Influence of Enhanced Variability with Zonal Wavenumber 1 on Arctic Oscillation in Late Winter to Early Spring in El Niño Conditions

Abstract

We investigated the relationship between the atmospheric variability in El Niño conditions and Arctic Oscillation (AO) during the period from late autumn to early spring, focusing on the vertical linkage between the troposphere and the stratosphere, based on a composite analysis. The results of the composite analysis indicate that the vertical linkage is the clearest in late winter to early spring, particularly in the three-month of February -April (FMA). In FMA, the upper tropospheric patterns and upward propagation of planetary waves with zonal wavenumber 1 are enhanced and contribute to a negative phase of the stratospheric Northern Annular Mode (NAM) in El Niño conditions.The results also indicate that the stratospheric negative potential vorticity (PV) anomalies associated with the negative phase of NAM induce a lowered tropopause, vertical compression of the tropospheric column, positive surface pressure anomalies in the polar region and hence the negative phase of the AO. This vertical linkage and the impact of sea level pressure near the pole are consistent with a quantitative estimation based on geostrophic and hydrostatic adjustment associated with the stratospheric PV anomalies.(Citation: Takemura, K., and S. Maeda, 2016: Influence of enhanced variability with zonal wavenumber 1 in El Niño conditions on Arctic Oscillation in late winter to early spring. SOLA, 12, 159−164,

Seasonal Predictability of the North Atlantic Oscillation and Zonal Mean Fields Associated with Stratospheric Influence in JMA/MRI-CPS2

“…With the quantitative estimate based on the method in the supplemental material, the surface pressure in balance with the stratospheric PV signal was estimated at 2.51 hPa, and it has the same order of magnitude as the actual signal of the surface pressure (1.13 hPa), as was shown previously by Takemura and Maeda (2016). Therefore, the mechanism suggested by AH02 may contribute to the high predictability of sea-level pressure (NAO/ AO).…”

“…They also provided quantitative estimates of the downward influence. Recently, Takemura and Maeda (2016) have quantitatively estimated the downward influence of the stratospheric composite anomalies on the troposphere during El Niño conditions based on AH02's approach.…”

“…We use the Japan Meteorological Agency/Meteorological Research Institute-Coupled Prediction System version 2 (JMA/MRI-CPS2; Takaya et al 2017), which is the latest operational seasonal prediction system of the JMA. In addition, we quantitatively estimated the downward influence of the signal from the stratosphere to the troposphere based on the approach by AH02 and Takemura and Maeda (2016).…”

A strong phase reversal of the Arctic Oscillation in midwinter 2015/2016: Role of the stratospheric polar vortex and tropospheric blocking

“…The associated downward propagation signal might result in the negative AO [Takemura and Maeda, 2016]. Thus, the El Niño event could be related to the negative AO in late January 2016, but it cannot explain the strongly positive AO in December 2015 ( Figure 1a).…”

“…As a consequence, El Niño winters tend to be accompanied by a weaker stratospheric polar vortex, especially in late winter [ Li and Lau , ]. The associated downward propagation signal might result in the negative AO [ Takemura and Maeda , ]. Thus, the El Niño event could be related to the negative AO in late January 2016, but it cannot explain the strongly positive AO in December 2015 (Figure a).…”