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The Atlantic Multidecadal Oscillation (AMO) affects climate variability in the North Atlantic basin and adjacent continents with potential societal impacts. Previous studies based on model simulations and short-term satellite retrievals hypothesized an important role for cloud radiative forcing in modulating the persistence of the AMO in the tropics, but this mechanism remains to be tested with long-term observational records. Here we analyze datasets that span multiple decades and present new observational evidence for a positive feedback between total cloud amount, sea-surface temperature (SST), and atmospheric circulation that can strengthen the persistence and amplitude of the tropical branch of the AMO. In addition, we estimate cloud amount feedback from observations and quantify its impact on SST with idealized modeling experiments. From these experiments we conclude that cloud feedbacks can account for 10% to 31% of the observed SST anomalies associated with the AMO over the tropics.

Strong El Nino events are followed by massive summer monsoon flooding over the Yangtze River basin (YRB), home to about a third of the population in China. Although the El Nino–Southern Oscillation (ENSO) provides the main source of seasonal climate predictability for many parts of the Earth, the mechanisms of its connection to the East Asian monsoon remain largely elusive. For instance, the traditional Nino3.4 ENSO index only captures precipitation anomalies over East Asia in boreal winter but not during the summer. Here we show that there exists a robust year-round and predictable relationship between ENSO and the Asian monsoon. This connection is revealed by combining equatorial (Nino3.4) and off-equatorial Pacific sea surface temperature anomalies (Nino-A index) into a new metric that captures ENSO's various aspects, such as its interaction with the annual cycle and its different flavors. This extended view of ENSO complexity improves predictability of YRB summer flooding events.

The global adjustment of the thermocline in response to deepwater formation is studied in a single mode model on a beta-plane. The signal is carried from ocean to ocean by Kelvin waves, which travel equatorward along western boundaries, eastward across the equator, poleward at the eastern boundaries, and then eastward around the southern tip of continents into the next ocean basin. The interior is filled by Rossby waves emanating from eastern boundaries. Stronger (weaker) deepwater formation induces an upward (downward) motion of the main thermocline in the world oceans. The adjustment is completed on centennial time scales.

Precursors for the Indian monsoon are known to be highly epoch specific in their skills in predicting the monsoon on seasonal time scales. We show that the various precursors are correlated with the monsoon, only when they are correlated with ENSO, which happened in the recent period 1951–1990, but not in the 1990's and the period 1911–50. This accounts for the skill in monsoon prediction during 1951–90. We find that ENSO and its precursors tend toward higher amplitude and 3–5 year periods in the 1951–1990 epoch, and toward decreased amplitude and 5–7 year periods in the 1911–1950 epoch. We argue that the shift to lower frequency and amplitude in the earlier epoch diminished the association between the monsoon precursors and ENSO, leading to diminished skill in predicting the monsoon in that epoch. However, the simultaneous relationship between the monsoon and ENSO has been stable over the past 140 years, suggesting that the monsoon—ENSO teleconnections are robust once ENSO is established. Changes in the frequency of ENSO have implications for statistical prediction schemes for ENSO and the monsoon.

Assimilating the sea level data from tropical Pacific tide gauges greatly improved the Lamont model prediction of the 1997/98 El Nino while retaining its overall performance during the past few decades. The implication is that the Lamont forecast system is limited by the observational data used for initialization probably probably as much as by its simplified model physics. The sea level measurements in the vicinity of the equator are extremely effective in correcting the model ocean state and preconditioning it for ENSO prediction.

[1] We use a mechanistic model of tree-ring formation to simulate regional patterns of climate-tree growth relationships in the southeastern United States. Modeled chronologies are consistent with actual tree-ring data, demonstrating that our simulations have skill in reproducing broad-scale patterns of the proxy's response to climate variability. The model predicts that a decrease in summer precipitation, associated with a weakening Bermuda High, has become an additional control on tree ring growth during recent decades. A nonlinear response of tree growth to climate variability has implications for the calibration of tree-ring records for paleoclimate reconstructions and the prediction of ecosystem responses to climate change.

[1] We propose that temporal variations within the marine plankton system can induce intraseasonal variations in sea surface temperature (SST) through the effect on solar penetration due to chlorophyll and other optically active organic components. Sensitivity studies with a simple model suggest that these small oscillations in SST may stimulate radiative-convective oscillations in the atmosphere which amplify them and thus induce or modulate significant variability in the coupled system. Long term bio-optical measurements in the Western Pacific, where satellite time series are degraded by clouds, would provide a test of our theory and would improve our understanding of the heat balance in this climatically important region.