Recent Reading

If you hadn't noticed last time I wrote about my reading, I enjoy reading old books, and books about old things.  One of the interesting, to me, things about math/science/engineering is that it is incremental.  Each generation builds on what the preceding generations learned or accomplished.  Related truth is that I can read some of the best work from all people, across all of time.  Books are my time machine.

Richard J. Gillings, Mathematics in the Time of the Pharoahs, Dover Books. 

Ed. T. L. Heath, The Works of Archimedes, Dover Books.

Tacitus, The Agricola and the Germania, Penguin Classics.

Craig Martin, Renaissance Meteorology: Pomponazzi to Descartes, Johns Hopkins University Press.

A. S. Kompaneyets, Theoretical Physics, Dover Books.

Michael W. Shaw, Kids and Teachers, Tardigrade Science Project Book, Fresh Squeezed Publishing.

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2016 Tough on Sea Ice Satellites

The last several weeks have been hard on the satellites people like me use most for determining sea ice coverage.  We use passive microwave instruments on a number of different satellites.  The 'passive' in its name means that it doesn't emit microwaves.  It just sits back and collects the emissions from where it's looking.  In this, the instrument is rather like our eyes.

Different centers use different instruments and different combinations of instruments.  The main ones are:
SSMI on DMSP F-15, launched on 12 December 1999 (pushing 17 years!)
SSMI-S on DMSP F-16, launched 18 October 2003 (pushing 13!)
SSMI-S on DMSP F-17, 4 November 2006 (almost 10!)
SSMI-S on DMSP F-18, 18 October 2009 (approaching 7)
SSMI-S on DMSP F-19, 3 April 2014 (only 2)
AMSR2 on GCOM-W, 18 May 2012 (nearly 4)

A word about the names.  SSMI is Special Sensor Microwave Imager.  'Imager' is the key word.  With satellites, 'imager' means that the instrument is designed to be able to see (mostly) the surface.  Handy for us sea ice people.  DMSP is the Defense Meteorological Satellite Program -- the US Department of Defense operates these satellites.  SSMI-S (or SSMI-SU) is the SSMI -- Sounder (or Sounding Unit).  Means that in addition to the regular SSMI observing of the surface, it also carries some sensors that can do 'sounding'.  Sounding is to see what's going on in the atmosphere rather than mostly the surface.  (Name comes from the weather balloons -- which collect data known as soundings.)  AMSR is Advanced Microwave Sounding Radiometer.  It's operated by the Japanese Space Agency (JAXA).  The advance is that it is able to see more detail and the much older designs in the SSMI and SSMI-S. 

So, to our stories of woe.  All of these instruments are designed for 5 years' operation.  F-15 giving (mostly) good data after 17 years is spectacular for this type of satellite.  Notice that most of these potential data sources are already past their design life.  Since February 2016:

F-16: the sounding channels quit working early February
F-17: April 5th data quality impaired on one of the surface imaging channels, data volumes sent are greatly reduced.
F-18: Mostly ok, but reduced volume of data.  Many orbits' data not making it through.
F-19: Data ceased flowing February 2
AMSR2: Data outage afternoon of April 15th through morning of April 16th.

F-15, the oldest of the crowd, is still sending basically normal data volumes at basically normal volumes.

So, hiccups all around the sea ice analysis world.  The NSIDC was using only the F-17 SSMI-S, so has to rebuild their system to work with another instrument.  The AMSR2 temporary outage affected some centers seriously as they relied only on that instrument.  The US NWS uses both F-15 and F-17, and so far seems to be ok.  I haven't checked the operating status of the OSI-SAF sea ice (European analysis).  If I remember correctly, they also use more than one instrument, so should also be ok.

More gory details below the fold ...

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Autism Awareness Month, 2016

A heads up that it's autism awareness month again.  Autism hasn't changed much in the past year, so I don't have much new to say.  My 2015 post covers what I have to say myself.  In brief: people are people, including autistic people.  People are all similar, because we're people.  And people are all different, because we are people.  All of this applies to autistic people too, no more, no less.

