Guest post by Philip Mulholland and Stephen Wilde

“No government has the right to decide on the truth of scientific principles, nor to prescribe in any way the character of the questions investigated.” Richard P. Feynman.

Figure 1: The Terrestrial Companions.

In this dual scene montage, we see on the left the Earth viewed by the DSCOVR: Deep Space Climate Observatory from its position in solar orbit at the sun side Lagrange Point.  In this view we also see the fully illuminated far side of the Moon as it transits the Earth at new moon on the 5th July 2016.

On the right is the iconic image of Earthrise taken on 24th December 1968 as Apollo 8 orbited the Moon.  The continent of Antarctica is clearly visible, fully lit as the Earth’s axial tilt presents the south pole towards the sun at the height of the austral summer.  The image is displayed here in its original orientation, though it is more commonly viewed with the lunar surface at the bottom of the photo. (Image Caption Credit NASA).

1. Introduction:

The history of Climatology is long and honourable, indeed the very concept of climate goes back to the Greek philosopher Aristotle, who identified the three main climatic zones known to the ancient world.  These zones are: –

A. The Torrid Zone – located to the south of Greece in Africa.

B. The Frigid Zone – located to the far north of Greece where lives Boreas, the god of the north wind and winter.

C. The Temperate Zone of Europe, where the four annual seasons occur, and Greece is most favourably located.

Aristotle’s three climate zones can be directly linked to the three main atmospheric circulation cells that we now recognise within the Earth’s atmosphere.  These three cells are: –

A.         The Hadley cell, which is a thermal cell, driven by solar radiation from space heating the planet’s surface.  Two zones of Hadley cells exist in our atmosphere, these are both found in the Tropics and are generally located between the Equator and the Tropic of Cancer in the northern hemisphere and the Tropic of Capricorn in the south.  The Hadley cell’s poleward limit is located in the Horse Latitudes; where a zone of descending air exists forming surface high pressure anticyclones.  It is the Hadley cell that is the defining atmospheric feature of Aristotle’s Torrid Zone.

B.         The Polar cell, which is also a thermal cell, but it is driven by atmospheric circulation caused by radiation cooling from the ground surface directly to space.  This radiative cooling produces an atmospheric surface inversion, that is most noticeable in winter.  The Polar cell’s equatorward limit is marked by the Polar Front, an oscillating band with an associated strong horizontal surface temperature gradient; above which is found the jet stream of the upper troposphere.  The Polar cell is responsible for the formation and surface export towards the equator of cold dense airmasses.  It is the Polar cell that is the defining atmospheric feature of Aristotle’s Frigid Zone.