[dorlomin]

I am going to start a thread that is aimed at giving the basics of meteorology and climate.

Not a discussion thread but one so that everyone discussing these issues has a basic founding in it and perhaps as an assistance to those prepping to give them a better insight into weather and reading synoptic charts and the like.

Given some of the errors of people posting I think a basic refresher course would be useful.

The three main weather cells.



Earths weather is driven by the sun and differences in temperature and pressure across the planet. The single biggest factor is the huge amount of energy coming from the solar irradiance at the equatorial lattitudes. This creates an enormous body of lifting air and water vapour called the intertropical convergence zone. This is normally located on the thermal equator (which moves with the seasons) and is where the earths atmosphere is the warming. A large body of hot and humid lifting air creates the huge tropical thunderstorms and the air lifts to the top of the troposphere. As it reaches the top it moves north until it cools enough to begin dropping. The air is then dissicated and heated adiabetically as it drops. This air is the source of many of the worlds great desserts located at the 30 deg lattitude. The sinking air then travels back to the equator (pulled as the lifting air creates low pressure). This movement completes what is called the Hadley cell

(more to follow)

[dorlomin]

The Hadley cell has a notable impact on sailing conditions (a few, I understand, are planning sailing as a means of PO preperation). Where it rises and falls it creates areas of little horozontal wind movement. In the doldrums near the equator this is the lifting of the air and at the horse lattitudes at 30deg this is the descending air.

In the previous post I commented on the deserts.

You can clearly see that most of them are around the 30deg lattitude mark.
Here is a map of the worlds sea currents.


Other than the subsidance of the hadley cell another key feature in the southern hemisphere deserts is sea currents. To the west of the Kalahari\ Karoo, the Atacama\ Peru and the West Australian deserts are cold currents that will not produce much percipitation. Hence so many of these areas are among the driest in the world.

[dorlomin]

The polar cell of circulation occurs because there is still enough energy from the sun at around 60 degrees lattitude to lift hot moist air to the tropopause. This air is then drawn towards the poles where it descends as very cold very dry high pressure zones.

This is part of the reason why the polar regions are among the worlds deserts, most notably Antartica which is the dryest continent on earth.

The ferrel cell (named after Will Ferrel) flows in the opposite direction to the other two with the air rising at near 60 lattitude and descending at around 30 lattitude. The ferrel cell is alot less distinct than the other two and functions to return the colder air to the warmer lattitudes.

[dorlomin]

Air parcels

I am going to jump away from air circulation for a moment and turn to some basic physics. This is a concept called 'air parcels' or 'fluid parcels'.

An air parcel is a theorectical small parcel of air in the atmosphere. It is used to illustrate changes in bodies of air as the move vertically in the atmosphere. As a parcel of air expands it will cool as it compresses it will warm. The expansion and compression are caused by the changes in surrounding air pressure at it gets higher in the atmosphere. This behaviour is comon to all gasses, the closer the atoms are pushed together the quicker their collisions will become: i.e. heat. Warm air rises and cool air sinks.

A lifted parcel of unsaturated (by water vapor) that starts of at 25C at sea level will cool to 15C by 1000m, 5C at 2000m and -5C at 3000m.

This behaviour has any number of important impacts on the weather and climate. Firstly it is why it gets colder as you increase altitude. But where the air stops rising this dynamic no longer operates, this region is called the 'tropopause' that and is where the tropospehere ends. The height of the troposphere is determined by the underlying temperature and varies from about 13km at the equator to about 6km in the polar regions. (For the next 30km above the tropopause is the stratosphere where the air steadily warms as you climb).

Edited to add illustration....

[Plantagenet]

Cool!

And how about the jet stream? Where does it fit in?

[Pops]

And air warms above the tropopause because? Solar radiation?

[Keith_McClary]

Sunlight carries about 1 kilowatt per square metre of energy to the Earth.

The Earth also radiates energy into space according to the Stefan-Boltzmann Law, proportional to the fourth power of the absolute temperature T.

The average temperature of the earth is the value of T for which these energy flows are equal.

[Tanada]

And air warms above the tropopause because? Solar radiation?

Ozone, specifically the Ozone layer which is above the Tropopause in the mid stratosphere. Ozone is a green house gas and absorbs Ultraviolet light re-emitting it as lower frequency light and infra red energy. Technically the O3 molecules become excited by ultraviolet the same way water molecules in your microwave oven become excited by microwaves, the energized molecules then bump into each other and the other gasses in the Stratosphere and heat then through collision impacts and direct transfer.

[dohboi]

Dor, thanks for these informative posts.

Just two points. Much of this is free from the technical terminology that sometimes makes your otherwise lucid writing hard to follow.

I did find it surprising in your first post that you linked "dessicated" (misspelled, by the way, in your text) to its wiki definition, even though it is a fairly common term, but left "adiabetically" un-defined, though, to me, it is much more opaque (though I could hazard a guess about its meaning from context, a guess confirmed when I finally got off my butt and looked it up.)

