34 LOCAL WEATHER

My impression is that  winter of 2016 has been unusually cold. But rather than trust my senses I went looking for data.

Cape Leeuwin is the closest station in the Australian ACORN network. The stated purpose of the network is to maximise the length of record and the breadth  of the coverage across the country.

The Cape Leeuwin lighthouse sits on a granite rock where the Southern Ocean meets the Indian Ocean at 34° 34′ south latitude. When the wind blows from the west it is the Indian Ocean temperature that is being sampled and when it blows from the north east its the air coming off the Australian continent. Three lighthouse keepers cottages made of local limestone sit in the lee of the lighthouse and the wind blows day and night.  At the rear of each house stands an external wash house with an old fashioned twin basin concrete trough and a wood fire heated ‘copper’ for boiling water. Its a lonely spot but the fishing is good. The nearest centre of population to the west is Cape Town.

Leeuwin position
Fig 1 South West of Western Australia, weather data stations on the Acorn network.
Cape Leeuwin
Fig. 2 Temperature at Cape Leeuwin lighthouse.

Black lines record the linear trend as calculated by Excel and indicate cooling. Red dotted lines track the highest summer maximums and the lowest winter minimums and they have a very similar slope to the black trend lines. Horizontal lines enable us to see that the minimum has declined by 0.7°C and the maximum by about 1°C. We know that over the last  five years there has been warming in the tropics that compares in its intensity to that seen prior to 1998. The trend at Cape Leeuwin is directly opposed to that.

ENSO 3.4

Notice the deformation of the curves in mid summer and the skinny little peak in 2014-15, not a good year to be trying to ripen a crop of grapes.

When the air blows off the continent in a warm year the temperature can reach 40°C but that is rare. By contrast there is very little variation in the minimum temperature but it does vary more in winter than summer.

The deformation of the winter minimums looks like ‘shark attack’. This is driven from the Antarctic. It works this way: A change in the intensity of polar cyclone activity in high latitudes modifies the differential pressure between the mid latitudes and the poles and also cloud cover. But for this influence we would see something like a smooth sine wave at the turning points in summer and winter. The beauty of having data for the minimum and the maximum temperatures is that you see the patterns of variability. When you average you lose information. The bits you lose are vital.When you average the temperature for the whole globe you are either a fool or a knave and I would immediately expect that you have an agenda to push.

I will describe the warming cycle that applies to the mid latitudes in the southern hemisphere but before I do let me suggest that these latitudes are very important to the global heat budget because water absorbs energy and acts like a battery and these latitudes are almost an uninterrupted sweep of water: When surface pressure falls at the pole it is accompanied by a warming of the stratosphere due to a build up in ozone. The falling pressure at the pole induces an enhanced flow of warm air from the equator.  Cape Leeuwin then warms in the middle of winter because the air comes from a warm place. At the same time more ozone descends in the mid latitude high pressure cells. Ozone warms by absorbing infrared. The warming of the air reduces cloud cover allowing extra solar radiation to reach the surface. In meteorological terms there is an increase in geopotential height as the atmospheric column warms, a reduction in cloud cover, that you could never directly measure, but you can infer the fact due to the fact that the surface warms. The cooling cycle is the reverse. It starts with a reduction in the ozone content of the air in high latitudes and rising surface pressure in the mid latitudes as polar cyclone activity falls away. Increased cloud cover cools the mid latitudes and cold air from the south finds its way more frequently into the mid altitudes.

The last seventy years has brought a secular decline in surface pressure in high latitudes and an increase in surface pressure in the mid and low latitudes as is apparent in figure 3. Nowhere is surface pressure higher than in the 30-40°  south latitude. The latitude of Cape Leeuwin  is 34° 34′ south. This latitude is home territory for a travelling band of enormous high  pressure cells of relatively cloud free air. When pressure increases cloud cover falls away.

pressure
Fig. 3 Evolution of sea level atmospheric pressure in the southern hemisphere since 1948.

The seventy year increase in surface pressure and the parallel increase in sea surface temperature in the low and mid latitudes of the southern hemisphere is documented in figure 4

SST and Surface pressure 1
Fig. 4

Figure 5 reveals that surface pressure at 40-50° south has risen very little while surface pressure at 50-60° and 60-70° south latitude has declined strongly. That is a function of relative area. Not shown is surface pressure over the polar cap that closely follows the trends at 60-70° south.

SST and SLP
Fig. 5

Notice that sea surface temperature rises and falls with  surface pressure throughout. This relationship is good for change in both directions in both the short and the long term. Notice the marked discontinuity in surface temperature at 60-70° south after 1976.

Naturally, the temperature increase across the latitude bands is uneven. The largest whole of period variation of 2°C is seen at 60-70° of latitude due to the increased incidence of warm north westerly winds with an abrupt shift between 1976 and 1978. The more or less parallel behaviour in the curves since that time is what we observe in mid and high altitudes, a classic cloud cover/wind direction response that occurs on short term like daily and monthly time scales, and also long term, annual, decadal and longer time scales. This response to the ozone content of the atmosphere drives short term change like that observed in figure 2 and long term change that I will document in the next post that will be devoted to one hundred and six years of data from Cape Leeuwin a treasure trove of  temperature information due to the diligence of lighthouse keepers in patiently recording the minimum and the maximum temperature every day, except on those few days where, unaccountably, they didn’t.

