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Lakes on The Sahara Desert

What has been happening this summer and this fall on the Sahara Desert...
Anomalous low temperature region
Anomalous low temperature region
Lakes in the mountains
Lakes in the mountains
September weather Sahara
September weather Sahara
August weather Sahara
August weather Sahara
Hi everybody. Here is something you might find interesting.<BR><BR>

A picture is worth a thousand words. I am uploading an image of the anomalous low temperature region in the mountains in the Western Sahara. There is also a satellite image showing lakes forming in the Saharan mountains (the green arrow). There are also some strange looking spots on the right side of the image (not sure what to make of that). I also have prepared two animated gifs that show the weather patterns on the Sahara in August and September of this year.<BR><BR><BR>

homepage: homepage: http://www.awitness.org/commentary/index.html


river 26.Oct.2015 11:14

Brent

At the moment the links to the images do not seem to be working, but assuming that it just takes some time...

If you look at the expanded image, there also appears to be a river flowing down the mountain side from the lake being pointed to by the arrow.

Comparison 26.Oct.2015 11:19

Brent

For comparison purposes this image is from April 2015 when the lakes were not visible
April 2015
April 2015

Vegetation health, more background info 26.Oct.2015 11:26

Brent

It is ironic that the world's healthiest vegetation is now found on the Southern border of the Sahara. Meanwhile the most stressed vegetation on earth seems to be found in the United States.
Vegetation health and stress for October 2015
Vegetation health and stress for October 2015

A little more background info 26.Oct.2015 11:35

Brent

The Sahara is a desert because of a persistent high pressure system that causes subsidence of air masses (falling) which prevents cloud formation. The air falls and is then expelled from the desert. According to the description of this phenomenon on the Wikipedia site:

The Sahara is the world's largest low-latitude hot desert. The area is located in the horse latitudes under the subtropical ridge, a significant belt of semi-permanent subtropical warm-core high pressure where the air from upper levels of the troposphere tends to sink towards the ground. The strong descending airflow causes a warming and a drying effect in the upper troposphere. The sinking air prevents it from rising and therefore prevents the adiabatic cooling, which makes cloud formation extremely difficult to nearly impossible.

The permanent dissolution of clouds allows unhindered light and thermal radiation. The stability of the atmosphere above the desert prevents any convective overturning, thus making rainfall virtually non-existent. As a consequence, the weather tends to be sunny, dry and stable with a minimal risk of rainfall. Subsiding, diverging, dry air masses associated with subtropical high pressure systems are extremely unfavorable for the development of convectional showers.



What has changed since this was posted on wikipedia is that a persistent low pressure has been parked over the Sahara for months and this is now causing this interesting weather pattern and convection and rainfall are now occurring on the desert (a few satellite images below-these are 'false color images' where the higher and colder the clouds are the more they are colored blue)
Hadley cell, falling air expelled from Sahara
Hadley cell, falling air expelled from Sahara
September convection
September convection
September convection
September convection

Why do you think this strange? 26.Oct.2015 16:53

Mike Novack

You don't have to go all the way to the Sahara to see evidence that lakes sometimes form in deserts. We have plenty of places right here in the US where there are dry (at the moment) lake beds. For example, the famous Bonneville Salt Flats where they do land sped record attempts.

The existence of sites likes these means that SOMETIMES (at long intervals) enough rain falls in their watershed to fill them, and then for a brief while, they are lakes again.

On maps of desert areas you often see these place marked out with doted lines, and dotted lines for water courses that appear to begin nowhere and end nowhere. That's how they show the places where there is SOMETIMES water. Maybe not in my lifetime or yours, but sometimes.

On the other hand, there are lots of such places on this planet. So even though for any particular one of these places it is rare that they have water, it is rather common that at any given time SOME of them do.

Apparently it's the Sahara's turn right now.