Lower ionosphere, lower atmosphere and IMF sector structure in winter

Joumol

0

of Atmospheric

Pergamon

Press

and Tenesniai Physics,

Ltd.1979.Printed

Vol.41,pp.993-998

in Northern

Ireland

Lower ionosphere,lower atmosphereand IMF sector stmcturein winter J. LASTOVI(~KA Geophysical Institute, Czechoslovak Academy of Sciences, Bofni II, 141 31 Prague 4, Czechoslovakia (Receioed 26 3~nua~

1978; in revised form 6 December 1978)

Abstra&-There are two basic types of IMP sector boundary crossing effect. One is observed in the IMP magnitude, geomagnetic activity, the nighttime lower ionosphere in high mid-latitudes and in an inverse form in cosmic rays, and is reasonably well explained. The other is observed in the noon lower ionosphere in high mid-latitudes and in the troposphere; its interpretation remains open. The interplanetary magnetic field (IMF) is one of the important phenomena playing a role in solar-

terrestrial relationships. There are three possible IMF effects. First, the effect of variability of the IMF north-south component B*, second, that of radial (&) or azimuthal (B,) IMF component polarity, and third, the effect of the IMF sector boundary crossing. The winter crossing effect appears to be the most significant in the midlatitude ionospheric absorption of radio waves (LA$TOVK?KA, 1977b), as well as in the lower atmosphere circulation, and it is therefore studied in the present paper. The data are studied over the period 1966-73. The winter is defined as the period 15 November15 March. The following data are used: (a) Solar radio noise at a wavelength of 10.7 cm. (b) IMF sector boundaries (SVALGAARD, 1975) and IMF magnitudes, B (IMF DATA, 1975). (c) Cosmic rays measured on ground at Apatity (67”33’N, 33”20’Ef and in their transition maximum in the stratosphere above Murmansk (68”57’N, 33”03’E) (Cosmc DATA, 1966-74). (d) A, indices of geomagnetic activity. (e) The radio-wave absorption in the lower ionosphere measured by the A3 method at 2775 kHz (52”17’N, 12”27’E, d = 518 km), 1178 kHz [55.O”N, 12.7% d =225 km (HHI DATA, 1966-73)], 272 kHz (49”34’N, 16”03’E, d = 236 km) and 245 kI-Iz [54.90N, 11.4”E, d = 180 km (HHI DATA, 1966-73)]. (f) The stratospheric temperature at the lo-mb level and the lo-mb level height (Mu-rno~oLOGISCHE ABHANDLUNGEN,1966-74) above BerlinTempelhof (52.5”N, 13.6’E). (g) The northern hemisphere atmospheric vorticity area index at the 500~mb level (VAI; Or..so~ et az., 1977). (h) Meteorological microseisms observed at the

Prague seismic station, which represent a response to meteorological activity in the North Atlantic frontal zone (ZATOPEK, 1976). The total number of well-defined sector boundary crossings under investigation is 72. Stratospheric cosmic rays, 272 kHz absorption and meteorological microseims are not available for the whole period of 1966-73. The years for which these data were studied are indicated in Figs 1 and 2. As regards 272 kHz absorption and microseisms, previous results (LASTOV&KA, 1976, 1977a) based on the boundary crossing list published by WILCOX (1975) are used. There are three types of effects of sector boundary crossings. The first type, shown in Fig. 1, consists of an increase across the boundary crossing lasting for several days (typically 3-4). There is a significant difference between the level before and after crossing. As a secondary (rather insignificant) criterion, +I--1 1. The +I-- ratio is the ratio of values observed in the away (+) sector to those in the toward (-) sector. All the curves were obtained by the use of the superimposed epoch analysis regardless of the type of crossing (A, curve is a logarithmic, not arithmetic mean). A rather short interval of *3 days is analysed, since the shortest sectors lasted for 4 days only (SVALGAARD, 1975). All the values are presented in the form I/&where I0 is the crossing day value. The shift of data points with respect to the days indicated is given by the fact that the sector boundaries are published to OOOOW (SVALGAARD, 1975). On one side of each curve the designation of the physical quantity and the scale are given, and on the other side the +/ratio, the number of crossings n and, if necessary, the period studied are shown. Figure 1 displays the first-type effect of the sector boundary crossing in the IMF magnitude B, in Al, and in a less developed form in the nighttime absorption of LF radio waves. An inverse effect, a 995

