PoS(ICRC2019)045 http://pos.sissa.it/ FORBUSH DECREASE FORBUSH Cosmic ray intensity, Forbush decrease, Coronal mass 2 1

3 Coronal mass ejections (CMEs) hurl huge volumes of magnetized [email protected] INTERPLANETARY MAGNETIC FIELD MAGNETIC INTERPLANETARY PARAMETERS AFFECTING COSMIC RAY COSMIC AFFECTING PARAMETERS Copyright owned by the author(s) under the terms of the Creative Commons Creative of by author(s)Copyright the terms the the under owned

 4.0). 4.0 International (CC BY-NC-ND License Attribution-NonCommercial-NoDerivatives phase of thephase solar cycle. of Key word: ejections. and Dst indices shows that all the three phenomena- andsolar, interplanetary geomagnetic interplanetary are parameters and connectedFDs is solar todiscussed cyclein detail. effect FD. Moreover is the foundfrequency The toof occurrence be of relationship slightlymajor shiftedFD between events for is largemore FDsin the as descending the author has studied seven largest ForbushMoscow Neutrondecrease Monitor Stationevents during aselected period offrom twelve years (1996- 2008), i.e., 23rd solar cycle. The analysis of CRI data with interplanetarymagnetic field |B|, its southward component Bz, solar wind velocity, Kp When the ejecta have an average windspeed greater than speed the upstream they solar interplanetary createshocks cause depression ain the cosmic shock. raycalled intensity The(CRI) Forbush large Decrease (FD). IMFspecifically associated with energetic X-ray flares. In the present the paper, Large variations Fds due caused to by fast CMEs are Abstract plasma into interplanetary space often referred to as ICMEs or ejecta.They are an important componentgeomagnetic activity when of they interact solarwith the Earth’s wind magnetosphere. and can cause enhanced M.K.Richharia Model College Physics, Govt. Science Department of INDIA M.P., Jabalpur, B.K.Soni College,Bilaspur(C.G.),INDIA. Girls Government M. L. Chauhan L. M. CollegeModel Physics, Govt. Science Department of INDIA M.P., Jabalpur, E-mail: PoS(ICRC2019)045 Author(s) he two-step T he two-step . T . 2 solar cycle has been carried out in the present paper. It is rd years, but even today this phenomenon is not understood fully, Cosmic ray Forbush decreases (FDs) have been studied for more sun spot numbers (SSN), sun spot spot sun area,sun (SSN), associated CME, numbers solar and theirflare location days on solar disk, before one-two the station: 9-15 April 2001, 4-10 November 2001, 22-28April November station: 9-15 November 2004, 13-19 2003, 24-30 July 2001, 28 October-3 have for searched the We 2005 & 9-15 SeptemberMay 2005. solar sources responsible above events for tracking by back the In this paper we investigate the affect of interplanetary of thisIn paper investigate we the affect magnetic field parameters – total & (IMF) southward B component Bz along with solar wind velocity ray on cosmic followingintensity (CRI) during time intervals the when FD 9%amplitude recorded neutron was Moscow by >= monitor (SSN), sun spot area, associated CME, one-twosolar disk, days the onset before solar of FD flare and their location on decreaseForbush ray records seems to in cosmic originate from the structure and sheath within the shock preceding the interplanetary coronal mass ejection [5]. following time intervals when the FD amplitude was >= 9% Moscowrecorded neutronby monitor station: 9-15 April 2001, 4-10 November 2001, July 2004, 13- November 2003, 24-30 November 2001, 28 October-3 22-28 19 May 2005 & 9-15 September sources responsible for above events by 2005.tracking back the sun spot numbers We have searched for the solar Forbush decrease in cosmicstructure within the ray shock and sheath preceding records the interplanetary coronal seems of interplanetary mass ejectionIn paper [5]. this investigate we the affect to originate from the magnetic field (IMF) parameters – totalalong B with& southward solarcomponent Bz wind velocity on cosmic ray intensity (CRI) during solar wind and they generally reach the near earth space inside called the so These disturbances are the cause