Dynamic boundaries of the ionosphere variability

Adv. Space Rex Vol. 27, No. 1, pp. 91-94,200l 0 2001 COSPAR. Published by Elsevier Science Ltd. All rights reserved Printed in Great Britain 0273-I 177/O] $20.00 + 0.00 www.elsevier.nl/locate/asr zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA PII: SO273-1177(00)00162-9 zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCB Pergamon DYNAMIC BOUNDARIES OF THE IONOSPHERE VARIABILITY T.L. GulyaevaJ,z and K.K. Mahajans 1IZMlR4N,RussianAcademyof Sciences,142190TmiIsk,hbww Regbn,Russia 2Spact? Reseati Center,BarfyckaI&4,00-7!6 Warsaw,F&&d 3NabbnalPhysiicalLaborato~, NewDelhi--110012, lndb ABSTRACT It. has been shown that the conventional threshold of &20% departures from monthly median cannot serve for reliably distinguishing quiet and disturbed ionospheric conditions at different latitudes/time-ofday/season/level of solar activity. After a 3 h filtering of daily-hourly foF2 critical frequency, for each 3 h UT bin new upper and lower variability boundaries are introduced, based on the extreme foF2 values normalized to the monthly median similar to assessments of warming-cooling of air temperature in meteorology. Application of so defined boundaries is made to long-term observations at 58 ionospheric stations world-wide for the period of 1942 to 1999 comprising in total more than 13,000,000 hourly foF2 values. 0 2001 COSPAR. Published by Elsevier Science Ltd. All rights reserved. INTRODUCTION The first historical specification of dynamic boundaries of the ionosphere storminess were made by Radio Propagation Laboratory, NBS (IRPL-R5, 1944). To distinguish storm in progress from local disturbances, standard boundaries for Washington D.C. were introduced in this Report assuming that different standards should be established for different locations over the world. For instance, one of the characteristics of a storm in the auroral zone is the occurrence of the intense sporadic E layers, especially at night; at mid-latitudes, however, sporadic E is generally less prevalent during ionosphere storms than at other times. The storm thresholds are different for negative and positive phases of a storm, by night and day, and for h’F and foF2. Although the monthly statistical dispersion of observed foF2 values are known to depend on hour, season and solar cycle phase (Gulyaeva et al, 1998), different fixed thresholds for disturbance have been accepted as a% (Piggott and Rawer, 1972) 5XIK (Kouris el al, 1998) or set of specific ranges (Gulyaeva, 1998). Definition of storminess compared to normal “quier values of ionospheric parameters is important in context of ionospheric modeling such as IRI (Bilitza, 1990) intended to represent the quiet ionosphere. In this study we specify the upper and lower variability boundaries as limits of applicability of quiet ionospheric models and maps based on monthly median of the F2 layer critical frequency. Data of 56 ionospheric stations worldwide are analyzed with their geographic coordinates and period of observation listed in Table 1. DATA PROCESSING RESULTS Daily-hourly observations of the F2 layer critical frequency foF2 are first smoothed with a 3h UT filter to reduce transient features that have a time-scale of less than 3h and to make the results comparable with relevant geomagnetic indices aa, ap, kp, etc. Relevant 8bins monthly mean (M) and median (MD), standard deviation (SD), maximum (MAX) and minimum (MIN) of foF2 and day-to-day trend of variability are calculated. Flexible thresholds are used for each location/month/3h-bin equal to (MD+MAX)I;! for positive deviation and (MD+MIN)/2 for negative deviation similar to assessments of warmingcooling of air temperature in meteorology. We were warned that in the case of ionospheric characteristics the extreme values might often be uncertain or even erroneous and therefore we should use deciles that are found better stafstically. These, however, have the disadvantage that they do not always characterize a disturbed behaviour because there are months with very few and others with many more 91 T. L. Gulyaeva and K. K. Mahajan zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHG 92 disturbed days. When normalized by the monthly median, the so defined percentage boundaries of the foF2 variability &lp and BOWare equal to (Gulyaeva, 1999): Bw = ((‘F2),7,ALi +?)