From this discussion there appears to be the impression that there is a nice distinct height at which there is a flat tropopause and then everything changes abruptly to stratosphere. This is not the case at all there are gravity / Kelvin waves that surge upward or along the atmospheric 'layers' sometimes these break leading to a effects like the sudden stratospheric warming and break up or reversal of the polar vortex. The stratosphere can have significant effects on the tropospheric behavior and vice versa.
"The atmosphere exhibits many wavelike motions with a variety of space- and timescales ranging from slow-moving planetary scale waves to much faster and smaller gravity waves, each playing important roles in the behavior of the stratosphere. It has long been known that conditions in the stratosphere are controlled by wave driving from the troposphere, but it has been assumed that the stratosphere has little effect on the troposphere. Stratospheric variations, especially variations in the strength of the polar vortex, appear to be involved in feedback processes that in turn alter weather patterns in the troposphere. Stratospheric variations are largest during the winter season, and they are influenced by changes in solar irradiance, volcanic aerosols, changes in greenhouse gases, ozone depletion, and the phase of the quasi-biennial oscillation (QBO).
Stratospheric circulation anomalies are caused mainly by wave forcing from the dense troposphere. Stochastic variations in the troposphere during northern hemispheric winter lead to high-frequency changes in the planetary wave flux upward into the stratosphere (Holton 1983).When these waves break, they deposit momentum in the stratosphere, slowing the zonal mean wind and weakening the polar vortex. The interaction of the waves with the mean flow tends to draw these zonal wind anomalies downward through the stratosphere (Andrews et al. 1987; Andrews 2000; Martin 2006)."www.springerlink.com/content/r717714347u17693/"A number of field-campaigns in the tropics have been conducted in the recent years with two different LIDAR systems at Paramaribo in Suriname (5.8 N, 55.2 W). The lidars detect particles in the atmosphere with high vertical and temporal resolution and are capable of detecting extremely thin cloud layers which frequently occur in the tropical tropopause layer (TTL). Radiosonde as well as operational ECMWF analysis show that temperature anomalies caused by equatorial Kelvin waves propagate downward, well below the cold point tropopause (CPT). We find a clear correlation between the temperature anomalies introduced by these waves and the occurrence of thin cirrus in the TTL. In particular we found that extremely thin ice clouds form regularly where cold anomalies shift the tropopause to high altitudes. This finding suggests an influence of Kelvin wave activity on the dehydration in the TTL and thus on the global stratospheric water vapour concentration. "
www.atmos-chem-phys-discuss.net/8/2849/2008/acpd-8-2849-2008-print.pdf
Tropopause to mesopause gravity waves in August: Measurement and modeling
"Global gravity wave distributions are retrieved from infrared emission limb soundings taken by the CRISTA instrument in August 1997 and by the SABER instrument in August 2003. The investigated altitudes cover the whole middle atmosphere from the tropopause to the mesopause. The data agree semi-quantitatively in their salient features and only small deviations due to the different meteorological conditions in the two years are observed. Of particular interest is the decrease of gravity wave activity at the top of the southern polar vortex and an accompanying shift of gravity wave activity towards the subtropics in the mesosphere. We emulate this feature by two conceptionally different models, the Warner and McIntyre spectral parameterization scheme and the GROGRAT gravity wave ray tracer. Both models indicate that saturation limits and gravity wave breaking are the governing processes in creating this structure. Also, both models can well reproduce the global distributions except for two important points: (1) convectively generated gravity waves in the northern subtropics are largely underestimated; (2) northern hemisphere high latitude activity is grossly overestimated. These points indicate that gravity wave distribution in general circulation models are not fully realistic. Refined measurements are required to constrain more realistic gravity wave source distributions."www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6VHB-4KPX93K-1&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&_docanchor=&view=c&_searchStrId=1052906845&_rerunOrigin=google&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=6ae311c6a5bb8f89353afc925bdd365aGreat points Nautonnier,
The thing is that most people nickel-and-dime the Earth's complex and highly variable climate to the point of not even understanding the basics of atmospheric science when it comes to the reasons why the Earth's climate undergoes changes, such as the coming new climate regime of global cooling.
