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Neutron Monitor Data for Jungfraujoch and Bern during the Ground-Level Solar Cosmic Ray Event on 20 January 2005
R. Butikofer and E.O. Fluckiger ¨ ¨ ¨ Physikalisches Institut, Universitat Bern Sidlerstrasse 5, CH-3012 Bern, Switzerland March 22, 2005

Abstract This repor t includes information on the processing and use of the data for the solar cosmic ray ground-level event (GLE) on 20 January 2005 obtained by the IGY and NM64 neutron monitors at Jungfraujoch and the special neutron monitor in Bern, all of which are operated by the Cosmic Ray Group at the University of Bern, Switzerland.

Neutron Monitors
http://cosray.unibe.ch

IGY neutron monitor at Jungfraujoch
The standard IGY neutron monitor with 18 BF3 -counters is housed on top of the Sphinx Observatory of the High Altitude Research Station Jungfraujoch. Geographic latitude: Geographic longitude: Effective ver tical cutoff rigidity, Epoch 2005.0: Altitude 46.55 N 7.98 E 4.5 GV 3570 m asl

This detector is an integral par t of the worldwide network of neutron monitors, and data of this monitor have been published regularly since 1958 (Debrunner et al., 1987).

IQSY-NM64 neutron monitor at Jungfraujoch
The IQSY-NM64 neutron monitor with 3 counter tubes is housed on the roof of the High Altitude Research Station Jungfraujoch. Geographic latitude: Geographic longitude: Effective ver tical cutoff rigidity, Epoch 2005.0: Altitude 46.55 N 7.98 E 4.5 GV 3475 m asl

This monitor has been in operation since 1986 (Debrunner et al., 1987; Schubnell, 1988). 1


Special neutron monitor at Bern
The special neutron monitor with 58 IGY-type counter tubes (Butikofer, 1988) is housed ¨ on the roof of the Physikalisches Institut of the University of Bern. Geographic latitude: Geographic longitude: Effective ver tical cutoff rigidity, Epoch 2005.0: Altitude This monitor has been in operation since 1977. 46.95 N 7.456 E 4.4 GV 570 m asl

Preparation of GLE Data
The last full hour (in UT) before the onset of the par ticle increase at Ear th was used as the baseline time interval, i.e. 20 January 2005, 0500 - 0600 UT. The data given in the data files for the Jungfraujoch neutron monitors are listed in Table 1. For the Bern neutron monitor, the same data are given with the difference that the smalltime data include 5- minute values only. All data are presented in the "Standard Format for Cosmic Ray Ground-Level Event Data" as suggested by Shea et al. (1987), and additions according to the document "STANDARD FORMAT FOR COSMIC RAY GROUND-LEVEL ENHANCEMENT DATA" at the GLE data base. The following names were used to identify the different monitors: JUNGFRAUJ for the 18-IGY and JUNGFRAU2 for the 3-NM64 neutron monitors at Jungfraujoch, BERN for the special neutron monitor in Bern. Hourly data 1-minute data Hourly data 19 20 20 20 21 Januar Januar Januar Januar Januar y y y y y 2005 2005 2005 2005 2005 0000 0000 0500 1900 0000 2400 0500 1900 2400 2400 UT UT UT UT UT

Table 1: Data given in the data files for the Jungfraujoch neutron monitors.

All counting rates of the neutron monitors were normalized with the same correction factors as used for the publications on our website http://cosray.unibe.ch and for data sent to the world data centers. The factors for the time interval during the event are given in Table 2 for the different sections of the neutron monitors. neutron monitor IGY neutron monitor Jungfraujoch NM64 neutron monitor Jungfraujoch special neutron monitor Bern section 1 0.885 0.975 1.067 section 2 0.908 0.976 1.000 section 3 0.792 1.010 1.060 / 1.000

Table 2: Correction factors used to normalize the counting rates of the neutron monitors during the event. Pressure corrected hourly averages were obtained from pressure corrected 1-minute values. The hourly pressure values were obtained by averaging the 1-minute pressure readings.

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Section 3 of the IGY neutron monitor at Jungfraujoch is the central section. Section 1 is west of section 3 (towards the building) and section 2 is east of section 3. In the NM64 neutron monitor Jungfraujoch section 1 is located toward the mountain, section 2 is the central section and section 3 is located toward the glacier. For the special neutron monitor in Bern section 1 is AL+AR+BL+BR and section 2 is CL+CR. In contrast to the data books where the count rates of the sections FL and FR are not taken into account, the data in this repor t include all sections of the special neutron monitor. Section 3 therefore is DL+DR+EL+ER+FL+FR. The correction factor for (DL+DR+EL+ER) is 1.060, whereas for (FL+FR) it is 1.000. For details see (Butikofer, 1988). ¨ In the special neutron monitor in Bern the counter tubes are placed at different positions relative to the absorbers. Therefore different barometric pressure coefficients were used for the pressure correction of the count rates of the different sections. The barometric pressure coefficients according to Butikofer (1988) were used, see Table 3. ¨ section AL, BL, CL, DL, EL, FL, AR BR CR DR ER FR barometric coefficient in % / mmHg -0.975 -0.961 -0.962 -0.920 -0.948 -0.928

Table 3: Barometric pressure coefficients for the special neutron monitor at Bern according to Butikofer (1988) ¨ The barometric pressure coefficient of -0.9557 % / mmHg given in line 3 of the header of the standard GLE format for the special neutron monitor in Bern corresponds to an average barometric pressure coefficient for the total count rate. The pressure measurements at Jungfraujoch were disturbed by turbulent and high speed winds as can be seen from Figures 1-3. Figure 1 shows the maximum wind speed per hour at Jungfraujoch for the time interval 20-21 January 2005. In Figure 2 the atmospheric pressure measurements at the three locations of the neutron monitor stations: IGY and NM64 at Jungfraujoch (1-minute data) and special neutron monitor at Bern (5-minute data) are plotted for 20 January 2005, 0400-1200 UT. Figure 3 shows the difference between the 1-minute pressure measurements at the IGY and the N64 neutron monitor locations at Jungfraujoch, p = pN M 64 - pI GY , in function of time. No attempts have been made to correct the atmospheric pressure measurements (Butikofer and Fluckiger, ¨ ¨ 1999).

