IHY WB 2-3 Sep. 23, 2009. Forecast of Geomagnetic Storm based on CME and IP condition. R.-S. Kim 1 , K.-S. Cho 2 , Y.-J. Moon 3 , Yu Yi 1 , K.-H. Kim 3 1 Chungnam National University 2 Korea Astronomy and Space Science Institute 3 Kyunghee University. Geomagnetic storm. - PowerPoint PPT Presentation
Forecast of Geomagnetic Storm based on CME and IP conditionR.-S. Kim1, K.-S. Cho2, Y.-J. Moon3, Yu Yi1, K.-H. Kim31Chungnam National University2Korea Astronomy and Space Science Institute3Kyunghee University
IHY WB 2-3 Sep. 23, 2009Hi, Im Rok-Soon Kim from Chung-nam National University.Today, I will present about the forecast of geomagnetic storm based on CME and IP condition.1Geomagnetic stormWhat is a geomagnetic storm?Disturbances in the geomagneticfield caused by gusts in the solarwind that blows by Earth.Large negative perturbations of Dst index are indicative of a geomagnetic storm.
Causes of a geomagnetic stormMain origin: Coronal Mass ejection (CME)Circumstance: Interplanetary condition2
Let me start with the general concept of geomagnetic storm.The geomagnetic storm is the disturbances in the geomagnetic field caused by gusts in the solar wind that blows by Earth.Large negative perturbations of Dst index are indicative of a geomagnetic storm.It is generally considered that the main cause of geomagnetic storm is the coronal mass ejection from the Sun.And also, the interplanetary condition is related with the storm occurrence.2Forecast of geomagnetic stormForecasts of a geomagnetic storm based on,IP condition for urgent warning CME parameters for 2~3 days early warning We use a two-step prediction for the storm forecast capability.
When we focus on the forecast of a geomagnetic storm, near Earth IP condition can give us urgent warning around one hour earlier. Comparing to this, If we forecast the geomagnetic storm by using only CME parameters, we have more times to prepare the storm, since it takes two or three days to propagate from the Sun to the Earth.But, in this case, the changes of CME characteristics increase the ambiguity in the storm forecast.So, we want to use both conditions to increase the storm forecast capability.3CME and geomagnetic storm4 What parameters of CMEs control their geoeffectiveness? Only a small portion of the CMEs result in the geomagneticstorms. For front-side and large angular width events (1997~2003),Source location (L)Earthward direction (D)Initial speed (V)Magnetic field orientationof CME source region (M)
This is the first part of our study.We examined what parameters of CMEs control their geoeffectiveness, since only a small portion of the CMEs results in the geomagnetic storms.For front side and large angular width events, we examined the relationship between Dst index as an indicator of geomagnetic storm strength, and each CME parameters, such as source location, initial speed, earthward direction, and magnetic field orientation of CME source region.These two figures shows how we measured the Earthward direction and magnetic field orientation of CME.Earthward direction is defined as the ratio of distance between the shorter CME front and the solar center to that of the longer CME front.If this value is close to 1, a CME is directly propagating toward the Earth.And magnetic field orientation is defined as the angle between the projection of the overlying potential field line on the solar surface and the direction toward the south pole.45 Speed The CME speeds are roughlycorrelated with the strength of geomagnetic storms, but even slow CMEs can trigger geomagnetic storms.Geoeffectiveness of CME parameters Location The source locations of geoeffective CMEs are asymmetrical in longitude. The offset 15 to the west gives the best results. Dst vs. distance from the offset
These two figures show the relations between Dst index and each parameters.First, from the examination of the distribution, we found that the source locations of geoeffective CMEs are asymmetrical in longitude.The best offset is fifteen degree to the west to get the best correlation.X-axis is the distance from the offset, and y-axis is the Dst index.The right figure shows that the CME speeds are roughly correlated with the strength of geomagnetic storm, but, even slow CMEs can trigger geomagnetic storms.56 Magnetic field orientation || 90 southward || > 90 northward All CMEs associated with the super storms (Dst -200 nT) have southward magnetic field orientations. Direction parameter The ratio of distance between the shorter CME front and the solar center to that of the longer CME front. The direction parameter hasbetter correlation than the other parameters.Geoeffectiveness of CME parameters
The direction parameter is defined as the ratio of distance between the shorter CME front and the solar center to that of the longer CME front.As you can see in this figure, the direction parameter has better correlation than the other parameters.As I already mentioned, the magnetic field orientation is defined as the angle between the projection of the overlying potential field line on the solar surface and the direction toward the south pole. So, if the absolute value of the angle is less than 90 degree, the CME has southward magnetic field in its source region.As you can see in this figure, all CMEs associated with the super storms less then -200 nT, have southward magnetic field orientations.67Geomagnetic storm prediction model Comparison of their correlations with the Dst index Direction parameter has the best correlation, but magnetic field orientation has the worst correlation. We divide the CMEs into two groups according to their magnetic field orientation.
