This chapter explores the characteristics of the atmosphere in spring. It relates the distribution of ozone and NOx to ozonesonde data and the temperature and movement of the air. My data sources are here for maps showing ozone and NOx profiles and here for ozonesonde data and here for maps showing temperature, pressure and wind.
The objective is to investigate the factors responsible for the composition, temperature, density and movement of the air. The discussion pertains to the origin of the planetary winds, cloud cover and surface temperature, in short climate change.
Above: Ozone at 50 hPa 11th to 13th September at six hourly intervals.
The diagrams above show ozone at the 50 hPa pressure level (20km) in the southern hemisphere at 6 hourly intervals. Observe that the rotation of the atmosphere above the Antarctic continent over 54 hours amounts to about half a circle. A full rotation at this rate would take 4.5 days.
It takes about 10 days for a mid latitude anticyclone to pass a point on the Earth’s surface at the latitude of southern Australia. It takes about five days for a polar cyclone to pass from one side of the continent to the other.
As the Earth spins on its axis the morning sun appears on the eastern horizon. The atmosphere moves from the west to the east rotating faster than the Earth itself. The rate of rotation of the atmosphere increases with latitude. In winter, in high latitudes, the rate of rotation also increases with height. This is counter-intuitive. It is commonly asserted that the heat that is absorbed in the tropics is providing the energy to drive the circulation of the air. In general, wherever energy is applied to a system, that is where the most vigorous response is to be found. The movement of the atmosphere, more exaggerated at the poles than at the equator, suggests that the force driving the circulation is being applied at or near the poles. In fact, the greatest depression of surface pressure and the greatest peak in atmospheric pressure on a global scale is to be found in the region of the Antarctic continent in winter. The strongest winds at the surface of the planet merge at 60-70° south latitude. The variation in the temperature of the Earth at every particular latitude is greatest in the middle of winter when the flux in the ozone content of the air is most extreme.
The distribution of ozone at 50 hPa might be described as annular or ring like in shape surrounding the pole. Tracers of ozone fan out towards low latitudes from nodes of relatively high ozone partial pressure. Such a node is located between Antarctica and Australia/New Zealand as seen in the diagram above.
The tracer pattern of ozone distribution is similar to what we observe when a broad bladed paddle is applied to a can of paint. As we stir, a vortex is created in the middle where the centre of the circulation is depressed in relation to the perimeter. Intuitively, the Antarctic circulation is driven in a similar fashion. There is obviously no broad bladed paddle at work. The differences in air density on either side of latitude 60-70° south that give rise to polar cyclones increase as the ozone content of the air is enhanced in winter. The seasonal descent of very cold mesospheric air over the pole chills the interior as the ozone content of the air increases outside the margins of that very cold mesospheric air. These developments together create a situation of atmospheric stress related to extreme differences in air density that is entirely local in origin. We know that the ‘zonal wind’ (east west) varies in conformity with geomagnetic activity. So it is likely that the driving force of this system is in part compositional (density related) and in part electromagnetic in origin.
This description of the forces responsible for the winds in high latitudes is very different to that given in the ‘climate science’ of this day. In fact climate science can not enlighten us as to the origins of the zone of extremely low surface pressure on the margins of Antarctica or the indeed the historical decline in surface pressure in high latitudes let alone the reversal in that process of decline that is currently under-way.None of these features rate a mention. Climate science is dominated by radiative theory and the notion that back radiation from ‘radiation absorbers’ like CO2 and water vapour drives surface temperature. Geographers are out of fashion. Mathematicians and Physicists who know little of the geography of climate hold sway.
Above: Ozone at 50 hPa at daily intervals.
The diagrams above show the state of the atmosphere at daily intervals. Every particular feature changes in shape over the 24 hour interval between one diagram and the next. There are locations centred on latitude 30° south where ozone partial pressure is low and atmospheric pressure tends to be persistently high. One such lies in the Indian Ocean to the west of Australia a second in the Pacific to the west of the South American continent. A third is located in the South Atlantic to the west of Africa
We can relate the distribution of ozone to that of the chemical family referred to as NOx as seen below. This family catalytically destroys ozone at any temperature. Like any reaction the higher the temperature the faster it will proceed. A catalyst is a substance that increases the rate of a chemical reaction without itself undergoing any permanent chemical change.