primary of high streams speed [2]. plasma geomagnetic storms [3]. On the other hand they also modulate the flux of galactic cosmic rays in the form of Forbush decrease [4]. speed flows of the solar geomagneticwind? What relation storms? exists betweencomprehensive study of [1]. seven FDsexceptionally large Forbush decrease events and In occurred in 23 order to now well answerestablished that halo theseCMEs produce large questionsdisturbances in the a than 60 several questions are yetmagnitude to of be FDs answereddisturbances of and the interplanetary medium, coronal mass ejections and high like: their What variety? determines How the are FDs associated with Study of Decrease ofForbush Large a 2017 July Introduction: 1. PoS(ICRC2019)045 rd Author(s) (cut off (cut ) at 1314 UT, featured by E ). ). 3 The of arrival theinterplanetary shock waves at the i.e., Earth, . This was the first large FD (~11%) event of maximum phase of 23 3.Data Analysis Interplanetary shock, ICME and magnetic cloud data are from ACE list Interplanetary shock, and magnetic ICME cloud data are from Geomagnetic storm scale is the according to (http://www. SSN, sun spot area spot sun SSN, and geomagnetic indices are obtained from flare dataSolar are and SSC sourced (ftp://ftp.ngdc.noaa.gov/) from data isCME archived theline on list from LASCO Hourly averagedHourly Bz, wind plasma B, IMF Solar speed, & Kp Dst Hourly averagedHourly ray cosmic variation in percent have been taken from http://wwwssg.sr.unh.edu/mag/ace/ACElists/ http://cr0.izmiran.rssi.ru/mosc/main.htm hemisphere). On 11 April 2001, shock, the observed fastby ACE CME(L1 point,drove ~an 240 interplanetary R flare of class X2.3 on 10 April 2001 at 0506 UT. Following the flare, Aprilflare a 2001 of halo classat 0506 X2.3 onUT. 10 CME was observed by LASCO/SOHO at 0530 UT with a linear speed of Thekm/s. 2411 active region had a complex delta class magnetic field with SSN equals 170 and SSN area equal to 930 msh (millionth of solar 1.1 of event FD (i) 2001 11 April, solar cycle. It originated fromAR 9415 (S23W09) which unleashed X-ray  disturbancesof and transients (  scales). swpc.noaa.gov/NOAA  (http://www.swpc.noaa.gov/ftpdir/).   ) (http://cdaw.gsfc.nasa.gov/CME_list real time station neutron database Moscow monitor of 37.32E) 55.47N, rigidity=2.43 GV, (  areindices data provided by OMNI (http://omniweb.gsfc.nasa.gov/). cycle is reviewed. 2.Dataused dataThe in sources our analysis used are:  increasing IMF intensity and SW velocity [1], hence to find the relation of FD with storm the variation in Dst and Kp indices is analyzed main duringphase of eachthe FD event. This analysis has space weather applications too, being studied occurrence byof very large manyFD events in the scientists descending phase of [6,7]. last solar Finally, the reason for fast forward shock, was identifiedintensity and the by SWP bulk speed in the the near-Earth space solarsudden wind data, increase andof as the the time IMF of the storm suddengeomagnetic storms commencementand large (SSC).FDs haveThe common intense origin and are observed simultaneously; the geomagnetic activity and CR modulation rise with Study of Decrease ofForbush Large a 2017 July of FD onset PoS(ICRC2019)045 B  Author(s) solar solar elocity, wind 4 , its southward component Bz, ,component southward its  B  Vertical line marks the arrival of IP shock wave Earth. wave at the shock the ofarrival IP line marks Vertical (from top to bottom) IMF IMF to top bottom) (from increased to 34 nT and Bz value fallen to -20 nT. Thus due to From figure 1, it is noticed that SW velocity jumped to 730 km/s,  Figure 1: Figure B & Bz as shown in Figure as& 1. Bz shown in Dst & Kp indices, and CR variation (all hourly averaged) plots from 9 to 15 April, 2001 at1AU. 2001 April, to 15 from (allhourly &9 Kp Dst variation plots averaged)indices, and CR (SSC) at 1343 UT approximately after 30 minutes of the arrival of shock. led by a fast forward shock causing FD at 1302 UT onApril 11 2001. The large IMF variations in this sheath They scattered the during FD. galactic