1. York University
Coupling of geomagnetic disturbances and GCRs flux with cloud covering and TOC at Abastumani
Goderdzi DIDEBULIDZE,
Tekle DIDEBULIDZE (Tbilisi State Medical University),
Maya TODUA
Abastumani Astrophysical Observatory
Tbilisi, Georgia

2. Abstract
We studied possible coupling of long-term trends and inter-annual changes of geomagnetic disturbances and galactic cosmic rays (GCRs) flux with the total ozone content (TOC) observed at Abastumani Astrophysical Observatory (41.75oN, 42.82oS) during These observations were carried out during cloudless conditions which allows us to investigate possible coupling of TOC and cloud covering with cosmic factors.
According to these data the annual and seasonal mean TOC and GCRs flux have negative trends. The tendency of decrease of the TOC is greater for geomagnetically disturbed days, which is evident for planetary geomagnetic indices Ap≥8 and Ap≥12. The TOC and corresponding number of cloudless days, observed on geomagnetically disturbed days, show their seasonal peculiarities. The TOC and GCRs flux decrease mainly during strong geomagnetically disturbed days (Ap≥50), except summer,
when in June, in spite of GCRs flux decreases, there is a tendency of its increase and decrease in the number of cloudless days. The observed sensitivity of TOC inter-annual distribution on cosmic factor are important for the troposphere-stratosphere coupling processes which may influence inter-annual variations of day- and night-time cloud covering processes. The different behavior of TOC at spring equinox and summer time on magnetically disturbed days could be coupled with different inter-annual distributions of number of cloudless days and nights and the presence of
semi-annual variations in them.
It is also noted that observed cloud covering and ozone content sensitivity on cosmic factors is important for climate change and human life.

3. Systematic observations of total ozone content (TOC) were carried out from Abastumani Astrophysical Observatory (AAO) during during visually cloudless days (CD). During this 37-year observational period, the total number of CD was Monthly numbers of CD vary from 227 to 531. These data allow us to investigate long-term and seasonal variations of these parameters and their possible mutual coupling under various helio-geophysical conditions. The presence of influence of cosmic factor on TOC and CD is analyzed during various levels of geomagnetic activity described by planetary geomagnetic Ap indices and also by galactic cosmic rays (GCRs) flux changes. Figure 1 shows that during geomagnetically disturbed days, for the values of the planetary geomagnetic indices Ap≥12 and Ap ≥20, noteceable decrease in TOC in March (spring equinox) and it increase in June occur. But during fall equinox (September) no important changes take place.

4. Figure 1. Inter-annual distribution of total ozone content (TOC)
at Abastumani for all observed cases (dark line), during magnetically
disturbed days with planetary geomagnetic index Ap≥12 (brown line)
and Ap ≥20 (red line).

5. Figure 2. The inter-annual distributions of monthly numbers of
cloudless days (CD) marked by circles: all CD (black line), at
Geomagnetic disturbances with planetary geomagnetic index
disturbed days with Ap≥12 (brown line) and Ap ≥20 (red line).

6. Figure 2 shows that inter-annual/seasonal distribution of cloudless days have some conjugate–like distribution with maximum in August, which for geomagnetically disturbed days shifts to September. This distribution is modulated by semi-annual variations (Didebulidze and Todua, JASTP, 2016), with maximum in March/September and minimal
value in June. This semi-annual type variations in the number of cloudless days causes similar variations in the monthly mean planetary geomagnetic Ap index shown in Figure 3. In the same cases monthly mean values of GCRs flux changes is minimal in June, where TOC changes on magnetically disturbed days is also noticeable.
Sensitivity of TOC on geomagnetic disturbances could be reflected in its long-term trend. Figure 4 shows the presence of negative trends in the TOC long-term variations. The TOC negative trend value for magnetically quite days (about DU/year) with Ap<12 increases for magnetically disturbed days (up to about DU/year) with Ap≥12.
For the considered cloudless days the Ap index has positive trend and
GCRs flux trend are negative (see Figure 5).

7. Figure 3. The inter-annual distributions of monthly mean values of Ap index (for Ap<50) during (upper panel) and normalized
GCRs flux observed by Tbilisi neutron monitor during
Normalized GCR values are calculated by , where X are GCR counts and is mean of all data for Ap<50. Circles with dashed lines -for cloudless days, and dots with solid lines – for cloudless nights at Abastumani in

8. Figure 4. Long-term trends of annual mean TOC for 1970-1993
at Abastumani for quiet days with Ap<12 (black line) and for
magnetically disturbed days with Ap ≥12 (red line).

9. Figure 5. Long-term variations and linear trends of the mean annual planetary geomagnetic Ap index (upper panel) and GCRs flux changes (lower panel) for days of TOC measurements (circles and full line –cloudless days) at Ap<50.

10. Figure 6. Long-term seasonal trends of TOC for 1970-1993 years
at Abastumani.

11. Table 1. Long-term trends (c. i
Table 1. Long-term trends (c.i. 95%) of mean seasonal Ap (Ap<50) index Galactic
Cosmic Rays (GCRs) flux (Almaty, Rome, and Tbilisi) during for all
day-nights, cloudless days and cloudless nights at Abastumani (Didebulidze and
Todua, JASTP, 2016)

12. CONCLUSIONS
We have shown that inter-annual distribution and long-term trends of the total ozone content (TOC) observed at Abastumani (41.75N, 42.82E) are sensitive to geomagnetic disturbances.
The spring-time decrease and summer-time increase in the TOC on geomagnetically disturbed days are accompanied by opposite behavior in the number of cloudless days. The summer time minimum number of cloudless days also is accompanied with important decrease in the GCRs flux, which shows its possible coupling with TOC.
The observed seasonal variability in the TOC during magnetically disturbed days can influence the semi-annual variability in the cloud covering.
Possible changes in the lower stratosphere ozone density under the influence of GCRs flux changes can affect the surface ozone content and its consequence on human health.
Acknowledgement: This study is supported by Georgian Shota Rustaveli National
Science Foundation Grant no. FR