Above: NOx at 50 hPa
The NOx that manifests in this ring like fashion originates in the troposphere and enters the Antarctic circulation from the north in a lateral fsashion. See the charts of NOx at 100 hPa below that indicates little or no NOx in high latitudes at this level. There is NOx in low latitudes but none near the poles.
The core of low NOx values at 50 hPa seen above contracts in diameter like the aperture of a camera over the ten days prior to August 30th. As it does so, day by day ozone is eroded.
Above: Nox at 100 hPa.
The distribution of NOx at 50 hPa on the 30th August can be compared to the distribution of ozone and the position of both in relation to the the zone of very low surface pressure that surrounds Antarctica.
I have traced the main features of the distribution of NOx in the diagram above and applied the resulting figure as an overlay on the figure below. NOx manifests in greatest concentration inside the annular ring of ozone rich air. That is as expected, given the ability of NOx to catalytically destroy ozone. The distribution of ozone is therefore a product of the movement of the air and is modulated by the presence or absence of NOx
In the same fashion, the figure indicating the distribution of NOx is overlaid on the map of surface pressure and wind at 250 hPa that is below. It is apparent that NOx is drawn into the ascending circulation created by polar cyclones. Air enters the circulation horizontally above 100 hPa and this air shows high concentrations of NOx and very little ozone. In the process it progressively floods the entire area over the Antarctic continent at the 50 hPa level. NOx closes in on the pole like the aperture of a camera. Bear in mind that the distance between the surface where pressure is measured and the 50 hPa level is 20 kilometres. At the surface the distribution of surface pressure is somewhat irregular. At altitude the circulation becomes increasingly smooth and ring like. This is the character of what is called the polar vortex. The vortex does not respect our notions of what is troposphere and stratosphere. It is not particular at all.
An ozonesonde consists of a small piston pump that bubbles ambient air into a cell containing 3 milliliters of 1% potassium iodide solution. The reaction of ozone and iodide produces a small electrical current in the cell, which is proportional to the amount of ozone. The ozonesonde is also interfaced with a radiosonde, which measures air temperature, pressure, relative humidity and transmits all of the data back to a ground receiving station. Total column ozone is calculated by integrating the ozone partial pressure profile up to the balloon burst altitude and adding a residual amount, based on climatological ozone tables, to account for ozone above the balloon burst altitude.
The ozonesonde data below was gathered at the US Amundsen Scott base at the south pole. The distribution of ozone in the diagrams below left relates to the 50 hPa level. Both diagrams relate to the 20th August 2015. Together they give us information about a vertical and a horizontal slice of the atmosphere.
AUGUST: On 26th August the partial pressure of ozone at 50 hPa at the pole is unaffected by the gradual ingress of NOx that is already in evidence on the 7th June at left because it begins only at the outer margins of the continent. The pole is as yet unaffected.
Above: Nox at 50 hPa. NOx occupies more and more of the space over the polar cap from June through to August. The seeds of the ozone hole are planted early. But on the 26th August the polar region is still NOx free.
KEY to diagram on the right: Fine black line: ozone on 26th August (see above). Green line: Generic indicator of pre-ozone hole extent, origin unknown. Blue line: Ozone partial pressure as measured 12 September. Red line: Temperature as measured on 12th September. Fine purple line: Temperature as measured on 26th August.
SEPTEMBER: By 12th September NOx is certainly beginning to erode the partial pressure of ozone over the pole but the extent of erosion depends not on the local temperature (-85°C at 70hPa) or the presence of sunlight (none), or the presence of noctilucent clouds, even though all may be favourable to chlorine chemistry but simply according to the patterns of movement in the air that progressively floods the polar cap with NOx. There are different air masses over the pole, different in their trace gas composition according to the presence or absence of NOx and this is the determining influence so far as total column ozone is concerned.
Notice that the seasonal minimum in total column ozone at the pole manifests between 50 and 100 hPa. There is a marked contrast between this deficit and the high ozone content of the air on the outside of the chain of polar cyclones. The formation of the hole exaggerates the contrast.
