Abstract
Abstract. The connection between the El Niño Southern Oscillation (ENSO) and the Northern polar stratosphere has been established from observations and atmospheric modeling. Here a systematic inter-comparison of the sensitivity of the modeled stratosphere to ENSO in Chemistry Climate Models (CCMs) is reported. This work uses results from a number of the CCMs included in the 2006 ozone assessment. In the lower stratosphere, the mean of all model simulations reports a warming of the polar vortex during strong ENSO events in February–March, consistent with but smaller than the estimate from satellite observations and ERA40 reanalysis. The anomalous warming is associated with an anomalous dynamical increase of column ozone north of 70° N that is accompanied by coherent column ozone decrease in the Tropics, in agreement with that deduced from the NIWA column ozone database, implying an increased residual circulation in the mean of all model simulations during ENSO. The spread in the model responses is partly due to the large internal stratospheric variability and it is shown that it crucially depends on the representation of the tropospheric ENSO teleconnection in the models.
Highlights
The El Nino Southern Oscillation (ENSO) is a tropical atmosphere-ocean phenomenon and a source of large-scale climate variability for the atmosphere – ocean system
The model simulations considered here are those used for the ChemistryClimate Model Validation Activity (CCMVal)-1 activity, of which many contributed to the last ozone assessment (WMO/UNEP, 2007)
The main results are summarized here: 1. In the lower stratosphere, the mean of all model simulations reports a warming of the polar vortex during strong ENSO events: The February-March temperature anomaly in the lower stratosphere is positive, significant and of the order of 2 K for the mean of all model simulations
Summary
The El Nino Southern Oscillation (ENSO) is a tropical atmosphere-ocean phenomenon and a source of large-scale climate variability for the atmosphere – ocean system. The purpose of this work is to extend these previous studies that analyzed the ENSO response in Chemistry Climate Models (CCMs), by systematically evaluating the response to warm ENSO in the pool of simulations for the recent past performed with the CCMs participating in the ChemistryClimate Model Validation Activity (CCMVal-1) of SPARC that are discussed in Eyring et al (2006) Many of these models contributed to the 2006 ozone assessment (WMO/UNEP, 2007). The negligible response may be partly due to the smaller SST anomalies that occurred for cold events during the period considered here This apparent little sensitivity of the Arctic stratosphere to cold ENSO derived from model results is consistent with the recent analysis of radiosonde temperature data by Free and Seidel (2009)
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