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Usually Forbush effect (FE) is observed simultaneously with the IMF increase.

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Usually Forbush effect (FE) is observed simultaneously with the IMF increase. - PowerPoint PPT Presentation


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COSMIC RAY VARIATION PROPERTIES DURING THE Forbush effects ASSOCIATED WITH FAR WESTERN solar sources. 1) Pushkov Institute of Terrestrial Magnetism, Ionosphere and Radio Wave Propagation RAS (IZMIRAN), 142190, Troitsk, Moscow region, Russia 2) Nuclear and Particle Physics Section, Physics Department, University of Athens

Eroshenko, E.(1), Belov, A.(1), Mavromichalaki, H.(2), Oleneva, V.(1), Papaioannou,A.(2), Yanke V.(1)

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Forbush effect is a result of influence of interplanetary disturbance on the galactic cosmic rays

Usually Forbush effect (FE) is observed simultaneously with the IMF increase.

Cosmic Ray (CR) decrease during the FE is created in a separate region of interplanetary space where the particle access from outside is difficult. The stronger IMF created this special area, the wider rigidity diapason of CR is exposed to this effect, the stronger CR modulation. As a rule, the deep Forbush decreases correspond to the big increases of the IMF intensity

fe magnitude imf intensity
FE magnitude - IMF intensity

Well known relation between IMF and CR parameters is obtained here on the extremely large statistical material (~2000 events).

The majority of points are concentrated nearly the regression line. But there is a group placed significantly higher this line. It looks as a result of more effective influence of a disturbance on the CR.

FE magnitude upon the maximal IMF intensity (1987 events).

Regression coefficient is 0.67.

modulating efficiency
Modulating efficiency

The majority of points are concentrated nearly the regression line, but there is a group placed significantly higher this line:

The giant FEs observed under significantly lower

IMF intensity.

The opposite examples, when relatively small FEs correspond to the large augments of the IMF.

We were interested in the events (red circled group) where small and moderate values of IMF corresponded to the large Af.

It looks as a result of more effective influence of a disturbance on the CR. The FE creation by the IMF increasing occurs with different modulating efficiency in different events. A degree of such the efficiency might be estimated as:

efficiency of the interplanetary magnetic field disturbance
Efficiency of the interplanetary magnetic field disturbance

KFB = AF/Bmax ,%/nT

This value may be

considered as a characteristic

of modulating ability of the

associated IMF disturbance.

The events have been selected with Kfb>0.36

Presence of data on the IMF.

Only the events separated by at least 24 hours have been taken. In total it turned out to be 120.

Such a selection was possible due to the special Database created in IZMIRAN.

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CR variations:

density and anisotropy

Solar

Interplanetary

Study is based on the characteristics of 10 GV CR, derived from the data of the world wide NM network

Geomagnetic

Observations

Database on the Forbush effects and interplanetary disturbances.

result of selection
Result of selection
  • For Kfb>0.36:

East (-90 -30) Central (-30-+30) West (30-90)

8 (14) events 6 (10) events 6 (9) events

Majority of these events are a kind of ‘anomalous’. They have amplitude Af>3% and occurred on a relatively quiet background: Bmax<20nT, Kp<6

  • For Kfb<0.36 (‘normal events’) :

E-24 C-62 W-13

  • One can see that in ‘normal’ events the central sources dominate whereas ‘anomalous’ FEs are mainly caused by the extreme eastern or western sources.
  • ‘Anomalous’ FEs were analyzed in details using the results of GSM
slide8

What did we start with?

  • Solar flares and CMEs 14 July 2005, which produced large disturbances of the solar wind, passed to the west of Earth.
eastern events normal among anomalous western are twice anomalous
‘Eastern’ events – normal among anomalous;‘Western’ – are twice anomalous.
  • Among FEs observable by the ground level methods a special class may be chosen which is characterized by relatively unsettled interplanetary and geomagnetic conditions. Majority of such ‘anomalous’ events is related to a release of solar substation from the eastern part of solar disk. However some singular events may be associated with far and very powerful western sources as well. Our aim was to study the distinctions in FEs caused by far eastern and western sources.
slide10

IMF, solar wind, geomagnetic data (Kp-index and Dst variations), cosmic ray density and anisotropy (A0 and Axy) during the FEs caused by the western solar sources: July 2005, W79 and April 1981, W52.