/2 x 100% zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQ Bb,=((fbF~mi4kd+1)/2x 100% (1) 1964 1958 12” 9 60 o-:rti 60 II III 1; 1 zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFE 80 100 120 140 P,% 60 80 100 120 140 P,% WZGhiMdoll 60 80 100 120 140 P,% ’ 60 80 100 120 140 P,% 60 80 60 80 100 120 140 P,% 100 120 140 P,% 0 Noon n Midnight Fig. 1. Histogram of occurrence number of the noon and midnight ratio P = foF2/kned, %, in the increment of 5% for the year of solar maximum (1958) and solar minimum (1964) at Sodankyla, Washington, and Kodaikanal. Negative deviations: P c lOO%, positive deviations: P > 100%. Vertical lines for the median (P = 100%) and SO% deviations (P = SO% and P = 120%). DAY -, zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Bl % AZ im 80 im m JR im zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA RG 80 JFMAYJJASOND MONTH J F M Fig. 2. Seasonal variation of the lower and upper variability Arkhangelsk (AZ), Juliusrue (JR), and Kerguelen (KG). AY J J A MONl?I S 0 N D boundaries of foF2 for midnight and noon 3 h UT bins at Ionosphere Variability 93 zyxwvutsrq Figure 1 illustratesdifferenceof distributionof the negative and positiveionosphericfoF2 deviationsfrom the median with time of day, geographic location and level of solar activity.Conventional positive and negative departures by GO% or 530% from the median fail to adequately represemworldwide changes of the ionosphere. Seasonal effects in Figure 2 are shown for local nighttimeand noon 3 h bins of time with data for each month averaged for all years of observation.Local 3 h UT bin for nighttimearound the world is equal to 23-00-01 h, 00-01-02 h or 01-02-03 h LT; for noon: 11-12-13 h, 12-1314 h, or 13-14-15 h LT, depending on longitudinaldiirence between LT and UT. While a high winter upper boundary is observed by night at Arkhangelsk (North hemisphere) during January and December, much smaller positive deviationsoccur at magnetic conjugate location Kerguelen (South hemisphere) for the same months of local summer, and vice versa for May to August, Results for the mid-latitudestationof Juliusruhshow a smaller seasonal variation. Smaller percentage deviationsby daytime than by night are obtained at all sites. All above features could be modeled as boundaries of the diurnal, seasonal, solar cycle and geomagneticvariabilityof foF2 for differentapplications. TABLE I. Geographic Coordinates and Period of Observationsof Associated IonosphericStations. STATION 1 LATI 1LONGI 1 YEARS 1 LATI 1LONGI YEARS STATION I 129 BEKESCSABA 146.7N )021.2E )X%4-1989 180.6~ lO58.OE 1957-1991 1 HEISS IS 30 OTTAWA 45.4N 284.1E 1942-1995 69.ON 033.OE 1957-1994 2 MURMANSK 31 ALMA-ATA 67.6N 020.4E 1957-1999 43.2N 076.9E 1957-1989 3 KIRUNA 32 SOFIA 42.7N 023.4E 1964-1999 4 SODANKYLA 67.4N 026.6E 1957-1999 33 ROME 41.8N 012.5E 19!%-1999 66.5N 0665E 1957-1999 5 SALEKHARD 34 TORTOSA 40.4N OOiI.3E 1968-1999 64.6N 016.6E 1957-1999 6 LYCKSELE 35 BOULDER 4O.ON 254.7E 19581999 64.6N 040% 7 ARKHANGELSK 1969-1993 36 WASHINGTON 38.7N 282.9E 1946-1967 62.ON 129.6E 1957-1993 6 YAKUTSK 37 ATHENS 6O.ON 030.7E 1957-1996 38.ON 023.8E 1961-1987 9 LENINGRAD 36 WALLOPS IS 37.8N 284.5E 1968-1999 60.ON 151.OE 19681999 IO MAGADAN 39 EL ARENOSILLO 59.6N 017.6E 1957-1996 II UPPSALA 37.1N 353.3E 1974-1999 46 TOKYOIKOKUBUNJI 58.6N 265.6E 1943-1995 35.7N 139.5E 1957-1999 12 CHURCHILL 41 POINT ARGUELLO 34.6N 239.4E 1969-1996 56.5N 084.9E 1957-1998 13 TOMSK 42 DELHI 56.4N 058.6E 1957-1998 14 SVERDLOVSK 28.6N 077.2E 1957-1986 15 MOSCOW 55.5N 037.3E 1946-1998 43 AHMEDABAD 23.ON 072.6E 1957-1999 44 MAUI 54.7N 020.6E 1964-1991 16 KALININGRAD 20.8N 203.5E 1957-1994 54.6N 013.4E 1957-1998 17 JULIUSRlkURUGEN 45 KODAIKANAL 10.2N 077.5E 1957-1987 46 HUANCAYO 53.3N 299.2E 1974-1998 16 GOOSEBAY 12.0s 284.7E 1957-1989 47 TAHITI 52.5N 104.OE 1957-1997 19 IRKUTSK 17.7s 210.7E 1971-1989 48 TOWNSVILLE 52.2N 021.2E 1958-1999 20 MlEDZESZYN/WARSAW 19.35 146.7E 1951-1998 21 SLOUGH 49 GRAHAMSTOWN 51.5N 359.4E 1944-1995 33.38 026.5E 1973-1996 50.5N 030.5E 19s1990 22 KIEV 50 CANBERRA 35.35 149.OE 1950-1994 23 DOURBES 51 HOBART 42.98 147.2E 1950-1998 5O.lN 004.6E 1957-1996 5O.ON 014.6E 1956-1995 24 PRUHONICE 52 KERGUELEN 49.45 070.3E 1965-1988 25 LANNION 48.5N 356.7E 1971-1999 53 PORT STANLEY 51.7s 302.2E 1967-1992 48.5N 135.lE 1959-1990 26 KHABAROVSK 54 ARGENTINE IS 65.28 295.7E 1971-1995 27 FREIBURG 55 TERRE ADELIE 46.lN 007.6E 1948-1974 166.78 