Indian Journal of Radio & Space Physics Vol. 33, December 2004, pp. 358-366
Variations of solar indices during the sunspot maximum years (1999-2002) of cycle 23 R P Kane lnstituto Nacional de Pesquisas Espaciais, INPE, C P 5 15, 12245-970, Sao Jose dos Campos, SP, Brazil E- mail : [email protected] Received 16 December 2003; .revised 19 May 2004; accepted 22 July 2004
Compari son of the evolutions of daily and monthly values of several solar indices during 1999-2002 indicated th at th e dail y valu es had large day-to-day flu ctuations with peak spacings differing considerably from the 27-day solar ro tation period. Plots of the percentage increases (trough-to-peak) versus temperature of the source regions of the va ri ous indices indicated a double-humped structure. The monthly values showed many peaks. T he average spac ing was -3.5 months ( - 100 days). The 12-month movin g averages showed considerable differences. Some indices reached a max imum near March 2000. Some of these decreased since then and continue to decrease at present; but some reached a minimum near January 2001 and remained steady th ere, or sta11cd increasi ng again to reach a probable max imum near June 2002. Some indices did not have a maximum in March 2000 and continued to increase till June 2002. T hus, the evolutions of the vari ous solar indices during th e sunspot max imum of cycle 23 ( 1999-2002) are substanti all y different from each other. Obvio usly. the dynamical upheavals in the photosphere reach upper levels of the solar atmosphere with varying intensities. Key words: Solar indices, Sunspot max imum, Solar cycle 23. PACS No.: 96.60 Qc; 96.60 Tf; 94.20 Vv
1 Introduction number of active regions and can persist for several 5 The sun is a hi ghl y active star. There are many (up to a dozen) solar rotations . 6 indices of sol ar activity currently in use. These indices In a recent communicati on , it was shown that the indicate activities at vari ous levels in the solar evolutions of the various indices during sunspot atmosphere, are produced by a number of different max ima and sunspot minima were not alike. In some mechanisms, and have a strong relationship with solar cycles, th e sunspot number (Rz) rose rapidly to a magnetic activity, whi ch is the engine driving all max imum and fell thereafter rapidly, giving the these indices. Based on the length of data record, the impression of a sharp peak, while in some other primary index of solar activity has been the Wolf cycles, th e ri se of K from the sunspot minimum (Zurich) sunspot number Rz, published by Wolf in the halted abruptly after a few years. The level remained vari ous issues of Astron. Mitt. ( 1858-1893) and by almost steady fo r the next few years givi ng the 12 others · • Presently it is generated by the Solar Index impression of a plateau, and then there was a sharp Data Center, Brussels. It has a prominent 11 -year fa ll up to the next sunspot minimum. Most of the 3 cycle, named after Schwabe .4. The cycles are other indices had coincided sharp maxima. In cases of numbered since 1750 (cycle 1= 1755 minimum to duplicate peaks, their evolution was not similar to the 1766 minimum). The next most prominent index has sunspot numbers. The latest data examined were up to been th e 2800 MHz, 10.7 em radio emission flux , about the end of 2000, and most of the indices showed recorded routinely by a radio telescope near Ottawa, a maximum during March-April of 2000. However, it Canada, since 14 Feb. 1947, which is presently was noticed later that the solar activity did not operated by th e National Research Council, using two decrease thereafter monotoni call y and many indices fully automated radio telescopes at the Dominion rose again to give a second maximum. In the present Radio Astrophysical Observatory, Pen tieton, Canada. paper, the behaviours of vari ous indices during All solar indices show an 11-year cycle, except that 1999-2002 are compared in detail. during sunspot minimum when sunspot numbers almost reach zero, most of the other indices reach a 2 Data minimum non-zero level, indicating the presence of All the data were obtained from NOAA websites magnetic acti vity even then. Solar acti vity occurs in http://www.ngdc.noaa.gov/stp and www.sec.noaa.gov. complexes, which are . localized areas having a Table 1 li sts the various radio emi ssions, line KANE: VARIATIONS OF SOLAR INDICES DURING THE SUNSPOT MAXIMUM YEARS 359
