31 August 2011

Too-early consideration of sea ice estimates

I won't let it stop me, but considering that it is still August as I write, it's premature to evaluate estimates of September's sea ice extent.  On the other hand, it's fun and easy, and some parts make sense even at this early date.

Last May I made, with colleagues, some estimates for September 2011's extent.  As usual, I also included some other forecasts for comparison.  The NSIDC figure for August 29th is:
Where I've added lines in red for the 30 year mean climatology of September extents (6.67 million km^2), the mean monthly September extents if we take a 30 year linear trend (5.31), and lines at 5.0 and 4.5 million km^2.

30 August 2011

Earthquake followup

Phil Plait showed the spectacular animation of seismic waves propagating across the US from the 5.8 Virginia earthquake last week, but left out part of the story.  A commenter, davenquinn,  picked up some details.  If you look at the video:

you see an enormous number of sensors in the Midwest and Great Plains.  These are areas not known for seismic activity, so what are they doing with so many sensors?
They are part of a travelling array (the 'transportable array') of seismometers, part of the Earthscope initative from the National Science Foundation.

The idea is to have a substantial number of seismometers moving stepwise across the US every few years.  Then, having a dense array of seismometers, particularly to have them in places that we don't normally, will show us things that we don't normally see.  That spectacular wave propagating across the country is one of those things.  Get in to the data and you start seeing that the seismic waves didn't travel the same speed in all directions.  And that tells us something about what the earth is made of.  No idea what is up, but take a look at the Texas-Louisiana area.  Early in the propagation of the waves, they follow along with the rest of the US.  But later in the animation, that area shows much larger amplitude variations.  Why?

In other words, more fun science to be done!

27 August 2011

Now twittering @rgrumbine

My thoughts, between earthquake, stolen wallet, and hurricane, are now more in line with twitter than blogging.  I'm @rgrumbine there. 

For tracking the hurricane and forecasts, I like the Weather Underground.  Specifically on the hurricane, the WunderMap (r)

But, speaking of the wallet, it was returned this morning.  Minus cash, but plus all the plastic and photos.

23 August 2011

My first earthquake

Yes, I was one of the many who felt the 5.8 to 5.9 earthquake centered in Virginia.  The final scoring and location will come from the US Geological Survey -- http://www.usgs.gov/  This is the first time I've noticed an earthquake in my life.  Growing up around Chicago and then living around here doesn't give you a lot of exposure.  The strongest here that I've been present for was 4.3 to 4.4, as I recall it.  I didn't notice it at all, not even in the sense of 'oh, so that's what was happening'.

This time, it was noticeable.  The initial stage was some fairly minor, fairly high frequency vibration -- similar to having some heavy trucks drive past, or some kinds of construction drilling.  Since there is construction going on in my area, I figured this was it.  For the first few seconds.  Then there was a rapid increase in the size of the vibrations, and a decrease in their frequency.  Rather than having some vibrations passing through the building, we moved to having the building itself swaying back and forth.  Earthquake!

By my count, I felt the quake for about 30 seconds.  (If that's too long compared to the USGS figures, blame my inner ears.)  Call it 20-30.  One friend estimated the swaying as being 4 cycles per second in the real quake phase.  My guess is closer to 2.  I'll have to see what the USGS has.  There are probably confounders from the engineering of my building.  So far, all seems ok at work and home.  Some of the more precariously perched items fell off book cases at home, but that's about it.  Fingers crossed that this is true for everybody.

A question popular in our parking lot at work (we'd been evacuated post-quake) was to wonder what fault line caused the quake.  My early answer, which was supported by a snippet on the radio (i.e., don't place a lot of confidence here) is that there was no fault line involved.  This is simply a much stronger version of the usual earthquake for this region -- adjusting to the fact that the Laurentide ice sheet is gone.  In areas that the ice sheet occupied -- down to southern Illinois or in to Pennsylvania -- the land sank under the weight of the ice sheet.  This squeezed some of the more fluid parts of the mantle out from there, and over to the areas in front (south) of the ice sheet.  That elevated the areas around, say, Virginia.  Once the ice sheet was removed, the fluid started oozing back to its original location.  As it does so, the crust creaks its way back in to position.  Creaking = earthquake.

08 August 2011

Is climate a random walk?

Let's pick up again the discussion between Tamino and me.  He has objected to my use of cumulative sums on the grounds that cumulative sums of random numbers have bad behavior statistically.  He's correct about that statistical point, naturally, which means caution is needed regarding the statistical part of my post on finding a climate normal.

But how concerned should we be as climate scientists?  Crucial to that concern is that climate be, to a fair degree, experiencing random variation.  It isn't, strictly.  As Tamino mentioned, there is certainly a trend in more recent years -- not purely random variation.  His criticism is more one against the cumulative sums method.  As Jim Bouldin mentioned in the comments recently, we do routinely transform variables in order to study topics of scientific interest.  In his case, plants.

I'll start by showing you an illustration of why Tamino is concerned.  This is a plot of the cumulative sum -- of a purely random variable, with uniformly random numbers in the range plus or minus 1 degree.  This is actually about 10 times too large for climate.  So the late period value of 40 really means 4 degrees.
Each tick mark is 1 month, but assumes that each month's random number is completely independent of each other.  That isn't the case, as Tamino has documented.  This curve manages to accumulate its 4 degrees in about 200 years.