114O.OE11964-1986 26 ROSTOV zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA 47.2N 039.7E 1957-1998 156 HALLEY BAY 175.58 1333.4E ll957-1980 It is worth noting that digital ionosondeswith automaticdata interpretationhave been installed in the eighties replacing manual data reduction with the analogous ionosondes (Reinisch, 1995). The comparison of manual versus automatic computer processing of the ionograms according to URSI guidelines (Piggott and Rawer, 1972) has shown that there is no statistical difference between the two types of data analysis (Jodogne, 1998). At the same time it is recognized that automaticallyscaled data may be incorrector may cut out data that manually would be accepted. The two types of ionosondesyield differences in calculated boundaries &p and Bbrr.This is illustratedin Figure 3 where long-term results with analogous ionosonde at Moscow and Freiburg and digital ionosondeat Goose Bay are shown year by year at November. Local 3 h UT bins during local sunrise are selected with the variabilityboundariessmaller or greater than the range of &20% in many cases. If 3 h filteringhad not been applied the boundaries defined in Eq. 1 would cover a larger region. So defined hourly boundaries may be helpful for HF propagationpredictions. T. L. Gulyaeva and K. K. Mahajan zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPO 94 180 140 \; 120 . 4 100 80 80 1940 lS7Q lSS0 -MO XFR fS60 +GS zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHG Fig. 3. Monthlyupper and lower variabilii boundariesof foF2 for November during 1946-1999 at Moscow (MO), Freiburg(FR), and Goose Bay (GS) at local sunrise. CONCLUSION A new definitionfor upper and lower variabilityboundaries,normalizedto the monthlymedian is proposed, based on an analysis of foF2 values averaged in 3 h UT bins. With our definitionthe dynamic boundaries are estabtisheddepending on the time of day, season, solar a&& and geomagnetic latitude. The so defined variability range is in most cases greater or less than conventional&20% departuresof foF2 from the monthlymedian. Available undisturbedionosphericmodels and maps can be accompanied in the future by relevant model of changes in the foF2 variability showing limits for quiet conditions. Such approach is relevant both for short-term and long-term assessments of the changes in ionosphere. The timing of our 3 h ionosphericdisturbanceindicescompares well with geomagneticindices aa, ap, kp, etc. and is helpful at estimatingday-today trends of variability. ACKNOWLEDGEMENTS Data used for the present study have been provided on CD-ROM, via Internet, on diskettes, in printed form by WDC-A for STP, Boulder, CO, USA; WDCB,_Moscow. Russia; WDC-CI, RAL, UK; WDC-CP, Kyoto, Japan; COST251 Databank, ICTP, Trieste, Italy; IDCE, Wm, paland; SGO, Sodankila, Finland; archive and library of IZMIRAN. The authors are grateful to Professor Bodo Reinisch for ttnapc&l grants allowing to present this paper at IRl-99 Lowell meeting. Editorial comments of Professor Karl Rawer and unknown Referees are greatly appreciated. The paper is dedicated to thousands of ionosonde stationpersonnelcontributingto hardware and softwaredevelopment,data acquisitionand reductionduringthe 2@ century. REFERENCES BilitzaD., lnernationalReference IonosphereIRI-99. Rept IWSMK~-R&S&Z, Lanham, MD, USA, 156 p., (1998). Gulyaeva T.L. , Logarithmicscale oftheionospheredisturbances.timgn. and Aeronomy,36, #I, 160-163,(1996). Guiyaeva T.L., S. Aggarwal, K.K. Mahajan, and S. Shastri,Variabilityof foF2 at low and middlelatitudes.A& SW Res, 22, # 6,847850 (1998). Gulyaeva T.L., Combined system for long-termand short-termassessmentof ionosphericfoF2 changes. C&Z517D@?~ Proc. COST251 Workshop,Madeira, Portugal, 165171, (1999). IRPL-RS, Criteria for ionosphericstorminess.Radii PropagationLab. Rept R+ NBS, Washington,D.C., USA, (1944). Jodogne J.-C., Manual versus automaticcomputerprocessingof from years of hourlydata comparison.Rept UAG-105;WDC-A for STP, Boulder,CO, USA, 16-21, (1998). KourisS.S., D.N. Fotiadis,and T.D. Xenos, On the day-to-day variationof foF2 and M(3OOQF2. A& Spaae Res, 22, #I6873 876 (1998). Piigott W.R., and K. Rawer, URSI Handbookfor lonogram Interpretationand Reduction. Rqa! UAGZ3,234, WDC-a far STP, Boulder,CO, USA, 360pp. (1972) Reinisch B.W. The Digisondenetworkand databasing. Rept UAGI#, WDC-A for STP, Boulder,CO, USA, 815 (1995).