Atmospheric Variations as observed by Adelaide and Buckland Park muon telescopes

1. ICRC 2013 - id 0277 Atmospheric Variations as observed by Adelaide and Buckland Park muon telescopes M.Berkova, R.Clay, E.Eroshenko, V.Yanke Institute of Terrestrial Magnetism, Ionosphere and Radiowave Propagation RAS of N.V. Pushkov (IZMIRAN), Russia The University of Adelaide, Department of Physics, Australia 1

2. Adelaide and Buckland Park muon telescopes The Adelaide telescope (34:93S;138:58E, altitude 50 m,H = 1013mb) ran from 2003 and operates up to present. It is of 1 m2 square, without lead, and records only vertical incident muons with the energy threshold close to 1 GeV,since it located on the second floor of six-floor building. The Buckland Park telescope (35:00S;140:00E; altitude of 50 m, H0 = 1013mb) is of 4 m2 area and except of vertical component also record muons from 4 azimuthal directions. It was run also in 2003, but was stopped in 2009 for modernization. 2 http://www.physics.adelaide.edu.au/astrophysics/muon

3. Adelaide muon telescopes / Data a continuousdrift about 2.73% per year What is the REASON??? Count rate of the Adelaide detector (vertical), correctedfor pressure Blue curve - the atmospheric pressure Comparison of the variations of count rates at Nagoya (vertical) and Adelaide (vertical),corrected for a drift. Reference period - 2009 year. 3

4. Adelaide and Buckland Park muon telescopes / Data Count rate for the Buckland Park detector, vertical(upper curve) and its variations relatively 2009 (bottomblack curve) which is compared with observable CR variationscorrected for a drift at Adelaide station. The good agreement when comparing variations oftelescopes of Adelaide and Buckland Park testifies, first,that the amendment on drift of a telescope of Adelaideis executed correctly and that the telescope of BucklandPark works steadily in the long-term plan. 4

5. Barometric Effect / Results pressure data: original corr for pressure b=(-0.136 ± 0.002)%/mb ρ=-0.93 b=(-0.171± 0.002)%/mb ρ=-0.93 Correlation between variations of original data and pressure for vertical telescopes at Adelaide and Buckland Park for Aug 2003 5

6. Technique of temperature effect estimation At the energiesrecorded by the ground level detectors (tens GV) thenegative temperature effect is observed density of temperature coefficient [L.Dorman] Densities of temperature coefficient at sea level [%/degree] effective temperature L.Dorman, E.Feinberg, UFN 59 (1956) 189-228

7. Temperature Data In the work the data of the Global Forecast System (GFS) temperature model representing by the National Centers for Environmental Prediction — NCEP (USA) has been used. NCEP,http://www.nco.ncep.noaa.gov/pmb/products/gfs/ The model output data are temperature at the 17 isobaric levels: observation level, 1000, 925, 850, 700, 500, 400, 300, 250, 200, 150, 100, 70, 50, 30, 20, 10 hPa for four times 00, 06, 12 and 18 hours every day.The data are interpolated on the grid of 1°x1° resolution. The accuracy of these models is about one degree for all isobaric levels and several degrees for the ground level. Therefore for surface temperature it isdesirable to use data of outside temperature measurements. Comparison of temperature on the sea level: themodel data (black), and directly measured near detector(the height of 2 m) in Adelaide (red curve) and BucklandPark (blue curve). Data for 2008 are obtained by sounding Atmosphere temperature profile in Winter (July 17,2007) and Summer (January 15, 2007) for Adelaide. TheGFS model data (lines) are compared with direct soundingin the Adelaide airport (black points- at 00UT, red ones at12 UT), (code meteostation 94672). 7

8. Temperature Effect / Results Reference period is 2009 Correlation between variations of CR intensity andeffective temperature in the atmosphere for vertical telescopes at Adelaide and Buckland Park 8

9. Temperature Effect / Results If to exclude extreme values, the temperaturecoefficient for a vertical telescope of Adelaide equals(0.40 ± 0.02) %/C, for Buckland Park- (0.69 ± 0.03) %/C. A bigger temperature coefficient for BucklandPark is caused, apparently, by significantly lower thresholdfor Buckland Park telescope, in comparison with 1 GeV athreshold for Adelaide telescope. The temperature coefficient for the inclined directions for Buckland Park equals(0.42 ± 0.04) %/C. Comparison of variations for Adelaide and BucklandPark vertical telescope (left scale) and variationsof effective temperatures dT/T eff (rightscale). Black bold curve is corrected for temperature effectcount rate variations. To check the drift correction: corrected for meteorological effects count rate variationsfor telescopes of Adelaide and Nagoyastations. The reference period is 2009. 9

10. Conclusions Initial data of a telescope of Adelaide contain continuous drift in 2.73 %/year which isn’t explainable yet. Data are used after correction for this drift. Comparison of the count rate variations of telescopes of Adelaide amended for temperature effect and data from Nagoya muon telescope showed efficiency of an applied method, and after correction for drift, long-term changes at Adelaide are in quite good agreement with Nagoya telescope data. The temperature coefficients for vertical muon telescope Adelaide is found to be (0.40 ± 0.023) %/C, for vertical muon telescopeBuckland Park (0.69 ± 0.03) %/C, for inclined components at Buckland Park(0.42 ± 0.04) %/C. A bigger temperature coefficient for Buckland Park is caused apparently by its essentially lower threshold for incident particles as compared with the threshold for Adelaide ( 1 GeV). Temperature coefficient