Part IV. The Ozone Hole - Current Research Work

Where Does All The Ozone Go?
A major European campaign, the European Arctic Stratospheric Ozone Experiment (EASOE) was organised to study the polar regions during the winter of 1991/92. Much new information was gained, but many questions still remained:
What caused the mid-latitude loss?
How were the losses over the poles linked to those at mid-latitudes?
While CFCs and the bromine-containing compounds known to destroy ozone over the poles are strongly implicated in the mid-latitude loss, many uncertainties remain.
In 1994 and 1995 European scientists conducted SESAME, the Second European Stratospheric Arctic and Mid-latitude Experiment. They investigated the processes occurring at both high and mid-latitudes and how they are linked. At the same time a US-led expedition considered similar processes in the southern hemisphere.
Day 20 (11 September '94)The latest European campaign is called THESEO (THird European Stratospheric Experiment on Ozone) which takes places from 1997-1999. Scientists from many European countries, including some of this site, are collaborating on a wide range of experiments to determine the processes responsible for depleting ozone in the lower stratosphere but at mid-latitudes over the northern hemisphere.
The European Ozone Reserach Coordinating Unit have full details of the THESEO programme. Visit their website to find out more about the missions planned, press releases and the latest report of the UK Stratospheric Ozone
Day 40 (1 October '94)Review Group.
Chemical Modelling
Most of the research work here at the Centre for Atmospheric Science involves various computer models of the atmosphere. These models 'blow' (or advect) chemical species around the globe using known or computed weather patterns - winds, temperatures and pressures. The rates of various chemical reactions are dependent on temperature, pressure, and, in the case of photolytic processes, the position of the sun. At each step of the model, the computer code attempts to predict what chemical changes will occur by solving the equations representing each reaction.
Day 56 (17 October '94)The schematic figure below gives some idea of the different parts of such computer models and the sequence of events are the model executes on the computer. Such models can be, and often are, very complex with many man-years work behind them.
Anatomy of Chemical Model
Different classes of model are used. These are:
Box Models consider just a single point in the atmosphere. Such models are comparatively cheap to develop and run on a PC or workstation. The advantage of such models is that very complex chemical reactions can be included since only the chemistry at a single point is simulated. This is very useful for comparing model simulations with measurements in idealised cases and also for developing less complex chemistry schemes which are used in multi-dimensional models.
Trajectory Models are the next step up from box models. Essentially a trajectory model is a 'box model that moves'. A trajectory of a point (or points) of air is calculated from known wind fields. The chemistry is then calculated for all points along the path that the parcel or air took. This type of model is very useful for determining the chemical properties of air reaching observation stations. By running very many chemical trajectory models, it is also possible to begin to develop a three-dimensional picture of the chemistry in the atmosphere.
Three-dimensional Models use the traditional technique of simulating the atmospheric system on a grid of latitude/longitude points and vertical levels (surfaces of constant Potential Temperature or Pressure). Such models have a realistic representation of the movement or meteorology of air as well as other processes such as clouds, solar radiation and so on. In a way, you can think of a 3D model as a grid of box models where the air it being moved through the boxes. As many points are being represented it becomes impossible to use the complex chemistry schemes found in box models as this would place too great a demand on computing power. As it is, these 3D chemical models of the atmosphere require the most powerful High Performance Computers around. In the UK we use the Cray supercomputer and Fujisu supercomputers at the Rutherford Appleton Laboratory in Oxford. Models and Observations Comparison of model results with observations both helps confirm our understanding of the processes responsible for ozone depletion, and can highlight those processes that require further study. A model of chemistry and transport has been used extensively in recent observational campaigns in the Arctic and Antarctic.The following graphics compare the output of the TOMCAT (grid-point) model with TOMS satellite data for the beginning of the Antartic spring - the ASHOE Campaign. TOMCAT was run on a resolution of approximately 5 deg x 5 deg. Further studies have used far higher resolutions.The TOMS instrument relies on backscattered sunlight for its measurements; hence for the Antarctic winter, data tends to be sparse and incomplete. This data came from the Meteor 3 Satellite. More information on TOMS is available here. Comparison between Model Results and Actual Satellite Data
Inline movie of comparison between TOMS satellite data and TOMCAT model run(1.7 Mb)
MPEG movie of comparison between TOMS satellite data and TOMCAT model run(366 Kb)
The model column ozone is very similar to that observed by satellite. Over the Antarctic continent there are low amounts of ozone, where there has been chemical destruction. Around the edge of the vortex, between 30S and 60S, there are higher amounts of ozone. These high amounts result from the transport of ozone from the region of production in the tropics. link....