Autumnal asymmetry in Autumnal asymmetry in geomagnetic activity in geomagnetic activity in

polar and pre-polar regionpolar and pre-polar region

Falayi, E.O. and Beloff, N. Falayi, E.O. and Beloff, N. Space Science Centre Space Science Centre

University of Sussex, UKUniversity of Sussex, UKeof20@sussex.ac.ukeof20@sussex.ac.uk

OverviewOverview

• SummarySummary

• Geomagnetic activity Geomagnetic activity

• Data analysis for 1990 - 2007 period Data analysis for 1990 - 2007 period

• Statistics of max H, max dH/dt, and AE index Statistics of max H, max dH/dt, and AE index

• ConclusionConclusion

SummarySummary• Geomagnetic activitieGeomagnetic activities often manifest as geomagnetically s often manifest as geomagnetically

induced current (GIC) in ground technology system. The induced current (GIC) in ground technology system. The maximum GIC values are proxy to the maximum value of maximum GIC values are proxy to the maximum value of time derivatives of the horizontal field (dH/dt). 289 time derivatives of the horizontal field (dH/dt). 289 substorm events were obtained from IMAGE magnetometer substorm events were obtained from IMAGE magnetometer data at Northern Europe, using Dst and AE indices to data at Northern Europe, using Dst and AE indices to determine the substorm events of varying strength (from -determine the substorm events of varying strength (from -90nT up to -1800nT) from 1990- 2007, and were 90nT up to -1800nT) from 1990- 2007, and were statistically analysed. In this study we found maximum time statistically analysed. In this study we found maximum time derivatives of the horizontal magnetic field statistically derivatives of the horizontal magnetic field statistically significant in October at auroral and subauroral regions. significant in October at auroral and subauroral regions. Seasonal variations are also seen, Autumn being more Seasonal variations are also seen, Autumn being more geomagnetically active than any other seasons, even geomagnetically active than any other seasons, even Spring. Our result shows a high correlation of 0.886 and Spring. Our result shows a high correlation of 0.886 and 0.854 at auroral and subauroral region. The test of 0.854 at auroral and subauroral region. The test of correlation between dH/dt and measured ionospheric correlation between dH/dt and measured ionospheric response (AE) shows closer relationship between dH/dt and response (AE) shows closer relationship between dH/dt and geomagnetic disturbance and this can improve our space geomagnetic disturbance and this can improve our space weather prediction systemweather prediction system. .

3D view of Earth’s Magnetospheric cavity3D view of Earth’s Magnetospheric cavity 3D view of Earth’s Magnetospheric cavity3D view of Earth’s Magnetospheric cavity

Data AnalysisData Analysis

• AE and Dst are used to define a substorms from satellite AE and Dst are used to define a substorms from satellite data from 1990 -2007.data from 1990 -2007.

• 169 substorms were obtained from Soroya Observatory 169 substorms were obtained from Soroya Observatory (auroral region) available from 1990-2007, also 120 (auroral region) available from 1990-2007, also 120 substorms were also obtained from Nurmijarvi Observatory substorms were also obtained from Nurmijarvi Observatory (sub auroral region) from 1992-2007 (Figure 1).(sub auroral region) from 1992-2007 (Figure 1).

• To examine horizontal geomagnetic field, the geoelcetric To examine horizontal geomagnetic field, the geoelcetric field is accompanied with varying field, indicating the time field is accompanied with varying field, indicating the time derivatives of the ground magnetic field dB/dt is proxy to derivatives of the ground magnetic field dB/dt is proxy to GIC activity especially with horizontal component (Viljanen GIC activity especially with horizontal component (Viljanen et al., 2001; Viljanen et al 2006).et al., 2001; Viljanen et al 2006).

• dH/dt=sqrt((dX/dt)^2+(dY/dt)^2) to compute ground dH/dt=sqrt((dX/dt)^2+(dY/dt)^2) to compute ground horizontal magnetic field which gives good reasonably horizontal magnetic field which gives good reasonably measure of the induction or GIC activity.measure of the induction or GIC activity.