Table 1--List of solar indices used in the present analysis
Solar indices Percentage changes Log T % Amp 27-day Ranges (%) during dai: numbers of 1999 Wavelength Temp.T (Av 97-98) 22-35 46-35 212-230 240-230 nm K
lntpi.N.Y,B Obscure Obscure Obscure Obscure Obscure X-rays 0.1-0.8 >2000000 >6 Abnormally large values Protons >I Mev -1000000 -6 Abnormally large values S.flares -1000000 -6 Abnormally large values EUV 26-34 <1000000 <6 8.1 29 32 Sunspots 5000 3.7 Obscure Abnormally large values Mag. F.Kitt 5000 3.7 138 138 74 70
UV lines He ! 1083.0 5000 3.7 30 30 22 38 Mg ll 280.0 6500 3.85 2.2 10 12 8 01 130.4 7060 3.85 3.7 15 17 13 CI 165 .6 7060 3.85 2.6 14 15 9 Sill 126.2 10000 4 6.8 27 28 22 Si II 153.0 10000 4 6.0 27 32 20 Sill 181.3 10000 4 3.8 17 18 17 Cll 133.6 12600 4.1 6.5 21 27 15 Si III 120.6 17800 4.25 8.7 44 39 28 HI 121.6 40000 4.6 5.0 20 22 19 Si IV 139.8 56700 4.75 6.3 33 33 23 He II 164.0 56700 4.75 9.5 41 50 53 CJV 155.0 100000 5 3.7 23 24 20 NY 124.1 200000 5.3 4.0 30 28 26 Radio MHz 15400 8800 4.95 1.9 16 21 16 22 8800 140000 5. 15 4.5 22 23 30 21 4995 200000 5.3 10.1 52 64 73 65 2800 FlO 300000 5.48 13.8 77 106 77 101 2695 315000 5.5 14.0 88 112 80 89 1415 415000 5.62 13.8 74 93 57 60 606 835000 5.92 9.2 4 1 58 28 27 410 1000000 6 9.4 40 109 27 27 245 1200000 6.08 8.8 79 203 56 69 emissions and other parameters for which data were The temperature of the 28.4 nm Fe XII line is about 2 used. The UV emissions lines are from a special MK, while that of 30.4 He II emission line is about UARS data product (solstice L2 lines) that is created 55,000 K. Thus, no single temperature can be by extracting the emission lines from the 0.1 nm attributed to this band, but an average value of spectral data by fitting Gaussian functions to the lines -200,000 K is assumed for illustration. and accounting for a continuum background spectrum The excitation temperatures of these line emissions 7 8 as a second degree polynomial. Therefore, these have been determined · by taking the ratio of 'solstice' emi ssion line fluxes are free of the excitation rates for two doublets of the same super underlying continuum, but some of these lines do multiplet9 at 0.15 nm resolution, but the absolute have blends with other emission Jines within the 0.15 temperature values may not be very accurate. nm spectral resolution. These 'solstice' data are (Emission temperatures are based on measurements available only up to the middle of 2001. Data were and theory, and different results can arise from available for SEM/SOHO EUY (26-34 nm) for 1996 different sets of data or different atomic theory/ onwards. However, the solar region in which these coefficients). The solar atmosphere, particularly over originate is not unique (private communications from active regions and complexes of activity, is highly Karen Harvey and Don McMullin). The 26-34 nm inhomogeneous. There is a chromosphere overlaid by wavelength range is produced at three levels: namely, a corona with a transition layer in between, but often upper chromosphere, transition region and corona. there are intrusions of material from the 360 INDI AN J RADIO & SPAC E PHYS, DECEMB ER 2004