Chapter one and Ted Fujita

Dr. Tetsuya Fujita, a.k.a. Ted, a.k.a. Mr Tornado was a meteorologist who spent most of his career at the University of Chicago.  When I was in graduate school, I was down the hall from him and a friend (Eric) was one of his students.  One day, Eric told me a Ted story.

Dr. Fujita held up a book on fluid dynamics (one of the central subjects for studying meteorology) and said to Eric "See this book?  I only know chapter one."  (maybe it was 'use'.  Been a few years.)  At the time, I thought it was more than a little exaggerated.  And it probably did have a fair amount of exaggeration (Ted wasn't above such things).  But, as I've continued my career and studies, I see more and more truth and wisdom in that comment.

I don't know about that particular book.  But as I re-open math and science books I read years or decades ago, I'm continuing to find meaning and importance very early in the text.  Not because I didn't learn enough of the early chapters to do well in class and tests, or to be able to apply the knowledge in later years at work.  Rather, because as I've worked more on the subject, or learned more outside it, I see that there are more and more connections to 'chapter one' material.  In that case, there's a lot of merit to looking back at chapter one and seeing how much deeper a knowledge I (you too, probably) can get from the later viewing.

Recent reading

I'm a bookaholic, I confess.  I have far more books than are strictly needed.  And I'm acquiring more essentially all the time.  (The freebies available via google, ibooks, kindle, nook, and many other venues don't exactly slow down my acquisition.)  On the other hand, I do eventually read them.  From recent (-ish) reading:

Hands on Meteorology by Zbigniew Sorbjan -- a book with something of everything for meteorology and middle school students (or older).  Some history, some biography, and a substantial chunk of hands on meteorology.  Plenty of experiments that you can do with minimal experience and equipment. 

Street-Fighting Mathematics: The Art of Educated Guessing and Opportunistic Problem Solving, Sanjoy Mahajan -- To get through to the end of this book, you'll want at least integral calculus.  But I mention it here because a) some of you have that background and b) those who don't: consider the title.  You can choose to consider mathematical problem solving as being something like a mixed martial arts, steel cage, match.  No holds barred either.  While math is often taught as a matter of exactness, and the one and only one correct answer, there's a broad swath in which coming up with a pretty good approximation is an excellent thing.  In practice, this is an enormous swath of science*.  See also my old post Fermi Estimate Challenge.

Native American Crafts and Skills, 2nd Ed., David Montgomery -- It's easy to make, say, a house when you already have plans, bricks, saws, (pre-cut!) lumber, plumbing, electricity, and so on.  But what do you do when you only have stone tools?  How about when you also have to make the tools themselves?  There's some serious intelligence involved in solving these problems.  This book has some of the solutions.  In a few cases, such as the shape and orientation of a Tipi, there's also a connection to meteorology and climate.

What We know About Climate Change, Kerry Emanuel -- This is a far smaller book than I expected from the title.  It also includes no math.  It's a good place to start reading on climate.  It won't take you long, and won't bury you in detail or math.

More to come ...


* Post to come about Ted Fujita, and his 'chapter one' rule.

Earth-Sun distance and Chandler Wobble

Continuing from The Pacemaker of the Chandler Wobble, Grumbine 2014:

The Chandler Wobble (CW) is a small variation in the orientation of the earth’s rotational axis [Chandler, 1891]. It has a period near 433 days [Liao and Zhou, 2004] (0.8435cycles per year, 0.0023095 cycles per day). Some source of energy for the Chandler Wobble  must exist because it dies out on a time scale of decades [Munk and MacDonald, 1960] if energy is not continuingly added. Gross [2000] found that atmosphere-ocean forcing on the earth’s rotation, computed in an ocean general circulation model driven by observed  meteorological parameters, provided that forcing. [O’Connor et al., 2000] also found wind forcing of the ocean to drive the pole tide. This source was questioned [Wunsch, 2001] partly on the grounds that the ocean was displaying a very narrow band response, but there was no reason to believe that the forcing itself was narrow band.