cosmic andrays thus swept away the sustained the depression in the CRI cosmic ray particles.The increase in solar wind dynamic pressure produced magnetopause compression marked by storm sudden commencement  ICME impacting on slow solar wind there was a sheath upstream of ICME  Study of Decrease ofForbush Large a 2017 July sudden jump in solar wind proton speed and high IMF magnitudes PoS(ICRC2019)045 Author(s) 5 November 2001 November : Summary plot as in figure 1 for the interval of 4-10 November, 2001 figure1interval for of plot: the 4-10 November, as in Summary Figure 2 Figure An energetic solar phenomena was observed inAR 9684 (N06W18) on 4th November 2001. The SSN was 186 and SSN area grew up to 1820 msh. It sparked a solar flare, X1.0 at 1603 UT and hurled halo CME (start on sametime 1810 km/s. with day speed 1635 UT) of favorable Bz conditions contributed to the large ring current development and intense storm was observed. The Dst dipped to -270 nT and planetary 2001. April reachedKp to a value equal on 11 to 8 (G4) 2001 of event (ii)FD 6 November, Study of Decrease ofForbush Large a 2017 July Large fraction of solar wind energy input to the magnetosphere under the PoS(ICRC2019)045 Author(s) November nd remained high for a few  B  6 was increased to 65 nT and Bz to -65nT.  B  : Summary plot as in figure 1 for the interval 22-28 November, 2001. the asNovember, Summary ininterval figure1 for 22-28 : plot Figure 3 On 22nd November and SS areaOn the SSN were 1310 msh, 143 and The disturbances reached earth and generated shock. The shockThe was disturbances reached earth and generated shock. respectively. AR respectively. 9704 erupted a halo CME at 2330 UT on 22 2001. Simultaneously, an M9.9 class solar flare was also emitted The CME witha traveled of towards 1437 km/s speed Earth. atUT. 2232 ppearance of neither with shock. started SSC coincided It with nor FD at hoursthe occurrence on 6 November 2001, five later of FD. 0648UT 2001 ofevent (iii)FD November, 24 geomagnetic storm of Dstand ~The Kp -300nT = storm 8. was categorized as G4 (severe) by NOAA scale. IMFhours, indicating a turbulent sheathdepressed region. for Hence, a CRI few also hours remained during the passage of high field. But the magnetic field strength, The solar wind velocity rose suddenly to 790 km/sec. Theseimply large values that ICME interacted with extent. theShock and Earth’sejecta producedmagnetosphere two tosteps FD awith structure no large magneticassociated cloud with it. The event was accompanied by an intense observed at 0125 UT, The 17 onset 0152UT. of FD was at UT 0115 which is 10 minutesminutes earlier than before the starttheAn intensivearrival FDof withshock. magnitude 10% was recorded by time of ICME majority i.e. of neutron monitors. Itpassage isof IP evident shock from was themarked figureby 2an extraordinary that large the increase in Study of Decrease ofForbush Large a 2017 July PoS(ICRC2019)045 B  Author(s) 7 and third one had 50% (25nT) jump in  B  lot of disturbances on 24 November 2001 at a distance 1AU from On 26 October 2003 two giant spots appeared on the face of the sun. Energetic particles accelerated by the flare and associated CME, . Since magnetic cloud structure was also found during the event period, index Dst dipped to -350nT causing a severe storm Kp = 9 (G=5). The event. The effect on EarthOctober at reflected0613UT with a recordby rise in solar thewind proton speed upappearance 1900 km/s. of IMFSSC increased onup to26 48nT -28nT, showing andhigh magnetospheric itsvariations. The southwardgeomagnetic activity component went to traveling with speed of 2459 km/s. The transit time of CME was ~ 19 has found to be consistent with as reported by This[13]. event is studied by [7] in detail. From figure 4, it is evident that the resulting ICME swept pass the Earth producing a shock ahead at 0558on UT 29 OctoberThen 2003. onset with no magnetic cloud associated with the of ICME was started at 0611UT The sunspot group rapidly increased in size and early hours of 28 October 2003 it occupied an area of 4520 msh with SSN