Showing posts with label perigee. Show all posts
Showing posts with label perigee. Show all posts

Thursday, April 26, 2018

Miami's Residents Now Factor Climate Change Into Housing Costs




It's been known for some time, at least 35 years, that South Florida will be 'ground zero' when the rising seas from climate change begin to have their most serious impact. Indeed, the image produced giving a U.S. Geological survey map - with projected inundations by 2035, was actually published first in a Science Encyclopedia from 1981.

More recently, it's come to the attention of those who live in Miami or Miami -Dade (the greater metro area) that some areas flood during heavy rainfall and even on sunny days - when high tides known as "king tides" can swell the sea.

In fact, a 2016 study in the journal Ocean and Coastal Management found that the frequency of flooding increased significantly in Miami Beach between 2003 and 2016, with rain-induced events jumping 33 percent and tide-induced events soaring more than 400 percent.

How are tide-induced events generated and how are they connected to climate change? An examination of the diagram below can help which serves to illustrate tidal effects at Barbados:

No photo description available.
It is not too difficult to see that the Moon would exert a pull, say  with force F1,   on the near point -  call it A on the Earth. By the same token, point B on the opposite side from A would be pulled  (say  with force F2) )nearer to the Moon than the water above it, thereby inducing a high tide at point B as well. In other words, two separate pulls, with F1 > F2,  resulting in two high tides at locations A  and B.  In this context one can appreciate the concept of differential gravitational pull.

Now, a "king tide" is the common term given to high ("spring") tides which occur when the Moon is at its closest position ("perigee") relative to the Earth.  The difference in distance works out to about 50,000 km or 30,000 miles.  That difference is enough to  generate a significant differential gravitational tidal pull at high tide - when the alignment is as shown.

In a normal situation such tides wouldn't constitute a flooding threat other than when the configuration occurs during a storm, e.g. hurricane. But to have it occur even on sunny days shows some other factor at work - and that other factor is incipient rising seas from climate change.  In effect, the sea level rise - even though it may only be measured in inches - is ample to flood the streets of Miami on sunny days if there is also a king tide on those days. 

That may still sound somewhat sketchy except now we have evidence from Miami property values that the rising seas from climate change  is factoring into realty assessments. Research published last Friday in the journal Environmental Research Letters  and reported in the WSJ (April 21-22, p. A3) shows that "single family homes in Miami Dade County are rising in value more slowly near sea level than at higher elevations."


Why is this? Well, it's entering into buyer considerations of possible "more frequent minor flooding in the short term and the challenge of reselling properties that  decades from now could be submerged. (Again, refer to the projected U.S. Geological survey map).''  The map of the Miami area showing effect of elevation on rate of price appreciation is shown below:


Where the more contrast colored purple section refers to greater effect on rate of appreciation.  The incredible conclusion of Harvard real estat4e professor (and author of the paper) Jesse Keenan, is that ordinary home owners are already factoring future sea level rise into their calculations.

 Reinforcing Keenan's work, the WSJ (ibid.) cites another new paper from researchers at the University of Colorado-Boulder and Pennsylvania State University. This paper "shows the trend in Miami is playing out across the country, with homes vulnerable to rising sea levels now selling at a 7 percent discount compared to similar but less expensive properties.".  In addition the paper "shows that the size of coastal discount has grown over time".  The same thing appears to be happening in Barbados, especially as hotels, beach houses now start to discount their rates after obvious sea level increase has eroded their once extensive beach fronts.

In the case of Miami it's an obvious testing ground for the vulnerability of housing markets to sea level rise- climate change because its elevation "is as little as 1 foot above sea level".

The WSJ cites one particular Miami native (Joel Fabelo) whose previous waterfront home "increasingly flooded in the final five days they lived there" - and "a half a dozen times each year when tides were especially high, water rose over the sea wall leaving mullets swimming on the lawn."

