Study on the impact of sudden stratospheric warmings in mid-latitude MLT region according to ground-based and satellite temperature measurements Medvedeva I.V.(1), Semenov A.I.(2) Chernigovskaya M.A.(1), Perminov V.I.(2) 1 - Institute of Solar-Terrestrial Physics (ISTP), Siberian Branch, Russian Academy of Sciences, Irkutsk, Russia; 2- Obukhov Institute of Atmospheric Physics (IAP), Russian Academy of Sciences, Moscow, Russia 38th annual European Meeting on Atmospheric Studies by Optical Methods, Siuntio, Finland, August 2011

Sudden stratospheric warmings (SSW) are an important manifestation of vertical dynamical coupling in the atmosphere. During strong SSW variations of dynamic and temperature regime in the middle atmosphere are observed, the disturbances during SSW cover large atmospheric range from troposphere to MLT heights. Major SSW occur when the westerly winds at 60N and 10hPa (geopotential height) reverse, i.e. become easterly (westwards). A complete disruption of the polar vortex is observed. Minor SSW are similar to major warmings however they are less dramatic, the westerly (eastward) winds are slowed, however do not reverse. Therefore a breakdown of the vortex is never observed.

Background It is known that mesospheric coolings are associated with SSWs. The key mechanism by Matsuno (1971) is now widely accepted: the growth of upward propagating planetary waves from the troposphere and their interaction with the mean flow. Liu and Roble (2002) predicted mesospheric cooling extending up to the heights of ~ 110 km with a secondary warming between km. Experimental results confirmed impact of SSW on MLT region were presented in (Myrabo et. al., 1984; Matveeva & Semenov, 1985; Walterscheid, 2000; Sigernes et al., 2003). Using the data of OH rotational temperature the authors revealed the mesopause temperature decrease.

Background However, association between SSW events and the MLT region is not fully understood. Questions about the timing of stratospheric and mesospheric disturbances remain. Myrabo et al. (1984) report a 1–2 day delay in the mesospheric response to a stratospheric event, and Hernandez (2004) suggests the mesosphere cooling is a 1–2 month leading indicator of stratospheric warmings, while the model result of Liu and Roble (2002) indicates little, if any, phase lag or lead between the temperature anomalies in the mesosphere and stratosphere. The height distribution of mesosphere cooling associated with SSW events is also not yet well established. Thus, (Siskind, et.al., 2005) using the SABER temperature data revealed that mesospheric temperatures between 0.7 hPa and 0.01 hPa (~52-80 km) show a significant anticorrelation with stratospheric temperatures during SSW. However, for pressures <0.01 hPa, this anticorrelation breaks down and near hPa (~88 km), which is the pressure associated with the peak of the OH* emission, the correlation coefficient is close to zero or slightly positive, in disagreement with calculations of Liu and Roble (2002).

The study is based on measurements of the atmospheric temperature, obtained in different longitudinal zones – Irkutsk (52N, 103E) and Zvenigorod (56N, 37E) - Study of variations in atmospheric temperature at the MLT heights during the winter stratospheric warming in using ground-based and satellite measurements data; - Comparison of satellite and ground-based measurements data on temperature at MLT height Objective

Analyzed Data : data about the variations of mesopause temperature (~87 km) obtained from ground-based spectrographic measurements of the OH emission (834.0 nm, band (6-2)) at ISTP and IAP observatories near Irkutsk (52N, 103E) and Zvenigorod (56N, 37E) respectively; satellite data on vertical temperature distribution in the atmosphere from MLS (Microwave Limb Sounder) aboard the spacecraft EOS Aura [ ECMWF stratosphere temperature data presented by Stratospheric Research Group of FU Berlin [ data on zonal temperature and wind of NCEP GDAS and CPC [ annual NCEP data for the Northern Hemisphere [ ext.gsfc.nasa.gov/Data_services/met/ann_data.html]

An example of the emission spectrum of the night airglow in the area of nm. Top side – OH and O2 bands. Mesopause temperature in Irkutsk and Zvenigorod was determined using the emission spectrum of OH(6-2). Measurements and data handling at both observatories were carried out by the same method. High-aperture diffraction spectrographs with receivers on the CCD matrix allowing to register the emission spectrum of the night sky in the near infrared region with high spectral (~ 2-3 A) and temporal (~ 2 min) resolutions were used. To determine the rotational temperature we used the first 3 lines of P-branch of the vibration-rotation band of OH(6-2). The temperature is determined with 1-2 K accuracy. Analyzed Data High-aperture diffraction spectrograph SP-50

Maximum temperature of the stratosphere at 10 hPa isobaric level (~31 km) for each analyzed SSW event YearTmaxDataTmax site coordinates K °N, 90°E K °N, 40°W K °N, 122.5°E K °N, 122.5°E The mean temperature of winter stratosphere at that altitude in quite conditions is ~ 210 К

