2.4 Air temperature gradient

Figure 4: A sample frame from the animation of the fourth visualisation, which shows how the temperature evolves as the altitude increases.

The fourth visualisation aimed to further investigate the temperature, this time at higher altitudes. It does this by using particle advection, by injecting massless particles at ground level and allowing them to ``float'' upwards in the temperature gradient field. This gives the effect of the particles rising as if they were only affected by the temperature and convection currents, without any regard for the wind or other effects. Further, the particles and their streamline-style paths are coloured according their temperature. This makes the overall view very natural -- the particles are coloured by temperature, and the paths they take the direction of the changing temperature.

The colours are selected such that that temperatures above are orange and yellow, temperatures between and are green, and temperatures below are blue in colour. This means that the particles ``switch'' colours when they pass these thresholds, giving good visual indication of what stage of cooling they are at.

Three separate points in time are considered, and an animation is generated for each. The three times are Midday (1pm AEST), Evening (7pm AEST) and Early Morning (4am AEST). It is hoped that these visualisations will exhibit differences since they are from different temperature conditions -- the midday case should be the warmest (at least at ground level), followed by the evening and then the early morning. Unfortunately, this distinction is not as clear as was originally hoped. The midday case was warmer overall, but there is very little difference between the evening and early morning cases. A preliminary attribution for this is the possibility that the results for the evening and early morning cases are skewed because the sun is still shining in the upper atmosphere.

Another noticable feature is how many of the particles have a general drift to the west. This is attributed to the fact that the earth is spinning underneath, and the temperature is the temperature of the air at these points -- hence, this may drift slightly with respect to the earth below.