The wind regime of the mesosphere and lower thermosphere during the DYANA campaign—II. Semi-diurnal tide

Journal

o/ .4mmspher1~ mid T~wc.irnol

Plm,m

Pergamon

Vol. 5h. No\

0021-9169(94)E0028-L

13) 14. pp. 1771~ 1752. 1994 Sarnce Ltd Bnta~n. All rIghta rcrerwzd 00219lh9’94 $7 0010.00

CopyrIght ( 1994 Elscvm

Prmted

I” Great

The wind regime of the mesosphere and lower thermosphere during the DYANA campaign-II. Semi-diurnal tide Yu. 1. PORTNYAGIN,* N. A. MAKAROV, * R. P. CHEBOTAREV,~A. M. NIKONOV,? E. S. KAZIMIROVSKY,$ V. D. KOKOUROV,~ V. V. SIDOROV,#A. N. FAKHRUTDINOVA,~ G. CEVOLANI,~~R. R. CLARK,~ D. K~~RSCHNER,** R. SCHMINDER,** A. H. MANSON,?? C. E.

MEEK,??

H. G. MULLER,$$ J. C. STODDART,~~ W. SINGER,@ and P. HOFFMANN@

*Institute of Experimental Meteorology, Scientific and Production Association “Typhoon”, Obninsk, Russia; tInstitute of Astrophysics, Academy of Sciences of Tajikistan, Dushanbe, Tajikistan ; $Siberian Institute of Terrestrial Magnetizm, Irkutsk, Russia ; SDepartment of Physics. Kazan University, Kazan, Russia: i Institute FISBAT, Bologna, Italy; 1TUniversity New Hampshire, Durham. New Hampshire. U.S.A. : **Geophysical Observatory, University Leipzig, D(O)-7261, Collm, Germany; ttlnstitute of Space and Atmospheric Studies, Saskatoon, Canada ; $$Department Physics, University Sheffield, Sheffield. U.K. ; asInstitute of Atmospheric Physics, D(O)-2565. Kuhlungsborn, Germany (Receiwd infinalform

26 Muy 1993; accepted I Jui~, 1993)

Abstract-Co-ordinated ground-based radar measurements carried out during the 15 January-l 5 March 1990 DYANA campaign at I4 different geographical sites have provided a good opportunity to investigate the characteristics of semi-diurnal tidal variations in the mesosphere/lower thermosphere over a wide spectrum of space/time scales. It is pointed out that significant differences of monthly mean tidal parameters observed at the various sites may be explained by latitudinal and longitudinal effects. Well-defined 2-3-week oscillations of the tidal parameters are found to be typical of all observational sites. Their estimated space scales do not contradict the hypothesis about a possible coupling between these oscillations and the low wave-number processes in the stratosphere. Tidal parameter oscillations with 2-5day periods may be explained to be effects of the nonstationary processes with longitudinal wave numbers s> 3.

I. INTRODUCTION Co-ordinated

measurements

of

wind

in

the

thermosphere

(c.. 80&105 km)

meso-

carried out at different geographical locations as part of the DYANA program provide a good opportunity to investigate characteristics of the semi-diurnal tidal (ST) variations over a wide spectrum of space/time scales. Table 1 shows the measurement sites and some characteristics of the obtained data. As follows from Table 1, the measurements were taken by three methods. The major part of data was obtained by the meteor radar method (MR). This method was applied at nine out of 14 sites. The spaced antenna method using medium-frequency radars (MF) was applied at three sites and, at the other two, the method of ionospheric drift measurements in the low-frequency range (LF) was used. It can also be seen from Table 1 that the majority of sites are located in the mid-latitude European region. The experimental data on which the studies are based are amplitudes and phases of semi-diurnal oscilpause/lower

lations, obtained by the harmonic analysis of time series of mean hourly wind velocities measured during the DYANA campaign from 15 January to I5 March 1990. The techniques used by the different teams to measure and process the data differed significantly and efforts are made to unify the experimental data presented for joint analysis. However, the problem of the compatibility of the data needs to be discussed. The previous comparisons of results of measurements taken in the same or closely spaced sites using the techniques MR and LF (PORTNYAGIN et ul., 1978), MR and MF (PORTNYAGIN et d., 1991), MF and FPI (MANSON rt al., 1991) help to solve the problem to a certain extent. To assess how the methods of measurement and processing influence the parameters under consideration we will outline the methods and refer to the materials in which they are described in more detail. The measurements in Obninsk. Volgograd and Khabarovsk were performed by the meteor radar method by sounding four regions in space with their centres at the height of 95 km and at a distance of 200 km from the radar. The scanning of the regions 1731

Yu. I. PORTNYAGIN et ~1.

1732

Table Site

Co-ordinates

Badary Bologna Collm Durham Dushanbe Juliusruh Kazan Khabarovsk Kuhlungsborn Obninsk Saskatoon Sheffield Tromso Volgograd

52 N 104 E 45’N 12’E 52 N 15’E 42 N 71’W 38N68’E 55 N 13;E 56 N 4Y’E 49 N 135 E 54 N 12 E 55 N 38 E 52’N 107 W 53N 2W 70 N 19’E 4YN44E

*The data for Juliusruh

was

performed

100 Hz

frequency

The results

by

of northward

LF MR LF MR MR MF MR MR MR MR MF MR MF MR

were combined

switching using

Method

an

radar

Heights

(km)

95 85-105 82-102 83-104 95 80-107.5 81-108 95 95 95 92--l 12 95 82-I 12 95

Period of measurements 15 January-l

5 March February 15 January-~15 March 18 January--21 February 15 January-1 5 March 15 January- 15 March 15 January-1 5 March 16 January-14 March 15 January--l5 March 15 January-1 5 March 15 January-1 5 March 15 January 15 March 15 January- 18 February 15 January- 15 March

