terms may be manipulated to appear mathematically similar to a modified static stability $M_{\rm eff}$. This $M_{\rm eff}$ differs over land versus over ocean at time scales up to many months due to surface energy flux balance. Apparently modest terms in the MSE budget can be acted on by the {\it GMS multiplier effect} which yields substantial precipitation anomalies due to the large ratio of the moisture convergence to the MSE divergence. Advection terms enter in several mechanisms, including advection of mean moisture gradients by anomalous winds ${\bf v}'\cdot\nabla \bar q$ in the Pacific. In eastward teleconnection, advection by mean winds is important to MSE and momentum balances in a {\it Kelvinoid solution}. The opposition of moist wave speed by easterly flow enhances {\it moist wave decay} mechanisms, permitting relatively small damping terms by surface drag and radiative damping to produce the substantial eastward temperature gradients seen in observations and simulations and contributing to precipitation anomalies. The leading mechanism for drought in eastern equatorial South America is the {\it upped-ante mechanism}: teleconnected tropospheric temperature anomalies induce moisture gradients between non-convective zones and convection zones where QE-mediation increases low-level moisture; mean winds advect the anomalous gradient to produce descent anomalies and negative precipitation anomalies. The upped-ante mechanism is also important to Atlantic ITCZ rainfall reductions, especially as SST equilibrates in passive-SST (coupled ocean-mixed layer) experiments. For fixed SST experiments, or while SST is adjusting during passive SST experiments, heat flux to the ocean is lost to the atmosphere and can induce descent and precipitation anomalies by several pathways, referred to as {\it troposphere/SST disequilibrium mechanisms}. These are important in the South Pacific and the Atlantic ITCZ.
DE: 3322 Land/atmosphere interactions
DE: 3339 Ocean/atmosphere interactions (0312, 4504)
DE: 3374 Tropical meteorology
DE: 3314 Convective processes
DE: 3319 General circulation
SC: Atmospheric Sciences [A]
MN: 2004 AGU Fall Meeting