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44thth European Space Weather Week, 5-9 November 2007, Brussels European Space Weather Week, 5-9 November 2007, Brussels

Ionospheric forecast over Europe Ionospheric forecast over Europe driven by IMF conditionsdriven by IMF conditions

Tsagouri I. and A. BelehakiTsagouri I. and A. BelehakiNational Observatory of AthensNational Observatory of Athens


The backgroundThe background

Prölss, G.W., On explaining the local time variation of ionospheric storm effects, Ann. Geophys., 1993.

Tsagouri et al., Positive and negative ionospheric disturbances at middle latitudes during geomagnetic storms,GRL, 2000

Belehaki and Tsagouri, On the occurrence of storm-induced nighttime ionization enhancements at ionospheric middle latitudes, JGR, 2002

Tsagouri and Belehaki, A new empirical model of middle latitude ionospheric response for space weather pplications, Advances in Space research, 2006


The aimThe aim

This contribution aims at:This contribution aims at:

the introduction of criteria for the on line determination of the introduction of criteria for the on line determination of the storm onset in real time from ACE’s observations, andthe storm onset in real time from ACE’s observations, and

the the reformulation of the model’s expressions in order to reformulation of the model’s expressions in order to include include the latitudinal dependence of the ionospheric the latitudinal dependence of the ionospheric response.response.

The data analysis was established on observations concerning 60 The data analysis was established on observations concerning 60 intense (Dst < -100 nT) or great (Dst < -250 nT ) storm events intense (Dst < -100 nT) or great (Dst < -250 nT ) storm events (Gonzalez et al., 1999)(Gonzalez et al., 1999) occurred in the time interval 1998 – occurred in the time interval 1998 – 2005.2005.


Determination of the storm disturbance onset Determination of the storm disturbance onset based on IMF observationsbased on IMF observations

Based on preliminary analysis and previous reports Based on preliminary analysis and previous reports the storm onset is accompanied by:the storm onset is accompanied by:

Increase of the Bmag (first indication). Bmag significant greater than 10 nT.

IMF-Bz < 0. Storm conditions (long lasting southward turning, Bz < - 5 nT).

The Dst decrease is triggered by the Bz southward turning.


IMF conditions (introduced criteria)IMF conditions (introduced criteria)

Based on the detailed analysis of the events the following set of criteria was established: • Rapid increase of the Bmag verified by dB/dt > 5 nT/h

• Bmag > 12 nT

• IMF-Bz southward turning either simultaneously or at maximum 4 hours later than the increase in Bmag: IMF-Bz < -5 nT for at least two hours.

Fine tuning of the criteria:

Determination of the “end” of an event: northward turning of IMF-Bz (IMF-Bz > -1 nT).


Ionospheric response over EuropeIonospheric response over Europe

The ionospheric observations were organized in eight groups based on:The ionospheric observations were organized in eight groups based on:

1. The latitude of the observation point 1. The latitude of the observation point middle-to-high:middle-to-high: latitudes greater than 45º latitudes greater than 45º

(Chilton, Juliusruh)(Chilton, Juliusruh)

middle-to-low:middle-to-low: latitudes from 30º to 45º latitudes from 30º to 45º (Athens, Rome, San Vito, Sofia, El Arenosillo and Tortosa) (Athens, Rome, San Vito, Sofia, El Arenosillo and Tortosa)

2. The local time (LT) of the observation point at the storm onset. 2. The local time (LT) of the observation point at the storm onset. Evening (19-00) Evening (19-00) Morning (01 – 06) Morning (01 – 06) Prenoon (07 – 12) Prenoon (07 – 12) Afternoon (13-18) Afternoon (13-18)


Ionospheric response: Ionospheric response: LT of the observation point in the LT of the observation point in the afternoonafternoon sector (13 – 18) sector (13 – 18)

Strong ionospheric depletion (over median conditions) of 50% maximum intensity is recorded in all latitudes.


Ionospheric response: Ionospheric response: LT of the observation point in the LT of the observation point in the eveningevening sector (19 – 00) sector (19 – 00)

Significant ionospheric disturbances Significant ionospheric disturbances (> 30 %) are recorded at middle-(> 30 %) are recorded at middle-to-high latitudes. In middle-to-low to-high latitudes. In middle-to-low latitudes the disturbances are less latitudes the disturbances are less intense but greater than 20 %.intense but greater than 20 %.


Ionospheric response: Ionospheric response: LT of the observation point in the LT of the observation point in the morningmorning sector (01 – 06) sector (01 – 06)

Intense ionospheric depletion Intense ionospheric depletion (~40%) is detected in (~40%) is detected in middle-to-high latitudes. middle-to-high latitudes.

No significant effects are No significant effects are observed in the middle-observed in the middle-

to-low latitudes.to-low latitudes.


Ionospheric response: Ionospheric response: LT of the observation point in the LT of the observation point in the prenoonprenoon sector (07 – 12) sector (07 – 12)

Intense ionospheric Intense ionospheric depletion (~40%) is depletion (~40%) is detected in middle-to-detected in middle-to-high latitudes. high latitudes.

