Temporal and Latitudinal Variation in Penumbra-Umbra Ratios of the Sunspots: Analyses of RGO, Kodaikanal and Debrecen Databases

Abstract

We study the latitudinal distribution and temporal evolution of the sunspot penumbra-umbra ratio ($q$ q ) for the even and odd Solar Cycles 12 – 24 of RGO sunspot groups, SC21 – SC24 of Debrecen sunspot groups and Kodaikanal sunspot dataset for SC16 – SC24. We find that RGO even (odd) Cycles have $q$ q -values 5.20 (4.75), Kodaikanal even (odd) cycles have $q$ q -values 5.27 (5.43), and Debrecen cycles have $q$ q -value 5.74 on the average.We also show that $q$ q is at its lowest around the Equator of the Sun and increases towards higher latitudes having maximum values at about 10 – 25 degrees. This is understandable because smaller sunspots and groups locate nearer to the Equator and have smaller $q$ q -values than larger sunspots and groups, which maximize at about 10 – 20 degrees at both hemispheres. The error limits are very wide, and, thus, the confidence in this result is somewhat vague.For the Debrecen dataset, we find a deep valley in the temporal $q$ q -values before the middle of the cycle. We show that this exists simultaneously with the Gnevyshev gap (GG) in the graph of the total and umbral areas of the large sunspot groups. Other databases do not show GG in their $q$ q -graphs, although GG exists in their temporal total area and umbral area.

Temporal and Periodic Analysis of Penumbra-Umbra Ratio for the Last Four Solar Cycles

“…This result is in accordance with the observations made by Jha, Mandal, and Banerjee (2019) with Kodaikanal data set. In both the types of spots we have detected some decrease in q value which may be related with the GG as indicated by Takalo (2023). We have further pointed out that 13-month moving average value of q exhibit 11-year periodic nature like other sunspot indices.…”

“…From the above-mentioned graphs, it is clear that q avg does not exhibit any particular trend in any of the hemispheres as well as the full solar disk and hence we therefore may conclude that this ratio is independent of the latitude distribution of a spot (Antalová, 1971;Hathaway, 2013;Jha, Mandal, and Banerjee, 2019;Hou et al, 2022;Takalo, 2023).…”

“…the relation of q 1 to both S and t is clearly nonlinear. Recently, Takalo (2023) studied the penumbra-umbra ratio utilizing the data of RGO, Kodaikanal and Debrecen observatory and noticed deep valleys in the temporal evolution of penumbra to umbra area ratio only in the Debrecen time series.…”