Seasonal variation of maximum time Seasonal variation of maximum time derivatives and maximum horizontal derivatives and maximum horizontal magnetic field magnetic field• The disturbance of max dH/dt peaks sharply in October, with The disturbance of max dH/dt peaks sharply in October, with

another peak in April at auroral region, while at sub auroral another peak in April at auroral region, while at sub auroral region October and November shows maximum occurrences region October and November shows maximum occurrences and with another occurrence in February and April. and with another occurrence in February and April.

• The max H possesses the same features at auroral and The max H possesses the same features at auroral and subauroral regionsubauroral regions with maxima occurrence in October, s with maxima occurrence in October, November, February and April (Figure 2). We also noticed that November, February and April (Figure 2). We also noticed that max H intensity is greater in subauroral than auroral region. max H intensity is greater in subauroral than auroral region.

• From Figure 3,From Figure 3, Autumn has the highest value of max dH/dt Autumn has the highest value of max dH/dt with another peak in Spring at auroral regionwith another peak in Spring at auroral region. A. Also at sub lso at sub auroral region, Autumn has the maximum values of auroral region, Autumn has the maximum values of occurrence with another peak in Spring but the difference occurrence with another peak in Spring but the difference between Spring, Winter and Summer are not well pronounced between Spring, Winter and Summer are not well pronounced

• While at sub auroral region, the max H intensity is not well While at sub auroral region, the max H intensity is not well pronounced between Winter, Spring and Summer but there is high pronounced between Winter, Spring and Summer but there is high value of maximum occurrence in Autumn, while in auroral region value of maximum occurrence in Autumn, while in auroral region Autumn and Spring shows high occurrences Autumn and Spring shows high occurrences

• seasonal seasonal variation of geomagnetic activity has been attributed to variation of geomagnetic activity has been attributed to IMF- effect this agrees with general increase of geomagnetic IMF- effect this agrees with general increase of geomagnetic activities at the equinoxes (Russell and Mc Pherron, 1973; activities at the equinoxes (Russell and Mc Pherron, 1973; Silverman, 1986; Hakkinen et al., 2003). As a result, more storms Silverman, 1986; Hakkinen et al., 2003). As a result, more storms occur during Autumnoccur during Autumnalal and Spring and Spring equinoxes equinoxes than Winter and than Winter and Summer. This implies that there must be a redistribution of the Summer. This implies that there must be a redistribution of the responsible ionospheric currentresponsible ionospheric currentss. .

• Bolduc et al (2000) concluded that the increasing part of the Bolduc et al (2000) concluded that the increasing part of the disturbance has greater time derivatives of horizontal magnetic disturbance has greater time derivatives of horizontal magnetic fieldfield;; maximum electric field is in opposite direction to the maximum electric field is in opposite direction to the electrojetelectrojet;; and variation in ground observation of dH/dt may be due and variation in ground observation of dH/dt may be due to intensity, location and orientation of the auroral electrojet. to intensity, location and orientation of the auroral electrojet.

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Figure 2. Monthly variation of max dH/dt from 1990- 2007 and 1992 -2007 (upper panel) and monthly variation of max H from 1990- 2007 and 1992 -2007 (lower panel).

GIS data analysis

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120 storm-time substorms of seasonal variation from 1992-2007 ( Nurmijarvi Observatory)

Figure 3. Seasonal variation of max dH/dt from 1990- 2007 and 1992 -2007 (upper panel) and seasonal variation of max H from 1990- 2007 and 1992 -2007 (lower panel).

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Figure 4. Hourly variation of number of time steps between 1990 – 2007 and 1992 -2007 when dH/dt exceeded 1nT/s at two IMAGE magnetometer stations. Soroya is located at auroral region and Nurmijarvi in subauroral region.