As this is complex climatology and space weather science, I will explain in the simplest terms as possible:
For one, as the Sun nears and then enters solar cycle #25, it begins the Sun's Grand Minimum. Now, since solar cycle #23 the Earth has been cooling (since 2003) and solar cycle #24 is also weak, which is the prelude to the Sun's quiescent phase.
Regarding why the Arctic polar region has warmed slightly is due to this:
The Earth's stratopause is the boundary between the Stratosphere and Mesosphere.
Now, the atmospheric pressure in this boundary region is 1/1000th of the atmospheric pressure at sea level so as liquid moisture reaches the edge of the reaction zone, the water is supercooled and frozen in the form of ice crystals known diamond dust.
Around the Earth is a thin layer of ozone in the middle atmosphere and ozone plays a role in the activity of the stratosphere (1-10 parts per million.)
Ozone and oxygen molecules in the stratosphere absorb UV radiation from the Sun, and acts a filter which prevents this radiation from passing down to the Earth's surface. Ozone is produced in the stratosphere by a process of photo dissociation of oxygen by ultraviolet light.
Earth’s atmosphere is made up of 21 percent molecular oxygen (O2) and 78% molecular nitrogen (N2.) The two molecules are the main components of the Stratosphere. A number of others include nitric oxide (NO); atomic oxygen (O); ozone (O3; and of course, water vapor.
Oxygen and ozone absorb 95 percent to 99.9% of the Sun's ultraviolet radiation, but only ozone is effective to absorb the most active ultraviolet radiance known as UV-C and UV-B.
Ozone levels in the atmosphere is always in a natural state of quasi-equilibrium but this is delicate and confined to the top upper part of the ozone layer.
The balance is governed by the activity of the Sun as UV radiation restores ozone but solar proton events destroys it. When the Sun erupts with high-energy protons the Earth's density of ozone layer in the stratosphere can decline as much as 10-15 percent.
The reaction zone is where the Earth's upper atmosphere sees these diamond dust ice crystals build up.
Lower stratosphere temperatures are isothermal about minus 60-degrees Celsius. This rises higher in the upper stratosphere attaining a maximum of 0-degrees Celsius at the stratopause.
Anyhow, after these high-energy solar proton events, it takes time for UV light to restore what the Sun's protons have destroyed in the ozone layer, which is why there are fluctuating holes in it from time to time.
The restoration of the ozone layer by the Sun is accomplished gradually as sunlight is also component of UV. Occasionally when you see these ozone holes show up at the poles, what you are seeing are voids in the ozone layer.
That's because ultraviolet radiation produces ozone when it meets oxygen in the atmosphere. But when you see the continuous darkness at the arctic in its winter season, UV radiation is blocked by Earth's tilt to the Sun. So any loss of ozone can't be repaired until sunlight reaches it by spring and then you see ozone holes gradually close up by summer.
The problem with the Sun's quiescent phase is that we are already seeing less ultraviolet radiance - more than the decline in total solar irradiance. What this amounts to is that the restoration effects of ultraviolet radiation on the Earth's ozone layer has gone down.
As a result, it shrinks the reaction zone where temperatures are at or above 0 degrees Celcius, so there are less ice crystal that can form and pulled into the the polar vortex region. Due to this the Arctic starts to slightly warm up.
As the Sun nears its quiescent phase, the amount of light in the ultraviolet ranges declines. This causes uneven distribution of ice crystals pulled into the polar regions and so those polar areas slightly warm up as the polar vortex weakens.
The ice crystals not pulled into the polar vortex falls into the jet streams, which then starts a process of building high-pressure blocking systems to develop. This changes the wind patterns and the jet stream alters from a zonal jet pattern to a meridional jet flow.
The meridional flow pattern forces all that cold air to migrate north to south, that is, from higher latitude to mid-latitude. It produces stronger wind speeds carrying with it severe storms.
Heavy snowfalls come about during winter seasons that are then followed by sub-zero polar vortex air masses that can lock itself in to become a long-lasting blocking ridge.
This is the weather of global cooling, and everyone who lives on Earth, in both hemispheres, had better get used to it between now and the early 2050s because that is what the Sun's Grand Minimum brings to the party - a new little ice age.