Seasonal and regional signatures of ENSO in upper tropospheric jet
characteristics from reanalyses
Abstract
Regionally and seasonally resolved relationships of upper tropospheric
jet variability to El Niño / Southern Oscillation (ENSO) in multiple
reanalyses are presented, with subtropical and polar jets analyzed
separately. Previously reported results confirmed herein include
strengthening of tropical jets associated with monsoons and Walker
circulation during La Niña and a statistically significant subtropical
jet latitude decrease (increase) during El Niño (La Niña) in the zonal
mean view in both hemispheres. However, subtropical jet latitudes
increase significantly during El Niño over the NH eastern Pacific in
DJF, and in different limited SH regions in MAM and SON. Subtropical jet
altitudes increase significantly during El Niño in the zonal mean in all
seasons (DJF / MAM) in the NH (SH). Subtropical jet windspeed
correlations with ENSO vary, showing increasing windspeed during El Niño
in both hemispheres in DJF and MAM. Polar jet correlations with ENSO are
typically not significant in the zonal mean, but there are a few
regions/seasons with significant correlations with ENSO, particularly in
the SH, where polar jet latitudes decrease over Asia and the western
Pacific in DJF, and increase over the eastern Pacific in JJA and SON,
during El Niño. Typically, significantly weaker (stronger) polar jet
windspeeds are associated with El Niño (La Niña) in the western than in
the eastern hemisphere in both NH and SH. All reanalyses analyzed agree
well. This work highlights the importance of regional and seasonal
variations in the upper tropospheric jet response to ENSO and provides
new information for model evaluation.