• We also understudWe also understudied the diurnal distribution for the hours with ied the diurnal distribution for the hours with max dH/dt as shown in Figure 4, an interesting result was max dH/dt as shown in Figure 4, an interesting result was observed at auroral region (Soroya), with maximum occurrence at observed at auroral region (Soroya), with maximum occurrence at the early morning with another occurrence at the midnight, while the early morning with another occurrence at the midnight, while in the pre midday the events disappear and also the events almost in the pre midday the events disappear and also the events almost disappear before the midday at subauroral region (Nurmijarvi). disappear before the midday at subauroral region (Nurmijarvi). This implies that night time is more significant than the day time.This implies that night time is more significant than the day time.

• Newell et al (1996), also relates the frequency occurrence of Newell et al (1996), also relates the frequency occurrence of electron acceleration in dark and sunlit conditions indicated by the electron acceleration in dark and sunlit conditions indicated by the solar zenith. It was observed that electron acceleration is common solar zenith. It was observed that electron acceleration is common in darkness indicating that darkness is a factor for the field aligned in darkness indicating that darkness is a factor for the field aligned potential drop to be produced.potential drop to be produced.

• Lyatsky et al (2001) concluded that geomagnetic activity is Lyatsky et al (2001) concluded that geomagnetic activity is maximum when the nightside auroral zones of both hemispheres maximum when the nightside auroral zones of both hemispheres are in darkness, which occur in Autumn and Spring. are in darkness, which occur in Autumn and Spring.

Regression analysis of max dH/dt, Regression analysis of max dH/dt, maxmax H and max AE H and max AE

Soroya Observatory Nurmijarvi ObservatoryVariablesVariables rr RR22 EquationsEquations

max (H) nT max (H) nT max AE max AE

0.9600.960 0.9130.913 max H=2188 +3.576 max H=2188 +3.576 max(AE)max(AE)

max max (dH/dt) T/s, (dH/dt) T/s, max (AE) max (AE) nTnT

0.8860.886 0.7860.786 max (dH/dt)= 5859.5 max (dH/dt)= 5859.5 +6.0375 max (AE) +6.0375 max (AE)

max max (dH/dt) (dH/dt) nT/s, max nT/s, max H (nT), H (nT), max AE max AE (nT), peak (nT), peak Dst (nT)Dst (nT)

0.902 0.902 0.8130.813 dH/dt= 37742.37+ 1.048 dH/dt= 37742.37+ 1.048 max(H) +2.682 max (AE) -max(H) +2.682 max (AE) -4.466 peak (Dst )4.466 peak (Dst )

VariablesVariables rr RR22 EquationsEquations

max (H) nT max (H) nT max AEmax AE

0.890.8966

0.800.8033

max H= 2898+5.144max max H= 2898+5.144max (AE) (AE)

max max (dH/dt) T/s, (dH/dt) T/s, max (AE) max (AE) nTnT

0.850.8544

0.720.7299

Max (dH/dt)= -8278.5 Max (dH/dt)= -8278.5 +2.6269max (AE) +2.6269max (AE)

max max (dH/dt) (dH/dt) nT/s, max nT/s, max H (nT), AE H (nT), AE (nT), peak (nT), peak Dst (nT)Dst (nT)

0.930.939 9

0.880.8822

dH/dt= -15508.6+ 0.1746 dH/dt= -15508.6+ 0.1746 max(H) -0.0175 max (AE) max(H) -0.0175 max (AE) +14.496 peak (Dst) +14.496 peak (Dst)

• In Soroya observatory (auroral region), there is high correlation In Soroya observatory (auroral region), there is high correlation of 0.886 value between max dH/dt and max AE with a coefficient of 0.886 value between max dH/dt and max AE with a coefficient of determination (rof determination (r22) of 0.7858 ) of 0.7858 which which implies that 78.58% of max implies that 78.58% of max dH/dt can be accounted for using AE index. dH/dt can be accounted for using AE index. While aWhile a correlation correlation coefficient is 0.955 coefficient is 0.955 was obtained between was obtained between maximum horizontal maximum horizontal magnetic field intensity (H)magnetic field intensity (H) and and AE index, with coefficient of AE index, with coefficient of determination (rdetermination (r22) 0.9129 impl) 0.9129 implyingying that 91.29% of max H can be that 91.29% of max H can be accounted for using AE index.accounted for using AE index.