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IMF, solar wind, geomagnetic data (Kp-index and Dst variations), cosmic ray density and anisotropy (A0 and Axy) during the FEs caused by the western sources: September 1977,( W58) and July 2006, (W34)

slide12
Vector diagram of CR anisotropy (Аху, Аz) and CR density variations А0 during the FEs associated with the western solar sources: W79(July 2005), W52 (April 1981), W60 (August 1989) and W57 (October 1989).
slide13

IMF, solar wind, geomagnetic data (Kp-index and Dst variations), cosmic ray density and anisotropy (A0 and Axy) during the FEs caused by the eastern sources: January 1968, E89) and November 1968, E42)

slide14

IMF, solar wind, geomagnetic data (Kp-index and Dst variations), cosmic ray density and anisotropy (A0 and Axy) during the FEs caused by the eastern sources: July 1973, (E45) and June 1999, (E~89)

slide15
Behaviour of the CR density А0 and anisotropy (Аху, Аz) during the FEs associated with Eastern sources on the Sun: Е58(July 1978), Е19(November 1989), E27(April 1985), Е60(June 2000).
slide16

EAST

WEST

02.04.81 W52

13.07.78 E58, E38

17.08.89 W60

04.06.00 E60

17.07.05 W79

12.04.69 E90

CR density (A0) and anisotropy (Axy) during the FEs from remote sources

slide17

21.09.77 W57

26.01.68 E39

24.11.68 E45

26.10.89 W57

31.07.73 E45

30.07.04 W72

15.07.99 E90

10.07.06 W34

CR density (A0) and anisotropy (Axy) during the FEs from remote eastern and western sources. Axy is essentially larger for western events (4.46-W, 2.91- E)

slide19
Compareof the vector anisotropy

The FEs for August 1989 (western source of W60 longitude) and for July 1978 (eastern event on the Sun with longitude -E58).

slide20
Data on the IMF, solar wind, CR density and anisotropy, geomagnetic indices during the FEs which are not identified with the sources but look similarly to anomalous effects associated with the western sources on the Sun.
slide21
Examples of non identified FEs but similar to anomalous effects connected with western localization of their sources.
slide22

CONCLUSIONS

  • In a majority of ‘effective’ events the Earth enters only a periphery of the interplanetary disturbance, the main part of which passes apart of Earth (to the East or to the West), but continues to exert strong and prolonged modulating influence on the CR near Earth.
  • Those events are preceded by powerful flares on the Sun, which are generally located far from the center of solar disk. The CMEs and interplanetary disturbances, caused these effects, appear to be of larger size and more complicated structure than it is visible near Earth.
  • It was possible to separate small but very definite group of large FEs which were not followed nor by the strong near Earth interplanetary disturbances neither by high geomagnetic activity but seems to be associated with great solar wind disturbances passed the West of Earth.
slide23
Those rare events strongly differ from typical FEs caused by western sources which are usually not big and very short. The selected Forbush-effects have more prolonged descent phase with a later minimum, and bigger increase of CR anisotropy. They essentially differ from the anomalous FEs caused by eastern sources by bigger size of CR anisotropy and less changes of its direction.
  • In the cases of far sources the CR observation give better information about real power of a disturbance than near Earth measurements of the solar wind. Moreover, we can suppose something about the events where there is no sufficient data for their identification. Here, the most essential feature of the CR reveals once again: they are an important tool of the heliosphere diagnostic.

A lot of thanks to all the providers of NM data from the whole world wide network supporting continuous monitoring of cosmic ray intensity:

http://cr0.izmiran.rssi.ru/ThankYou/main.htm.

slide24

THANK YOU

THANK YOU

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