equal to 230. On same day a powerful flare of X17.2 class was sparked from AR 10486(S16E08). atThe explosion0951 hurledUT a halo coronal mass ejection at 1130 UT  the galactic cosmic rays are also scattered away pressurefield in the magnetic cloud. from the high magnetic event) (Halloween 2003 of event FD (iv) October, 29 The Dst index started decreasing after few hours after the onset of FD and had same pattern as CRI variation wereThere three on 24 shocks reported forward MAG by have same origin. indicating that the phenomenon may November, at 0538UT, 0800UT and at 0900UT in which second one had 400% (30nT) jump in between 22 geomagnetic November and CRI data can to be viewed showin the 28figure dependence 3.of TheCRI ontime interplanetary Novemberprofiles magnetic field conditions. Large FDs are caused by big 2001increase in IMF is noticed by above analysis. for interplanetary, SSC & FD occurred simultaneously.elevated Thewith a solar maximum value wind of speed1050 km/s.reached got IMF to total highly amagnetic field high value ofAll -25nT. these 58conditions favoured an nTextreme storm withwith minimum Dst its southward component~ Bz-220nT to and Kp index ~ 9 (G5). The variation graphs in the interval caused Earth. The expanding ICME swept past our planet at 0656 UT along with magnetic cloud on 24 November. It was preceded by a shock at 0538 with UT sudden decrease in cosmic ray density i.e. FD ~ 9% at 0533 The UT. SSC appeared with above events at 0554 ThisUT. implies that the shock, Study of Decrease ofForbush Large a 2017 July PoS(ICRC2019)045 Author(s) 8 maximum is less in comparison to the FD  October - November 2003 November October - and maximum FD were at the same time, but

B October to 3 November, 2003. November, October to 3   B  : Summary of the data as described in figure 1 for ininterval figure1 28Summarydataas for the described : of the Figure 4 One can notice that the arrival of shock coincides with the onset of and the peak of the magnitude of FD can be accountedvelocity because value ofmore to the large of solar wind FD

29 October 2003. In connection29 October In 2003. the ray monitors flux, to cosmic neutron all over the world recorded a decrease of in 20-30% their counts; the largest this of cycle. FD solar Study of Decrease ofForbush Large a 2017 July strong depression in cosmic ray flux was registered (~22%) at 0600 UT on PoS(ICRC2019)045 Author(s) July 2004 July 9 July 2004 July July, became bigger than the planet Jupiter. It exploded nd : Summary of the data as described in figure 1 for ininterval figure1 24-30, Summarydataas for the described : of the A major FD event (~10%) was observed in the declining phase of Figure 5 Figure solar cycle on 26 July 2004. The sequence of solar events related to it rd Earth at 2230 in the form of in succession shock forward of at 2250 UT. SSC ICME structure at 2249 UT and produced were: high sun spotwere: ~ 130 and raised sunspot high area sun ~ number msh 1440 were observed on 25 July 2004, the active region 10652 (N04W30) continued to grow since 22 M2.2 solar flare at 1337 UT onhalo 25CME A Julyfollowed 2004. it with starting time of 1454 UT and speed of 1333 km/s. The CME reached at of FD which can FD of be usedspace for weather forecasting [12]. ofevent (v)FD 2004 July 26, 23 Study of Decrease ofForbush Large a 2017 July event of There6 isNovember a2001. time lag in the onset of Dst and onset PoS(ICRC2019)045 Author(s) ~ 26 nT and Bz  B  10 May 2005 May and sunspot area was measured as 1280 msh. th May 2005. The blast produced a CME at 1712UT. Its speed The blast at produced 1712UT. a CME May 2005. th th In spite of declining phase the sun became very active in May 2005. A seven day summary (from 22 to 27 July 2004) of different Figure 6: Summary of the data as described in figure 1 for the interval 13-19 May, 2005 the May, interval infigure16: 13-19 Summary dataas for the of described Figure