15January-26

Data Daily Daily zonal only Two-day sliding. Tonal only Four-day means Daily Ten-day means. ronal only Two-day means sliding Two-day in the week Three-day means sliding Daily Four-day means Four-day means Four-day means Daily

with the data from Collm.

antennae

with

electronic

commutator.

and eastward

measurements

only. Measurements were of the radial velocities of meteor trail drifts ; from these the horizontal wind components were determined for each sounding region at hourly time intervals. The time series of data which were obtained is subjected to harmonic analysis for which the first four harmonics divisible by 24 h are isolated. A detailed description of equipment and observational technique is given in P~RTNYAGIN et al. (1978). The meteor radar in Kazan is equipped with a height measurement system. This allowed wind velocities at 3 km height intervals from 80 to 110 km to be measured. The measurements were taken in four directions-north, east, south and west, with the aerial system rotating every 5 min. Then the average hourly wind velocities were calculated with the data for eastwest and north-south combinations. The parameters of semi-diurnal variations were found by harmonic analysis of two-day intervals from average hourly wind values, by one-day-sliding throughout the DYANA campaign. The instrumentation system, observation and processing technique used in Kazan have been described by SIDOROVet al. (I 981). In Dushanbe the measurements were made with the aid of a meteor radar sounding in four directionsnorth, east, south and west. A quarter of the transmitting power was connected simultaneously to each of the four antennae and reception was performed simultaneously from the four directions of the sounding. When the average hourly wind velocities were calculated, east-west and north-south measurements were combined. The measurement results are referred are presented

1

to the mean height of the meteor zone-95 km. The harmonic analysis was performed on 24-h intervals of hourly wind velocities. In this way the amplitudes and phases of semi-diurnal variations were obtained for the whole DYANA campaign. The instrumentation and measurement technique applied in Kuhlungsborn are covered in detail in PORTNYAGINet cd.(1978). It should only be mentioned that the meteor radar in Kuhlungsborn is not equipped with a height measurement system. The results of measurements are given for the average height of the meteor zone (95 km). The sounding was carried out in two directions-north and east with the sounding direction changed every half hour. The harmonic analysis was done for 24-h intervals from average hourly wind velocities. After that the values of amplitudes and phases were smoothed by a window of three days with a one-day sliding. The description of the meteor radar in Sheffield, the technique of data measurements and processing used by the researchers can be found in KINGSLEY c’t al. (1978). A meteor radar in Sheffield had a height measuring system and operated continuously throught the DYANA campaign. The results discussed in this study, however. are only those for the average height of 95 km and averaged over four-day intervals. Measurements in Bologna were at three height intervals centred at 85. 95 and 105 km heights. The zonal component of wind velocity was measured only. The Bologna radar parameters and the technique are outlined in CEVOLANIand HAJDUK ( 1978). In Saskatoon and Tromsn the wind was measured by the spaced antenna method with the aid of radars operating in the middle frequency range (MF). At both sites the identical measurement technique and

Semi-diurnal tides instrumentation of similar characteristics were used. The detailed description is given by MANSON et al. (1990). Wind profiles in the 80-I 10 km region at 3-km height and 5-min time intervals were measured from which the average wind speeds were calculated. To enhance the statistics, harmonic analysis was applied to four-day intervals to obtain prevailing wind and tidal parameter variations. The low S/N for the Troms0 radar leads to a reduction of wind/tide amplitudes. Comparisons with rocket and VHF radar systems at Andenes (MANSON et al., 1992) have shown that the values must be increased by 1.56; values shown here are so adjusted. The data for Juliusruh which were obtained by the spaced antenna method with the radar operating at 3.18 MHz (HOFFMANNrt al., 1990) were combined with the data from Collm. During the DYANA campaign six values of the IO-day means of the amplitudes and phases for the zonal component of ST for 3-km intervals in the 72.5-107.5 km height region were obtained. In the Collm observatory the measurements were carried out by registering the drifts of ionized inhomogeneities in the low-frequency range (LF) at 177. 225 and 272 kHz (SCHMINDERand KURSCHNER, 1990). The average monthly wind profiles to 80- 110 km and corresponding daily values for the average height of 95 km were obtained, the latter by harmonic analysis. The technique of recording the drift of ionized inhomogeneities in the low-frequency range was used in Badary. From the results of measurements at this site the daily amplitudes and phases of ST were determined at the mean height of 95 km during the whole DYANA campaign. The meteor wind system in Durham (U.S.A.) is a coherent pulsed radar operating on 36.8 MHz. Two transmitting and receiving antenna systems are looking northeast and northwest and yield both zonal and meridional wind profiles in the 83-104 km region (CLARK. 1975). Four-day means ST parameters for 10 days in January and 12 days in February during the DYANA period obtained by harmonic analysis processing of four-day data sets with two-day sliding were presented for analysis. As indicated above. the data used for joint analysis were. to a certain extent. non-uniform. To make them comparable they had to be additionally processed. First, the phases of semi-diurnal variations were reduced to the same form of presentation. They were presented as the time (local solar time) for the maximum zonal semi-diurnal component of wind velocity in the eastward direction and in the northward direction for the meridional component. Second, because a part of the data was presented as fourday averaged data (Saskatoon, Sheffield. Tromsa).