Are Miami's home owners loopy?  Are they too susceptible to global warming "blurtations"? Nope, they have their heads screwed on straight and they know what they know - and what they see with their own eyes. Moreover, like  nearly all the reinsurance companies (e.g.  Munich Re) they have climate change factored into their tables, costs, plans.  They better, because they will be ground zero as the planet's sea level continues its inexorable rise owing to melting ice caps, and the Greenland ice sheet.

Monday, September 28, 2015

"Super Blood Moon" Provided A Fantastic Sight

No automatic alt text available.
The Super Blood Moon as it appeared to us Sunday night at roughly 8:35 p.m. local time.


It isn't very often that two separate astronomical events occur in conjunction as they did Sunday night. That is,  the coincidence of a maximal area Moon (30 % larger than normal) along with a total lunar eclipse. The maximal area Moon is also called a "super Moon" because of the enhanced diameter and occurs because the Moon is at the point of its orbit called perigee - or the closest point to Earth.


The total lunar eclipse, meanwhile, occurs when the Moon passes completely  through the Earth shadow when Sun, Earth and Moon are in alignment. as depicted below:

No automatic alt text available.
Note the alignment (top) fixes the Sun at one end (left) and the Moon at the other with Earth in between. The light  from the Sun - on intersecting the Earth -  produces a smaller, darker umbra and a lighter outer shadow cone called the penumbra.  If the lunar transit is such that the Moon (as seen from Earth ) only passes through the penumbra, we have a partial lunar eclipse.

If, on the other hand, the Moon passes through the darker umbra, we have a total lunar eclipse and what is called a "blood Moon" because the lunar surface appears reddish or ochre on account of being seen through the Earth's atmosphere. Thus, we observe the Moon as seen in the photo we took.


As may be inferred from the diagrams, on account of the Earth casting a much larger shadow than the Moon (say when there are solar eclipses) the duration of lunar eclipses is longer, including the total phase. An entire lunar eclipse can last for hours as opposed to minutes for the solar eclipse.


Janice and I were fortunate that the weather was terrific and the sky perfectly clear when we went out at about 8:05 p.m. I had my binoculars (7 x 35mm) and Janice used a digital camera mounted on a tripod to take the photo. We took a series of about 8 photos, and decided the one displayed here had the best resolution.


Of course, though the sight may have even inspired fear in some - there were no supernatural associations to be extrapolated. It was a purely natural event that occurs every 2-3 decades. In cade you missed this one, you won't see another until 2033.

Tuesday, August 12, 2014

Capturing the 'Super Moon'

No photo description available.
Well, almost the Super Moon.  First, the defined super Moon occurs when the full Moon (or new Moon) coincides with closest point (perigee) in its elliptical orbit resulting in an observed disk which has the largest apparent diameter. Thus, the full Moon that appeared Saturday and Sunday could be defined as such a "super Moon" - with the phase then changing (slightly) to gibbous by Monday. Well, it was on Monday - last night - that we captured the photo above. Saturday and Sunday night were washouts on account of cloudy weather, rain.

Some of the Moon's phases in a basic diagram are shown below

Image result for Moon phases diagrams

Thus, the super Moon technically occurred in the diagram at the 'Full' position, and is now on its way to 3rd quarter. So, we observed the Moon just slightly past Full, but the apparent angular diameter was still nearly 14 percent larger than it normally is.

Finding a good spot to observe was difficult at first because as the Moon rose many trees - including from neighbors' yards- obscured it. But even a peek through a couple of the trees showed a splendid sight with its apparent size further enhanced by the effects of atmospheric refraction near the horizon.

As it rose to about 5 degrees altitude, we were able to observe it from the south side of our front yard. I had my 'Admiral' 12x telescope and Janice set up her digital camera.  She was able to photograph it at about this altitude though some low cloud and haze still obscured the surface details - which is why it appears as a blankish disc.

Meanwhile, I stayed until the altitude reached 10 degrees and could easily observe the lunar 'rays', the crater Tycho, as well as lunar seas such are Mare Imbrium.

We now look forward to the next super Moon on Sept, 28 and are hoping for better observational conditions!