NCEP Data for the Northern Hemisphere. In January-February 2008, January 2009 and January 2010, there were very intense, long time winter SSW, covering large part of the Northern Hemisphere. The SSW in January 2011 was less intense, however well- pronounced in zonal stratospheric temperature at 50 N. SSWs in are among the most intense events in the Northern Hemisphere since Especially remarkable was the SSW in January 2009, when the stratospheric temperature reached record values. This event is described in a number of publications (Labitzke, 2009, Harada et al. 2009). Ellipse – periods of analyzed SSW events

2009 Zonal Mean Temperature (60-90N) SSW oscillatory nature during period of about a month Zonal Mean Temperature (50N)

Zonal Mean Wind 50-80N Major SSW 2009 – 10 hPa zonal circulation reversal

SSW in January hPa (~31 km) 3 hPa (~40 km)

Results Altitude-temporal maps of the atmospheric temperature distribution according to the MLS AURA for the region of Irkutsk and Zvenigorod (search radius is 900 km) 2008 During SSW , stratospheric temperature disturbances of large spatial scales were observed.

2009 The temperature disturbances in almost the entire middle atmosphere and significant change in the vertical distribution of temperature occured.

2010 The largest temperature increases were observed in the stratosphere at altitudes of km. Registered cooling of the atmosphere at altitudes of MLT was distributed very irregularly in both altitude and time.

2011

a)Т of the stratosphere averaged for hPa (39-49 km) levels, Aura data; b) T of the mesopause region averaged for hPa (84-88 km) levels, Aura data; с) Т ОН (~87 km), ground- based data Zvenigorod : During all analyzed SSW events decrease in T of the mesopause region was observed. Irkutsk: the pattern is not so well-definite. Thus, during the period of the SSW 2008, oscillations of the atmospheric temperature at altitudes both the stratosphere and mesopause with periods of about 6-8 days were observed.

Quantitative characteristics of the relationship of day-to-day T stratosphere ( km) and T mesopause (84-88 km) values during the SSWs has been obtained by regression analysis of Aura data For SSW , Zvenigorod and SSW 2009, Irkutsk, the regression dependency was revealed: Tmes= -(0.35±0.04)*Тstr + 288±12, r = -0.55, r - correlation coefficient Irkutsk: Correlation between Tmes and Tstr for the SSW 2008 and 2010 practically absent. Probably, this is due to the longitudinal manifestation of nature of the interaction of dynamic and thermal processes during analyzed periods of SSW. In any case, this result as the result of the work (Siskind et. al., 2005), does not correspond to model calculations (Liu & Roble, 2002), predicted a steady decrease in MLT temperature of up to heights ~110 km during the SSW.

Zvenigorod CrossCorrelation Functions of T strat (39-49 km) and T mes (84-88 km). First variable: Tstrat, Lagged: Tmes. In the European longitudinal zone Tmes decreased almost simultaneously with increase of the T strat. Negative correlation of T str and T mes. Maximal correlation coefficients at Lag=0 r=-0.62 r=-0.59 r=-0.57

In the East Asian longitudinal zone - a reaction temperature of the mesopause on the SSW did not reveal a stable tendency. Manifestations of the influence of SSW on the mesopause region in the East Asian longitude zone is more complicated than in the European one. Irkutsk CrossCorrelation Functions of T strat (39-49 km) and T mes (84-88 km). First variable: Tstrat, Lagged: Tmes

Altitude of the mesopause is changing as altitude of the stratopause change also. We compared the ratio of the temperatures of the stratopause and mesopause, at the altitudes where mesopause and stratopause were located each day. The value of this ratio changed from 1.1 up to 1.9 during analyzed SSWs. This ratio could be probably used as quantitative characteristic of manifestation of the complicated processes of interaction between lower and upper atmosphere during SSW events.

The analysis of the atmospheric temperature variations according ground- based and satellite data during the events of winter stratospheric warming in revealed a disturbances in the middle atmosphere from the stratosphere to the mesopause. Regression and correlation dependency of day-to-day temperatures of the stratosphere and mesopause during the SSW were obtained. It was revealed that manifestations of the influence of SSW on the mesopause region in the East Asian longitude zone is more complicated than in the European one. In the European longitudinal zone Tmes decreased almost simultaneously with rise of the T strat. In all these SSW events, when the stratospheric temperature increases by ~ 30 K, the temperature in the mesopause decreased by ~ 20 K. In East Asia - a reaction of the mesopause temperature on the SSW did not reveal a stable tendency. These results may indicate on a possible longitudinal effect of SSW on the thermal and dynamic regimes of the middle and upper atmosphere. The ratio of the temperatures at the stratopause and mesopause, at the altitudes where mesopause and stratopause be located each day was analyzed. This ratio could be probably used as quantitative characteristic of manifestation of the complicated processes of interaction between lower and upper atmosphere during SSW events. Comparison of satellite and ground-based data on mesopause temperature showed a pretty good agreement Conclusions

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