Sunspots are regions on the Sun's surface which appear noticeably darker than
the surrounding area. The average temperature of the sun is approximately
5500deg Celsius, wheras on a sunspot the temperature is significantly lower
but still only go as low as roughly 3500deg C. Sunspots come in a great
variety of sizes on average, approximately 50000 miles in diameter (median).
They are believed to be caused by activity in the Sun's very powerful
magnetic field and more and larger ones are present during the solar maximum,
the peak of magnetic activity during the solar cycle, which generally lasts
11 years, and large flares and phenomena like Coronal mass ejection.

Our project was about finding patterns in the changes of sunspots appearence
on the sun during the solar cycle. So we analysed at what latitude, on the
sun, the sunspot appeared at over a large number of days in particurlarly
analysing it over the solar cycle shown (which lasted a bit longer than
usual, 12.6 years) to see if some sort of variations occurred and seeing if
those found were of any significance.

We used sunspot latitude verus time (fig. 1) between 1995 to 2015, and
applied Fourier transformation(FT) algorithm to find most probable time
periods. In order to apply this method we used 'Wavelet' analysis code. The
power of the output gives maximum probability

We studied a sample time series of a stellar flare. Here we see a long term
trend in the data because of the flare and we wanted to investigate the short
term periods. The First step before applying FT was to detrend the data then
we applied the same method to find a power spectrum. In this case confidence
or significance levels corresponding to various time periods.

We focussed on short term appearences of the sunspots. We first noticed the
trend along ~9.5 years. So we decided to study variations within that time
frame taking northern and southern hemisphere separately. But we found that
it was skewing the data. So we tried the FT over average length of the Solar
cycle (SC). We still found that the data didnt provide any meaningful
results.

We then found out that this particular SC was for 12.6 years, and performed
wavelet analysis on the data. This showed periodicities at 30 days, 60 days
and 100 days. But since we were interested in short term variation we then
filtered the analysis for 30 days and 60 days. At 30 days we see that the
leading hemisphere is lagging at 60 days. This is because the emergence of
Sunspots is blocked by already present layer of dense magnetic fluxes. Thus
new sunpots would appear later in one hemisphere than the other. This affects
the dynamo process of the SC, and leads to asymmetries. These asymmetries may
lead to weaker SCs.

Upon applying the similar wavelet analysis. We find that there are possible
periodicity at 40s (90 to 100% confidence). We discussed causes of these
periodicities. These could be due to the following : 1.) Planets - When
planet goes in front of the parent star. But this would take at least
days. 2.) Sunspots - Assuming the star is Sunlike, the we would expect
sunpots to vary every 30 days. Thus this cannot be possible cause. 3.) Other
eruptions like Coronal mass ejections (CMEs), prominences and so on. These
would last for few days again. So we rule this out. 4.) Flares - These would
last for days but we see variations in short periods of time. These variations
could be due to fluctuating plasma during the eruption. As this plasma is
along a flux tube, such periodicities can be related to high-frequency waves.

Last Revised: 2016 August 3rd |