HEIGHT-LATITUDE STRUCTURE OF PLANETARY WAVES IN THE STRATOSPHERE AND TROPOSPHERE. V. Guryanov, A. Fahrutdinova, S. Yurtaeva

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1 HEIGHT-LATITUDE STRUCTURE OF PLANETARY WAVES IN THE STRATOSPHERE AND TROPOSPHERE INTRODUCTION V. Guryanov, A. Fahrutdinova, S. Yurtaeva Kazan State University, Kazan, Russia When constructing empirical models of middle atmosphere (CIRA-, CIRA-) the main attention is focused on zonal-averaged fields of wind, temperature and geopotehtial and also on annual and semiannual harmonics of these parameters. Last decade thanks to (owing to) efforts Middle Atmosphere Group at the UK Meteorological Office global grid data of mentioned parameters up to the altitudes of upper stratosphere have emerged. These data allow one to construct empirical model of stratosphere with three-dimensional resolution. In particular, using Fourier analysis, one may investigate three-dimensional spatial structure of thermodynamical fields. In present paper from BADC UKMO stratospheric assimilated data for the Northern and Southern Hemisphere period of - for the altitude region from to. Hpa amplitudes, phases and a contribution to dispersion of zonal and geopotehtial, zonal and meridional wind for wave number and were calculated. Month mean (-) fields of meteorological elements were used. Such procedure leads to smoothing of all time oscillations with the period less than days. Because of this obtained amplitudes and phases characterize such large-scale wave processes, which may be considered as stationary. It is in this meaning that we shall further use the term stationary planetary waves. HEIGHT-LATITUDE DISTRIBUTION OF AMPLITUDE OF PLANETARY WAVES In figures and height-latitude distributions of amplitudes of geopotehtial zonal harmonics with wave number and are correspondingly represented. One can see that in Northern Hemisphere space disturbance of geopotehtial field due to first two zonal harmonics is higher than in Southern Hemisphere. As this takes place the amplitude of first harmonics in Northern Hemisphere achieves the maximum values ( m) in January at the latitude N and height km. In Southern Hemisphere similar maximum ( m) is observed in spring (September-October) at the latitude S within height interval - km. In troposphere, high wave activity, due to the first harmonic of geopotehtial is observed during the cold period of Northern Hemisphere at the northern out lying area of subtropical jet stream (-N). In troposphere of Southern Hemisphere elevated values of amplitude of first harmonic of geopotehtial are observed during the whole year within latitude zone -S with the maximum in cold period (more then m). In stratosphere the role of first harmonics is of high importance. It s contribution to dispersion in the most part of stratosphere of both hemispheres exceeds % and in winter period extratropical latitudes higher km in Northern Hemisphere and higher tropopause in Southern Hemisphere it exceeds %. In tropical area space structure of geopotehtial field is more complicated. Here the contribution of first harmonic is decreasing. It achieves the lowest values in stratosphere (less then %) in equatorial area during almost the all months of a year within the height interval - km, that is in area, with the most defined quasi-biennial oscillations of zonal wind. Height-latitude distribution of the second harmonic of geopotehtial is of more complicated structure. In winter period of Northern Hemisphere in stratosphere two maximums of amplitude are clearly defined in lower and higher stratosphere. In this way in January in lower stratosphere amplitude maximum of second harmonic ( m) is centered at the latitude N and height km. In this case high amplitude values are