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Figure 1: Maximum wind speed per hour at Jungfraujoch in the time interval 20-21 January 2005. Source: www.meteoschweiz.ch

Figure 2: Atmospheric pressure measurements at the locations of the three Swiss neutron monitor stations: IGY and NM64 at Jungfraujoch (1-minute data) and special neutron monitor at Bern (5-minute data) on 20 January 2005, 0400-1200 UT.

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Figure 3: Difference of pressure measurements (1-minute data) between IGY and NM64 neutron monitor locations at Jungfraujoch in mmHg on 20 January 2005, 0400-1200 UT.

Measurements of Swiss neutron monitors
In the Figures 4-6 the relative pressure corrected counting rates of the Swiss neutron monitors are plotted for 20 January 2005, 0400-1200 UT. To illustrate the influence of the pressure measurements affected by turbulent and high speed winds on the count rates of the neutron monitors the ratio (Not pressure corrected count rates)/(Pressure corrected count rates) are plotted in Figures 7-9.

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Figure 5: Relative pressure corrected 1-minute data of NM64 neutron monitor at Jungfraujoch on 20 January 2005, 0400-1200 UT.

Figure 4: Relative pressure corrected 1-minute data of the IGY neutron monitor at Jungfraujoch on 20 January 2005, 0400-1200 UT.

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Figure 6: Relative pressure corrected 5-minute data of special neutron monitor at Bern on 20 January 2005, 0400-1200 UT.

Figure 7: Ratio (Count rates not pressure corrected)/(Count rate pressure corrected) of 1minute data of IGY neutron monitor at Jungfraujoch on 20 January 2005, 0400-1200 UT.

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Figure 8: Ratio (Count rate not pressure corrected)/(Count rates pressure corrected) of 1-minute data of NM64 neutron monitor at Jungfraujoch on 20 January 2005, 04001200 UT.

Figure 9: Ratio (Count rates not pressure corrected)/(Count rates pressure corrected) of 5-minute data of special neutron monitor at Bern on 20 January 2005, 0400-1200 UT.

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In the following tables the characteristics (onset time, maximum) of the GLE data of the Swiss neutron monitors are listed.

IGY Jungfraujoch
1-minute values Onset Pre-increase Max1 Max2 5-minute Onset Max1 Max2

0654 UT 0654-0657 UT 0705-0706 UT 0724-0725 UT

4% 11.4% 11.2%

values 0650 UT 0700-0705 UT 0715-0720 UT

8.7% 9.2%

NM64 Jungfraujoch
1-minute values Onset Pre-increase Max1 Max2 5-minute Onset Max1 Max2

0652 UT 0652-0657 UT 0703-0704 UT 0715-0716 UT

4% 11.3% 11.2%

values 0650 UT 0705-0710 UT 0715-0720 UT

9.1% 8.9%

Special neutron monitor Bern
5-minute Onset Max1 Max2 values 0645 UT 0705-0710 UT 0725-0730 UT

9.9% 6.6%

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Conditions for Use of Data
The Swiss neutron monitor data may be used under the following conditions: 1. You agree to acknowledge the source of the data in any published use. Example: "Jungfraujoch neutron monitor data were kindly provided by the Cosmic Ray Group, Physikalisches Institut, University of Bern, University of Bern, Switzerland" 2. You agree to send a copy of any paper using these data to: Erwin Fluckiger ¨ Physikalisches Institut University of Bern Sidlerstrasse 5 CH-3012 Bern / Switzerland 3. You may share these data with colleagues, provided you inform them of these conditions. While the published data are accurate to the best of our knowledge, we reserve the right to correct errors without notifying users. Acknowledgments: The operation of the neutron monitor is suppor ted by the Swiss National Science Foundation, grant 200020-105435/1 and by the International Foundation High Altitude Research Stations Jungfraujoch and Gornergrat (HFSJG), CH-3012 Bern, Switzerland.

References
¨ Butikofer, R. (1988). Zum Wiederaufbau des Multiplizitatsneutronenmonitors in Bern. ¨ ¨ Master thesis, Physikalisches Institut, Universitat Bern, Switzerland. Butikofer, R. and E. Fluckiger (1999). Pressure correction of neutron monitor measure¨ ¨ ments in turbulent winds (abstract). In ISSI Workshop "Cosmic Rays and Ear th, March 21-26, 1999, Bern, Switzerland. Debrunner, H., E. Fluckiger, and M. Schubnell (1987). Present and Future Activities of ¨ the Bern Cosmic Ray Group in the Field of Solar Neutrons. In Workshop on Solar Neutrons; 20th International Cosmic Ray Conference, Volume 9 of Special Repor t of the A.F. Ioffe Physico-Technical Institute of the Academy of Sciences of the USSR, Moscow. Schubnell, M. (1988). Zum Nachweis solarer Neutronen auf Jungfraujoch. Ph. D. thesis, ¨ Universitat Bern, Switzerland. Shea, M., D. Smar t, J. Humble, E. Fluckiger, L. Gentile, and M. Nichol (1987). A re¨ vised standard format for cosmic ray ground-level event data. 20th ICRC, Moscow, Conference Papers 3, 171.

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