We see below that between 12th September and 15th October NOx floods the polar cap between 100 hPa and 50 hPa and the ozone simply disappears. The outer perimeter of the chain of polar cyclones marks an abrupt transition between high ozone values and virtually none at all. This is the month when surface pressure falls to its annual minimum at 60-70° south. This is not a coincidence. Surface pressure is a function of the vorticity of polar cyclones in turn a function of differences in air density between the northern and southern perimeter of this chain of polar cyclones. With zero ozone on one side of the vortex and a variable amount of ozone on the other side the stage is set for variability that arises entirely according to change in the partial pressure of ozone.
The polar circulation is now changing quickly as the stratosphere undergoes its final warming. See below. There is a strong increase in the temperature of the air above 50 hPa between mid September and mid October.
Notice the warmer air above 25km. Over the polar cap there is insufficient ozone in the air and insufficient air density to allow ozone to make a strong contribution to the temperature of the air above about 25 km in elevation. The increase in the temperature of the air that we observe in this month reflects a reduced influx of very cold mesospheric air and is due entirely to atmospheric dynamics. Warmer air from lower latitudes begins to occupy the polar cap as the polar vortex contracts in diameter and its degree of penetration. The two are actively mixed in the rapidly rotating cross currents of cold descending and warm ascending air across the polar vortex. As we will see the very cold air from the mesosphere enters laterally rather than vertically.
OCTOBER: A reminder: Surface pressure at 60° to 70° south falls to its annual minimum in October when the contrast between the ozone content of the ‘hole’ and its margins is greatest. There should be no doubt as to the motive forces behind this circulation and it has nothing to do with heating in the tropics or any of the circuitous arguments of those who theorise in the world of fluid dynamics who assume that all atmospheric motions can ultimately be put down to heating at the equator and the movements of air masses on a spinning circular orb. A pennyworth of observation is more valuable than a pounds worth of theory.
Below we see that 15th October marks the climax in terms of the presence of NOx over the continent. Unfortunately there is no data for NOx after the 25th November and we have to rely on the distribution of ozone as the sole indicator of the air flow. This is no real hardship because we know that one is always the mirror image of the other. Notice however that NOx declines in concentration after 15th October.
Above: NOx at 50 hPa.
Between the 15th October and the 18th November the air over the pole warms strongly as we see below and the vortex of cold air that descended over the pole is no more. The air in the core of the circulation has a temperature of -53°C on 10th October, and is surrounded by warmer air that is at -15.7°C at its warmest with much colder air on the perimeter and the core of the circulation ends up at -17°C a month later. The air outside the vortex remains at the same temperature.
NOVEMBER: The increase in the temperature of the air at 10 hPa (30 km) is reflected in the ozonesonde data for the 18th November. Total column ozone has increased but there is still a marked deficit between 100 hPa and 50 hPa that would be described as an ‘ozone hole’. This deficit can not be accounted for in terms of chlorine chemistry because the air at 50 hPa is now too warm for this to occur. The distribution of ozone simply reflects circulatory phenomena. The diagram at left shows that the greatest deficit in ozone is not above the pole but in the core of the now wandering circulation of swiftly warming air that is no longer locked into its winter position over the pole.
DECEMBER: It is plain from the diagram at left that the presence or absence of ozone is a product of the movement of the air masses. The ozonesonde data shows that at the 100 hPa level ozone is still heavily depleted by comparison with the August pattern indicating that disparate winds in the horizontal domain account for the presence or absence of ozone in the air. The blue ozone curve indicates fluctuating levels of ozone between 10 and 15 km in elevation and certainly a deficit by comparison with the month of August.
The red temperature line shows that a very definite tropopause is established at 9km (250hPa) in elevation associated with an increase in the ozone content of the air to only 4ppm that is sufficient at this pressure level to cause an increase in the temperature of the air. This indicates a reduced exchange of air in a north south direction and the establishment of relatively calm conditions. The surface pressure gradient between the continent and southern ocean is now falling away from its October extreme. Atmospheric pressure at 60-70° south latitude is now rising steeply as is seen below.