J. LA$TO~&KA

996

@IO0

I.05

n=69 I.05 -

1.0

272kHr l,o night

245 kHa night

:+/-)-0.99 n=41 63-70 I.1 *, 0.9

n=72

0.7 @=

1.00 n.21 72-74

1.0 CR ground 0.995

B(IMF)

a=

0.9

1.07 n=26

-3

-2

-I

+I

+2

geomagnetic activity is followed by enhanced precipitation of hard electrons (E z 40 keV) into the lower ionosphere at higher mid-latitudes (e.g. TULINOV et al., 1975). The increased precipitation results in an increase of nighttime ionization and, thus, or radio wave absorption in the nighttime lower ionosphere. The effect of hard electrons is significant on 245 kHz at L = 2.7 (LAUTER, 1977), but rather insignificant on 272 kHz at L = 2.1, this being in agreement with the boundary crossing effects found. Hence the first-type effect of boundary crossings can be reasonably explained. This effect, however, does not penetrate down deep into the stratosphere and the troposphere. The second type of boundary crossing effect is no effect. No effect is observed in stratospheric parameters, in the lo-mb level height and temperature, and in the geographic region where some effects are observed in the lower ionosphere. The third and most interesting type of IMF

t3

- 12 Microseisms

Fig. 1. The first type of the IMF sector boundary sing effect in various physical quantities.

decrease across the boundary crossing, is observed in cosmic rays (on the ground as well as in the stratosphere). The condition +/-z 1 is fulfilled for all the quantities. In order to estimate the statistical significance of data points, the significance of the difference between extreme mean data points for all curves is given in Table 1. Only the 272 kHz result is not significant; a slightly lower significance of the IMF B result is due to a small number of crossings. The following mechanism explaining the first type of observed pattern can be suggested: A direct modulation by IMF, either by B or by its southward component, the boundary crossing behaviour of which is quite similar to that of B (SCHREIBER, 1977), causes the observed effects in cosmic rays and geomagnetic activity. An increase of Table

1. Statistical

significance

B

A,

CR ground

88%

99%

97%

2775 kHz noon

1178 kHz noon

85%

75%

- I.1

cros-

- 1.0 a.o.97 n=72

v’ 245kHz noon

1.0 -

(+/-20.97 n=62

0.96 n- 70

1.05 1176 kHz

Fig. 2. The third type of the Ih4F sector boundary sing effect in various physical quantities.

of the difference The first-type CR strato 98% The third-type 24.5 kHz noon 98%

51

‘.05

1.0 a=

between

extreme

effect 272 kHz night

mean data points

245 kHz night

55%

98%

effect VA1 1200 UT

VA1 0000 UT

microseisms

99%

90%

80%

cros-

Lower ionosphere, lower atmosphere and IMF sector structure in winter boundary crossing effect is shown in Fig. 2. The data are presented in the same form as in Fig. 1. The third-type effect consists of a deep depression related to the boundary crossing day (the minimum is observed within the first 24-h interval just after crossing). There is no significant difference between the level before and well after the crossing. The +/- ratio is a little lower than 1 (0.97-0.98). Figure 2 displays the third-type effect of the IMF sector boundary crossing in various parameters related to the lower ionosphere (noon absorption on 245, 1178 and 2775 kHz) and to the troposphere (vorticity area index at 500 mb at 1200 and 0000 UT and meteorological microseisms). The first-type effect is observed on 245 kHz at night, but the third-type effect is observed at noon on the same frequency and at the same heights (2775 and 1178 kHz noon absorption). Surprisingly enough, the third-type effect is higher in the troposphere (about 15% in VAI, 1200UT) than in the lower ionosphere. A similar conclusion was obtained by SCHLEGEL et al. (1977). The significance of the difference between extreme mean data points (Table 1) is high enough for tropospheric parameters (microseisms-low number of crossings). It is somewhat lower for noon ionospheric absorption due to a weaker boundary crossing effect (particularly at 1178 kHz). The third-type effect is observed not only in the lower ionosphere as is the first-type effect, but it penetrates down into the troposphere and is observed also in the surface meteorological activity (microseisms). It is not observed in the mid-latitude stratosphere, however. The physical mechanism responsible for the observed effect remains open. The mechanism is connected neither with cosmic rays nor directly with geomagnetic activity, as shown by the different