1733

the data for other sites for which daily values were available were subjected to the procedure of linear interpolation to fill in the data gaps and then smoothing was done with a five-day window with oneday sliding. For comparison with the model profiles, calculations were made of average two-weekly and monthly amplitudes and phases for all height intervals for which measurements were taken. For the interpolation and smoothing procedures an algorithm for calculating vector (geometric) averages was used in which cosine and sine coefficients for the Fourier series were calculated for each value of amplitude and phase and then the time series of these coefficients were subjected to interpolation or smoothing with subsequent reversed transition to amplitudes and phases.

2. MEAN MONTHLY PROFILES OF SEMI-DIURNAL TIDAL PARAMETERS Despite a large body of information on the behaviour of ST parameters obtained during the DYANA campaign the regularities of seasonal-latitudinal variations of these parameters can be found only for a limited latitudinal range (it is connected with the locations of sites) and mainly for three months of the year when the campaign was conducted-January, February and March. Even so. a series of rather definite conclusions on the variability of mean monthly parameter values was arrived at. Before analysing the data. consider the problem connected with the method of averaging tidal parameter values. The fact is that the exact period of the DYANA campaign in January and March included only a half of a month. Therefore the question immediately arises : how close are the mean two-week values to the mean monthly values’? In this connection it should be noted that at some sites the measurements in January and March were carried out during the whole month. Therefore it was necessary to estimate the degree of difference between mean two-week and mean monthly values for these months. To have more statistics such a comparison was also realized for February when observations were carried out during the whole month at all sites. It turned out that the difference between mean two-week and mean monthly values is comparatively low and has the same order for all observation months. It should be taken into account that the root-mean-square deviations from mean monthly values for semi-diurnal tidal amplitudes are only several m/s and for phases are less than 1 h. Therefore for January and March at those sites where observations were conducted during two weeks

1734

Yu. 1. PORTNYAGIN rt ul. llO-

105 -

looI! 2

95-

‘S a 90 -

85 -

80 -

I

I

I

I

I

10

20

30

40

50

It-JAmplitude

I 10

I 20

I 30

I

I

I

40

50

60

m/s

-6-3 --bl -2 Fig. 1. The height profiles of zonal (a) and meridional (b) amplitudes of semi-diurnal February

for monthly

llO-

means (1) and for the first half (2) and second half of the month area shows the r.m.s. deviation of monthly means.

tides in Kazan in (3). The dashed

. (4

105 -

90 -

85 -

80 -

I 3

I 4

I 5

I 6

I 7

I 8

I I I I I l,,I I I 9 10 11 12 13 14” 3 4 Phase (LMT) h -1

I 5

-2

I I 7

8

I I I I I I I 9 10 11 12 13 14 15

---b3

Fig. 2. As in Fig. 1 but for the semi-diurnal

we shall use the average two-week values as mean monthly values. Figures 1 and 2 are used as an illustration where, for Kazan, the vertical profiles are presented of mean monthly and mean two-week values of ST amplitudes and phases. It will become clear that the degree of difference between these profiles is much

I 6

tidal phases.

less than the differences between profiles for various sites and theoretical model profiles. Figures 3,4,5 and 6 show the vertical profiles of ST amplitudes and phases for the very high-latitude site Tromsn with theoretical profiles according to the model of FORBESand VIAL (1989) and GAVRILOV and

Semi-diurnal

10

20

I

I

I

30

40

50

I,

I,

tides

.

1735

I

10 Amplitude m/s

I

I

20

30

I 40

I 50

___ 1 1’ 42 Fig. 3. The height profiles of zonal (a) and meridional (b) amplitudes of semidiurnal tides at 70’N fol January. lPmodel of Forbes and Vial, I’mPmodel of Gavrilov and Kajdalov. 2-Tromso data.

110 (a) 105 -

Amplitude ___

1

-

m/s 1’

-0-2

Fig. 4. As in Fig. 3 but for February.

KAJDALOV (I 990). The data for January and February are available. In January the experimentally measured amplitudes of tides over practically the whole height interval were less than the model amplitudes and varied insignificantly with height. According to the model of Forbes and Vial, the amplitudes of ST

increase strongly with height and do not reveal a tendency to saturation, i.e. termination or reduction of increase with the height as compared with the exponential growth with the height according to the simplest tidal theory (CHAPMAN and LINDZEN, 1970). In the model of Gavrilov and Kajdalov the effect of

1736

Yu. I.PORTNYAGIN etul. 1lOC

I

,

3

4

5

6 7

8

9 10 11 12 13 14 15

, 3

( 4

, 5

, 6

, 7

, 8

, 9

, I I I 10 11 12 13 14 15

Phase (LMT) h

___

1

-2

&3

Fig. 5. As in Fig. 3 but for the semi-diurnal

tidal phases

(b)

85 -

, 3

4

5

6

7

8

9

,

10 11 12 13 14 15

,

,

,

,

,

3

4

5

6

7

8

9

10 11 12 13 14 15

Phase (LMT) h mm_

1

-

1’

42

Fig. 6. As in Fig. 5 but for February.

saturation is observed, however, only at 95 km and above. In February the experimental data above 95 km are absent for technical reasons. At lower heights the experimental amplitudes are significantly larger than the theoretical ones. The agreement between experimental and model vertical profiles of phases for 70”N in January and February (Figs 5 and 6) is good above 90 km; at

heights below 90 km for February (Fig. 5) the experimental values of phases differ significantly from the theoretical values. Overall, there is a difference in phase slope (wavelength) which is especially clear in February (35 km models, 75 km observation). The largest body of experimental data on ST parameters is obtained during the DYANA campaign in the 49956 ’ N latitude range. Figures 7-12 present the