2 also observed in troposphere of middle latitudes. In upper stratosphere the intensity of second harmonics is less and it s maximum is located at the latitude N and height - km. In Southern Hemisphere similar structure is retained, but the intensity in the centers is reverse: in upper stratosphere it is higher than in lower. So in June in lower stratosphere maximum of second harmonic amplitude ( m) is observed at the latitude S and altitude km and in upper stratosphere it is observed at S and km and achieves m value. With some variations the similar picture is observed in the other months of a year. In stratosphere the influence of geopotehtial second harmonic is limited. In most part of stratosphere it s contribution in dispersion does not exceed %. The exception is tropical zone, especially in the range of quasi-biennial oscillations, which contribution in dispersion is over -% all over the year. In Southern Hemisphere summers the polar area of upper stratosphere also stands out, here contribution of second harmonic in dispersion runs to %. In troposphere the second harmonic is of considerable importance in middle troposphere above the equator (it s contribution all over a year is more than -%) and in polar area of upper troposphere during the Northern Hemisphere (%). In figure and monthly averaged height-latitude distribution of zonal harmonics of zonal wind with wave number and are represented. In figures and the similar data are shown for meridional wind. From these illustrations one can see that both harmonics amplitudes for zonal and meridional wind in Northern Hemisphere run to higher values than in Southern Hemisphere. It refers both to stratosphere and troposphere. A comparison of first harmonic amplitudes of zonal and meridional wind shows, that they run to approximately equal maximum values - m/s in Northern Hemisphere in January, and - m/s in Southern Hemisphere in September-October in upper stratosphere. However their height-latitude distribution of amplitudes is essentially differ. In the field of zonal wind in both hemispheres two centers with approximately equal intensity are clearly defined: in middle latitude and in polar area. In so doing these centers of maximum amplitude values are separated by the regions of local minimum, which are located at the latitudes N and S correspondingly. Such structure is observed from October to March stratosphere of Northern Hemisphere and from August to November in stratosphere of Southern Hemisphere. Unlike zonal wind for first harmonic amplitudes of meridional wind the distribution with one maximum in polar area is characteristic. In so doing in Northern Hemisphere from October to March the area of maximum values shifts down from the height km to the height km. In Southern Hemisphere such situation in polar stratosphere is observed during the period from August to November. Contrary to the first harmonic, the second harmonic amplitude for meridional wind in stratosphere reaches higher values than for zonal wind. In this case for both components of wind the amplitude of second harmonic in Northern Hemisphere is - times larger than in Southern one, in which amplitude values in stratosphere throughout the year don t exceed - m/s. The exception is upper stratosphere region between S and S, where from August to October the second harmonic amplitude of zonal wind reaches - m/s. In Northern Hemisphere in winter period for meridional wind field the second harmonic is characterized by existence of high values area embracing almost entire stratosphere and troposphere with the maximum - m/s at the height - km and latitude N. Height-latitude distribution for second harmonic amplitude of zonal wind is of more complicated structure. In winter period of Northern Hemisphere it is characterized by three centers of large values in stratosphere. So in January local maximums are located at the following heights and latitudes: km and N ( m/s), km and N ( m/s), km and -N ( m/s). For the second harmonic of zonal wind high values near the tropopause are observed throughout the year. As in the case of geopotehtial the basic structural feature of fields of zonal and meridional wind is the dominant contribution of first harmonic to dispersion in stratosphere. Here there are large areas, especially in upper stratosphere and in extratropical latitudes where the contribution to dispersion for both wind components exceeds %. To a greater extent it is defined in the field of zonal wind during cold period of Northern Hemisphere. A contribution of wind second harmonics to dispersion is mach less. For zonal and

3 meridional wind the contribution of the second harmonic to dispersion reaches % only in polar troposphere in winter of Northern Hemisphere. SPATIAL DISTRIBUTION OF PHASE OF PLANETARY WAVES Phases ψ and ψ allow to judge about geographical position of crests and troughs of planetary waves with wave number and correspondingly. Phase value ψ coincides exactly with the crest longitude at the given latitude circle. There are two crests and two troughs at the wave with zonal number. For such a wave the longitudes of crests will have a values ψ and o ψ +. In figures - geographical position of climatic wave crest with wave number is represented at the various levels for January -. One may notice, that the wave crests in polar area in the whole considerate atmospheric layer are located in narrow longitude sector W--E. In stratosphere the longitudes of wave crests coincide with the position of stratospheric climatic area of high pressure Aleutian anticyclone. In tropical zone especially in troposphere geographic position of crest is unstable. In winter period within latitude interval - N a stable shift of wave crests with zonal number with height to the West is observed. This fact according to theoretical concept (T. Matsuno, ) is favorable to propagation of wave energy from bottom to top. In Southern Hemisphere similar situation is observed within latitude interval -N. CONCLUSIONS. In the average, during the considered period in Northern Hemisphere larger values of amplitudes of spatial planetary waves of geopotential, zonal and meridional wind are observed both for first and for second harmonic. In this case maximum of first harmonic amplitude is observed in upper stratosphere in Northern Hemisphere during winter period, and in Southern Hemisphere in spring.. In stratosphere of extratropical latitudes for all discussed parameters the first harmonic is prevailing. Its contribution to total variability exceeds %. The contribution of geopotential second harmonic reaches % in equatorial region in troposphere and lower stratosphere during the whole year and also in polar troposphere during cold period.. From data for latitude-longitude distribution of maximum amplitude phase of planetary waves with wave numbers and at various levels in atmosphere three-dimentional representation of the structure of wave fields of geopotential, zonal and meridional wind has been obtained. It has been found, that the most favorable conditions for vertical propagation of planetary waves with wave numbers and take place in winter period within latitude zone - N. ACKNOWLEDGEMENTS The work was supported by the INTAS (grant No --). We are grateful to the British Atmospheric Data Center, which provided us with access to the Met Office UARS Pressure Level Data. REFERENCES Matsuno T., Vertical propagation of stationary planetary waves in the winter Northern Hemisphere, J. Atmos. Sci.,, -,.

4 Fig.. Geopotential amplitude wave number (-).

5 Fig.. Geopotential amplitude wave number (-).

6 Fig.. Zonal wind amplitude wave number (-).

7 Fig.. Zonal wind amplitude wave number (-).

8 Fig.. Meridional wind amplitude wave number (-).

9 Fig.. Meridional wind amplitude wave number (-).

10 W E W E Fig.. Geopotential phases wave number and (-).

11 W E W E Fig.. Geopotential phases wave number and (-) SH.