chromosphere into the corona and vice versa with the Fi g. 1 show the density p, which decreases rapidly transitio n regio n acting as an adapti ve skin between with altitude. the chro mospheric and th e coronal pl asmas. However, For radi o emi ssions, data are obtained from the fo r indices integrated over the whole sun (full disc WDC-A Archive, Boulder, and the average was averages) and over long time intervals, marked calculated for the data fro m Sag, uTIore Hill , di fferences in the height dependence of vari ous Massachusetts (SGMR); Palehua, Hawaii (PALE); parameters between acti ve regions are expected to San Vito, Italy (SVTO); Learmo nth, A ustrali a cancel o ut. Fig ure I shows an example of the (LEAR), for noon-time values at frequencies 245, temperature-height profil es as deri ved by Fontenla el 410, 606, 14 15 ,2695 , 4995,8800 and 15400 MHz. lo al. , fo r the quiet sun. In th ese profiles, the The temperatures of the regions of origin of these temperature d rops fro m abo ut 6,000 K at the radio emi ssions are obtained as discussed earlier by photosphere to 4,800 K at the temperature minimum, Kane et ali i. whi ch li es roughl y 500 km above the photosphere. T he temperature then ri ses again to about 104 K at an 3 Plots of daily values altitude of about -2000 km, where the transitio n Table 2 represents the sample of dail y values of regio n is located. In the thin transiti on layer (a few radio frequency (average for LEAR, PALE, SGMR, kilo metres thi ck), the temperature rises to about 5 x SVTO) for 17-30 Jan. 2001. 105 K. As height increases further, the te mperature As can be seen in Table 2, the day-to-day variati on ri ses to a typi cal coronal value of about 106 K is abnormall y large at 245 and 410 MHz. This is (assumed in the present example to have reached at because, in hi gh solar acti vity, there is frequent burst about 3000 km above th e photosphere). These heights emi ssio n, whi ch lasts fo r several ho urs and the effect are signifi cantl y lower over acti ve regions, as may be seen even in dai ly values fo r several indicated in Fig. 1 by the dashed (broken) line. In any continuous days, notably at low frequencies. We have case, these heights are o nl y approximate o nes and will tried to o mit such abnormall y hi gh values from the be considered o nl y in a relati ve way, i.e., in general, analysis of monthly values, but the procedure is hi gher the altitude, larger th e temperature. The dots in obviously subjective and valu es, especiall y fo r 245 MHz, may still have co nsiderable pollutio n from burst 3 e mi ssions. Also, it may be noted th at thermal radio .. e mi ssion has two components, i.e. th ermal gyro 0 3000 .. resonance from th ermal plasma trapped in the E 0 magneti c fields over sunspots, and th ermal free-free -"" '" w 2500 .. emi ssio n fro m acti ve regio ns elsewhere. At very high a:: ~ w Q frequencies li ke 15 GHz, the e mi ssio n would be I e ., q;, il 0.. C) ~-=-'--__.b,.t E_~ T RA N S I - 2100 largely free-free, as th e ambient magneti c fie lds are If) o 2000 .. SUN - REG I ON III ACT I VE too weak fo r gyro-resonance. At low frequencies such ot 1Ir ------170 0 I as I GHz, the emission woul d be opticall y-thick 0.. 1500 I" (J () thermal emi ssio n, as gyro-resonan t contri butio ns W ~ > I 0 0. o I f) en would be screened out. At intermediate frequenc ies, co I G 0 ~ C 11 0 .0 both th e processes would contribute. At very low
TE M PERATURE J K atte mpt is made to get a rough idea about the frequency dependence of radi o emi ssion, but results at Fig. l - Tc mperalure (full line) and density (dots) d istri bution o f low frequencies, notabl y at 245 MHz and, to some the average q ui et SUIl . ind icating approximate depths o f various extent, 4 10 MHz would be unreli abl e. solar e illi ssions 10.1:1.20 [The dashed li ne shows the temperature pro fi le above solar acti ve regions (hi gher te mperatures at simil ar Fig ure 2 shows plo ts of th e dai ly values of 2800 hc: ight s). 1 M Hz (1 0. 7 cm) solar radio e mi ssion fl ux (henceforth KANE: VARI ATIONS OF SOLAR INDICES DURING T HE SUNSPOT MAXIM UM YEARS 36 1
Table 2-Dai ly va lues of radio frequency intensities fo r 245-1 5400 MHz during 17-30 Jan. 200 I
