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Solar Constant, Sunspots and Solar Activity SOLAR CONSTANT, SUNSPOTS AND SOLAR ACTIVITY R.Sumathi¹, R. Samuel Selvaraj² ¹ Department of Physics, Quaid-E-Millath government college (W), Chennai ijcrr Tamil Nadu. Vol 03 issue 11 ²Department of Physics, Presidency College, Chennai, Tamil Nadu Category: Research Received on:08/06/11 E-mail of Corresponding Author: [email protected] Revised on:20/06/11 Accepted on:01/07/11 ABSTRACT This paper deals with study of sunspot numbers and solar energy since 1755. Number of sunspots and solar energy varies for each solar cycle. The duration of solar cycle is from 9 to 11 years. It varies every time. Solar cycle is the time interval from a sunspot minimum to the next sunspot minimum. ______________________________________________________________________ Keywords: Solar Constant, Sunspot The solar constant includes all types of solar Number and Solar activity radiation, not just the visible light. It is measured by satellite to be roughly 1,366 INTRODUCTION watts per square meter (W/m²).The actual Solar constant is an average quantity of direct solar irradiance at the top of the solar energy at normal incidence received by atmosphere fluctuates by about 6.9% during the earth‘s atmosphere from the sun. It is a year (from 1,412 W/m² in early January to about2 calories per minute incident on each 1,321 W/m² in early July). When solar square centimeter of the upper atmosphere. irradiance is measured on the outer surface The actual value of the energy varies with of Earth's atmosphere, the measurements several factors. The most important factor is can be adjusted using the inverse square law the earth‘s distance from the Sun which to infer the magnitude of solar irradiance at changes from surface to surface because of one AU and deduce the solar constant. the earth‘s elliptical orbit. For computing the varying distance from the Sun, and typically value of solar constant, astronomical unit or by much less than one part per thousand average earth-sun distance is used. from day to day. Thus, for the whole Earth In space, solar radiation is practically (which has a cross section of constant; on earth it varies with the time of 127,400,000 km²), the power is day and year as well as with the latitude and 1.740×1017 W, plus or minus 3.5%. The weather. The maximum value on earth is solar constant does not remain constant over between 0.8 and 1.0 kW / m². The average long periods of time but over a year varies annual amount of isolation varies between much less than the variation of direct solar 950 and 1100 kWh / m², depending on the irradiance at the top of the atmosphere region. arising from the ellipticity of the Earth's 36 International Journal of Current Research and Review www.ijcrr.com Vol. 03 issue 11 November 2011 orbit. The approximate average value cited Imager instrument on SOHO, shows these 1,366 W/m², is equivalent to 1.96 calories changes to be small, about 0.001%. per minute per square centimeter, or 1.96 The rise and fall of solar activity follows an langleys (Ly) per minute. approximately 11 year cycle. The solar The sunspots vary in number, size, and activity is composed of sunspots, flares and duration . There may be¹ up to 20 or 30 coronal mass ejection. spots at any one time .The sunspot may be in size between 1000 and 2000 km diameter MATERIALS AND METHODS with a life cycle from Data for each solar cycle, its period and hours to months. Each sunspots consists of maximum number of sunspots in each cycles two regions a dark central portion of sun have been taken from spot is umbra at a temperature of around http://www.ngdc.noaa.gov/stp/solar/SSN/sss 4000°c and a surrounding lighter portion of .html. Using the data ,calculated the total sun spot is radiance from the sun varies with sunspot penumbra at a temperature of about 5000°c . number using the relationship: E=1366.82+(7.71x10‾³x R) W/m² (1) The average number of spots and their mean area fluctuate over time with a mean period Where E is the solar energy reaching the of about 11.3 years. As the sunspot cycle Earth and R is the number of sunspots. develops the older spots fade away and new more numerous spots appear at lower Observation are recorded in a graph with latitudes. Sunspots activity has been solar cycle(X-axis),SSN,Solar energy(Y- measured by using the wolf num ber for axis). Solar cycle aboutn300 years. This index (also known as and maximum sunspot number are given the Zurich number) uses both the number of Table I. From March 1755 to October 2008 sunspots and the number of groups of there were 23 solar cycles. sunspots to compensate for variations in measurement. A 2003 study by IIya The time interval from a sunspot minimum Usoskin found that sunspots had been more to the next sunspot minimum is called a frequent since the 1940s than in the previous solar cycle. The period from 1755 to 1766 1150 years.