Waiting for the sunrise...not long to go now! We will see the disk of the sun again in two days time but the maximum solar elevation will not be positive until 16.7. It is difficult to describe the effect of the return of the sun after more than a month of days consisting of a few hours of twilight and the rest of the day darkness - just as with the changing seasons it signifies a new beginning and, in a short while, the return of life as the penguins return to start their nesting preparations all over again. To us it also means that the time of our stay here is getting shorter. It feels like turning a corner and heading towards something finite.

Midwinters celebrations were undertaken with the appropriate grandeur and humility that can be expected. Numerous midwinters greetings were exchanged between Antarctic stations (McMurdo, South Pole, Rothera, Halley, Dumont D'Urville, SANAE, Scott Base, Syowa, Signy and so on) and some faxes were also received from old ANARE (Australian National Antarctic Research Expeditions) expeditioners. The midwinters celebration started with a polar plunge (-1.8 C water) in the morning followed by a brunch and a bath in the old snow melter (37 C water), pre-dinner canapes and drinks, the most delicious dinner (see the above photo of the dinner table) and finallly the midwinter's play and other entertainment such as poetry, songs and guitar music. I feel very privileged to have experienced this Antarctic tradition that has gone uninterrupted since the first winterers started it in Scott's and Shackleton's days.

Since I last made an entry we have acquired a lot of new lidar data with the weather staying nice and clear for several days at a time permitting collection of near-contiguous datasets. PSCs were first detected above Davis on 13.6 and have been present in every observation since then. I also obtained some visual images of them and in the above photo they can be seen as white wavy streaks in the sky. These are type 1 PSCs which consist of either solid nitric acid tri/dihydrate or supercooled solutions of water, nitric acid and sulfuric acid. The "ripples" just discernible in the photo are probably gravity wave effects. The stratosphere within the polar vortex above Antarctica has been progressively depleted of nitric acid since late May and, lately, water vapour as a result of continous condensation of these clouds as the air whirls about the pole. The daily Aura MLS plots clearly demonstrate this annual phenomenon and by late June the depletion of nitric acid within the vortex low temperature region (where temperatures are below ~196K) was nearly complete. Heterogeneous processing of chlorine compounds by these clouds is also visible as the increasing mixing ratio of ClO outside the polar night terminator and the depletion of HCl inside the vortex. PSCs contribute to ozone depletion in two ways. Firstly they allow heterogeneous (multi-phase) chemical reactions to proceed on the particle surfaces that would not proceed via gas-phase-only mechanisms (the "usual" ozone depletion cycle). These reactions liberate chlorine from its main reservoir species HCl and ClONO2. Secondly the existence of polar stratospheric clouds allows irreversible removal of nitrogen and water from the stratosphere which in turn allows ozone depleting reactions to continue longer (due to the effect of this removal on chlorine partitioning). This latter process, sedimentation, proceeds by downfall of solid phase cloud particles from stratosphere to troposphere.

The uplifting events of the past weeks naturally include the launch of the Discovery and its safe arrival at the ISS. I can never watch a launch without an intense feeling of pride and hope - if only we could reach further and conquer the biggest challenge of all - to not obliviate ourselves before we reach the technology and maturity to explore (and inhabit) the rest of the solar system. And the Milky Way. And the local group. And the supercluster. Or maybe another civilisation finds us first - if they do I hope that they are less fearful and aggressive of the new and unknown than we are.