JANUARY: Features of the atmosphere include a very definite tropopause at about 9km in elevation. The top of the atmospheric column is cooling from its December peak as the upper circulation receives a marginally increased contribution of cold air from the mesosphere. We see at left that the bulk of the air at 50 hPa over the Antarctic continent is little differentiated in terms of its ozone content. Between the equator and 30° south the ozone content of the air at 50 hPa is much affected by the elevation of NOx and water from the troposphere that occurs in summer. We see that the interaction of the troposphere and the stratosphere is important in modulating the ozone content of the air above about 8 km in elevation at the poles and double that elevation at the equator. It is not the so called Brewer Dobson circulation that is responsible for the increase in ozone partial pressure in higher latitudes but the freedom from erosion by NOx from the troposphere and the low ionisation pressure in winter.
THE MARKED VARIETY IN OZONESONDE PROFILES ELSEWHERE ON THE PLANET
Summit Station at latitude 72° north is located on the highest part of the Greenland ice sheet. Land in high latitudes promotes high surface pressure in winter and low pressure in summer. In winter low pressure zones tend to locate over the ocean. The absence of a stabilising land mass in what is the Arctic Ocean means that the pattern of polar cyclone activity is much less annular than it is about the Antarctic pole. Apart from a persisting low pressure zone that establishes over the north Pacific most locations at 50-70° north experience low surface pressure on an intermittent basis.
Above: Ozone at 50 hPa between the 6th and the 14th March 2016.
There is a well established relationship between the ozone content of the air and surface pressure that goes back to the observations of Gordon Dobson and others prior to the 1920s. On the 6th March at Summit station Greenland, cold, ozone deficient air manifests in a lateral flow between 10 and 25 km in altitude and surface pressure is accordingly high. It is the elevated ozone content of the air on the 12th March that is responsible for low surface pressure.
Referring again to the sonde data, note the variation in the height of the tropopause between the 6th and the 12th March, the much cooler denser stratosphere at and about 50 hPa on the 6th and the strong response to the presence of ozone at 7 km in elevation on the 12th March and again at 20km of elevation. This illustrates the fact that the temperature of the stratosphere is a response to two influences. The first is the presence of ozone and the second, regardless of ozone content, the very different temperature of the air according to its origin.
Let us note that the high latitude stratosphere in both Antarctica and the Arctic is far from a quiescent medium. There are strong lateral flows beginning from as low as 7km of elevation in some locations but higher in others. It is the ozone content of the air above 7km in elevation that determines surface pressure and not the other way round.
Secondly, let us note that from one year to the next there is a large variation in the concentration of ozone in the atmosphere as is evident by comparing the diagrams above and below.
Above: Ozone at 50 hPa between the 6th and the 14th March 2015
Thirdly, let us note that the ozone structure at 50 hPa is very different in comparable spring months between the Arctic and the Antarctic. The Arctic is relatively supercharged with ozone and the vortex is both highly variable in terms of the its shape and also its location. The Antarctic works at more moderate levels of ozone but it maintains a stable vortex with an extreme gradient in ozone partial pressure and hence surface atmospheric pressure between the inside and outside of the vortex. The vortex plays a much stronger role in modulating the ozone content of the southern hemisphere than it does in the northern hemisphere and drives down the ozone content of the entire southern hemisphere. In fact it can be demonstrated that the southern vortex modulates the ozone content of the global atmosphere on inter-centennial time scales and in doing so modulates the distribution of atmospheric mass and hence the planetary winds, cloud cover and surface temperature. Ozone therefore modulates the distribution of energy and the temperature gradient between the equator and the poles.
2. Suva, Fiji
Suva is the capital city of Fiji located at 18° south latitude on the margin of a very large area of high surface pressure that spreads eastward to South America. We see that total column ozone values at this latitude are comparable to the Antarctic in summer and there is a marked deficit in ozone between about 7 and 17 km in elevation, not greatly different to the circumstance in the Antarctic in October.There is a similar ‘hole’ to that in Antarctica but the Suva hole is invariable. If air of this nature travels to Antarctica (and it does) it will be seen to be NOx rich and ozone poor.