Er, it accumulates that climate wandering in only 200 years!.  That and the smooth curves, suggest why we cannot take climate to be random wandering over long periods.  Volcanoes suggest why we cannot do so for short periods either.  Intermediate periods might be ok physically.

Endogenous Retroviruses and a Different Writing Style

One of the blogs I keep an eye on is erv, Endogenous RetroViruses, by Abbie Smith.  Not the usual language you'll see here (some over PG-13), and certainly different style (Abbie doesn't believe in the ', for instance).  But for some discussion of biology, particular parts involving viruses and especially endogenous retroviruses (surprise), it's a good place to go.

I'll note that back when I was thinking about blogging, Abbie was one of the people who gave me some ideas on approach.

Some articles to take a look at for a sample of the blog:

What is normal, and how it matters in examining bees
Open Access Publishing -- and some limits
How immunization works
Antivaccinationism and death by measles
AIDS and CD4+ T-cells
Blood groups and viruses
Antibodies and dengue
Pursuing science and results
Zinc and the common cold
The Timetree of life
Scientists being slandered
Scientists and media

04 August 2011

Is it really normal?

Is my previous post about finding a climate normal really ok, or fatally flawed for statistical reasons?  This wasn't how I was planning on doing so, but it provides a good chance to discuss some ideas about doing science and statistical versus physical significance.

In my note, I took a look to see if it was possible to find a period in which climate (as defined by the HadCRU temperatures) behaved in a way that we think of climate as doing -- some warming, some cooling, and totalling to no real change.  That put me in mind of a cumulative sum, and the result was that it was indeed possible to find such a period -- 1850-1940.  It could well have been that it was not possible to find such a period, or at least not one long enough to be interesting for climate.  That would have told us that our notion of climate was not something that the climate system respected -- time to learn more about climate and update our thinking. 

A second part of that post was my conclusion that something changed around 1940.  This is a statistical conclusion, made by eyeball inspection.  Quite a hazardous thing to do and Tamino shows ample reason to be leery of that conclusion, given the statistical nature of cumulative sums.  On the other hand, the deviations he shows from his noise simulation reach only about 50, versus the 300+ of mine using real data. 

So where are we? 

02 August 2011

How to find climate normals?

It's that time of the decade when the official 'climate normals' are computed -- according to the rules of the WMO and NOAA (in the US).  But can we find a better way of deciding 'normal'?  I'll do some thinking out loud here, and invite you to play too.  Could we even be so lucky as to find a way of defining climate normal in such a way that we don't need to worry about an early period of 'coming out of the Little Ice Age', or a later period of Anthropogenic Global Warming.

In previous posts, I illustrated that there are principles which lead to the requirement of 20-30 years to define a climate average and, separately, 20-30 years to define a climate trend.

In those approaches, we were able to make good use of the adage that climate is what you expect.  It was only after 20-30 years of data that our expectations for the mean or trend would be stable -- would not depend sensitively on how long a period we chose to be our data period.

This time, I'll pick up with a different notion or description.  A common description of climate is also that sometimes its warmer and sometimes it's cooler, but it all averages out in the end.  Let's start by looking at the Hadley-CRU temperatures, back to 1850, month by month.  I'll start with looking at temperatures relative to the average over the entire data set:
For the earlier part of the record, we see the deviations being both above and below the reference value.  On the other hand, the last 26+ years, every month since December 1984 -- 317 consecutive months, has been above the reference value.  That's not a sign of sometimes warmer, sometimes cooler.  That's the recent period being different from 'normal'.  For instance, because of a warming trend.  If you're younger than 26, you have never seen a month where the global mean was as cold as the 161 year average.  On the other hand, looking at the early part of the record, we see some years warmer than 'normal' even though most are cooler.  Further (look directly at the original data, don't take my word) there are no periods as long as even 20 years of continual below reference temperatures.  In other words, the Little Ice Age, insofar as it was global, had ended by 1850.

01 August 2011

Giant Mutant Imperial Moths

Here's the title-bearer:

He's about 5", 8 cm from wing tip to wing tip.   The reasons I call him a mutant are a little more obvious in this top view:
He's got 5 legs.  You can see the front left leg, and the doubled front right legs.  The photo couldn't capture it, but I did verify two more back legs.  He also seems to not have antennae, and moths do normally have some, including members of this family.

For completeness, here's the bottom view:
For more technical information, see http://www.butterfliesandmoths.org/species/Eacles-imperialis

It was my first time seeing one of these.  I had seen two other moths of this size -- a Luna moth many years ago, and a Polyphemus a few years ago while I was running in a 24 hour relay.  Turns out they're all in the same family, the Saturniidae.

He was extremely patient with my photography and my wife going in and out of the sliding doors.  Stayed put for several hours. 

Like other members of this family, the adults don't eat.  Go back to the top view -- no mouth parts.  The adults try to reproduce, the females lay their eggs, and a few days later they die.  Their main period of life is as a caterpillar.  I've been calling this a male because it seems (the top link and further checking around the net) that the females are a more straightforwardly yellow.  It is the males who have fair amounts of purple/brown.