I suggest that the atmosphere-ocean variability near the Chandler Wobble period, among others, is paced by variation in earth-sun distance. The earth-sun distance, in addition to annual and semi-annual variations due to the elliptical shape of the earth’s orbit, varies due to perturbations from the moon (29.53 day period and others), Venus (292, 584, 417, 1455, ... days), and Jupiter (399, 199, 439, 489, ... days). The size of these variations is small, the largest being the 29.53 day lunar synodic period (31*10−6 Astronomical Units), amounting to approximately 0.08 W/m2 on a plane perpendicular to the sun at the top of the atmosphere. See Table 1 for more precise periods and the amplitudes of distance variations corresponding to them.

Horizons [Giorgini et al., 1996] was used to provided 6-hourly earth-sun distance and osculating elements for 1 Jan 1962 00 UTC through 31 Dec 2008 18 UTC. Table 1 was derived by harmonic analysis of those data at precise frequencies to determine purely cyclic variations in the earth-sun distance. The leading terms are, of course, the annual and semi-annual cycles from the elliptical orbit. Following this, however, are perturbations in Earth-Sun distance due to the moon, Venus, and Jupiter. Note that the orbital elements are not precisely locked to the periods given. The osculating (instantaneous) orbital elements vary; the osculating year varies from 364 to 366 days, for instance [Giorgini et al., 1996]. Consequently, there are residuals near the annual period. But they are far smaller than the main line. The anomalistic year, 365.259635 days [Observatory and Observatory, 2001], is the period between successive perihelia. This has been found to be the appropriate period for climate temperature analysis rather than the tropical (vernal equinox to vernal equinox) year [Thomson, 1995]. As we will be drawing the conclusion that earth-sun distance is important, even for small variations, the anomalistic year is the self-consistent one to use here. 

Previous analyses of orbital variation at relatively high frequency (high compared to, e.g., Milankovitch periods [Milankovich, 1941]) have used annual average orbital parameters [Borisenkov et al., 1985; Loutre et al., 1992], precluding them from examining periods shorter than 2 years and aliasing some of the periods examined here. Also, those works were examining the earth’s tilt, rather than earth-sun distance. Gravitational torques have been examined previously as the main driver of the Chandler Wobble and rejected [Munk and MacDonald , 1960; Lambeck , 1980], which means only non-gravitational external forces, such as earth-sun distance, force Chandler Wobble at these periods, if any external sources do. 

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The Pacemaker of the Chandler Wobble

Abstract: The Chandler Wobble is one of the largest circumannual periodic or quasi-periodic variations in the earth's orientation.  After over a century of searching for its forcing, it was found to be caused by atmospheric circulation and induced ocean circulation and pressure.  The question of why there should be such forcing from the atmosphere has remained open. I suggest that variations in earth-sun distance cause this forcing to the atmosphere and thence the ocean.  Analysis of earth-sun distance, earth's orientation, and atmospheric winds shows a coherent relationship between the atmosphere and earth orientation at just those periods expected from earth-sun distance variation.  As this is a general mechanism, it can be used in examining regular climatic variations on a wide range of periods and for climate parameters other than the earth's orientation.

-- -- -- -- -- -- -- 

That is the abstract for the paper I link to below.  It's not a peer-reviewed paper in the sense of being in a peer-reviewed journal.   But it has been reviewed by an expert in the field (William P. O'Connor), who was quite favorable.

I am posting the idea and paper here.  Long past time for the ideas to be discussed.  If they're shredded in the blogosphere, so be it.  I have quite a bit more than what I've put in the document. Over the next few days and weeks, I'll post more of those additional materials as well.

The Pacemaker of the Chandler Wobble, Grumbine 2014