• In Nurmijarvi observatory (sub auroral region), the correlation In Nurmijarvi observatory (sub auroral region), the correlation coefficient of 0.854 exists between max dH/dt and max AE coefficient of 0.854 exists between max dH/dt and max AE indices with coefficient of determination (rindices with coefficient of determination (r22) 0.7287 implies that ) 0.7287 implies that 72.87% of max dH/dt can be accounted for using max AE index. 72.87% of max dH/dt can be accounted for using max AE index. We also estimate the geomagnetic activity using max H and max We also estimate the geomagnetic activity using max H and max AE index, with high correlation coefficient of 0.8959 with AE index, with high correlation coefficient of 0.8959 with coefficient of determination (rcoefficient of determination (r22) 0.8027 which implies that ) 0.8027 which implies that 80.27% of max H can be accounted for using AE index. 80.27% of max H can be accounted for using AE index.

169 storm-time substorms from 1990-2007 (Soroya Observatory)

max(dH/dt) = 6.0375max(AE) + 58595

R2 = 0.7858

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max(H) = 3.5756max(AE) + 21884

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max(dH/dt) = 2.6269 max(AE) - 8278.5

R2 = 0.7288

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Max(H) = 5.4144Max(AE) + 28975

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Figure 5: Linear regression graph

ObservatoryObservatory WinterWinter SpringSpring SummerSummer AutumnAutumn

Max dH/dtMax dH/dt

Auroral Auroral regionregion

16.92%16.92% 29.76%29.76% 20.8620.86 32.47%32.47%

Max dH/dtMax dH/dt

Sub auroral Sub auroral regionregion

18.89%18.89% 22.25%22.25% 18.54%18.54% 40.32%40.32%

ConclusionConclusion• The greatest occurrence of geomagnetic activity was observed during the Autumnal season.The greatest occurrence of geomagnetic activity was observed during the Autumnal season.• The early morning and midnight are more geomagnetically disturbed than the daytime. The early morning and midnight are more geomagnetically disturbed than the daytime.

Lyatsky et al (2001) established the fact that geomagnetic activity is maximum when the Lyatsky et al (2001) established the fact that geomagnetic activity is maximum when the nightside auroral zones of both hemispheres are in darkness which occur in Autumn and nightside auroral zones of both hemispheres are in darkness which occur in Autumn and Spring.Spring.

• There is a good correlation between the pairs of (max dH/dt and AE index) and (max H and There is a good correlation between the pairs of (max dH/dt and AE index) and (max H and AE index).AE index).

• From our results, 72.88% and 80.09% of geomagnetically induced current can be predicted From our results, 72.88% and 80.09% of geomagnetically induced current can be predicted using max dH/dt and AE index at Nurmijarvi observatory. using max dH/dt and AE index at Nurmijarvi observatory. Also 78.58% and 91.29% of Also 78.58% and 91.29% of geomagnetic activity can be predicted using max H and AE index at Soroya observatory.geomagnetic activity can be predicted using max H and AE index at Soroya observatory.

• However, ionospheric dynamo is considered as one of the key parameters in the generation However, ionospheric dynamo is considered as one of the key parameters in the generation of ionospheric current and fields. When the ionospheric dynamo is disturbed, it produced of ionospheric current and fields. When the ionospheric dynamo is disturbed, it produced ionospheric electric current and electric field at the high latitude ionosphere during ionospheric electric current and electric field at the high latitude ionosphere during geomagnetic storm. Ionospheric current subsequently produced variation in the geomagnetic storm. Ionospheric current subsequently produced variation in the geomagnetic field at the Earth surfaces as well as geomagnetically induced current in the geomagnetic field at the Earth surfaces as well as geomagnetically induced current in the ground.ground.

• From our finding, we have high GIC values when auroral electrojet were formed by coupling From our finding, we have high GIC values when auroral electrojet were formed by coupling of the solar wind with magnetosphere when the Bz turned southward and solar wind of the solar wind with magnetosphere when the Bz turned southward and solar wind velocity increasedvelocity increased..