Categories
AGW Omniclimate

Solar Images Archive and the Identification of Sunspots

2008 08 22 K
A sunspot, or not a sunspot?

2nd UPDATE Sep 5 – Image issues fixed. Or so I believe…

1st UPDATE Sep 5 – There are issues with the OAR server and some images are not showing properly. I will try again to source those images, or switch to MLSO’s.

Who would have thought that counting sunspots were such an opinion-based activity, near a minimum in solar activity?

After the back-and-forth revelations about August 2008 being spotless for the whole of humanity apart from one observer in Catania, Italy, whose keen eye has made both SIDC and NOAA change their mind, a friend pointed me in the direction of two web-based PSPT Solar Images Archives, one from 1996, beyond the usual SOHO stuff.

And an analysis of those archives reveals not only how different can the Sun appear at different wavelengths (a trivial concept, after all) but also how what looks like a sunspot in one image may be pretty much invisible in another.

But if some sunspots appear to be much easier to identify if the “correct” filters are used during observation, wouldn’t a more precise definition of “sunspot” be needed? For example “it appears in at least 3 filters” or “it can be seen in the SOHO MDI channel” or whatever else.

Otherwise when the Sun will wake up later this year or next, the count of sunspots is going to be truly enormous, and comparisons with the past impossible.

============

What is the PSPT?

The Precision Solar Photometric Telescope (PSPT) [by the National Science Foundation (NSF)] produces seeing-limited full-disk digital (2048×2048) images in the blue continuum (409.4nm, FWHM 0.3nm), red continuum (607.1nm, FWHM 0.5nm), CaII K (393.4nm, FWHM 0.3nm) […] with an unprecedented 0.1% pixel-to-pixel relative photometric precision. […]
The National Solar Observatory (NSO) designed and built three PSPT units, a prototype which is currently in operation at the Osservatorio Astronomico di Roma (OAR), and two primaries for installation at NSO Sac Peak and Mauna Loa Solar Observatory (MLSO).

OAR provides “full disc images of the Sun from 1996” to today. The corresponding MLSO query page is hosted by the University of Colorado and starts in 2005.

====

A few words on the available filters:

1. K (393.3nm)

Light at this wavelength is extremely faint but when the brilliant photospheric emissions are filtered out, the Ca II K line provides important information on the large-scale magnetic field structure in the chromosphere.

Because the blue Calcium K Line (393.3 nm) is sensitive to magnetic fields, magnetically active structures show up in high contrast against the surrounding chromosphere. Places where moderate magnetic fields exist show up bright whereas images of high magnetic fields are dark.

2. B (409.4nm “blue continuum”)
3. R (607.2nm “red continuum”)

The difference between those images can be used to identify sunspots.

4. C (430.6nm, the so-called G-band)

Many observations in the G-band are done in order to investigate the photospheric bright points and the connected magnetic elements, making use of the increased contrast of these structures

In the G-band the photospheric faculae show high contrast even near the solar disk center

5. G (535.7nm)

Used because free of Fraunhofer lines, this filter sits at the top of solar irradiance. It is the band used for measurements of the Sun’s diameter from the ground

 

===

Let’s look now at the Aug 21-22 situation, when the only activity of the month has been reported. Well, there is something going on, but it’s only apparent in the K filter.

Remember, the K filter takes very faint light. Humans looking in the normal visible bands (B, R and most of all G) cannot see anything at all.

2008 08 21 K
2008 08 21 K
2008 08 22 K
2008 08 22 K
2008 08 21 B
2008 08 21 B
2008 08 22 B
2008 08 22 B
2008 08 21 R
2008 08 21 R
2008 08 22 C
2008 08 22 C
2008 08 21 C
2008 08 21 C
2008 08 21 G
2008 08 21 G
2008 08 22 G
2008 08 22 G

===

Following are the pictures from June 20, when last numbered spot #1000 has been seen or maybe not.

Now there is something to look at in the B, R and G filters, but once again it’s only K that reveals the thing whole.

2008 06 20 K
2008 06 20 K
2008 06 20 B
2008 06 20 B
2008 06 20 R
2008 06 20 R
2008 06 20 C
2008 06 20 C
2008 06 20 G
2008 06 20 G

===

As a way of comparison, look at the pictures from Jul 14, 2005, when sunspots were aplenty, in all filters.

2005 07 14 K
2005 07 14 K
2005 07 14 B
2005 07 14 B
2005 07 14 R
2005 07 14 R
Categories
Climate Change Data Global Warming Omniclimate Sun

Actually, It's 71 Days Without A Sunspot

READ ON FOR THE SPOT-THE-SPOT CHALLENGE

Confusion reigns tonight on the date the last sunspot has been seen. Until yesterday, it had been July 18 with sunspot #1000.

But all of a sudden yesterday, a “pore” with a date of Aug 21 has been classified as “sunspot” by the SIDC and then the NOAA. Trouble is, nobody seems to have seen it apart from one observer in Catania, Italy.

Probably, as per Leif Svalgaard’s comment at Anthony Watt’s blog:

really, no spots or one tiny one doesn’t make any difference

Also, from another of Svalgaard’s comments

There are indications that the modern counts are too high with possible repercussions for reconstructions of TSI and the climate debate.

But if that’s true, then I can contend that the current spotless period is 71 days, starting with the end of sunspot #999 on June 23, 2008. And continuing to this day.

That makes the current spotless period the second longest ever (behind the 92 days of Apr 8 to Jul 8, 1913).

===========

Sunspot #1000 in fact, was likely no “proper sunspot” at all. By that I mean a sunspot that would not have been spotted in the past, given its extremely tiny size.

The SOHO MDI archive may show something but only if the observer knows where to look (no I will not give clues). Chances are, none would have spotted it in 1913 either.

AND NOW FOR THE SPOT-THE-SPOT CHALLENGE: I am posting the July 17-20 series (remember, sunspot #1000 has been reported for July 18-20…good luck with finding it!):

(I RECOMMEND CLEANING YOUR DISPLAY FIRST…)

SOHO Jul 17
SOHO Jul 17
SOHO Jul 18
SOHO Jul 18
SOHO Jul 19
SOHO Jul 19
SOHO Jul 20
SOHO Jul 20

===========

(spoiler ahead)

 

 

Here’s the one and only one picture of sunspot #1000 I have found on the internet, in an Australian internet forum. Its author clarifies, though:

The spot is not as big as shown, just a product of the poor seeing/focus

Sunspot #1000
Sunspot #1000

Just compare all the above with the pictures from Jun 21, where a proper sunspot is visible indeed:

SOHO Jun 21
SOHO Jun 21

How many pores and microspots were flickering in and out of existence during the Maunder Minimum, one wonders…

Categories
Data Omniclimate Science

How Is Solar Cycle 24 Doing?

Spotless Periods
Spotless Periods

This page about solar cycle 24 is in Italian but should be easy to understand. Here the rankings of cycle 24 so far, since 1849:

(a) current number of spotless days: 37 (17th longest ever, and counting)

(b) number of spotless periods longer than 20 days: 5 (5th)

(c) number of spotless days: 415 (9th)

Actually, the “spots” that have been claimed for around July 19, didn’t look like sunspots to me at all. Without them, the number of spotless days is 64, that is the third ever.