4 research outputs found
Hemispheric sunspot numbers 1874--2020
We create a continuous series of daily and monthly hemispheric sunspot
numbers (HSNs) from 1874 to 2020, which will be continuously expanded in the
future with the HSNs provided by SILSO. Based on the available daily
measurements of hemispheric sunspot areas from 1874 to 2016 from Greenwich
Royal Observatory and NOAA, we derive the relative fractions of the northern
and southern activity. These fractions are applied to the international sunspot
number (ISN) to derive the HSNs. This method and obtained data are validated
against published HSNs for the period 1945--2020. We provide a continuous data
series and catalogue of daily, monthly mean, and 13-month smoothed monthly mean
HSNs for the time range 1874--2020 that are consistent with the newly
calibrated ISN. Validation of the reconstructed HSNs against the direct data
available since 1945 reveals a high level of consistency, with a correlation of
r=0.94 (0.97) for the daily (monthly) data. The cumulative hemispheric
asymmetries for cycles 12-24 give a mean value of 16%, with no obvious pattern
in north-south predominance over the cycle evolution. The strongest asymmetry
occurs for cycle no. 19, in which the northern hemisphere shows a cumulated
predominance of 42%. The phase shift between the peaks of solar activity in the
two hemispheres may be up to 28 months, with a mean absolute value of 16.4
months. The phase shifts reveal an overall asymmetry of the northern hemisphere
reaching its cycle maximum earlier (in 10 out of 13 cases). Relating the ISN
and HSN peak growth rates during the cycle rise phase with the cycle amplitude
reveals higher correlations when considering the two hemispheres individually,
with r = 0.9. Our findings demonstrate that empirical solar cycle prediction
methods can be improved by investigating the solar cycle dynamics in terms of
the hemispheric sunspot numbers.Comment: Accepted by Astron. Astrophys. 12 page
Maximal growth rate of the ascending phase of a sunspot cycle for predicting its amplitude
Forecasting the solar cycle amplitude is important for a better understanding
of the solar dynamo as well as for many space weather applications. We
demonstrated a steady relationship between the maximal growth rate of sunspot
activity in the ascending phase of a cycle and the subsequent cycle amplitude
on the basis of four data sets of solar activity indices: total sunspot
numbers, hemispheric sunspot numbers from the new catalogue from 1874 onwards,
total sunspot areas, and hemispheric sunspot areas. For all the data sets, a
linear regression based on the maximal growth rate precursor shows a
significant correlation. Validation of predictions for cycles 1-24 shows high
correlations between the true and predicted cycle amplitudes reaching r = 0.93
for the total sunspot numbers. The lead time of the predictions varies from 2
to 49 months, with a mean value of 21 months. Furthermore, we demonstrated that
the sum of maximal growth rate indicators determined separately for the north
and the south hemispheric sunspot numbers provides more accurate predictions
than that using total sunspot numbers. The advantages reach 27% and 11% on
average in terms of rms and correlation coefficient, respectively. The superior
performance is also confirmed with hemispheric sunspot areas with respect to
total sunspot areas. The maximal growth rate of sunspot activity in the
ascending phase of a solar cycle serves as a reliable precursor of the
subsequent cycle amplitude. Furthermore, our findings provide a strong
foundation for supporting regular monitoring, recording, and predictions of
solar activity with hemispheric sunspot data, which capture the asymmetric
behaviour of the solar activity and solar magnetic field and enhance solar
cycle prediction methods.Comment: 11 pages, 11 figures, accepted for publication in the Astronomy &
Astrophysic
An analysis of the solar differential rotation from the Kanzelhoehe sunspot drawings
We present here the results of the behaviour of the solar differential rotation during solar cycles no. 20 and no. 22, derived from Kanzelhoehe sunspot drawings (Kanzelhoehe Observatory for Solar and Environmental Research, University of Graz, Austria).
The positions of sunspot groups were determined using a special software Sungrabber. Sunspot groups were identified with the help of the Greenwich Photoheliographic Results (GPR) and Debrecen Photoheliographic Data (DPD) databases, covering solar cycles no. 20 and no. 22, respectively. In order to calculate the sidereal angular rotation rate ω and subsequently solar rotation parameters A and B we used two procedures: a) daily motion of sunspot groups and b) linear least-square fit from the function CMD(t) for each tracer, where CMD denotes the Central Meridian Distance.
The sample was limited to ±58º in CMD in order to avoid solar limb effects. We mainly investigated velocity patterns depending on the solar cycle phase and latitude
An analysis of the solar differential rotation from the Kanzelhoehe sunspot drawings
We present here the results of the behaviour of the solar differential rotation during solar cycles no. 20 and no. 22, derived from Kanzelhoehe sunspot drawings (Kanzelhoehe Observatory for Solar and Environmental Research, University of Graz, Austria).
The positions of sunspot groups were determined using a special software Sungrabber. Sunspot groups were identified with the help of the Greenwich Photoheliographic Results (GPR) and Debrecen Photoheliographic Data (DPD) databases, covering solar cycles no. 20 and no. 22, respectively. In order to calculate the sidereal angular rotation rate ω and subsequently solar rotation parameters A and B we used two procedures: a) daily motion of sunspot groups and b) linear least-square fit from the function CMD(t) for each tracer, where CMD denotes the Central Meridian Distance.
The sample was limited to ±58º in CMD in order to avoid solar limb effects. We mainly investigated velocity patterns depending on the solar cycle phase and latitude