An interesting variation in the ozone content of the air occurs in the troposphere. It is clearly related to the shape of the temperature profile. As ozone dissipates from these stratified layers into the air above and below it will affect cloud cover. In October and November average rainfall in Suva is in excess of 200 mm per month. Surface temperature varies between 23 and 26°C across the year peaking in February. As the air warms it has the capacity to absorb more moisture. In a warming regime clouds will disappear resulting in a warmer surface on land or increased absorption of energy by the sea. We call this weather on daily time scales, seasonal variation on inter-annual time scales and climate change on longer time scales and its all entirely natural in origin.
The tropopause is well marked and much elevated at all times of the year. The temperature profile above about 18 km in elevation indicates a strong response to the presence of ozone that is only possible in relatively still air. The temperature of the air increases at elevations above 27km (20hPa) despite the falling away of ozone partial pressure indicating a strong contribution from ionising short wave radiation from the sun in the very exposed latitudes close to the equator. Above 20 hPa there is only 2% of the atmosphere to intercept short wave energy from the sun.
3. Pago Pago
Pago Pago is situated at 14° south latitude in the south west Pacific. The ozone regime is very similar to that at Suva. Notice the temperature response to the presence of 5-6ppm ozone quite close to the surface on 9th December. As Gordon Dobson observed, it is not uncommon to find parcels of very dry air from the stratosphere in places where they are least expected.
4. Huntsville Alabama.
Huntsville Alabama experiences a great deal of diversity in the nature of the air masses, the ozone content of the air, the ozone profile, the speed and ozone content of the wind at different elevations and therefore the height of the tropopause. Note that on the 12th March there is a minor temperature response despite the presence of 10 ppm ozone at 13-15 km of elevation. This suggests that an influx of relatively ozone rich air from higher cooler latitudes is responsible for the low temperature, apparently a relatively frequent phenomenon. On the 2nd March at 10 km in elevation we have 10 ppm ozone and no temperature response at all.
5 Trinidad Head, Humbolt County, Northern California 40° north latitude
Trinidad Head is much subject to a rising and falling tropopause as the ozone content of the air changes with the origin of the travelling air masses. The stated total column ozone value for the 20th January of 99999 Dobson Units illustrates the magnitude of the error that is possible when using ‘climatological tables’ to infer total column ozone when the helium balloon carrying the ozonesonde bursts at a low altitude.
- Ozone maps surface pressure. The primary driver of change in surface pressure globally is the variation in the ozone content of the air between the surface and 50 hPa.
- The variability in the ozone content of the air manifests in both the troposphere and the stratosphere in the main between between about 7 km in elevation through to 20 km in elevation (350 hPa to 50 hPa).
- The vigorous lateral circulation of the air at and above 250 hPa is a prime driver of the ozone content of the air at particular locations on a day to day basis. The lateral movement of the air in the upper troposphere-lower stratosphere is associated with changes in surface pressure and weather on day to day time scales.
- Ozone at 4 ppm in the lower troposphere can drive an increase in the temperature of the air. This will affect cloud cover and in a regime of changing ozone partial pressure that will drive change in climate. This appears to be the mechanism behind the observed relationship between geopotential height and the temperature at the surface of the planet.
- Change in the ozone content of the air is responsible for change in the weather on day to day intervals and the climate on longer time scales. As Gordon Dobson discovered in the 1920’s Total Column ozone maps surface atmospheric pressure. Unfortunately ‘climate science’ went on a mathematical picnic in the 1960’s and has yet to return to the task of coming to grips with the nature of weather and climate, as it is observed and as it evolves. Dobson was first and foremost an observer and secondly an enormously resourceful inventor of instruments to gather the data necessary to describe the nature of the atmosphere and its modes of change. He left little in the way of written work but his ‘Exploring the Atmosphere’ of 1963 is seminal.
- The atmosphere has a history that is indissolubly linked to the evolution of surface atmospheric pressure at 60-70° south latitude.
LINKS TO EARLIER CHAPTERS
How the Earth warms and cools in the short term….200 years or so…the De Vries cycle
Links to chapters 1-23