Matching Features Between Land Surface and Atmospheric Circulation (by Diego Fdez-Sevilla)
Two models, GFS (left) and ECMWF (right), forecast for the 25th April a High pressure enclosed over Greenland matching exactly its size.
The isobars indicating atmospheric pressure gradients are matching Greenland’s land surface almost like isolines of a topographic map.
Actual state of the Arctic and Greenland
At this part of the year Greenland is surrounded by Sea ice, principally on its North and West sides (see following images).
The heights can be used to estimate surface temperatures since height of a pressure surface is related to the mean temperature of the air below it but surface temperatures can not be used to estimate height of a pressure surface unless we consider convection.
Convection occurs when air near a surface is heated by radiation and conduction, expands
and begins to rise, being lighter than the surrounding air. To replace the rising air, cooler air is drawn in from above the surrounding surface. Convection requires a surface to irradiate heat. Since Greenland is mostly surrounded by Ice that can not be the answer for the High pressure above it since Ice melt when absorbs heat.
The only mechanism for Ice to incorporate Energy in a system without melting is by reflection, which is called Albedo.
Albedo is a non-dimensional, unitless quantity that indicates how well a surface reflects solar energy. Albedo (Î±) varies between 0 and 1. Albedo commonly refers to the “whiteness” of a surface, with 0 meaning black and 1 meaning white. A value of 0 means the surface is a “perfect absorber” that absorbs all incoming energy. Absorbed solar energy can be used to heat the surface or, when sea ice is present, melt the surface. A value of 1 means the surface is a “perfect reflector” that reflects all incoming energy.
Albedo generally applies to visible light, although it may involve some of the infrared region of the electromagnetic spectrum. You understand the concept of low albedo intuitively when you avoid walking barefoot on blacktop on a hot summer day. Blacktop has a much lower albedo than concrete because the black surface absorbs more energy and reflects very little energy.
Sea ice has a much higher albedo compared to other earth surfaces, such as the surrounding ocean. A typical ocean albedo is approximately 0.06, while bare sea ice varies from approximately 0.5 to 0.7. This means that the ocean reflects only 6 percent of the incoming solar radiation and absorbs the rest, while sea ice reflects 50 to 70 percent of the incoming energy. The sea ice absorbs less solar energy and keeps the surface cooler.
Snow has an even higher albedo than sea ice, and so thick sea ice covered with snow reflects as much as 90 percent of the incoming solar radiation. This serves to insulate the sea ice, maintaining cold temperatures and delaying ice melt in the summer. After the snow does begin to melt, and because shallow melt ponds have an albedo of approximately 0.2 to 0.4, the surface albedo drops to about 0.75. As melt ponds grow and deepen, the surface albedo can drop to 0.15. As a result, melt ponds are associated with higher energy absorption and a more rapid ice melt.
Questions and answers
I can consider two possible scenarios. The models are accurate or not. But then, some major questions raise here.
One would be if the models overestimate the difference in albedo between Snow and surrounding Sea Ice when they simulate their effect over atmospheric pressure at the sea level. Consequently the mapping of the extent of Land Being Covered by Snow marks the margins for the High pressure to develop.
But, considering that the models are accurate, several major questions arise:
- The impact of Land Cover is strong enough to define the conditions driving the evolution of Atmospheric Processes (in this case High Pressure) involved in Atmospheric Circulation. That brings more evidences about the influence of continentality, and the activities carried inland, over the atmospheric circulation.
- The level of transformation on Land Use and Cover required to have an impact over atmospheric processes can be as small as the differences triggered in albedo between Ice cover and Snow cover.
Commonly reported Albedo values from different surface types.
Surface Albedo value %
Gravel road 12
Bare soil 17
Green grass 25
- Climatic events and Meteorological features rely on the amount of energy being incorporated into the atmosphere. This is a function dependent not only on the amount of energy being transferred but also on the composition and amount of particles and molecules transferring and carrying the energy through the atmosphere. In a volume of atmospheric space containing few molecules of gases (like the outer space) the transference of energy would be more difficult independently of the amount of energy being irradiated.
Synergistic interactions exist between:
- Land Cover and Use with
- Albedo and Surface Temperature
- which are linked with Atmospheric Pressure developments,
- which are related with Atmospheric Composition and Behaviour
- and all of them are dependent on Energy flows and gradients.
This post is part of a bigger piece of work looking into the synergistic interactions and the relevance of the role played by Land Cover over Atmospheric Circulation and the Meteorological Processes associated. The situation over Greenland seems to be a perfect example pointing out the existence of such strong interactions and synergy as much as it has also been observed in the behaviour of the atmospheric circulation over the Amazones.
There are many factors interacting throughout feedback loops in our climate, and here, I have just looked at the impact generated by alterations in albedo. This example highlights the necessity for not underestimating the relevance from spread changes in Land Cover and Use across all continents changing the albedo properties of surfaces, and their potential impact over the global atmospheric circulation.
Feel free to add your comments.
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(This post is part of a more complex piece of independent research. I believe that the hypothesis that I have presented in previous posts in this blog (here, here and here) could help to understand present and possible future scenarios in atmospheric circulation. However, this is an assessment based on observation which needs to be validated throughout open discussion and data gathering. So please feel free to incorporate your thoughts and comments in a constructive manner.
Any scientist working in disciplines related with the topics that I treat in my blog knows how to judge the contribution that my work could potentially add to the state of knowledge. Since I am in transition looking for a position in research, if you are one of those scientists, by just acknowledging any value you might see from my contribution would not only make justice to my effort as independent researcher, but ultimately, it will help me to enhance my chances to find a position with resources to further develop my work.
If you feel like sharing this post I would appreciate to have a reference about the place or platform, by private or public message, in order for me to have the opportunity to join the debate and be aware of the repercussion which might generate d.fdezsevilla(at)gmail.com)
For anybody interested in the posts related with this discussion here I leave you those more relevant in chronological order (there are comments bellow some of them. Please check them out):
- New theory proposal to assess possible changes in Atmospheric Circulation (by Diego Fdez-Sevilla) Posted on October 21, 2014. http://wp.me/p403AM-k3
- Why there is no need for the Polar Vortex to break in order to have a wobbling Jet Stream and polar weather? (by Diego Fdez-Sevilla) Posted on November 14, 2014. http://wp.me/p403AM-mt
- Gathering data to make visible the invisible (by Diego Fdez-Sevilla) Posted on December 22, 2014. http://wp.me/p403AM-pN
- State of the Polar Vortex. Broken? From 29 Nov 2014 to 5th Jan 2015 (by Diego Fdez-Sevilla). Posted on November 29, 2014. http://wp.me/p403AM-o7
- Probability in the atmospheric circulation dictating the Weather (by Diego Fdez-Sevilla) Posted on January 15, 2015. http://wp.me/p403AM-rm
- Meteorological Outlook Feb 2015 (by Diego Fdez-Sevilla) Posted on February 7, 2015. http://wp.me/p403AM-sU
- Revisiting the theory of “Facing a decrease in the differential gradients of energy in atmospheric circulation” by Diego Fdez-Sevilla. Posted on February 10, 2015. http://wp.me/p403AM-to