5/25/2023 0 Comments Enso chicago![]() ![]() ![]() ENSO events differ in amplitude, temporal evolution, and spatial pattern. Anomalous warming or cooling conditions are associated with a large-scale east–west sea level pressure seesaw, termed the Southern Oscillation, which represents the atmospheric manifestation of the coupled ENSO phenomenon ( McPhaden et al. The term El Niño refers to warming of the tropical Pacific Ocean occurring every 2–7 yr, while the opposite cold phase is known as La Niña. Improved determination of ENSO predictability, teleconnections, and impacts requires a better understanding of event-to-event differences in ENSO spatial patterns and evolution.Įl Niño–Southern Oscillation (ENSO) is a naturally occurring phenomenon in the tropical Pacific that has global impacts of great relevance to society. Color shading of dots in the EP (CP) panel indicates the value of the projection on the CP (EP) optimal initial conditions. Note that the tropical SST growth factor (indicated by the range of the ordinate) for the EP pattern is almost 4 times greater than for the CP pattern. (bottom) Projection of observations onto the optimal initial conditions for SST anomaly amplification over a 6-month interval vs the projection onto the optimal evolved SST state 6 months later, for the (c) EP and (d) CP patterns. Note that within this linear framework, the opposite-signed patterns lead to cold events. Anomalous SST is indicated by shading (contour interval is 0.25 K), thermocline depth by contours (contour interval is 5 m, where black is positive), and zonal wind stress by black vectors (scaled by the reference vector 0.02 N m −2, with values below 0.002 N m −2 removed for clarity). (b) As in (a), but for the evolution of the second pattern (which leads to a CP-type ENSO). (a) Evolution of the first pattern (which leads to an EP-type ENSO) shown as maps at t = (top) 0 and (middle) 6 months. The initial conditions (i.e., optimal structures) are obtained by determining a linear stochastically forced dynamical model from SSTAs, thermocline depth anomalies, and zonal wind stress anomalies, over the period 1959–2000. (right) The spatial patterns of SSTA for specific warm and cold events of either type are shown, with a contour interval of 0.25☌.Įvolution of SSTAs from (top) the initial conditions to (middle) the final states 6 months later. Blue dots in the left panel correspond to events for which the leading principal component (used as CP index) exceeds one standard deviation. CP events are identified using the leading principal component of the SSTA residual after removing the SSTA regression onto the Niño-3 index. Events after 1945 are considered EP (red dots) when the Niño-3 index exceeds one standard deviation. Events prior to 1945 are colored in gray. Each dot corresponds to the extreme positive or negative value over the NDJ of each year in the region 2°S–2°N, 110☎–90°W. Anomalies were obtained from the National Oceanic and Atmospheric Administration (NOAA) extended reconstructed SST dataset ( Smith and Reynolds 2004) over the period 1900–2013, as departures from the 1945–2013 climatology. (left) Distribution of boreal winter SSTA extrema in the longitude–amplitude plane.
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