I737

Semi-diurnal tides

(4

(b

ioa

90

80

Amplitude _-_

-0-r-2

1

10 m/s

I

I

I

I

20

30

40

50

-***-

3

-6-

4

Fig. 7. The height profiles of zonal (a) and meridional (b) amplitudes of semi-diurnal tides at 5&55 N for January. lPmodel of Forbes and Vial, I’Pmodel of Gavrilov and Kajdalov, 2 --~Karan, 3PSaskatoon. 4-PCollm + Juliusruh. SPBadary, 6_Khabarovsk, 7PKuhlungsborn. 8-Obninsk, 9----Sheffield. I OP Volgograd

105 -

85 -

80-

Amplitude m/s

--_

1

-0-s-2

-...-

3

-

4

Fig. 8. As in Fig. 7 but for February.

vertical profiles of these parameters for Saskatoon, Kazan, Collm-Juliusruh and model profiles for 55”N as well as the mean monthly values of ST parameters at 9.5 km for some sites where measurements were carried out without accurate determination of heights (Obninsk, Kuhlungsborn, Sheffield, Badary, Khab-

arovsk and Volgograd). It should be noted that assigning meteor radar data to this average meteor height has been shown (MANSON et cd., submitted) to produce a negligible effect when compared to differences in the results caused by longitudinal effects. This conclusion is confirmed also by Fig. I3 where it is

Yu. I. P~RTNYAGIN et al.

1738

105

100 B 24 4.E 95 a 90

as

80 Amplitude m/s ---

1

&

1’

-

2

-*a.-.

3

---b

4

3

A

4

Fig. 9. As in Fig. 8 but for March.

PHASE (LMT) h ---

1

-0-r-2

-**.-

Fig. IO. As in Fig. 7 but for the semi-diurnal tidal phases in January.

clearly seen that the degree of difference between data, shown at 90, 93 and 96 km is comparatively low. It is clear why in our analysis the effect of meteor radar data averaging in height can be neglected. Figure 7 shows the mean monthly (or averaged two week) values of ST amplitudes from various sites in January. By way of analysing this figure, one can note the following :

l At heights of more than 90 km there is a significant disagreement between experimental and theoretical model curves (however, above 103 km these discrepancies between data for Saskatoon and model values obtained by Gavrilov and Kajdalov decrease significantly). In this case at all heights on the average the experimental values of amplitudes are mainly lower than the model values ;

Semi-diurnal tides The increase of amplitudes with height for European sites (Kazan, Collm-Juliusruh) is not observed in some height intervals at all, or it is rather insignificant as compared to the increase of amplitudes with the height in the Canadian sector (Saskatoon) ; l At 95 km there are significant differences between amplitude values for various sites, in this case a regular coupling of the degree of difference and the distance between sites is not noted, so the degree of difference between data for Obninsk and Kuhlungsborn (26 difference) is significantly less than between the data for Kuhlungsborn and Collm (3 ) or Collm and Sheffield (4 ) ; l The greatest difference between experimental data is observed for the zonal component of ST amplitude.

l

In February (Fig. 8) all regularities mentioned above are retained; however, the degree of disagreement between various experimental and model curves decreases (except that there is an increase in difference above 103 km between data for Saskatoon and the model by Gavrilov and Kajdalov ; and below 90 km between data for Kazan (zonal components) and model values. Besides. it is worth noting that there is a significant increase of ST amplitudes for Sheffield. and that Kazan values are now consistently larger than at Saskatoon. In March at the heights above 85 km and below 100 km the ST amplitudes increase significantly in Saskatoon, so that below 95 km they are considerably higher even than model values (as in Kazan), whereas for Collm-Juliusruh the amplitude values remain less than the model ones. So, in March the difference between experimental data for European and Canadian regions is a maximum during the DYANA campaign period. Over the three months the observed variations are larger than in the models and often in a different sense. It is interesting to note a certain tendency to grouping the data referred to 95 km (Fig. 9); it is noted that. apart from Sheffield, data for European sites are clustered near the data for Kazan, while data for the Siberian site of Badary and the Far East site Khabarovsk are near data for Saskatoon. Mean monthly (or mean two week) values of the ST phase are presented in Figs 10, 11 and 12. As seen from Fig. IO(b), in January the minimum differences between experimental and model values of phases are observed in the 90-95 km height region ; and, though below 90 km the degree of difference increases. the agreement between experimental and model values may be considered on the whole as being satisfactory. If nonlinearity in the vertical phase profiles is neglected, the mean vertical wavelength of ST from data for the 90P100 km height region, which is well statistically

1739

supported, can be estimated within 1,9 z 30-50 km. Such a value of wavelength is in good agreement with climatic data for ST at moderate latitudes of the Northern Hemisphere for winter (MANSON et cd.. 1989). In February (Fig. 11) the differences between various vertical profiles of phases (as well as data for the average height 95 km) are close to January values. except for the significant differences from model phase profiles for Saskatoon below 100 km. At the same time there is significant scatter in the mean values of vertical wavelengths. For Kazan, i_!~!exceeds 100 km while for Saskatoon i/?” zz 50 km. The values of in! for Collm-Juliusruh and model values fall within the values for Kazan and Saskatoon. In addition there a tendency for 0‘ to increase over Europe when passing from January to February. In March (Fig. 12) below 95 km there are the largest differences between vertical phase profiles, both model and experimental. The difference between phase values at 95 km for sites without height resolution is also maximum. Above 95 km the difference in results (except Kazan) decreases. The profiles for Saskatoon are very similar to those in February. Otherwise the phase values below 95 km are tending to later times. while model values are tending to earlier times, Vertical wavelengths vary from 30 to 120 km. In this case an exact definition of vjertical wavelength values for some cases is difficult due to nonlinearity of the vertical phase profiles. It is also of interest to compare the data for the latitudinal belt 4349 N, where the Durham, Bologna, Khabarovsk and Volgograd stations are situated. These data together with the model data for 45 N are shown in Figs I4 and 15. As can be easily seen from these figures the experimental amplitudes are again, as a rule, less than the model ones. The above-mentioned regularities in the height profiles of the ST parameters for the midlatitudinal stations are in general confirmed by Figs 14 and 15. But there are also unexpectedly large differences between Bologna data and other data in February, which we cannot explain by a longitudinal effect, because the Durham, Volgograd and Khabarovsk data at 95 km are very close to each other. Maybe some specific regional effect is responsible for this difference. The collection of the data for 95 km from all observational sites together with corresponding theoretical latitudinal dependencies of the ST parameters is shown in Figs 16 and 17. From a consideration of these figures several definite conclusions may be made : (a) the theoretical ST amplitudes for moderate latitudes are overestimated; (b) there is a tendency for decreasing experimental amplitudes from high to

