Tag: total eclipse

The Subtropical Jetsteam Versus the Total Eclipse

A double threat exists: clouds associated with two features: the subtropical jet and a low-pressure area moving in from the southwest U.S.

From The Cliff Mass Weather Blog

Cliff Mass

We are now close enough to the April 8 total eclipse that the skill of our models is now appreciable.

And many of these increasingly skillful forecasts indicate a real threat to good viewing over Texas and much of the Midwest, where many plan to go.

A double threat exists: clouds associated with two features: the subtropical jet and a low-pressure area moving in from the southwest U.S.

This blog will describe these important features and the current uncertainties in the forecast.

Let me start with the forecast cloud cover near the time of the Monday eclipse (11 AM PDT, 2 PM EDT, 8 April) made by the European Center model this morning.  The center of the line of totality is shown by the blue line.  If this forecast was exactly correct, folks in Texas would be ok, but the cloud fields will surely shift a bit.

There are two major cloud fields to be concerned about.  The first is a long line of clouds (red arrow) associated with the subtropical jet (or jetstream).  The other is a cloud field associated with a low-pressure center over New Mexico and Colorado.  A shift in either feature, which is pretty much guaranteed, would be a real problem.
The predicted cloud field of the U.S. model (the GFS) is also very bad for eclipse lovers (see below), with the subtropical jet stream clouds moving right into Texas and most of the path of totality covered with clouds.

So what is a subtropical jetstream?

Many of you have heard about the polar or midlatitude jet stream, the one that generally affects the Pacific Northwest.  But there is another jet stream to the south, the subtropical jet stream (see picture below), which is located near the northern boundary of the tropics.

The subtropical jet stream often entrains moisture (and clouds) from the tropics that moves into the midlatitudes.   

In fact, there was a nice subtropical jet stream this morning, which brought loads of moisture into the southwest U.S.

The other crucial element of this forecast is the upper-level low/trough that is over the southwest, with a second low over South Dakota (see charter below at the same time as the pictures above).  This chart shows the situation around 18,000 ft (500 hPa). There is upward motion and clouds to the east of these features.

There is technology to get at the uncertainty in this forecast, looking at an ensemble of many forecasts, each slightly different.  The following “plume diagram” shows the amount of water vapor above Dallas, TX for each of the forecasts.  The critical time is shown by the red arrow. Many of the forecasts show a lot of water vapor, which means lots of clouds.  Not good.

The new U.S. (GFS) forecast just came out (below).  The subtropical jet stream moisture covers Texas, and clouds from the northern low and associated frontal clouds are messing up much of the path over the Midwest.  

At this point, I would probably head to northern New England.  There is still some uncertainty in the prediction, but we should pretty much know the final story by Friday.

New Research Finds that Solar Eclipses are Harder to See Due to Global Warming

Interestingly it turns out that such eclipse-viewing problems are increasing as the earth warms up due to increasing levels of carbon dioxide and other greenhouse gases.

A Total Eclipse of the Sun. Dramatic Solar Eclipse illustration.

From Cliff Mass Weather Blog

Cliff Mass

There is a lot of concern about cloudiness obscuring the sun during next Monday’s total eclipse.

Interestingly it turns out that such eclipse-viewing problems are increasing as the earth warms up due to increasing levels of carbon dioxide and other greenhouse gases.

A recent study in the Journal of Climate Statistics by Professor Wade Rocston of the University of Western East New Brunswick documents a significant (23%) increasing trend in cloud-obscured solar eclipses.

The origin of the increasing cloud cover is clear according the Professor Rocston.  Increasing CO2 leads to global warming.  Such warming results in more evaporation and the moisture content of the air increases with temperature (see below).  This leads to more clouds and thus greater obscuration of solar eclipses.

The moisture content of air increases with temperature, which leads to more clouds

To give you some perspective on this issue, the first study documenting the increased clouds in a warming world is found in a 1986 paper by A. Henderson-Sellers:

This ground-breaking study found increased springtime clouds over Texas and the rest of the eclipse path (see below, cross-hatched shading indicates increasing clouds):

According to the ICCC, the International Committee on Climate Change, which includes leading climate scientists from around the world, solar eclipses have become 24% less visible due to climate change-related cloudiness increases.  Their analysis suggests that if CO2 concentrations remain at their current level, the associated warming and increased cloudiness will result in nearly 46% of total eclipse events being obscured by clouds by the end of the century.

The inability to see total eclipses is one of the lesser-known impacts of global warming, but it is areal loss for astronomers and the rest of us.  I look forward to a detailed discussion of this unfortunate situation in a future article by the Seattle Times ClimateLab reporters.

Finally, happy April 1.