Da tes Radi o fre gu e n c~ int e n s it ~ (a rbitr a r~ un its) at fre gu e n c~ (MHz) Janu ary 245 4 10 606 1415 2695 4995 8800 15400
17 24 52 68 128 140 183 289 54 1 18 23 54 75 137 156 197 295 54 1 19 2 1 48 7 1 140 15 5 199 303 549 20 25 48 7 1 145 156 200 300 546 2 1 4 1 55 73 148 155 199 3 10 552 22 60 67 77 159 164 209 320 556 23 52 66 80 167 175 223 327 57 1 24 89 154 9 1 164 185 223 331 552 25 82 88 96 169 188 239 345 580 26 24 57 72 166 175 2 16 340 574 27 5 1 57 82 162 177 2 17 322 534 28 40 59 85 165 195 2 16 3 16 559 29 26 58 8 1 158 169 208 3 17 557 30 28 62 78 162 178 209 3 14 53 1 Mean 42 66 79 155 169 2 10 3 16 553 Std.dev 22 27 8 13 15 14 16 15 SD % 54 4 1 10 8 9 7 5 3
150 300 3 50 DAY NUMBER
Fig. 2-Plots of the dail y va lu es of the 2800 MH z (F lO) solar radio emi ssion flu x fo r 1999, 2000, 200 1 and 2002 (unit 10.22 joul es/sec/sq.m/hertz lEach number has been multiplied by 10 to su ppress the decimal point). The events marked by hori zont al lines were selected for detailed studies.] referred to as FlO) for 1999, 2000, 200 I and a part of pl ots of dail y values for each event fo r all th e solar 2002 (in unit of 10-22 joul es/sec/sq.m/hertz. Each indices included in Table I. number has been multiplied by 10 to suppress the In the first event [Fig. 3(a), day numbers 1-60 of decimal pa in!.). There are considerabl e day-to-day 1999], there were two prominent peaks (average flu ctuati ons, mostl y of solar rotati on ori gin , though locations day 22 and day 46, indicated by vertical th e peak spacin gs deviated considerably from 27 lines) with a spacing of 24 days. All indices had peaks days. For examinati on, three events were chosen within a day or two of these positions. However, the (marked by hori zontal lines), each of 60 continuous relati ve heights of these two peaks were di ffe rent fo r days (day numbers 1-60 of 1999; 200-260 of 1999; different indices. For radio emissions, the second peak \ 80-240 of 2000) and each having two prominent was hi gher. A glaring exception was FlO (2800 peaks. (Many other events could al so be chosen as MHz), which had the second peak smaller, in contrast hav in g two prominent peaks, but onl y these three are to even the nearby radio frequency 2695 MHz, which chosen as a reasonable sample). Figure 3 shows the had the second peak hi gher. This is because the value 362 INDIAN J RADIO & SPACE PHYS, DECEMBER 2004
(b) 1999 (c12000 o 220 240 near earth had peaks diffe rent fro m the solar indices. MHz 245 No data were avail able for EUV.
410 In th e second event [F ig. 3(b), day numbers 200-
606 260 o f 1999], there were two prominent peaks
i4 !5 (average locations day 2 12 and day 240, indicated by
2695 verti cal lines, average spacing 28 days), but onl y fo r rn hi gher radi o frequencies (1 4 15 MHz and higher), and 2BOO th e second peak was lower for 14 15 MHz, hi gher fo r 4995 2695, 2800 MHz onl y and then lower for 4995 and BBOO 15 400 8800 MHz. The EUV (26-34 nm) had both peaks equal. There were no complete data fo r Si III and Ly
PROTON a , but He I, Mg H and the solar fl are index (SF) had
EUV the second peak hi gher, while magnetic fi eld and (2fi-34 ) sunspots had both peaks almost equal. Thus, in ® contrast to the first event, results were not similar fo r G) all parameters in corona or in chromosphere. ® In th e thi rd event [Fi g. 3(c), day numbers 180-240 of 2000], th ere were three prominent peaks, near day numbers 201 and 227. The third peak was mostl y lower th an the first two. But fo r some indices, the first peak was hi gher than the second peak , while for some other parameters, it was the other way round. Thus, the juxtapositions of the second peak with respect to the first peak differed from parameter to parameter with no clear-cut relati onship with any
o 60 200 220240 260 solar region (corona, chromosphere, etc.). T he 19<;19 1999 systematic rati os reported by Donnell y et al.12 are not DAY NUMBEH seen in all events.