(b)

85 -

f 3

f 4

f 5

I I 6

7

f 8

I

I I

f i \I

1 I

9 10 11 12 13 14 I5

Phase (LMT) h ---

1

-o--

f’

-

2

-***-*

3

4

I

Fig. I 1.As in Fig. 8 but for the semi-diurnal tidal phases in February.

85

80 3

4

5

6

7

8

9

10 11 12 13 14 1.5

Phase (LMT) h m.-_ Fig.

1

--o-r

-2

VARIABILITY

3

4

4

12. As in Fig. 9 but for the semi-diurnal tidal phases in March.

lower latitudes; (cf while there is a general accordance in experimental and theoretical ST-phase dependence with latitude, the phase dispersion for February is definitely larger than for January. 3. DAY-TO-DAY

-.*.-

OF SEMI-DIURNAL

TIDAL

PARAMETERS

On the background of ~onlparatively slow seasonal variations of ST parameters at all sites, variations

are observed with periods which in meteorology are classified as ‘natural synoptic periods’. Conventionally these variations can be separated into variations with periods of several days (the first natural synoptic period) and with the periods of 2-3 weeks (the second natural synoptic period). The variations of ST amplitudes and phases smoothed over 45 days (Fig. 13) at three height levels for Kazan, Saskatoon and Tromso illustrate the fact that the intensity of 2j-week variations exceeds significantly the difference

Semi-diurnal

tides

1741

Zonal

Meridional

+(a)

b

10

Peb

March ..... . 1

Fig. 13. Amplitudes

20

Jan _--2

10

20

Feb

20

March

_3

(a) and phases (b) of semi-diurnal tides in Kazan (I), Saskatoon for altitudes of 90 km (I), 93 km (2) and 96 km (3).

in ST parameters caused by vertical gradients of these parameters. So, even the measurement results at some mean height of 95 km present reliable information on regularities of variations of ST parameters with periods of 2-3 weeks. It is surely remarkable that there are significant similarities in their temporal variations in Fig. 13 in spite of the considerable distances between these three locations. Figures 18, 19(a) and 20 (a,b) show the ST phase and amplitude values averaged over 4-S days at 95 km for some sites situ-

10

(II), Tromse,

(III)

ated in a narrow latitudinal belt but with different longitudes. In spite of the presence of evident differences between the data obtained at various sites, some general regularities in the amplitude and phase behaviour can be noted. It is clear from Fig. 18 that practically at all sites, except Saskatoon, during the last 10 days of January the amplitude of ST decreased significantly and in the first 10 days of February it increased abruptly. This regularity is registered for the zonal as well as for the meridional components. For

Yu. I. PORTNYAGIN CI al.

I742

Meridional

Zonal

LOO-

85 I

I

0

I

I

10

20 ms-’

(b)

30 rn.9.l

.

1

\ ;

\

IO

-

\

\

f

\

I

\

\

I I

\

\

\\I \ \\\ \* l

I

,A.

iX /

I.

\

\ \ \

\

. \ \

I 1

P

6

7

8

9

10

11

+++%-

LMTh I-.-

LMT h 2+3

Fig. 14. The profiles of zonal and meridional 49’N for January (l-Durham, 2-Bologna,

x

4

A

5 ___

amplitudes (a) and phases (b) of semi-diurnal tides at 43 3-Khabarovsk, 6-Volgogrdd. S-model of Forbes and Vial).

the first half of March there is a general tendency for the ST amplitude to decrease as compared to values in previous months. The profiles of sector 2 also showed differences between Canada and Europe. In February there are distinct differences in the amplitude variability at various sites, though there is a tendency for amplitudes to increase in the period from 15 to 25 February. A correlation between the data for the sites referring to the second latitude belt 45-49”N [Bologna, Volgograd, Khabarovsk (Fig. 19(a)] is practically not observed. It should be noted that the distance in longi-

tude between even the nearest sites-Bologna and Volgograd-is more than 30 Latitudinal variations of amplitudes for the available data are illustrated in Fig 19 (b,c). There are some similarities in the structure of the variability with a possibility of phase shifts between 49-56 and 3% 49‘. Note that similarities depend upon component. However, the range of considered latitudes is comparatively limited. The character of the variations of ST phases presented in Fig. 20 also demonstrate significant variations during the DYANA interval. These variations

Semi-diurnal

tides

I743

Meridional

X

A*

00

I *I I

I I /

0

0

I

/

I‘

I l

I 1

.

0

10

ms-l

r

I

20 ms-1

30

.

