Manifestations of Different El Nino types in the Dynamics of Extratropical Stratosphere

The behavior of planetary wave with zonal wave number 1 (PW1) at the heights of middle and upper stratosphere during different El Nino types has been considered. The sets of 5 winters have been chosen for each El Nino type using the table of available extended Multivariate El Nino Southern Oscillation (ENSO) Index values and index for identifying different types of El Nino Modoki events. Comparing planetary wave response and residual circulation under various conditions caused by Modoki I, II, and canonical El Nino, it has been revealed identical features associated with any of this type. The activity of travelling waves has been presented at three latitudes (2.5, 27.5, and 62.5) of Northern Hemisphere to follow the changes in behavior of waves. Travelling waves determined at 2.5°N latitude during every El Nino type have similar wave activity distribution despite the different location of SST anomaly. The standing waves activity at 27.5°N latitude during Modoki II type is similar to this activity during canonical one. This similarity disappears at lower latitudes, where wave amplitudes every canonical winter do not distinguish each other greatly especially standing and westward propagating waves.


Introduction
El Nino Southern Oscillation (ENSO) is the phenomenon, which has three phases and irregular cycle of a coupled ocean-atmosphere interaction. Over the years, El Nino -the "warm" phase of ENSO phenomenonhas become very popular due to free access to scienti c information and community-wide discussion. The considerable part of the population in tropical regions is familiar with this 'coupled' climate event. The reason is extreme weather, which is observed during this ENSO phase. Fish population die or migrate these years since the normal upwelling is absent and coastal ecosystem changes. Increased convection above warmer Paci c brings raised precipitation. This results in heavy rains and devastating oods. While South America suffers from oodwaters, severe droughts occur in Indonesia and Australia (Ward et  Stronger El Nino events interfere as global atmospheric circulation via remote impacts. The movement of atmospheric heat sources directed to the East lead to uncommon winter weather at higher altitudes. Sea Surface Temperature (SST) and pressure anomalies can affect even the stratosphere trough the teleconnections. The Aleutian low tends to deepen and goes southward during El Nino. This leads to the strengthening of wave activity ux upward to stratosphere and the weakening of polar vortex (Gar nkel and and Kim 2011) and eastern Paci c (EP or canonical) (Larkin and Harrison 2005;Hurwitz et al. 2014;Domeisen et al. 2019). It is noted that there is more substantial and rapid response of Aleutian low to eastern Paci c El Nino type in contrast to central Paci c (Yu and Kim 2011;Sung et al. 2014). The polar stratosphere exhibits a more pronounced warming and, as a consequence, the polar vortex weakening during EP, while there is no consensus on CP mostly due to differences in its de nition.
In order to distinguish two types of El Niño, several methods and indices have been suggested. The El Niño type can be determined by comparing the values of the Niño3 and Niño4 indices Yeh et al. 2009). The SST anomalies, furthermore, in the tropical southeastern Paci c (150-90°W, 0°-10°S) represent El Niño Modoki events as well (Qu and Yu 2014 Forbes et al. 1997). They induce meridional circulation that is why latitude of 2.5°N has been included in the present study. Latitude of 27.5°N allows demonstrating variability of travelling planetary waves, while at higher latitudes these waves are obfuscated by the standing and quasi-stationary waves (Pogoreltsev et al. 2009). The extratropical lowfrequency westward propagating normal atmospheric modes are well observed at higher mid-latitudes (e.g. 62.5°N) since their amplitudes are the greatest here (Salby 1984;Fedulina et al. 2004 The amplitudes of zonal harmonics with zonal wave numbers 1 in the geopotential height are presented in propagating components is to some extent arti cial. Two waves with the same period and amplitudes that propagate westward and eastward can be presented as a standing wave. Analyzing the activity of stationary planetary wave with zonal wave number one (SPW1) it is worth considering its impact on the mean ow. However, in the momentum and energy equations, the wave sources of momentum and heat are compensated by advective momentum and heat uxes (Charney and Drazin 1961).
To ll this gap, the alternative approach can be applied. It is the calculation of the transformed Eulerian mean circulation (TEM, Andrews and McIntyre 1976) that has been used in the present study. The essence of this method is the consideration of the so-called residual mean meridional circulation (RMC), which is a combination of eddy and advective mean transport.

Results
The amplitudes of SPW1 during different El Nino types are presented in (not presented) and 62.5°N (Fig. 5-7 (Fig. 5). The reason is likely in different stratospheric processes and zonal ows that in uence waves' distribution and make them behave in a certain way. In canonical El Nino winters (Fig. 6f-j), there is a two-week pause while any eastward wave activity is absent, at the beginning of January. Traveling planetary waves (the normal atmospheric modes, ultra-fast Kelvin wave, etc.), unlike atmospheric tides, do not have permanent sources, therefore they exist (observed in the results of wavelet analysis) in the form of bursts of wave activity at certain periods that are not tied to a speci c time interval (Salby 1984 (Fig. 8a, b, c) and amplitudes of Kelvin waves (Fig. 8d, (Fig. 9a, b, c). The magnitudes of amplitudes do not exceed 200 meters in Modoki II event ( Fig. 9b), but they reach 250 meters in Modoki I event (Fig. 9a)  Taking into account the amplitude overstating at 2.5°N and altitude limitation of JRA-55, the residual circulation has been calculated using MERRA2 (The Modern-Era Retrospective analysis for Research and Applications, https://gmao.gsfc.nasa.gov/reanalysis/MERRA-2/) reanalysis data for every December (Fig. 11,   12, and 13, left panels) and January (Fig. 10, 11, and 12, right panels). The distribution of residual circulation in these two months should be enough, allowing for that the wave activity begins in December and January, to assume that any dependence upon El Nino type is there. December in 1987/88 and 1992/93 shown in Fig. 10 (  It is di cult to estimate the amplitude wave spectra averaged over 5 months of cold season since the amplitudes of nonmigrating diurnal tides and Kelvin waves are found to be overestimated all years up to 1979.
General shape of curves taking into account maximal amplitudes of standing and traveling waves in Modoki I and canonical winters look similar. Modoki II differs by smaller amplitudes and smoother curves. This difference especially reveals at the mid-latitudes, where wave amplitudes every canonical winter do not distinguish each other greatly especially standing and westward propagating waves.
Residual circulation in every considered winter has no identical features especially in November and December.
Taking into account the various origin location of SST anomaly, re ected in MEI values and time, when this anomaly is begun to observe, it is possible to conclude that this information as initial is not enough. This observation suggests that the other troposphere-stratosphere processes of equal importance interfere directly or via teleconnections in uencing the propagation of planetary waves into the stratosphere.
In the present study the only PW1 has been considered, while the smaller harmonics can show interesting results with the similar analysis. Strong amplitudes with magnitudes more than 1000 meters of stationary planetary waves with zonal wave number 2 (SPW2) are observed in the same winters as for SPW1, some of them even in the same months. Considering SPW2, the wave activity in March attracts attention. Amplitudes of more than 500 meters are common in March during Modoki I conditions. The opposite situation is during Modoki II phase -any wave activity is absent already in the second half of February. Canonical winters demonstrate weak wave activity in the rst decade of March or there is no any activity at all. But that's beyond the scope of this paper.

Declarations
Author Contributions: TE designed the research, wrote the paper and performed the analysis. AK developed software packages for calculating the RMC. AP helped to design and interpret the manuscript. SS, CW, and WK provided valuable suggestions to the interpretation of obtained results. All authors have seen, discussed and approved this version of the manuscript.