Fi g. 3- Plots of the da il y values (arbit ra ry units) of various solar indices fo r 60-day intervals I(a) Day numbers 1-60, 1999, (b) Day 4 Day-to-day changes with temperature in solar numbers 200-260. 1999 and (c) Day numbers 180-240.2000.] atmosphere Lean (} menti oned that emi ssions at the shortest U V of F lO on a singie day, namely 20 Jan. 1999 was wavelength s typicall y ori gin ate mostl y from th e solar abnormall y hi gh (23 1). The nearby values were o nl y atmosphere. Woods et al. 14 mentioned that, in general, 170, and if thi s value is used, th e second peak th ere is a decrease in vari abili ty w ith in creasing becomes hi gher (marked by an additional dashed wavelength , because th e larger wavelengths emerge line), j ust as for 2695 MHz. However, a pollution fro m deeper layers in the solar atmosphere where from burst emi ssions in 2695 M Hz is not rul ed out thermal effects of sunspots and pl ages are relatively completely. For chromospheri c parameters, th e two small. Thus, the vari ability shoul d be larger fo r lower peaks were almost equal, though fo r sunspot number, wavelengths. However, such a pattern is valid onl y th e second peak was sli ghtly hi gher. Di fferent indices fo r the ' background continuum'. For th e vari ous had di fferent relati ve proporti ons of the first and indi vi dual emission lines superposed on th e second peaks with the corona and photosphere hav ing continuum, th e flu xes and their vari abilities are [h e second peak larger, and in between chromosphere known to be very di fferent from th ose of th e having equal peaks. For an earli er example in the AE background continuum. Di fferent wavelength s could E data, Donn ell y et al.12 had reported that th e ratios of ori ginate in the same altitude (or temperature) region the first peak near 9 ov. 1979 to the second peak of th e solar atmosphere and may show si mi lar near 13 Dec. 1979 were 0.95, 1.04, 1. 11 , 1.22, 1. 36 magnitudes of percentage variabilities. Or, similar and 1.54 fo r Ly-a, L y -~ , 304 A, 284 A, 335 A and wavelengths could o ri gin ate from different parts F l O. T he interpl anetary parameters N (number (chromosphere, corona , etc.) and may have different density), V (wind speed) and B (total magnetic field) vari abilities. There is also anoth er complication. KANE: VARI ATIONS O F SOLAR INDICES DURING THE SUNS POT MAXIMUM YEA RS 363
LOGI T - 40 4·5 5-5 6·0 Many wavelength s on glllate fro m mo re th an one t X- RAY 20 (a) AV. AMP. 27- DAYWtWES region. For example, the Ly-a radiati on is formed in 15 1997 -1999 7 10 . the chromosphere and transition region The peak 5 0 emi ssion also depends upon the state of solar activity. Rz • 100 ~M6MHZ MAG F (bl EVENT I 245 For quiet sun, the peak Ly-a emi ssio n is near 40,000 80 141 5 ON 22-35, 1999 K in the lower transition region, while for the plage 60 4995 Fl O 40 He! 606 410 model, it is ncar 70,000 K in the hi gher transition 20 0 10 . • Rz region Thus, wavelength may not necessarily be a 100 MAG F Ie) EVENT II 80 good criteri on to judge the depth in solar atmosphere. ON 46 - 35,1999 o'! GO . On the other hand, temperature would probabl y be a w' 40 Hel fairl y satisfactory indicator of the altitudes as In '"z 20
1999 2000 2001 2002 1999 2000 2001 2002 would fit well if shifted towards smaller J J J AU temperatures (-60,000 K) or larger temperatures f05 (b ) ~H Z 245 45 ~ (-1,000,000 K) (dashed line). ·95 ../ CCMA 1·05 ~ 41 0 F E (viii) The values for 245 MHz (and even 410 MHz in : ~; ~JL1 4 1 5 6 ~ 1·0 event II) are far above the general pattern. This 1·0~~69~ 2695 ~ MA ~~ ~ ~ may have a physical implication, but it was 10 ~FIO ______280 ~ 800 ~AP4995 noticed that many daily values were abnormally 1-0 FE .... large and were probably polluted by individual 1.0 ~ MA 880~ . 9~4 00 - bursts. Some weeding has been done, but was 1·00 JL 15400 .95 ~-RAY probably not enough. 1.0 FE >- 2 . . • _ • . A...... __X-RAY .5 ~OC t:: 0 ~~ -, I PROTO~ FE Thus, the two-humped structure seems to be valid ~ 5 ~v PROT OC FE w 0 EUV 0 ~UV for all events, though the percentage magnitudes may f- __ ~ . . >-..A.. • EUV 1·0 ~ 1·0 ~ ---.rv...... ·8 HP. 1 differ from event to event. As an explanation, two ~.