.I \ -\\ I. \\ I \h*x

\\ I. ‘1, \

\3.

I

I

l

\ I

7

8

9

10

11

I

203

.: I

\I

456785

LMTh

]-.-

I

LMTh X

4

fi

5 ___

Fig. 15. As in Fig. 14 for February.

at various sites are somewhat different, with the maximum phase variations being observed in Dushanbe and the minimum in Sheffield. In this case the phase shifts between zonal and meridional components, close to 3 h on the average, corresponds to a clockwise wind vector rotation caused by ST. However, in some periods this difference deviates considerably from 3 h, which is indicative of significant variations in the ST mode composition during these periods. Such variations, together with variations in the absolute phase values for most of sites, are clear in February. Figure 21 shows the results of crosscorrelations between the smoothed values of ST parameters for some sites separated by different distances.

It is evident from the figure that for the meridional component of the ST amplitudes a distinct correlation is observed for pairs of sites located close to each other, whereas for such sites as Obninsk-Badary (38”E, 104 E) and ObninskPSaskatoon (38 E. 107 W) such a correlation is practically absent near zero lag. A good correlation for European pairs is observed in the zonal component of ST amplitudes. In this case. unlike the meridional component, the correlation between data in Obninsk and Kazan is practically absent. A correlation between ST phase values is above the confidence level for close sites (Obninsk--Kuhlungsborn. Kazan) but practically absent for the same pairs

I744

YIJ. I. PORTNYAGIN of ai. Meridional l

I

I

l

I

0 *

0

70°N 65

60

55

50

45 40°N

J 1 7O’N 65

*

.

1

1

I

60

55

50

I

I

45 40”N

l l-2 * 3 Fig. 16. Monthly means amplitudes of semi-diurnal tides vs. latitude at 95 km for January

(b) from observational

sites pointed

(a) and February in Table l---I. according to model of Forbes and Vial-L? and Gavrilov and Kajdalow 3.

Obninsk-Badary and Obninsk-Saskatoon, as in the case of the amplitudes. However, a correlation between meridiona1 phase components for ObninskKuhlungsborn is also insignificant. It should be noted that there is a consistent peak in correlograms for ObninskLSaskatoon, in both amplitude and phase, for iags of -5 to -9 days. This is consistent with pianetary scale wave effects upon the tides. But even maximum correlation coefficients for these pairs of stations do not exceed 0.4. For a simplified but effective estimation of the role of ST parameter variations with the first natural synoptic period, for some sites, we processed the daily values of ST amplitudes by subtracting averaged fiveday values from these values. So, the intensity of ST parameter ‘pulsations’ in the 2-5 day period interval was estimated with the help of a comparatively common procedure of simplified filtering of the daily mean values. Figure 22 presents the results of such an analysis using data for Obninsk and Kazan. It is clear that the intensity of the variations of ST parameters with periods of 2-5 days is rather high for both the zonal and meridional components and can be compared utith the intensity of ST var~tions in the period interval of 2-3 weeks. Data for Kazan at three height levels

give information on the vertical structure of these variations and allow us to conclude that vertical gradients of pulsation values are coInparatively small. The comparison of results for Obninsk and Kazan shows that the pulsation character at these two sites is somewhat similar, especially for the zonal component of ST amplitude. Spatial scales of ST amplitude variations with the period of two to five days seem to exceed the distance between these observation sites. However, a more detailed analysis of data obtained at all sites will be necessary to draw definite conclusions on spatial and temporal structures of such variations.

4. DISCUSSION The regularities of the mean monthly ST parameters testify to significant (beyond the limit of errors) differences between experimental data obtained at various sites, as well as between experimental and theoretical model values. As pointed out above. such discrepancies are not explained by different methods of observation. In our opinion the primary reason for these differences is the noIl-zonality of the ST source excited in the stratosphere (mainly in the ozone field).

1145

Semi-diurnal tides Meridional

Zonal

5’

//

(‘4 0

13 .

12 ll10 9L

3m-i

8 -* l6I IOON

r

l

I 60

I 50

I I 40’N 70°N

I 60

I 50

I 40”N

Latitude

Latitude l

1

-2

*3

Fig. 17. As in Fig. 16 for phases of semi-diurnal tides.

as well as of the background zonal wind in the region of ST propagation. According to the analysis carried out by SINGER et al. (1994), the degree of non-zonality of stratospheric zonal wind and ozone field is a minimum in January. The stratospheric warming in February and the spring reversal developments initiated in March in the lower thermosphere certainly increase the degree of non-zonality. However, in this case the differences between experimental profiles of ST amplitudes associated with different longitudes increased (see for example Figs 7-9). Moreover, in January there are observed the greatest disagreements between experimental data and mean zonal numerical model profiles of ST amplitudes. At the same time the experimental values of ST phases are close to each other and to model values in January. In February and March. when the non-zonality of various parameters in the middle atmosphere increases, there is a sig-

nificant difference in phases and in the vertical wavelength values and, hence, in the mode composition of ST for various sites. So a preliminary conclusion is that vertical profiles of the ST phase are a more sensitive parameter relative to non-zonal processes such as strato-mesospheric warmings, or seasonal reconstructions of a thermobaric regime in the middle atmosphere, than ST amplitudes. A large body of experimental data is required to confirm this conclusion. Extra information on the relationship between stratospheric warmings and ST parameters can be obtained by analysing the variability of ST in different periods. It is known that in the strato-mesosphere the wind regime parameter variations with periods of about 2-3 weeks, as a rule, are associated with the development and intensification of planetary wave processes with low longitudinal wave numbers 1 and

Yu. I. PORTNYAGIN cf ul

I746

MeridionaJ

50

30

\

20 40 10~

z

10 0t

I I

Kuhlungsbom A jt Collm

“J-L

IO

jl

0 i:

3 :

dinsk

1R,

10

I I

it

0t

n

20 10

-it

30 0I

L

10 20 0E

Badary IIt

J

Sa&tLon

20 10 30 I

o-

10

20

10

Jan Fig. IS. Day-to-day

20

10

March variablhty

01”anpl~tudes

of the semi-diurnal latiludes K-56 N.