SSN became 100 on 13 Sunspot 10758 (N12E11) unleashed a on 13 1613UT strong M8.0 class solar magnetic field. was and in about it km/s 33 hours 1698 hit Earth’s flare at particle scattering by solar Therewind. was no magnetic cloud observed on 2004. 26 July of event (vi)FD 2005 15 May ~ -20nT, larger then shielding of averagecosmic rays in the value. way to EarthAll i.e. an FD2228 these UT eventon 26 occurred July 2004.at The disturbance conditions in magneticEarth’s field could produced a be assessed by fall in Dst index. It went to -200nT with max Kp = 9.depression The in CRI appeared to be caused by enhanced convection and interplanetary (B and Bz), geomagneticintensity can be viewed in Figure These5. graphs show how the interaction (Kp and Dst) andof intense cosmicflare and ray fast CME influenced magnetosphere flux. The impactand of ICME resulted incosmic a sudden jump in ray solar wind velocity to 1020 km/s. The IMF fluctuations got enhanced; Study of Decrease ofForbush Large a 2017 July PoS(ICRC2019)045 Author(s) , ~ 18nT and , ~ 18nT  B B , ~ 55nT and Bz ~   B  11 Though the SSN on 9 September 2005 was only 59 but the area was As a consequence a fast forward shock was observed at 0205 UT on May ahead of ICME at 0238 UT with magnetic cloud structure. The scale. on September 11, while abnormalities of Dst seen coincidingThe approximately onsetwith of FD was at hours later. 0049UT, to have started a few arrival of shock. The influence severe on(Dst ~ -150nT) with max Kp the= 9 & G5; an intense stormEarth’s on NOAA magnetic field was also previous events but the to thecontributed high jump in solar wind speed that had increased to 1000 amplitude of FD iskm/s so the effect of solar still wind velocity is found to be larger more significant in here. case This of is large FDs. Fromabnormalities (including Bz & Vsw) seem to have figurestarted at about 0100UT 7 it is noticed that the interplanetary flux due to scattering of particles.amplitude startedA at 0049 ForbushUT on September 11, depression2003.The shock arrived ofat about 13% the time approximately same as the onset of FD after 29 hours of CME lift The interplanetary parameters raised values to high off. Bz decreased to -8nT both were less in comparison to the values during solar flare (X6.2) on 9 September 2003 at 1913UT and hurled halo CME at 1948 UT, the speed of CME was very fastobserved withoutUT at 0114 any magnetic cloud. It followed a large shock ~ 2257 km/s. An ICME was at 0100 on September11 at Earth, a compressed plasma and turbulent field region (shock/sheath) driven by ICME produced the decrease in cosmic ray storm with deepest Dst ~ -260nT and ~9. Kp maximum storm with deepest ~ -260nT Dst 2005 of event (vii)FD 11 September, large ~ 1450 msh. The active sunspot 10808 (S12E67) generated a strong density is lower [10]. The passage of ICME resultedwind invelocity toincrease a ofhigh valuesolar of 960 km/sec. The interplanetary magnetic field also became strong and turbulent with its -40nT. The large southward IMF Bz triggered an extreme geomagnetic By this the correlation of FD with all the parameters can be evaluated. One notes that large FDs are caused by high IMF structures size (comparedof Earth) convicted byto the solar wind pastthe the Earth, the interplanetary remnants of the fast coronal mass ejection (ICMEs). The amplitude of FDan is largest when the Earth is located deep inside an ICME where GCR 15 and decrease in neutron counts i.e. FD of an impact caused at 0239 UT SSC was registered on 15 May 2005 at 0218 UT with amplitude ~ 11.0%. The graphs in figure 6 help us to analyse the 1AUoverall on Earth’s magnetosphereaffect as wellof as cosmicsolar rays reaching eventsat ground. at Study of Decrease ofForbush Large a 2017 July PoS(ICRC2019)045 Author(s) 12 September, 2005 September, In the present analysis we examined seven extreme Forbush decrease Figure 7: Summary of the data as described in figure 1 for the interval 9-15 Sept., Sept., for the 2005 datadescribed interval 9-15 of 1 in figure Figure the 7: Summary as weather applications. Understanding the behavior of such super active 23: April11 2001(AR 415), 6 & 24 November 2001 (AR 684 & 704), 28 October 2003 (AR 486), July 2004 (AR 652), September 