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J/ApJ/793/L4   Polar network index for the solar cycle studies   (Priyal+, 2014)

Polar network index as a magnetic proxy for the solar cycle studies. Priyal M., Banerjee D., Karak B.B., Munoz-Jaramillo A., Ravindra B., Choudhuri A.R., Singh J. <Astrophys. J., 793, L4 (2014)> =2014ApJ...793L...4P (SIMBAD/NED BibCode)
ADC_Keywords: Sun ; Magnetic fields ; Solar system Keywords: magnetic fields - Sun: activity - Sun: faculae, plages Abstract: The Sun has a polar magnetic field which oscillates with the 11 yr sunspot cycle. This polar magnetic field is an important component of the dynamo process which operates in the solar convection zone and produces the sunspot cycle. We have direct systematic measurements of the Sun's polar magnetic field only from about the mid-1970s. There are, however, indirect proxies which give us information about this field at earlier times. The Ca-K spectroheliograms taken at the Kodaikanal Solar Observatory during 1904-2007 have now been digitized with 4kx4k CCD and have higher resolution (∼0.86 arcsec) than the other available historical data sets. From these Ca-K spectroheliograms, we have developed a completely new proxy (polar network index, hereafter PNI) for the Sun's polar magnetic field. We calculate PNI from the digitized images using an automated algorithm and calibrate our measured PNI against the polar field as measured by the Wilcox Solar Observatory for the period 1976-1990. This calibration allows us to estimate the polar fields for the earlier period up to 1904. The dynamo calculations performed with this proxy as input data reproduce reasonably well the Sun's magnetic behavior for the past century. Description: The spatial resolution of the Ca K spectroheliograms taken at Kodaikanal (hereafter KKL) is about 2 arcsec and the exit slit of the spectroheliograph yields a spectral window of 0.5 Å centered at the Ca-K line at 3933.67 Å. Ermoli et al. (2009ApJ...698.1000E) pointed out that the Kodaikanal archive hosts the longest homogeneous record, with fewer variations in spatial resolution. The earlier version of the 8 bit data at Kodaikanal is sufficient to study those plage area with high intensity contrast, but does not provide the required photometric accuracy to properly identify the network structures because of the small intensity contrast of these features. Therefore, we have designed and developed two digitizer units, using a 1 m labsphere with an exit port of 350 mm which provides a stable and uniform source of light with less than 1% variation from the center to the edge of the light source. The CCD camera with 4kx4k format, a pixel size of 15 u square, and a 16 bit read out, operating at temperature of -100°C, was used to digitize the images. The Ca-K network can be clearly seen because of the high spatial resolution of digitization (0.86 arcsec). File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file fig2.dat 87 14 Scatter plot of KKL PNI values with the Wilcox Solar Observatory (WSO) polar field measurements for the period of 1977-1990. fig3ab.dat 61 82 PNI and MWO facular counts for the years 1909-1990. fig3c.dat 25 8 A correlation plot between the strengths of solar cycles and the PNI values at the preceding minima. fig4.dat 57 8 PNI asymmetry of the nth cycle minimum phase is plotted against the sunspot area asymmetry of the (n+1)th cycle.
See also: J/ApJS/169/439 : Models of solar magnetic structures (Socas-Navarro, 2007) J/A+A/539/A13 : Solar bipolar magnetic fields (Yamamoto, 2012) J/ApJ/752/126 : Modeling the magnetic field in the solar corona (Yamamoto+, 2012) Byte-by-byte Description of file: fig2.dat
Bytes Format Units Label Explanations
1- 4 I4 yr Obs.Y Year of the observation 5 A1 --- f_Obs.Y [m] Flag on Obs.Y (1) 7- 15 F9.3 --- KKL-PNI-N KKL Polar Network Index North 17- 23 F7.3 --- e_KKL-PNI-N Error in KKL-PNI-N 25- 32 F8.3 --- KKL-PNI-S KKL Polar Network Index South 34- 39 F6.3 --- e_KKL-PNI-S Error in KKL-PNI-S 41- 51 F11.8 --- WSO-PF-N WSO Polar Network Index North 53- 63 F11.9 --- e_WSO-PF-N Error in WSO-PF-N 65- 75 F11.8 --- WSO-PF-S WSO Polar Network Index South 77- 87 F11.9 --- e_WSO-PF-S Error in WSO-PF-S
Note (1): Flag as follows: m = Indicates a solar minimum year, red symbols in the figure.
Byte-by-byte Description of file: fig3ab.dat
Bytes Format Units Label Explanations
1- 4 I4 yr Obs.Y Year of the observation 6- 14 F9.3 --- KKL-N KKL Polar Network Index North 16- 24 F9.3 --- KKL-S KKL Polar Network Index South 26- 34 F9.5 --- MWO-N MWO polar facular count North 36- 43 F8.4 --- MWO-S ? MWO polar facular count South (1) 45- 52 F8.3 --- SA-N Northern hemisphere sunspot area 54- 61 F8.3 --- SA-S Southern hemisphere sunspot area
Note (1): Blank values indicate NaN values.
Byte-by-byte Description of file: fig3c.dat
Bytes Format Units Label Explanations
1- 6 F6.1 yr Obs.Y Year of the solar minima (1) 8- 12 F5.1 --- Rmax Maximum sunspot number of the cycle n+1 14- 22 F9.4 --- PNI KKL Polar Network Index value at end of cycle n 24- 25 I2 --- Cycle [15/22] Solar cycle number
Note (1): The last data point corresponding to solar cycle 22 was not included in the figure as the analysis was restricted up to 1990 and cycle 22 includes the years 1985-1995.
Byte-by-byte Description of file: fig4.dat
Bytes Format Units Label Explanations
1- 2 I2 --- Cycle [15/22] Solar cycle number 4- 11 F8.4 --- SA-N Northern hemisphere sunspot area 13- 20 F8.4 --- SA-S Southern hemisphere sunspot area 22- 29 F8.5 --- SAA Sunspot area asymmetry (1) 31- 39 F9.4 --- KKL-PNI-N ? KKL Polar Network Index North 41- 48 F8.3 --- KKL-PNI-S ? KKL Polar Network Index South 50- 57 F8.5 --- KKL-A ? KKL Polar Network Index asymmetry (2)
Note (1): Calculated as (SA-N - SA-S)/(SA-N + SA-S). Note (2): Calculated as (KKL-PNI-N - KKL-PNI-S)/(KKL-PNI-N + KKL-PNI-S).
History: From electronic version of the journal
(End) Prepared by [AAS], Tiphaine Pouvreau [CDS] 21-Apr-2017
The document above follows the rules of the Standard Description for Astronomical Catalogues.From this documentation it is possible to generate f77 program to load files into arrays or line by line

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