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Ionospheric Response to the Solar Eclipse on 20 March 2015


The solar eclipse over Northern Europe on 20 March 2015 was a fascinating event for people in Europe (see Fig. 1).

 





Fig. 1 Scheme of the solar eclipse on 20 March 2015 (left panel) and solar eclipse as seen at DLR Neustrelitz during the maximum obscuration phase (right panel).

As Fig. 1 shows, the eclipse occurs between 8:00 and about 11:40 UT, starting in North West Europe and then moving towards the Northeast in Northern Europe. Outside the totality zone the shadow of the eclipse was visible in varying degrees all over Europe. 

Considering the obscuration function of the sun during the eclipse, the solar irradiation was switched off and on in a well-defined manner. Due to the strong solar radiation changes dynamic processes were initiated in the atmosphere and ionosphere causing measurable impact e.g. on the temperature and ionization. Here we present only the effect of the solar eclipse on the ionospheric ionization and associated radio wave propagation as monitored in the Ionospheric Monitoring and Prediction Center (IMPC) of DLR in near real time.


GPS measurements

Due to the close coupling of the solar illumination with photoionization processes in the Earth’s atmosphere the ionization level follows the obscuration function in a certain way.

We are able to show the behavior of the total ionospheric ionization over Europe by near real time monitoring of the total electron content (TEC) of the ionosphere. Currently, IMPC uses 1 Hz streaming mode GPS measurements provided by various GNSS networks such as the International GNSS Service (IGS) and EUREF distributed via BKG Frankfurt.

Here we present animations of original TEC maps and differential TEC maps obtained by subtracting 27 days medians from the actual TEC map values on 20 March 2015. Both animations enable the visitor to see clearly the ionisation loss due to the solar eclipse in its dynamic.





Fig. 2 Animation of European TEC maps on eclipse day. For further details on TEC mapping see [1].





Fig. 3 Animation of differential TEC maps (difference between eclipse day maps and corresponding 27 days medians).


From the scientific point of view the solar eclipse can be considered as an active experiment with a well-defined variation of the solar illumination as discussed in earlier publications [2, 3, 4, 5].



Vertical Sounding

Ionosonde parameters such as F2 layer critical frequency foF2 and peak density height hmF2 as measured at the ionosonde stations Juliusruh (JR055, Leibniz-Institut für Atmosphärenphysik e.V., Germany) and Pruhonice (PQ052 Institute of Atmospheric Physics ASCR, Czech Republic) are routinely delivered to DLR with a temporal resolution of 15 minutes. In IMPC the vertical sounding data are then combined with corresponding TEC data for deriving the equivalent slab thickness. The derived equivalent slab thickness is a measure of the shape of the vertical electron density profile which may change dramatically during ionospheric perturbations.

During the solar eclipse, the key parameters mentioned above and shown in the figures below, indicate strong variations clearly deviating from the nominal behavior. The time interval, where the obscuration function (calculated at the ionosonde locations) is non-zero, is highlighted by a gray shadow.










Fig. 4 Peak density variations measured at the vertical sounding stations Juliusruh and Pruhonice during the eclipse day (upper panel). The corresponding TEC variation is seen in the middle and related slab thickness variation is seen in the lower panel. It is interesting to note that the ionosonde data indicate wavelike processes which superpose to the eclipse bite out in ionization.



VLF propagation

Since the eclipse impacts ionization of all ionospheric layers it is expected that also the bottomside ionosphere changes rapidly with the eclipse. Accompanied VLF propagation measurements indicate some changes of signal strength and phase during the eclipse event. DLR just establishes a Global Ionosphere Flare Detection System (GIFDS) that will be ready next year [6].




Fig. 5 During the solar eclipse of March 2015, the receiver in Neustrelitz also recorded the effects of the event on several frequency channels (Navy stations) between 20 to 100 kHz. Different propagation paths show different stages of obscuration during the solar eclipse. The obscuration for each transmitter-receiver path is marked in gray.


As the signals obtained from different links show, there is a clear variation of the signal strength during the eclipse period which shall be analyzed in more detail in the future.




References

[1] N. Jakowski, C. Mayer, M. M. Hoque, and V. Wilken (2011), TEC Models And Their Use In Ionosphere Monitoring, Radio Sci., 46, RS0D18, doi:10.1029/2010RS004620, 2011

 

[2] N. Jakowski, H.D. Bettac, B. Lazo, L. Palacio, L. Lois, The ionospheric response to the solar eclipse  of 26 February 1979 observed in Havanna/Cuba, Phys. Solariterr., No.20, 110-116, 1983

 

[3] N. Jakowski, S. Schlueter, S. Heise, J. Feltens, 1999. Satellite Technology Glimpses Ionospheric Response to Solar Eclipse, EOS, Transactions. American Geophysical Union, 80, 51, 21 December 1999.

 

[4] N. Jakowski, S. Heise, A. Wehrenpfennig, S. Schlueter, 2001. Total electron content studies of the solar eclipse on 11 August 1999, CD-ROM, Proc. IBSS, Boston, 4-6 June, 2001, 279-283

 

[5] N. Jakowski, S. M. Stankov, V. Wilken, C. Borries, D. Altadill, J. Chum, D. Buresova , J. Boska, P. Sauli, H. Hruska, L. Cander, Ionospheric behaviour over Europe during the solar eclipse of 3 October 2005

 

[6] D. Wenzel, N. Jakowski, J. Berdermann, Chr. Mayer, C. Valladares, B. Heber, "Global Ionospheric Flare Detection System (GIFDS)", in review, JASTP 3/2015