I 10

20

JZUI tides (live-day

I 20

I

March slidmp)

for 95 km at the

Semi-diurnal tides

-_+

,

1141

\&-\,--c--

m

Obninsk

Badary

I I I I I ‘0’ ’ ’ 10 20 10 20 10 20 10 20 10 20 Feb March Jan Feb March Fig. 19. Day-to-day variability of zonal (I) and meridional (II) phases of semi-diurnal tides (five-day sliding) for 95 km: (a) at 52.-56 N : (b) at 45--49-N ; (c) at 38, 49 and 56 N ; (d) ronal phases in Sheffield and Bologna.

01 ’

’

I

10 20 J4ltl

2 superimposed on the background of seasonal variations. This wave activity effect upon the source of ST (ozone and water vapour) and upon the background zonal wind in the region of ST propagation in the strato-mesosphere, can result in a corresponding response of ST parameters in the lower thermosphere. However, such a tidal reaction appears not to be so directly and unambiguously bound to the increase or decrease of ST amplitudes with the processes which develop during strato-mesospheric warmings. This is confirmed by Fig. 23 which compares the behaviour of ST amplitudes and prevailing wind during the DYANA campaign at different sites, as well as the zonal wind values at 60 N and temperature gradient between 60 N and the pole at IO hPa during the same period. It is clear that even the zonal prevailing wind in the lower thermosphere reacts differently at different

longitudes [for details see NAUJ~KAT et (11.( 1990)] to stratospheric warmings which developed in the second 10 days of February [Fig. 23(e)]. The behaviour of ST amplitudes is such that significant increases or decreases in the amplitudes were registered during the stratospheric warming as well as beyond this period. At the same time it is worth noticing that a certain correlation exists between meridional prevailing wind and ST amplitudes (less evident at Saskatoon). If it is considered that a meridional wind in the lower thermosphere is mainly ageostrophic and is specified by the value of momentum flux divergence, caused by internal gravity waves, planetary waves and smallscale turbulence (MIYAHARA et al.. 1991), it is probable that these sources can affect both the propagation and saturation of ST in the lower thermosphere and the meridional prevailing wind itself.

Yu. I

I748

01

PORTNYAGIN cf al.

.

1.1

10 20 Jan

I

I

10 20 Feb

I

I

I

10 20 March

Fig. 20. Day-to-day vambllity of amplitudes of the semi-diurnal tides (five-day sliding) for Y5 km: (a) at 4549’N; (b) XI 3X,4Y and 3’ N; (c) for Sheffield and Bologna.

Semi-diurnal

tides Meridional

Zonal (a) 0.8 -

-0.4 -0.6 -

&I 0.6 -

-1

w--2

Fig. 21. Cross-correlation functions Kuhlungsborn (I). Obninsk-Kazan

-x-

3

_._.B

4

-5

of semi-diurnal tidal amplitudes (a) and phases (b) for Obninsk(2), Obninsk-Badary (3), Obninsk~~volgograd (4) and ObninskSaskatoon (5) Meridional

10 20 January

10 March

10 20 February -1

Fig. 22. Amplitude

pulsations

20 January w--s

20 10 February

10 March

2

(see the text) : (a) in Obninsk at 95 km (1) and Kazan (b) in Kazan at 90 km (1) and at 93 km (2).

at 95 km (2)

:

17.50

YLJ. 1. PORTNYAGINet cd,

amal

Meridional

A2

Jan

Feb

March

C”

-1 .. .. ,.. 2

Jan

Feb

March

Fig. 23. Day-to-day variabilit); of the prevailing wind (I) and the amplitudes of semi-diurnal tides (2) (fiveday sliding) in Kuhiungsborn (a), Obninsk (b), Badary (c) and Saskatoon (d). (e) Mean zonal wind (I) at 60 ‘N and temperature differences [ ‘Cl between 6OW and the Pole at 10 hPa (II).

In Fig. 24 the result of a cross-correlation analysis of the data for 95 km from different sites is shown. The correlation has been calculated for zero time lag. We have used only the observations from sites well distrib~lted along latitude 55 N and for which rather contiiluously four to five day averaged data were available ; there were eight stations : Saskatoon, Sheffield, Ku~~lungsbor~~, Colfm. Obninsk, Votgograd, Kazan and Badary. So. in Fig. 24 not all the data are completely independent. Figure 24 helps to obtain a rough estimate of the possible longitudinal

scale of the ST amplitude oscillations with the second synoptic period. The experimental dots are fitted by an art&al curve which is calculated as the superposition of the oscillation with the longitudinal wave number 1 and with amplitude equai to 0.7 and an oscillation with wave number 2 and amplitude equal to 0.3. It is worth noting that the dispersion of the correlation coefficients for the zonal component is significantly larger than for the meridonal componellt. This result does not contradict the idea of the possible indirect coupling between second synoptic

Semi-diurnal tides

P

Fig. 24. Cross-correlation coefficients of zonal (I) and meridional (2) amplitudes of the semi-diurnal tides vs longitudinal differences between the pairs of sites, located in latitudional belt 49-56 N. (3) The analytic curve (see the text).