~ ~~ HeI ' : ~ ~_~ possibilities need examination. Can a simple model of 1.00 Mgn .99 / 4 a chromosphere of a uniform temperature of about 10 ·98 ~ MAG ·98 KITT 6 1·0 KITT 1·0 ~ K and an overlaid corona of temperature 10 K, with ·8 ~ MAG ·8 MAG . F MPSI fixed but different scale heights in the two regions and I . O~ M PSI 1.0 ~ 5 CA-K 5 ~---....loO,. ..----a... a pressure balance across the transition region, lead to . EMDX INT· EMDX .9 51 FE 2 ... ~ . )., .. _ SOL 2 a double-humped structure? This needs further I v.jV\J A~.V ~ FLA I ~ exploration. Alternatively, at frequencies near about 3 10 ~ ~~~T ' 0 ~ ·5 ·5 GHz, there will be increasing contribution by gyro ~--'---'-'---' J J J J J resonance which correlates well with sunspot 1999 2000 2001 2002 1999 2000 2001 2002 numbers. This could result into a double-humped MONTHS structure. This too needs further exploration. Fig. 5-Plots of (a) Monthly values and (b) 12-month movin g averages of various solar indices for 1999-2002 (fractional units with respect to the average of 2000-200 I). 5 Plots of monthly values Figure 5(a) shows a plot of the monthly values for not be indicated on the y-axis). The following are 1999- 2002 (a few of these are not mentioned in noteworthy: Table I as their daily values were not available). There are several peaks (shown by dots) in roughly (i) Most of the indices had a maximum near March the same months for all indices, indicating that these 2000. fluctuations are genuine. With 8-9 peaks in -28 (ii) Some indices decreased monotonically months, an average spacing of 3-3.5 months (-100 thereafter, but some had a mll1lmUm near days) is indicated which is smaller than the -155-day January 200 I and either stayed there or started 16 periodicity reported by Rieger et ai. and Lean and rising again thereafter. l7 Brueckner . A correlation analysis indicated the (iii) Some indices did not have a maximum near following: March 2000 and continued to ri se ti II 2001 end. The radio emissions at 1415,2695,2800,4995 and For these, the 12-month moving averages did 8800 MHz were well correlated with each other as not yet show a decline, but monthly values well as with X-rays, EUV, Mg II, surface magnetic showed considerable declines, indicating that the fields (Kitt Peak as well as Mt. Wilson), Ca K index 12-month moving averages mi ght have reached and even sunspots, indicating that the peak-matching a maximum. Data for the next few months was quite good. should settle this issue. However, the correlatio!ls hardly exceeded 0.85, (iv) A correlation analysis indicated that some indicating some dissimilarities. indices were very well intercorrelated (410, 606, Figure 5(b) shows plots of the 12-month moving 1415 MHz with each other; 2695, 2800, 4995 averages (6 months of monthly data of Fig. 5(a) are MHz, Mg n with each other; EUV with Rz), but lost at each end). All values are fractions with respect poorly correlated with some others (2800 MHz to the average level of 2000-2001 (the vertical bar on with EUV or Rz). This is strange, since Rz and the EMDX plot is the scale for EMDX, which could 2800 MHZ are usually reported as having KANE: VARIATIONS OF SOLAR INDICES DURING THE SUNSPOT MAXIMUM YEARS 365
correlation exceeding 0.98. These dissimilarities onwards up to June 2002, but EUV and smoothed l8 are illustrated in detail by Kane . sunspot number have remained steady since Janu ary 2001. Thus, neither FlO nor Mg II have evolved 6 Discussion and conclusions parallel to EUV, turning them unsatisfactory as Comparison of the evolutions of daily and monthly proxies for EUV. Some of the correlations for the 12- values of several solar indices during 1999-2002 monthly values for 1999-2001 are as follows: FlO reveals the following: with Mg II is 0.94; EUV with sunspots is 0.92; but EUV with FlO is only 0.57, and EUV with Mg II is Daily values: only 0.49. Variations of solar radiations in th e UV and EUV bands have important implications for day-to (i) The daily values indicated large day-to-day day and long-term variabilities in the