On that point, does the air dropping onto the poles also warm up some as it falls and compresses? If so, does this keep the poles warmer than they otherwise would be?

[dorlomin]

Cool!

And how about the jet stream? Where does it fit in?

Bang in between the major circulation patterns. So far as I understand there can be quit big pressure difference between the big circulation patterns and this will cause alot of air to move between them, but as this air moves it is subject to what is called the 'coriolis force'. That is the earth spins at different speeds at different lattitudes (the equator has a lot further to travel in one day than the poles) as the air moves in a straight line it appears to gain alot of velocity as the ground speed below slows (increasing lattitude) and speeds up (decreasing lattitude). This movement also creates a pressure differential that pulls in air behind it.

The jet tends to be very thin and reasonably broad.

Thats a basic explanation, the jet stream is a pretty complex beast it seems and I dont undertand in 100%. I was really shocked when I found out that the coriolis effect was such an important part of it.

[dorlomin]

but left "adiabetically" un-defined,

Adiabetic heating is where the air is compressed into greater density as it drops. This means there are more atoms in a smaller space with the same amount of energy, this shows ap as more collisions or heat.

On that point, does the air dropping onto the poles also warm up some as it falls and compresses? If so, does this keep the poles warmer than they otherwise would be?

Very very much so! When skeptics and warmists talk about climate they often like to drop in the phrase 'energy transfer' about the climate system. But the troposphere is much lower at the poles so when the air desends it has less distance to travel and be compressed by. So it gains less heat than it would over the mid lattitudes and over Greenland and Antarctica the ice sheets can be nearly 3km thick so the air does not have far to desend there! The air at the top of the troposphere can be as low as -60C so at 10C increase per kilometer down the air desending is not going to get all that warm. But at the equator what would be heat is transfered into thermal energy as rising air currents and phase change from water to water vapour, this helps cool the tropics, the heat is then either dissapated into space or carried further up the lattitudes where it returns to heat as it is compressed desending.

[Tanada]

So I was looking through the temperature records for my spot on the map in the Great Lakes/upper midwest and something odd I noticed. There are more extreme climate records for the 1950's than any other decade. In the 1950's this area set four all time monthly high temperatures but also set one all time monthly low temperature record, all of which are still standing today. November has one of each, a high record of 80F set November 1, 1950 followed by a monthly record low of 2F set November 24, 1950. The other record highs were set on January 25, 1950, August 31, 1951 and October 3, 1953.

Civilian air travel in the early 1950's were rare, so perhaps the same pattern has not repeated recently because of large numbers of contrails, but this was during the post WW II boom economy and coal haze was very much a common weather factor back before the Clean Air Act was created in the 1970's.

So any suggestions for what caused this period over several years when weather was unusually warm? Remember those four high temperature marks are still the records for those months, out of a 130 year long instrumental record.

[dissident]

So I was looking through the temperature records for my spot on the map in the Great Lakes/upper midwest and something odd I noticed. There are more extreme climate records for the 1950's than any other decade. In the 1950's this area set four all time monthly high temperatures but also set one all time monthly low temperature record, all of which are still standing today. November has one of each, a high record of 80F set November 1, 1950 followed by a monthly record low of 2F set November 24, 1950. The other record highs were set on January 25, 1950, August 31, 1951 and October 3, 1953.

Civilian air travel in the early 1950's were rare, so perhaps the same pattern has not repeated recently because of large numbers of contrails, but this was during the post WW II boom economy and coal haze was very much a common weather factor back before the Clean Air Act was created in the 1970's.

So any suggestions for what caused this period over several years when weather was unusually warm? Remember those four high temperature marks are still the records for those months, out of a 130 year long instrumental record.

The problem with such point temperature records is that they don't give a proper view of the regional and global temperature anomaly. In some sense they are "measure zero" data that is irrelevant. Of course, the inference is that there was some mesoscale or synoptic structure driving them so the points are correlated with more non-local temperature distributions. However, they are still in the "noise" category and raise the whole issue of variability and confusion surrounding it. If one were to sample continental middle-latitude temperatures around the globe for centuries and over every point one would get these clustered "outliers" showing up over and over. But they are not associated with the global atmosphere-ocean energy content. It is common to use such outliers to implicitly claim that the whole system is undergoing the same deviation from the mean. This of course is utter BS.

To answer your question specifically would require analysis of synoptic (weather) charts for the weeks in question. Which air masses were transported into this region and what sort of circulation existed at the time. Coal haze is composed of sulfate which has the effect of cooling and not heating. But that is a dangerous generalization. It is possible that the weather conditions were such that near-surface layers of sulfate haze contaminated with soot formed that acted like a greenhouse lid with dark tint. Sulfate aerosol is composed of water and sulfuric acid which will be a good infrared absorber but also a good visible band reflector. If it is mixed with soot then it becomes a strong absorber of visible light as well and could act to heat the layer of air it occupied even if absorption of visible band radiation is reduced at the surface.

Coal related pollution has a high soot content in addition to sulfuric acid. Temperature inversions could have trapped this pollution near the ground and created the local radiative transfer conditions for temperature spikes.