The next largest variation in temperature  is seen in the tropics where variation in the intake of cold waters from high altitudes gives rise to big variations in sea surface temperature that are unrelated to cloud (very little anytime) or winds (very light). The next largest variation is in the latitude of Cape Leeuwin at 30-40° south where the  variation is 0.97°C. This core region for travelling anticyclones of descending air. These HIGHS are greatly susceptible to variations in geopotential height that proceed in concert with surface temperature. This is documented in figures 6 and 7.  Increased geopotential height always brings warming.  The contrast in temperature according to wind direction is less here than in high latitudes adjacent to the Antarctic ice cap. It is safe to conclude that the response of surface temperature to increased geopotential height in low and mid latitudes is chiefly due to a change in cloud cover.

SST and GPH low
Fig 6
SST and GPH high
Fig 7

In examining this data one must remember that geopotential height is simply the height of a pressure surface. For example the 500 hPa  pressure level is found on the average at 5500 metres above sea level. When the air below that pressure level is warmer, geopotential heights will exceed 5500 metres and the warmer the atmospheric column the higher one has to go to get to the pressure surface. Heights change on daily and weekly time scales and are clearly associated with change in surface temperature and cloud cover. High heights are associated with high pressure anticyclones that bring fine sunny weather. At Cape Leeuwin low heights are associated with polar cyclones, high winds, cloud streaming in from the north west and frontal rainfall. The latter is the winter pattern and the former is the summer pattern.

There is also a close relationship between air temperature and the geopotential height at particular pressure levels as we see in Fig 9 and 10. In these figures we are looking at  heights at the 200 hPa level where the presence of ozone is associated with Jet stream activity. When heights vary at 200 hPa they  vary in the same direction at 500 hPa and 700 hPa because in these high pressure cells the air constantly descends. Cloud can be found at all levels, especially in the early part of the day. Clouds that exist as multi branching crystals of ice  have a relatively large surface area are highly reflective.

Temp and GPH low
Fig 9
Temp and GPH 2
Fig 10

Notice the overt expression of the 1976 climate shift between 15° south and 40° south where anticyclones circulate. This change is expressed as the jump in sea surface temperatures in the tropics as seen across the latitude bands in figure 6 and even more so at 60-70° of latitude in figure 7 where change in the wind direction is associated with a large change in surface temperature.

Notice also the strong drop in surface pressure at 50-60° south in the 1990’s that is associated with a fall in geopotential heights and also sea surface temperature.

What is described here is not new to ‘climate science’ as it existed fifty years ago. But most of the cohort of scientists that learned their trade in the satellite age will be unfamiliar with this train of thought.

Edward N Lorenz of the Massachusetts Institute of Technology back in 1950 published an article entitled  ‘The Northern Hemisphere Sea-level Pressure Profile’ and the abstract reads as follows:

The variations of five-day mean sea-level pressure, averaged about selected latitude circles in the northern hemisphere, and the variations of differences between five-day mean pressures at selected pairs of latitudes are examined statistically. The northern hemisphere is found to contain two homogeneous zones, one in the polar regions and one in the subtropics, such that pressures in one zone tend to be correlated positively with other pressures in the same zone and negatively with pressures in the other zone. Considerable difference is found between the seasonal and the irregular pressure-variations which result from mass transport across the equator, but the seasonal and the irregular variations of pressure differences resemble each other closely, as do the seasonal and the irregular pressure-variations which result from rearrangements of mass within the northern hemisphere. The most important rearrangements appear to consist of shifts of mass from one homogeneous zone to the other. These shifts seem to be essentially the same as fluctuations between high-index and low-index patterns. The study thus supports previous conclusions that such fluctuations form the principal variations of the general circulation, and also shows that, except at low latitudes, the seasonal pressure-variations are essentially fluctuations of this sort. The possibility that the seasonal and the irregular variations have similar ultimate or immediate causes is considered. 

Prior to 1979 when satellites were used to obtain data for the entire globe very little was known about the Southern Hemisphere where the most powerful driver of the atmospheric circulation is to be found. Although the Arctic Oscillation had been well documented the Antarctic Oscillation had not. Lorenz did not have the data at his disposal. Today we do. But, nobody is looking!

At one time people were aware that the surface pressure relationship between the mid and the high latitudes changed over time. Nobody knew why. Some canny researchers documented a correlation with geomagnetic activity implicating  the solar wind but the  actual mechanism  eluded them.

Gordon Dobson’s students explored this issue as soon as they had a single years data for total column ozone as he recalled in 1968 in his lecture ‘Forty Years Research on Atmospheric Ozone at Oxford: a History’, in these words:

Chree, using the first year’s results at Oxford had shown that there appeared to be a connection between magnetic activity and the amount of ozone, the amount of ozone being greater on magnetically disturbed days. Lawrence used the Oxford ozone values for 1926 and 1927 and in each year found the same relation as Chree had done. 