terrestri al fluctuations with peak spacings differing 21 23 atmosphere - and hence need to be estimated considerably from the 27 -day solar rotation accurately. period. (ii) Some individual events with large peak-to trough ranges were examined. Plots of the Acknowledgements percentage increases (trough-to-peak) versus Thanks are due to Helen Coffey and Edward Erwin temperature of the source regions of the various for help in getting data from the NOAA websites, and indices indicate a double-humped structure (low to Dick Donnelly, Thomas Woods, Kent Tobi ska, amplitudes in lower chromosphere, transition Karen Harvey, K K Mahajan, N K Sethi, Atila Oz g u~ region and upper corona; high amplitudes in and Donald McMullin for providing some data upper chromosphere and lower corona), similar privately and for useful discussion and suggestions. to that reported by Kane '5. Thanks are also due to the anonymous referees for their valuable suggestions. This work was partially supported by FNDCT, Brazil, under contract FINEP- Monthly vailles: 537/CT. (i) The monthly values show many peaks. The average spacing is -3.5 months (-100 days). References (ii) In the 12-month moving averages, some indices I Waldmeier M, The sunspot activity in the years /6 / 0-/ 960 reached a maximum near March 2000. Some of (Schulthess & Company AG, Zurich), 1961 . these decreased since then and continue to 2 McKinnon J A, Sunspot IIl1mbers /6/0- / 985 in UAG Report. NOAA Boulder. Colorado, USA,Vol. 95, 1987, p. 11 2. decrease at present, but some reached a 3 Schwabe S H, Astroll Nachr (GermaIlY). 20 Nr. 473 (1 843) minimum near January 2001 and remained 283. steady there, or started increasing again to reach 4 Schwabe S H, Astroll Nachr (Germany.) 21 Nr. 495 ( 1844) a probable maximum near June 2002. Some 234. indices did not have a maximum in March 2000 5 Gaizauskas V, Zwaan C, Harvey K L & Harvey 1 W. and continue to increase till June 2002. Thus, the Astrophys J (USA), 265 (1983) 1056. evolutions of the various solar indices during the 6 Kane R P, Ann Geophys (Frallce), 20 (2002) 741 . sunspot max imum of cycle 23 (1999-2002) are 7 Vernazza 1 E, Avrett E H & Loeser R, Astrophys J (USA), substantially different from each other. Suppl. Ser. 45 (1981) 635. Obviously , the dynamical upheavals in the 8 Woods T N, Tobiska W K, Rottman G 1 & Worden J R, J photosphere reach upper levels of the solar Geophys Res (USA), 105 (2000) 27195. atmosphere with varying intensities. 9 Zirin H,. The Chromosphere in Astrophysics of fh e SII II (Cambridge University Press), 1988. Ch. 7 10 Fontenla J M, White 0 R, Fox P A, Avrett E H & Kuruez R These differences have an important implication for L, Astrophys J (USA), 518 ( 1999) 48. proxy purposes. Since the publication of solar UV and II Kane R P, Vats Hari Om & Sawan! H S. Sol Phys EUV data from AE-E (1977-1981), efforts have been (Netherlands), 201 (2001) 181. made to model the EUV using 2800 MHz flux as a 12 Donnelly R F, Hinteregger H E & Sheath D F, J Geophys proxy. Later, Ly-a, X-rays and Mg II were also Res (USA), 91 ( 1986) 5567. incorporated as proxies (Ref. 19 and references 13 Lean 1, J Geophys Res (USA), 92 (1987) 839. therein). During 2001-2002 [Fig. 5(b)], FlO and Mg II 14 Woods T N ef a/., J Geophys Res (USA), 101 (1996) 954 1. continued to rise considerably from January 2001 15 Kane R P, J Geophys Res (USA). 107 (A 10) (2002) 1298. 366 INDIAN J RADIO & SPACE PHYS, DECEMBER 2004
16 Rieger E, Share G H, Forrest D J, Kanbach G, Reppin C & 20 Vernazza J E. Avrett E H & Loeser R, Astrophys J (USA), Chupp E L. Na/ure (UK). 312 (1984) 623. Suppl. Ser. 30 (1976) I. 17 Lean J L & Brueckner G E, As/raphys J (USA). 337 (1989) 21 Kane R P, Trivedi N B, Tanaka Y. Hajime Y & Pathan B M, 568. Illdial! J Radio & Space Phys. 32 (2003) 25 1. 18 Kane R P, J Ceophys Res (USA), J08 (A I2) (2003) 1455. 22 Kane R P, Illdiall J Radio & Space Phys. 32 (2003) 344. 19 Tobiska W K. Woods T, Eparvier F, Viereck R. Flyod L, Bouwer D, Rottman G & White 0 R. J AIIIIOS & Sol Terr 23 Chandra H, Kov alam S & Vincent R A, Indiwl J Radio & Phys (UK). 62 (2000) J233. Space Ph )'.\'. 3 I (2002) 237.