Empirical geomagnetic storm prediction model Formula to predict the geomagnetic storm strength (Dst index)For southward events,For northward events,ParameterccLocation0.25Speed-0.29Direction parameter-0.60MFO-0.12
7This is the comparison of their correlations with the Dst index.As the results, the direction parameter has the best correlation, but magnetic field orientation has the worst correlation.So we divided the CMEs into two groups according to their magnetic field orientation to forecast geomagnetic storm because they seem to have different mechanism to trigger the geomagnetic storm.From these studies, we established the empirical model for prediction of geomagnetic storms with initially-observed CME parameters at the Sun.The model is expressed by two formulae to predict the geomagnetic storm strength for southward events, and northward events.78Evaluation of the storm prediction model
Forecast based on the storm prediction model The relationship between observed Dst index and predicted Dst index for northward events (cc=0.81) is better than for southward events (cc=0.67).8Then we calculated the predicted storm strength, and compared with observed Dst index.As you can see in these figures, the relationship between observed Dst index and predicted Dst index for northward events is better than for southward events.It means that our model produces better prediction for northward events than southward events. As you can see in these figures, all super storms (Dst -200 nT) are associated with southward CME. These events are extraordinary and degrade the prediction capability of our model especially for southward event.
8Evaluation of the storm prediction modelForecast based on the storm prediction modelFor 64 halo or partial halo CMEs associated with M and X class solar flares, yes prediction: predicted Dst -50 nTyes observation: the occurrence of a geomagnetic stormThe mean probability of geomagnetic storm is about 63% (40/64) and 44 events are correctly forecasted (69%).
To improve the forecast capability of our model, we examine IP condition. ObservedPredicted YesNoTotalYes361652No4812Total402464We also evaluated this model by using statistical method.For 64 halo or partial halo CMEs associated with M and X class solar flares, yes prediction is defined when our model predicts that dst index will be lower than -50 nT, the criterion of a geomagnetic storm.And yes observation means the occurrence of a geomagnetic storm.As the result, The mean probability of geomagnetic storm is about 63% and 44 events are correctly forecasted.In this table there are 16 false alarms and 4 misses. If we can reduce this incorrect prediction, the forecast will be improved.So we examined the IP condition for our events.9IP Condition of geomagnetic storm
Interplanetary parameters (Echer et al., 2008)What IP parameter has the strongest relation with storm strength among the IP condition such as the magnetic field, electric field, solar wind speed and dynamic pressure.Most strong storms (Dst -100 nT) have peak Bs between 1020 nT, and peak Ey between 510 mV/m.There are some studies about interplanetary condition of the geomagnetic storm including Echer et al.They examined what IP parameter has the strongest relation with storm strength among the IP condition such as the magnetic field, electric field, and solar wind speed and dynamic pressure.Most strong storms have peak Bs between 1020 nT, and peak Ey between 510 mV/m.
10IP Condition of geomagnetic stormGonzalez -Tsurutani empirical criteria (1987)Bs 10 nT or Ey 5 mV/m for t 3 hFor the storms with Dst > -150 nT, 50% of the storms are satisfied.For the storms with Dst -150 nT, 93% of the stronger storms are satisfied.Our storm criteria is Dst -50 nT We need to modify these criteria.
Gonzales and Tsurutani made an empirical criteria for the selection of geomagnetic storm.The southward component of magnetic field have to larger than 10 nT or y component of electric field have to larger than 5 mV/m for longer than 3 hours.They showed that the 50% of the weaker storms with Dst larger than -150 nT are satisfied this criteria.In contrast to this the 93% of the stronger storms with Dst less than -150 nT are satisfied,As already mentioned, our storm criterion is less than -50 nT.So, we need to modify these criteria.11
IP Condition of the 64 CMEDataInterplanetary Bz and EyACE Magnetic Field 1-Hour Level 2 Data (B)ACE/SWEPAM Solar Wind Experiment 1-Hour Level 2 Data (V)E=-VB Ey=-BxVz+BzVx12For this, we examined the interplanetary Bz and Ey component for our 64 events.Southward component of the magnetic field can be obtained from ACE magnetic field data.y component of the electric field can be calculated from this equation, so we used the ACE solar wind speed data.Then we carefully check the Bz or Ey value.