period oscillations in the lower thermosphere and the above mentioned low wave number processes in the strato-mesosphere. However, it is obvious that additional data are strongly needed to support this result. As to the variability of ST parameters with the first synoptic period (2-5 days) (Fig. 22), their interpretation is complicated by the fact that, in the spectra of the principal stratospheric parameters in the extra tropical zone, the energy contribution of variations with these periods is smaller than the energy of variations with the second synoptic period (PORTNYAGIN and SVET~IXROVA, 1977). Meanwhile, in the troposphere and lower thermosphere of middle latitudes the amplitude of atmospheric parameter variations with periods of 2L5 days is comparable to the amplitude of variations with the second synoptic period. Earlier one of the authors (PORTNYAGIN, 1991), using a limited amount of data, estimated the spacetime scales of inhomogeneities with first synoptic periods in the prevailing wind and ST field in the lower thermosphere. These, in longitude, amounted to 3000 km for the zonal prevailing wind and 1500 km for the meridional prevailing wind and ST parameters.

1751

If it is considered that the space scale of about 1500 km (if this scale is taken to be equal to I,‘4 of the wavelength in longitude) at moderate latitudes corresponds to zonal wave numbers S > 3, one can conclude that the structure of disturbances with first synoptic periods in the tidal wind field of the lower thermosphere may be connected with the processes other than the processes with low wave numbers S = I and 2 typical of the stratosphere. This is a possible indication of the increasing role of travelling planetary waves in the troposphere and lower thermosphere as compared to quasi-stationary waves. Therefore nonstationary tropospheric planetary waves modulating vertically propagating internal gravity waves (caused by dissipation or interaction between wave-mean flow or wave--wave interactions may be considered as a possible source of ST parameter oscillations with several day periods. In the lower thermosphere these waves may modulate the conditions of ST propagation and dissipation. Despite comparatively low amplitudes, various normal modes of Rossby waves are observed in the stratosphere in the period range of 2-5 days (VINCENT, 1987; WALTERSCHEID,1980). Hence, it can be assumed that distinct pulsations of ST parameters with periods of three to four days as showing in Fig. 22 may also be caused by a modulating action of normal modes (2,3). (3,4) and with the period of two days-mode (3.3) (SALBY and ROPER. 1980). In addition the equatorial waves of Kelvin type and mixed Rossby-gravitational waves (HOLTON. 1975) modulating the ozone source of ST may be considered as a possible source of two to five day variability of ST parameters at the equator. The possibility of generation of quasi-wave disturbances with parameters close to those of tropospheric nonstationary waves is not to be excluded in the lower thermosphere, for example, through the mechanism of baroclinic instability in sjtu. Such disturbances in the region of ST propagation may also significantly affect its parameter variability. It is clear that for a thorough understanding of the nature of the variations of ST parameters additional, global distributions of experimental data are necessary.

REFERENCES CEVOI.ANIG. and HAJDUKA. CHAPMANS. and LINDZENR. S.

1978

CLARK R. R. FORBES.I. M. and VIAL P. GAVRILOVA. A. and KAJDALOV HOFFMANNP.. SINGERW. and KENER D. et ul.

1975 1989 1990 1990 1975

HILTON J. R.

1970

Bull. Asrron. Insr. Czech. 30, 297 307 Atmospheric Tides (Thermul and Grarrtutionul). D. Reidel, Dordrecht, Holland. .I. utnzos. Sci. 32, 1689. J. atn~os. ierr. Plys. 51, 649. Geomqn. Aeron. 30, 47448 I. Zeii. Mrtcor-ol. 40, pp. 405412. Metror. Monqqr. Vol. 15, No. 37. American Meteorological Society.

1752

Yu. 1. PORTNYA~IN et al.

KINGSLEY S. P., MULLER H. G., NELSON L. and SCHOLEFELDA.

1978

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MANSON A. H., MEEK C. E., BREKKE A.

1992

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and TROUNDSEN T. MANSON A. H., MEEK C. E., LLOYD N. and MCEWEN D. J.

1991

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1992

PORTNYACIN Yu. I., FAKHRUTDINOVA A. N. and ISHMURATOVR. A. MANSON A. H.. MEEK C. E. and TEITELBAUMH. er al. MIYAHARA S., PORTNYA~IN Yu. I., FORBES J. M. and SOLOVJEVAT. V. NAUJOKAT B., LABIT~KE K. and LENCHOW R.

Wind regime at 80-I 10 km at midlatitudes of the northern hemisphere. J. atmas. few. Phvs. (submitted).

1989 1991

J. atmos. terr. Phys. 51, 579. J. yeophy. Res. 96, 122551238.

1990

POKTNYA~IN Y u. I. PORTNYA~IN Yu. I., FORBES J. M. and FRASER R. A.

1991 1991

PORTNYAGIN Yu. I. and SHPRENGEKK. (eds)

1978

The stratospheric winter 1989/90. DYANA Campai,gn Handbook, Part III, pp. 164183. Cc. AN SSSR. FAO, II, No. 3, 236-242. Dynamics of the Antarctic and Arctic mesosphere and lower thermosphere regions. Part 2. The semidiurnal tide. Ann. Geophys. (submitted). Wind Measurements at 90-100 km Altitudes hi’ Groundbased T~hniques (343 pp.). Gidrometeoizdat, Len-

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1977 1980 1990 1981 1990

FAO, 13, No. 13, No. I, 8Om-90. J. atmos. Sci. 37, 237-244. Zeit. Meteorol. 40, pp. 316321. Meteor. issled. M. No 7, pp. 83.-89

1987 1980

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therPre-