² has been chosen as solar cycle 1. So far, we Relationships between sunspots and solar have 23 solar cycles. luminosity are to know to exist since the historical sunspots area record began in the The features of solar cycles are given in the 17th century 7. The correlations are now table 1. known to exist with decreases on luminosity caused by sunspots (generally <0.3%) and For the maximum sunspot number the increases (generally < + 0.05%) caused both corresponding solar energy was calculated by facule that are associated with active using Eq.(1) and their values are given in region as well as the magnetically active Table 2. ‗bright net Work³. Variations in the solar diameter might cause variations in output, but recent work, from Michelson Doppler 37 International Journal of Current Research and Review www.ijcrr.com Vol. 03 issue 11 November 2011 TABLE I: List of solar cycles tracked since 1755⁵⁶⁷ Cycle Started Finished Duration(years) Maximum (monthly SSN) 1 March 1755 June 1766 11.25 Jun 1761 (86.5) 2 June 1766 June 1775 9.00 Sep.1769(115.8) 3 June 1775 September 1784 9.25 May1778(158.5) 4 September 1784 May 1798 13.66 Feb 1788(142) 5 May 1798 December 1810 12.58 Feb1708(49.2) 6 December 1810 May 1823 12.42 Apr.1816(48.7) 7 May 1823 November 1833 10.50 Nov.1829(71.7) 8 November 1833 July 1843 9.75 Mar.1837(146.9) 9 July 1843 December 1855 12.42 Feb.1848(131.6) 10 December 1855 March 1867 11.25 Feb.1860(97.9) 11 March 1867 December 1878 11.75 Aug.1870(140.5) 12 December 1878 March 1890 11.25 Dec.1883(74.6) 13 March 1890 February 1902 11.92 Jan 1894 (87.9) 14 February 1902 August 1913 12.50 Feb 1906 (64.2) 15 August 1913 August 1923 10.00 Aug 1917 (105.4) 16 August 1923 September 1933 10.08 Apr 1928( 78.1) 17 September 1933 February 1944 10.42 Apr1937(119.2) 18 February 1944 April 1954 10.17 May 1947 (151.8) 19 April 1954 October 1964 10.50 Mar 1958 (201.3) 20 October 1964 June 1976 11.67 Nov1968(110.6) 21 June 1976 September 1986 10.25 Dec 1979(164.5) 22 September 1986 May 1996 9.67 1Jul 1989(158.5) 23 May 1996 October 2008 12.42 Mar 2000(120.8) 38 International Journal of Current Research and Review www.ijcrr.com Vol. 03 issue 11 November 2011 Table II Observed sunspot Number and calculated Solar Energy SOLAR CYCLE MAX.SUNSPOT NO. SOLAR ENERGY 1 86.5 1367.487 2 115.8 1367.713 3 158.5 1368.042 4 142 1367.919 5 49.2 1367.199 6 48.7 1367.195 7 71.7 1367.373 8 146.9 1367.953 9 131.6 1367.835 10 97.9 1367.575 11 140.5 1367.903 12 74.6 1367.395 13 87.9 1367.498 14 64.2 1367.315 15 105.4 1367.633 16 78.1 1367.422 17 119.2 1367.739 18 151.8 1367.99 19 201.3 1368.372 20 110.6 1367.673 21 164.5 1368.088 22 158.1 1368.039 23 120.8 1367.751 39 International Journal of Current Research and Review www.ijcrr.com Vol. 03 issue 11 November 2011 RESULT It is found that solar energy value varies REFERENCES with sunspot numbers. From the study of 1. Burrogh ―Extraterrestrial influences‖, 23 solar cycle,19th cycle had maximum Cambridge,(121 sunspots and corresponding solar energy is 2. Usoskin,Ilya G,solanki,SamiK, higher compared to other cycles. This Schtissler,Manfred,Mursula,Kalevi,Alan study can be useful for climate analysis. ko,Katja(2003),‖AMillennium Scale Sunspot Number Reconstruction. DISCUSSION 3. Willson RC Gulkis s.Janssen M.Hudon The variation of solar energy in each cycle H.S. Chapman GA (February is less than 1% of the average solar energy 1981),Observations of solar irrandiance for 23 solar cycles hence the variation is Variability, Science 211 (4483) 700-2 marginal. Though it seems marginal even a doi:10.1126/science 211448.700PMID change of 0.5% in TSI can affect the 17776650 earth‘s climate through following feedback 4. Burrogh, Weather cycles real or mechanism. imaginary, Cambridge,141(1992). 1. Increased absorption of solar UV 5. Kanw, R.P.
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