Tropical ENSO teleconnections
I became interested in the ENSO teleconnection to the remote tropics from my thesis work on the Tropical Atlantic ITCZ, in particular the finding of a direct connection between Atlantic ITCZ rainfall with the magnitude of convection over the eastern equatorial Pacific (Chiang et al. 2000). At the time, the literature on tropical ENSO teleconnections had an aethereal quality to it: there was mention of an ‘atmospheric bridge’ and ‘anomalous Walker circulations’ with loops drawn showing the zonal overturning circulation changes. Adam Sobel had then just started at Columbia he gave a talk on his ‘weak temperature gradient’ ideas and the control of ENSO on tropical tropospheric temperature. It struck me as an appealing way to think about the tropical ENSO teleconnection problem.
In Chiang and Sobel 2002 we proposed a mechanism based on the observation that ENSO controlled tropospheric temperature variations throughout the entire tropics. The idea is that once El Nino induced remote tropical tropospheric warming, the remote convection adjusted to be consistent with the warming. The mechanism is explicit about the causal linkages, and also appealed to recent developments in tropical atmospheric dynamics, namely weak temperature gradient and convective quasi-equilibrium.
Ben Lintner and I developed this idea further. Chiang and Lintner 2005 showed that this mechanism was able to explain why there was warming almost everywhere in the tropics after an El Nino, and despite the apparent complexity of the surface flux responses in different regions. Lintner and Chiang 2005 explored to what extent the weak temperature gradient assumption could be used to explain the tropical precipitation response to an El Nino event (it is applicable up to a point). Lintner and Chiang 2007 examined the transient adjustment of the remote tropical climate to El Nino conditions, finding support for the idea originally proposed in Chiang and Sobel (2002) of a significant disequilibrium effect in the remote rainfall response to El Nino. It also attributes the lag in the remote tropical ENSO response to the thermal inertia of the remote tropical oceans.
Chiang, J.C.H., Kushnir, Y. and Zebiak, S.E., 2000. Interdecadal changes in eastern Pacific ITCZ variability and its influence on the Atlantic ITCZ. Geophysical Research Letters, 27(22), pp.3687-3690.
Chiang, J.C.H. and Sobel, A.H., 2002. Tropical tropospheric temperature variations caused by ENSO and their influence on the remote tropical climate. Journal of climate, 15(18), pp.2616-2631.
Chiang, J.C.H. and Lintner, B.R., 2005. Mechanisms of remote tropical surface warming during El Niño. Journal of climate, 18(20), pp.4130-4149.
Lintner, B.R. and Chiang, J.C.H., 2005. Reorganization of tropical climate during El Nino: A weak temperature gradient approach. Journal of climate, 18(24), pp.5312-5329.
Lintner, B.R. and Chiang, J.C.H., 2007. Adjustment of the remote tropical climate to El Niño conditions. Journal of climate, 20(11), pp.2544-2557.