2005Mayhave (ARcompiled 808). We and compared the properties 2005 (AR 759), and of FDs which has the potential of yielding a lot of information for space interplanetary manifestation ofICME/MC, large CME IMF variations, includeddecrease in cosmic ray flux and suddenenhanced geomagnetic This activity. paper shocks rise in preceded summarizes solar the by extreme wind solar velocity, activity decrease eventsand during the maximum and declining phase of the solar cycle its implications via Forbush events in the period (1996-2008) in association with andsolar, interplanetary geomagnetic parameters to find cosmicthe ray causesneutron ofmonitor largecounts atdepressions initiation of FDsthe isin linked to the appearanceEarth. of active regions on Itsolar disk is observed thatwhich the erupted fast CMEs associated by strong flares. The effects of Results and Discussion Study of Decrease ofForbush Large a 2017 July PoS(ICRC2019)045  , and B Author(s)   B B  13 the magnitude of FD isthe magnitude high correlated values of FD of to 6. The disturbances in magnetosphere increase the value of 5. The interaction of ICME with solar wind is reflected in abrupt 4. All FDs discussed have fast forward shocks ahead of ICMEs 3. For producing large FDs, CME should be Earth directed and 2. The magnitude2. of FD does not depend on SSN though the sun spot 1. All the1. active regions responsible for large FDs were located close is maximum ~65 nT for 6 November 2001 event whose for magnitude 10% is maximumis ~65 nT interplanetary magnetic field intensity. The IMF magnitude and direction are the most important parameters controlling the magnitude of magnetic Butstorms. less related to its southward component Bz. It is not clear that why relation was found between an average magnitude ofand the the product maximal solar of wind velocity and the maximal IMF the Forbush Effect This fact will be analysed in with future wider intensity (HmaxVmax). data. range of main FD. cause of jump in Vsw (maximum observed for each event.The magnitude of FDlarge valueis related to solar wind is 1900 km/sec velocity onis another 29outcome of October this investigation. 2003) According to [1] close scatter GCR away from the Earth. The generations of shocks upstream of particles whichfast ICMEs accelerators may be important energetic of produce short-term (Forbush) decreases in the galactic comic ray intensity [9]. Out of seven events, three events are associated with magnetic clouds excluding largest event, implying that magnetic cloud structure is not the flares, fast CMEs accompanied by strong solar flares are the main cause of above events. The magnitude of FD is well dependent on angularand its width. speed of CME associated with them, which imply interplanetary shocks are necessary to should should be ableThe linear to speed drive shocks. of CME associated with all to be was maximum found thanFds 1300 km/s value greater 2459 with of km/s. Since all events are associated with fast halo CMEs and intense solar component, Bz [8]. area is above the median value (800 msh) for all events. It is noted that the and spot area spot sun number for sun highest is 29 October event 2003 event of the solar cycle 23. the largest which is events inferences can following the be drawn – CMEs originating close from center to the disk (most of to center. the disk which become front-sidegeomagnetic halos) storms directly provided impact their Earth magnetic and field produce has a southward Study of Decrease ofForbush Large a 2017 July regions is very important for prediction purposes [7]. On comparing these PoS(ICRC2019)045 Author(s)

was lesser 48  B  , 103–124, 1990 (Errata 13 , (7) 2638–2645, 1993 (7) 5 , 2,1991. , 14 14