997

boundary crossing effects associated with these quantities (cf. Fig. 1). Nevertheless, we know three properties of the mechanism. First, it appears to essentially skip across the stratosphere, at least in high mid-latitudes. Second, and more important, the effect observed is ‘quietening’ instead of ‘disturbing’, in both the lower ionosphere and the troposphere, i.e. it is switching off rather than switching on an energy source. Third, as absorption data show, the mechanism seems to be connected with the daytime rather than with the nighttime. This unknown mechanism is able to affect the weather. In conclusion it can be said that the effects of the interplanetary field sector boundary crossings are distinctly expressed in the lower ionosphere and the troposphere. However, no effect is observed in the stratosphere in high mid-latitudes. All the boundary crossing effects are either small or of medium importance only. They appear simultaneously within 1 day at all altitudes. There are two basic types of effect. One consists of an increase across the sector boundary and a significant difference between the level before and after the boundary crossing. The other consists of a deep depression related to the boundary crossing day. The former is observed in the IMF magnitude, geomagnetic activity, cosmic rays (in an inverse form) an in the nighttime lower ionosphere in the high midlatitudes, and is reasonably well explained. The latter is observed in the noon lower ionosphere in high mid-latitudes and in the troposphere with a probable response in the weather. Its interpretation remains open. All the results are obtained for winter. As LASTOVI~KA (1976, 1977b) showed for absorption, some of the IMF effects can differ considerably in other seasons.

REFERENCES

COSMICDATA HHI DATA

1966-1973 1966-1973

IMF DATA

1975

LASTOVICKAJ. LA$TOVI&CAJ. LA$TOVI&A J.

1976 1977a 1977b 1966-1974

OLSON R. G., ROBERTSW. 0. and GERETY E.

1977

SCHLEGEL K., ROSE G. and WIDDEL H. U.

1977 1977

SCHREIBERH. 6

Cosmic Data, Nauka, Moscow (in Russian). HHI Geophys. Data 1968-1973, ZISTP-HHI, Berlin, G.D.R. Geophys. Messreihen 1966-1967, Kuhlungsborn, G.D.R. Interplanetary magnetic field data, WDC-A Rep. UAG-46, NOAA, Boulder. Geomagn. Aeronomy 16, 364 (in Russian). Studia geophys. geod. 21, 168. Trau. Inst. Gbophys. Acad. Tchbcosl. Sci. 1977, Academia, Prague (in print). Met. Abh., Aerol. Daten Berlin-Tempelhof, D. Reimer, West Berlin. Solar-Terrestrial Physics and Meteorology: Working Document II, p. 84, SCOSTEP Secretariat, Washington. J. afmos. tet7. Phys. 39, 101. Z. Geophys. 42, 437.

998

J.

LA&TOVI&A

SVALGAARD L.

1975

TULINOV V. F., FEIG~NB M., ZHUTCHENKO Yu. M., LIPO~ECKXIV. A. and NOVIKOVL. S. WILCOX J. M. Z.&OPEK A.

1975 1975 1976

Solar-Terrestrial Physics and meteorology: A Working Document, p. 72, SCOSTEP Secretariat, Washington. Kosm. Issled. 13, 513 (in Russian). J. atmos. terr. Phys. 37, 237. Acta Univ. Oul. A43, 21 (also in Spec. Rept. IASPEI Corn. Microseisms).

Reference is also made to the following unpubiished material: LAUYER E. A.

1977

HHI-STP-Rep.

No 10, ZISTP-HHI,

Berlin, G.D.R.