Posted by: erl happ | March 11, 2009

“The atmosphere dancing” …… the short version

This is a description of how the sun causes El Nino and La Nina.

La Nina cooling

The strength of the polar vortex depends upon the absolute density of the atmosphere above the pole.

When the sun is quiet the paucity of short wave radiation enables the atmosphere to contract. In this condition it is little affected by the solar wind because the wind needs particles with an unbalanced electrical charge (ions) to work with.

When the atmosphere above the pole is dense and compact the Polar vortex is strong.

The Polar vortex brings compounds of nitrogen from the mesosphere that directly erodes ozone from the stratosphere.

The mixing of mesospheric air with stratospheric air is observed between the pole and 40° latitude.

The fall in the ozone content also occurs in the interaction zone between the stratosphere and the troposphere. The temperature of the air varies directly with its ozone content.

The fall in temperature in the upper troposphere is associated with increased density of ice cloud and greater reflection of the suns rays. Less reaches the surface.

This fall in the ozone content of the upper troposphere  is also associated with a strengthening of the mid latitude pressure cells that drive the trade winds and the westerlies.

El Nino warming

When the sun is active there is more short wave radiation.

The ionosphere and the thermosphere are inflated.

The solar wind can then move the atmosphere.

A geomagnetic disturbance (measure of the solar wind) is associated with a thinning of the atmosphere over the poles.

The polar vortex weakens and the ozone content of the stratosphere and upper troposphere increases.

The temperature of the upper troposphere increases causing evaporation of the ice cloud.

More solar radiation then reaches the surface.

The high pressure cells at mid latitudes are weakened and the Trade winds falter.

How do we know that the polar atmosphere thins under the joint stimulus of greater levels of ionising short wave radiation and the solar wind?

As the vortex weakens the increase in ozone content at high latitudes causes dramatic warming. At precisely the same time the stratosphere over the equator cools. This association indicates a shift in the atmosphere from the pole towards the equator.

A comparison of 10hPa temperature over Antarctica and over the equator reveals that the relationship is systematic.

Cycles of heating and cooling

ENSO has a cyclical period of about four years. But there is a longer cycle which produces a tendency towards warming or cooling to persist over multiple solar cycles.

Examination of the temperature at 10hPa over the poles reveal long term cycles of increasing and decreasing temperature. 10hPa temperature over Antarctica increased dramatically in the period 1974-1978. Since that time 10hPa temperature has been slowly declining. This indicates ozone loss associated with a strengthening vortex and a weakening solar driver. The sun has weakened in terms of both its sunspot and geomagnetic activity.

Where is the fluctuation in ozone content in the stratosphere and upper troposphere greatest?

The largest fluctuation is seen outside the vortex at latitudes 30-60°.  This is the zone inhabited by the subtropical high pressure cells that are part of the Hadley cell. The expansion and contraction of the Hadley cell is the essence of climate change as it is observed in the troposphere.

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Responses

  1. Thank You!
    I will be refering people here for this also.

  2. Great Praisee Erl. What do you think modulates the multidecadal cycle? Is it quasi periodic depending on solar cycle strengths?

    • Hi Tallbloke,
      There is a multididecadal swing but the period changes over time. No individual solar cycle is ENSO neutral. Looking at the past, the swing in the Southern Oscillation index can be extrapolated for the next solar cycle.

      I think a big conditioning influence is the concentration of ozone in mid latitudes of the southern hemisphere. That depends upon the strength of the vortex. Weak sun means strong vortex. But it also means the concentration of nitrogen oxides falls away. Pity that we only have data on temperature in the stratosphere since 1948. We really need 100 years or more.

      If we are indeed about to experience another grand minima the next thirty years will tell us a lot. The little data that exists for the early 1800s and also the example of what happened in the weak solar cycle 23 suggests that the La Ninas will be deeper and the El Ninos stronger when the sun is weak. If the ionising radiation and the solar wind are both weak the oscillation is less modulated by the sun and more by the natural tendency of the Earth to swing between strong cooling that dries the atmosphere and strong warming that humidifies it, but at a rate that is insufficient to provide enough cloud cover to stop the warming, until the atmosphere is near saturation and a cooling cycle is set in train.

      But, its all very vague.

      Perhaps the residual warmth in the ocean will be the source of prolonged evaporation tending to lengthen the cooling cycles. The current La Nina looks like its going to continue, at least while the sun is weak. But it is all the time drying the atmosphere. It can not last forever.

      It’s a multi-factorial problem.


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