Early observers of ‘sudden stratospheric warmings’ had a suspicion that the phenomena were somehow connected with the sun. Researchers like Van Loon and Labiske pointed out that the solar cycle was clearly associated with aspects of the behaviour of the stratosphere.

But these lines of investigation became matters for the fringe dwellers in the atmsopheric sciences, the sort of people who don’t get invited to dinner parties, when Houghton took over from Dobson at Oxford , a mathematician and a physicist and a devotee of the notion that the carbon dioxide content of the atmosphere governed near surface temperature. At that point climate science fell into a hole of superstition and conviction based not on observation but ‘belief’. Climate science morphed into a religion. Houghton went on to chair the IPCCC body responsible for linking the activities of man with climbing surface temperature. Naturally at that point climate science then began to attract a lot of interest and funding, particularly in the United States where NASA under James Hansen saw the opportunity to create a role for itself in keeping an eye on what was happening. The time of the self funded gentleman scholar, like Dobson was over the time for proselytisers had arrived and the gravy train was immense. Even Australia’s CSIRO had a cohort of more than a hundred scientists working on the problem.

To this day there is no appreciation of the origin of the circumpolar trough of very low surface pressure that surrounds Antarctica.  There is no appreciation of the role of ozone in creating that trough or its role in driving high wind speeds in that part of the upper troposphere that overlaps with the lower stratosphere, the origin of upper air troughs, no appreciation of how these troughs propagate to to surface to initiate a ‘cold core’ polar cyclone. Where ignorance and superstition rule the day there can be no appreciation of the role of the polar atmosphere in driving the entire circulation, the atmosphere super-rotating about the planet in the same direction as the planet spins but faster at higher latitudes and altitudes, fastest at the point where the atmosphere begins to conduct electricity (although it does so all the way to the surface) where it dances to the tune of the solar wind. The notion that the Earth exists in an interplanetary environment held in ordered embrace by  electromagnetic fields where the atmosphere is the outer mobile skin that is first  affected by those forces and so driven to rotate and thereby to some extent dragging the Earth with it, the whole apparatus working like clockwork that is forever wound up by the thermonuclear furnace at its very core….all thoughts of this nature are now anathema.

One could give most of the climate scientists trained since the start of the satellite age free membership of the Flat Earth Society. They would fit in very nicely.

IF CAPE LEEUWIN HAS BEEN COOLING WHILE AN EL NINO EVENT HAS BEEN BUILDING IN THE TROPICS WHAT HAS  BEEN HAPPENING ON THE EAST COAST OF AUSTRALIA?

Coffs long
Fig 11 Coffs Harbour 20 years minimum daily temperature

Coffs Harbour is 3° of latitude closer to the equator than Cape Leeuwin. This coastal town is subtropical and is the home of the Big Banana. It experiences a 12°C range in its minimum  as against 8°C at Cape Leeuwin. Cold air flows off the continent in winter driving the minimum lower. The other main driver of local temperature is the temperature of the  ocean waters flowing southwards down the coast. Warm water is present in winter in El Nino years due to the build up of warmth across the tropics and the anticlockwise rotation of the Pacific Ocean. It is in winter that the differential pressure driving the westerlies of the southern hemisphere is  at its maximum speeding the flow of the Antarctic circumpolar current that flows northwards towards the equator on the eastern sides of the Ocean basins and southwards on the western sides of the ocean basin. In this circumstance one would expect change in the winter minimum at Coffs simply because the winds that drive the currents blow harder in winter. I refer of course to the roaring forties the furious fifties and the screaming sixties.

The dotted lines at  the limits of the range are horizontal. Judged by eye, they indicate no warming or cooling.  The trend calculated by XL descends.

Nowhere in the course of this analysis have I referred to carbon dioxide in the air, a matter  that is irrelevant to atmospheric dynamics and the course of change in surface temperature. In the next chapter I look at 106 years of data from Cape Leeuwin that is as representative of conditions in the Southern Indian Ocean, as you are likely to find in the data from a single weather station..

 

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9 thoughts on “34 LOCAL WEATHER

  1. “notice the marked discontinuity in surface temperature at 60-70° south after 1976….”. By this chart alone it looks more like a re- continuity. Ie poor prior to 1978 and typical afterwards.

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    1. Correlation is the word rather than continuity. But both apply to this situation I think. I have not figured out what is going on at 60-70° south latitude prior to 1976. Any suggestions? The correlation with GPH looks as if its direct so that suggests cloud driving temperature.

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  2. Hmm, I am looking closely at the 60-70S GPH at 200 HPa. Its flat- like the dog that did not bark. Maybe its the SST thats the anomoly here. I have read there were large changes in ice coverage which might change albedo and cloud coverage. I am currently distracted by waves…..rossby, Kelvin, magentic, earth, etc and Coriolis. Did not realise their were so many… Grant Money?. Anyway, the reason I am looking here is the moisture, ozone and velocity is just outside the SH vortex and inner vortex breakouts seem to be where the extremes occur. so what causes split vortexes. Anyway, thats my barrow. Yours is going well and I will get back to 1978. Its a niggle.

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