, Phys. Fluids, B Fluids,Phys. Nuovo Cimento Soc. Ital. Fis, C uovo Cimento Soc. Ital. Fis. C Ital. Fis. Cimentouovo Soc. N the large IMF variations in the shocked plasma scatter the 9%). It is seen that high amplitude FDs have occurred in the  Forbush effects (FEs) are usually observed simultaneously with ~ -150 nT for 11 September 2005 event. The magnitude of FD has corrige, relationships, The authors are grateful to the research working in teams Moscow We have a preliminary presented decreases Forbush 7 analysis of that We 8. The solar cycle effect is not very significant in case of very large 7.The Dst index is deepest ~ -350 nT for 29 October 2003 event and [2] Gosling, J. T., Coronal mass ejections: The link betweenThe Coronal solar and mass ejections: T., J. Gosling, [2] geomagnetic activity, Preka-Papadema, Mavromichalaki, H. Moussas, X. Caroubalos[3] P. C, UGC for sanctioning TRF for research work. this TRF forUGC sanctioning References M., Storini, Galactic[1] cosmic-ray modulation and solar-terrestrial Acknowledgements neutron monitor station, ACE/Wind, LASCO/SOHO, OMNI, and NOAA data centers for providing the related data. Mrs. Manjula Jain is thankful to were recorded during solarconsequences associated with the cycle seven sets of events 23. were well observed The so we have an extremely rich data solar set, which has the potential of yielding a origin and lot geospace of information for understanding the behavior of transient decreases in raycosmic flux and space weather applications. are most common near solar cycle.maximum There arebut fewer occurthan 10 throughoutFds greaterthe thanoccur around sunspotsolar 10%maximum but notablyper not in cyclethe year orand so just they after solar maximum [11]. FD events ( descending phase of solar cycle in more number: the maximum amplitude FD was found in beginning of declining phase .We can say that large Fds lowest no linear relation with Dst index, though large FDs are always associated with intense geomagnetic storms (K = 8 or 9). This seems to be useful for space weather forecasting [14]. nT. nT. However, galactic cosmic rays and thus sweep away the cosmic rayfound true. particles [4] is an increase in the Interplanetary Magnetic Field (IMF) strength.As a rule, decreases Forbush correspond to big increases in [11]. the IMF large Study of Decrease ofForbush Large a 2017 July event and fori.e. the 28 Octoberlargest 2003, value of PoS(ICRC2019)045 Adv. Author(s) Mexico, 2007, Kluwer Acad. KluwerPublishers, Ray Conference, Cosmic 15 Cosmic Rays in Atmosphere and Underground, Proceedings of the 30th International , 109, A002117, doi:10.1029/2002JA009814, 2004. 1–12, A002117, , 109, Vol. 27,No. 3, pp. 625-630,2001 27,No. Vol. Geophys.Res. Relations, 6, pages 195-208, 10. Vol. terrestrial effects, AIP Conf. Proc., 516,120–139. Conf. Proc., AIP terrestrial effects, Schwenn R. Dal Lago A, 1033 Geophys (France), 23 (2005) Huttunen E & Direct and Indirect GanzalezWeather: Karel Kudela, Rays Cosmic and Space W D, Ann ICMEs and solar wind electric field relationships,Adv. Space Res., 2119-2123. 35 (2005) Cane CoronalH.V., Mass Ejections and Forbush Decreases, Space 2000 93, 55-77, Sci. Rev., October–November 2003 JOURNAL OF GEOPHYSICAL GEOPHYSICAL OF October–November 2003 JOURNAL 2005 10.1029/2005JA011268, VOL. 110,doi: RESEARCH, Richardson Ian & July, Ejections ICRC, During Merida, 1996-2007, 30th 3-11 Mexico, Hilary Cane, Interplanetary2007 Coronal Mass and space weather due to extreme events, ILWS WORKSHOP 2006, WORKSHOP and space weather due to extreme events, ILWS 19-24, 2006 GOA, FEBRUARY Gopalswamy N, L. G. Cliver, Barbieri, Plunkett, Lu, E. and W. S. P. R. M. Skoug, Introduction to violent Sun-Earth connection events of G. Yanke G.What Yanke determines the Magnitude of forbush decrease? Space Res. Dorman L.I., Netherlands, 2003 Akiyama, Coronal andmass S.ejections GopalswamyYashiro, N., S. the July 2005 solar extreme events from the low corona to the Earth, 600-604 In Space Res., 43 (2009) Adv. J. [12] Storini, M. (2005), Transient phenomena in the heliosphere [13] and [14] [10] Ahluwalia H.S., Y. Kamide, Gnevyshev gap, Forbush decreases, [11] [9] [9] [8] [8] [6] [6] [7] [4] Ifedili, S. O., The two-step Forbush decrease: An empirical model, V. and A. B. Struminsky, Oleneva,A. V. Eroshenko,A. E. V, A. [5] Belov Study of Decrease ofForbush Large a 2017 July Papaioannou, E. A.Mitsakou, Hillaris, Space storm measurements of