Polar Network Index as a magnetic proxy for the solar cycle studies Priyal, Muthu, Karak, Bidya Binay, Munoz-Jaramillo, Andres, Ravindra, B., Choudhuri, Arnab Rai & Singh, Jagdev Dipankar Banerjee

Kodaikanal Data Archive The synoptic data taken in the Ca II K spectral line with spectroheliographs at KKL (1907 to 1999), at MWO (1915 to 1985) and NSO (1963 to 2002). Ermolli et al.: 2009 evaluated the image quality and contents of three digitized Ca II K spectroheliogram time series of the Arcetri, Kodaikanal, and Mt Wilson photographic archives and remarked that Kodaikanal have consistency Newly digitized data of KKL is hosted at

Precursor Predictions Precursor techniques use aspects of the Sun and solar activity prior to the start of a cycle to predict the size of the next cycle. The two leading contenders are: 1) geomagnetic activity from high-speed solar wind streams prior to cycle minimum and 2) polar field strength near cycle minimum. Magnetic field data exists for three cycles only Geomagnetic Prediction ~ 160 ± 25 (Hathaway & Wilson 2006) Polar Field Prediction ~ 75 ± 8 (Svalgaard, Cliver, Kamide 2005)

Munoz-Jaramillo et al. 2012, calibrated a century of MWO facular observations using magnetic data from WSO and MDI Polar faculae data is a good proxy of the evolution of the polar fields. Correlations between polar flux at minimum and the amplitude of the cycle.

Hinode observation showed that the magnetic field in the solar polar region are of isolated, patch-like shape and broadly distributed in the entire polar area. They are also very small and have short life compared to the sunspot.

Association of Polar network Bright elements and magnetic patches The longitudinal flux density magnetograms, also known as stokes V/I magnetograms, were obtained using Na I D line of Narrow Band Filter Imager. Longitudinal magnetograms give location, polarity and a crude estimate of fux of magnetic field components along the line of sight. 3 Sigma contours from Broad Band Filtergram images in Ca II H band

Ca – K images from Kodaikanal We expect the spatial intermittency of the magnetic field to persist even at the chromospheric level.

Scatter plot of KKL PNI values with WSO polar field measurements for the period 1976–1990. Red symbols correspond to the solar minima.

A correlation plot between the strengths of solar cycles and the PNI values at the preceding minima.

The dashed lines show the theoretical sunspot numbers (blue and red corresponding to the northern and the southern hemispheres). The theoretical solar cycle is obtained by first considering the yearly number of eruptions and then smoothing it. The solid lines show the observed sunspot area data (blue for north and red for south).

The polar field at the sunspot minimum appears to be the best predictor for the strength of the next cycle. Since reliable direct measurements of the polar field exist only from 1970s, reconstructing its history at earlier times has become a major challenge in solar research. Our newly digitized Ca-K data at the Kodaikanal archive allow us to identify small features even in the polar region with low contrast. Using an automated thresholding method, we have developed a completely new proxy (PNI) for the Sun's polar field and created a PNI index time series. We then combine it with MWO polar flux measurements in order to obtain a calibration factor which allows us to estimate the polar fields for a period over which direct magnetic field measurements are not available.

Finally we use this newly derived proxy of the polar field as the input in a flux transport dynamo model. We find that it reproduces the Sun's magnetic behavior for the past one century reasonably well. We believe that our data will provide a new tool to understand and model the solar magnetic cycles in past.

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17 Combining Polar Faculae and Sunspot Areas can also give HMF B Andrés Muñoz-Jaramillo, 2012 MDI Threshold Filter Counting Polar Faculae