Positive storm effects in the Positive storm effects in the prenoon/afternoon prenoon/afternoon sectors constitutes the sectors constitutes the ionospheric storm time ionospheric storm time response in middle-to-response in middle-to-low latitudes (~ 30%).low latitudes (~ 30%).


Discussion of the resultsDiscussion of the results

According to our results,

• Systematic positive storm effects are observed at middle-to-low latitudes during daytime hours and about three hours later than the storm onset (for storm onset in the prenoon sector). The positive phase penetrates to the evening sector.

• Negative storm effects are systematically observed in middle-to-high latitudes independently on the LT of the observation point at onset and in the middle-to-low latitudes in the nighttime hours. The negative phase is first detected in the evening sector while it is expanded in the daytime hours as the storm develops and recovers.

All the above, indicate that the ionospheric storm time disturbances that follow the storm onset time as it is determined from ACE observations are consistent with Prölls (1993) and Fuller-Rowell et al. (1994; 1996) phenomenological scenario.


Validation tests (quiet intervals)Validation tests (quiet intervals)


Validation tests (disturbed intervals)Validation tests (disturbed intervals)


Modeling the ionospheric response: Modeling the ionospheric response: Time delay in negative phase onsetTime delay in negative phase onset

The time delay in ionospheric negative phase onset in respect to the LT of the observation point at onset. The LT effect is clearly demonstrated.


Modeling the Ionospheric Response: Modeling the Ionospheric Response: Reformulation of the model’s expressionsReformulation of the model’s expressions

Middle-to-high latitudes

• Four LT sectors

• Predictions are provided for 24 to 40 hours ahead


Modeling the Ionospheric Response: Modeling the Ionospheric Response: Reformulation of the model’s expressionsReformulation of the model’s expressions

Middle-to-low latitudes

• Three LT sectors

• Predictions are provided for 18 to 24 hours ahead


Application of the modelApplication of the model

1.1. Determination of the storm onset in UT Determination of the storm onset in UT based on IMF observations from ACE based on IMF observations from ACE (introduced criteria)(introduced criteria)

2.2. Determination of LT of the observation Determination of LT of the observation point at onsetpoint at onset

3.3. Estimation of the time delay in Estimation of the time delay in ionospheric responseionospheric response

4.4. Application of the model’s expressions on Application of the model’s expressions on the quiet ionosphere (monthly medians)the quiet ionosphere (monthly medians)


Validation tests for middle-to-high latitudes: Validation tests for middle-to-high latitudes: JuliusruhJuliusruh station station

The model’s predictions are satisfactory correlated with actual observations (during quiet and disturbed ionospheric conditions)

In general, the model’s predictions underestimates the ionospheric disturbances (30%).


Model’s prediction over climatology Model’s prediction over climatology (Juliusruh)(Juliusruh)

SeasonSeason % improvement% improvement

SummerSummer

N=12N=1241%41%

EquinoxEquinox

N=19N=1954%54%

WinterWinter

N=5N=533%33%

• N is the number of days

• % improvement = ((RMSE(monthly median)-RMSE(model)/RMSE(monthly median))x100 (Araujo-Pradere and Fuller-Rowell, 2002)


Validation tests for middle-to-low latitudes: Validation tests for middle-to-low latitudes: Rome stationRome station

The model’s predictions are satisfactory correlated with actual observations (during quiet and disturbed ionospheric conditions)

Once again, the model’s predictions underestimates ionospheric disturbances (slightly greater than 30%).


Model’s prediction over climatology (Rome)Model’s prediction over climatology (Rome)

SeasonSeason % improvement% improvement

SummerSummer

N=6N=651%51%

EquinoxEquinox

N=9N=942%42%

WinterWinter

N=5N=539%39%

• N is the number of days

• % improvement = ((RMSE(monthly median)-RMSE(model)/RMSE(monthly median))x100 (Araujo-Pradere and Fuller-Rowell, 2002)


SummarySummary

The proposed method was further improved to anticipate more localized The proposed method was further improved to anticipate more localized predictions over Europe. In particular, predictions over Europe. In particular,

1.1. Quantitative criteria for the determination of the storm onset from IMF Quantitative criteria for the determination of the storm onset from IMF observations were introduced, and observations were introduced, and

2.2. the models expressions were reformulated to include the latitudinal the models expressions were reformulated to include the latitudinal dependence of the ionospheric response.dependence of the ionospheric response.

Extensive validation test were also performed for two European stations well Extensive validation test were also performed for two European stations well separated in latitude in order to investigate the methods performance. separated in latitude in order to investigate the methods performance.

The results gave evidence for significant improvement over climatology (up to The results gave evidence for significant improvement over climatology (up to 54%) for all seasons, while the method’s predictions presents satisfactory 54%) for all seasons, while the method’s predictions presents satisfactory accuracy in respect to actual observations. accuracy in respect to actual observations.

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