Bz minimum and Ey maximum Bz -5 nT, Ey 3 mV/mIP Condition for 64 CMEDuration time of Bz, Ey criteria t 2h
Left two figures show the relationships between Bz minimum and Dst index and Ey maximum and Dst index.As you can see, we confirm that the Bz and Ey component of our events are very strongly related with Dst index as shown in many other studies.These vertical lines are indicate -50 nT, our storm criterion.And the horizontal lines are indicated Bz is -5 nT and Ey is 3 mV/m.In the figures, most geoeffective events are in this Bz and Ey criteria.But, we have to see why these events didnt associated with the storm even though their big disturbances.So, we checked the duration time of Bz and Ey criteria.It is clear that if the duration time is longer than the time criteria as indicated by horizontal line, all events are geoeffective.But, there is no significant relation between storm strength and duration time, in both cases. 13Forecast using IP criteriaIP criteriaWe select the criteria for moderate storms (Dst -50 nT) Bz -5 nT or Ey 3 mV/m for t 2 hFor 64 events, 90% of the storms are in the IP criteria.80% are correctly forecasted (51/64) (cf. CME parameter: 69%) ObservedPredicted YesNoTotalYes36945No41519Total402464 ObservedPredicted YesNoTotalYes361652No4812Total402464So, we modified IP criteria like this, and then, we forecast the geomagnetic storm.For 64 halo or partial halo CMEs associated with M and X class solar flares, yes prediction is defined when the IP condition is satisfy this criteria.And yes observation means the occurrence of a geomagnetic storm.For 64 events, 90% of storms are in the IP criteria.80% are correctly forecasted. Its higher than that of the forecast based on CME condition.When we compare is with the forecast based on CME condition, the 7 false alarms are removed.14Forecast using CME and IP conditionFor 64 eventsCME criteria: storm prediction formulae IP criteria: Bz -5 nT or Ey 3 mV/m for t 2 hour
CME criteriaIP criteriaForecastYesYesYesNoNoNoYesNoNoNo ObservedPredicted YesNoTotalYes32537No81927Total40246480% are correctCME criteriaIP criteriaForecastYesYesYesNoYesNoYesYesNoNo ObservedPredicted YesNoTotalYes402060No044Total40246469% are correctWe tried to find the best way to couple the CME and IP criteria.As you can see in the table, For best forecast capability, that is the highest success rate, a CME must satisfy the IP criteria as well as CME criteria to forecasted as geoeffective.But, if we dont want to miss any geoeffective events, we can forecast the geomagnetic storm when a CME satisfy one of the CME criteria or IP criteria.Because in that case all storm is forecasted.1516Conclusions
Empirical geomagnetic storm prediction modelFormulae to predict the geomagnetic storm strength (Dst index) based on CME parametersFor southward events,For northward events,Empirical IP criteriaFor more better forecasts, we consider the IP conditions, since the CME characteristics can change during its propagation.Our empirical IP criteria: Bz -5 nT or Ey 3 mV/m for t 2 h 90% of the storms satisfy the IP criteria.For 20 exceptional events, 15 cases can be explained by the IP conditions.Forecast using CME and IP conditionsWe found that all geomagnetic storms occur when the CME conditions or IP conditions are satisfied. This is our first conclusions.From the examination of the geoeffectiveness of each CME parameter, we made the empirical geomagnetic storm prediction model.And then for more accurate forecasts of geomagnetic storm, we consider the IP conditions, since the CME characteristics can modified during its propagation.We examined the Bz and Ey of our events and made the empirical IP criteria like this.Then 90% of the storms are in this criteria.Comparing with the forecast based on CME parameters, in the 20 exceptional events, 15 cases can be explained by IP condition.If we use both CME and IP conditions for forecast of geomagnetic storm, we can improve the forecast capability.
Earthward direction parameter (D) AdvantagesThe direction parameter can be directly estimated from the coronagraph observation it can reduce the ambiguity of location caused by occulting disk.It includes both of the CME propagation and angular effect of cone model.
1718CME parameters Magnetic field orientation angle (Song et al., 2006) Magnetic reconnections between southward interplanetary magnetic field and the northward directed geomagnetic field occur at the day side of magnetopause and then transport energy from the solar wind into the magnetosphere. If we assume that the magnetic field orientation of a CME is preserved...