Weather Around The World, 9/22: Tropical Moisture Reaches The Desert; Equinox; Melting Permafrost

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Home / Weather Around The World, 9/22: Tropical Moisture Reaches The Desert; Equinox; Melting Permafrost
Several inches of rain are expected in Arizona from the remnants of a tropical system. Flooding could result. Photo courtesy of NOAA.

Several inches of rain are expected in Arizona from the remnants of a tropical system. Flooding could result. Photo courtesy of NOAA.

Parts of the west will get relief from the high fire danger thanks to a wandering tropical depression from the Pacific.

The sun will be above the northern hemisphere for the last time for almost six months today and early tomorrow.

There’s a stationary cyclone in the middle of Atlantic Ocean.

And a new report warns of the danger of melting arctic permafrost.

Let’s go Around The World.

Not Even Worth A Name, But Plenty Wet

Last week, this column confessed to underestimating the danger of a tropical storm of minimal windpower. This week, we have a tropical system in the eastern Pacific that will bring drought-relieving rain to Arizona and New Mexico — and the weather system didn’t even get strong enough to be called a tropical storm and get a name.

Flash flood advisories are in effect in Arizona for up to three inches of rain. The remnants of the minimal tropical cyclone that began its journey off the coast of Mexico, moved parallel to the coast, then crossed inland over Baja California and mainland Mexico, will dump its remaining moisture on the desert southwest today and tomorrow.

Some Surprising Things About The Equinox

The autumnal (northern hemisphere) equinox will take place tomorrow morning, September 23, 2015, at 08:22 Universal time (4:22 a.m. in New York). That is the precise time at which the sun is directly over the equator in its path from the northern hemisphere to the southern. Well, big hoo-ha, you say. No coins will be issued; no one will even stop for a moment of meditation. But there are actually a couple of interesting and surprising facts connected with the equinoxes.

First of all, the word equinox means, literally, equal night. But the almanac-listed times for sunrise and sunset in New York tomorrow are 6:44 and 6: 52, respectively. This doesn’t sound like ‘equal night.’ And here’s why.

The definition of sunrise and sunset are the times of the first ray of light and the last. Since it takes the sun eight minutes to completely clear the horizon (4 minutes to get so the horizon cuts the sun in half), the night gets shortchanged.

Just for the record, the date of equal night by the standard definition of day and night in New York this year is September 26, on which date the sum will rise and set at 6:47, a.m. and p.m., respectively.

Now you would think that the time between the autumnal and following vernal equinox would be equal to the time between the vernal and following autumnal equinox — wrong again. Vernal equinox, 2016 will occur on March 20. That’s 18o days after tomorrow.  From spring to fall will be 185 days.

How can that be? Is some mysterious force accelerating the earth during northern hemisphere winter? Well, yes, if you consider gravity a mysterious force. Johannes Kepler worked out the laws of planetary mechanics and found that gravity would accelerate a planet as it neared the sun.

Since the earth’s orbit is not round, and since the perihelion (closest approach to the sun) is in January, the earth moves faster in the northern hemisphere winter than in summer. Mystery solved.

The Meandering Of Tropical Storm Ida

The forecast calls for Tropical Storm Ida to remain nearly stationary for several days before drifting north. Forecast courtesy of National Hurricane Center.

The forecast calls for Tropical Storm Ida to remain nearly stationary for several days before drifting north. Forecast courtesy of National Hurricane Center.

The ninth named storm of the Atlantic hurricane season is stuck in the middle of the ocean. Steering winds are nonexistent, and Tropical Storm Ida is just spinning; it is expected to do so for at least three more days.

One might think that a tropical cyclone spinning as if on a stationary bike over relatively warm water would be a recipe for developing a powerhouse storm. But when a tropical storm is stationary, a feedback mechanism begins to work against it.

The profile of water temperature with depth finds the warmest water at the surface, fairly rapidly decreasing with depth. A tropical storm causes the surface water to mix with water from below, reducing the temperature of the surface water and sapping the storm’s energy feed.

The latest forecast calls for Ida to lose strength while it’s stationary, then gain some back as it moves slowly northward later in the week.

Melting Permafrost Could Release CO2 And Methane

An article published in Nature Climate Change on Monday calculates the economic impact of the release of CO2 and methane from permafrost melting at the current rate: $43 trillion. This amount is calculated as excess of the damage done by direct emissions from the burning of fossil fuels.

Studies like this make all sorts of assumptions that may or may not prove to be correct, but the results of potential feedback effects of anthropogenically-caused global warming should be taken seriously.

Change Of Seasons, Change Of Weather

Now that the equinox has passed, temperatures will accelerate towards the winter minimum in the northern hemisphere. How is the waning sunlight affecting the weather where you live?

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