Hajar Mountains Oman II, 2014

The 2014 trial had two additional ATLANT™ sites, an expanded and more targeted gauge network and additional instrumentation. In particular, two SODAR vertical wind profilers were installed to measure horizontal wind speed and direction and vertical wind speed above the H1 and H2 ATLANT™ sites.

The 2014 trial also employed a randomised crossover design, in this case applied to two pairings of two ATLANT™ sites. Four statistical models were used to identify and measure whether the ATLANT™ systems generated a rainfall enhancement signal during the trial. These included a ‘corridor’ and a ‘wedge’ model using data from H1 and H2, intended to provide estimates that are comparable to the data and methodology used in 2013, as well as a ‘corridor’ model using data from all four ATLANT™s, and a ‘corridor’ model using data from H1 and H2 combined from the 2013 and 2014 trials.

All of the models generated significant ATLANT™ attributions (rainfall enhancement effect) with estimates very similar to 2013. The data for the full 2014 trial gave a very large estimate of the enhancement effect, however there are reasons to be circumspect about this result. The estimates obtained by combining H1 and H2 data from 2013 and 2014 provided perhaps the most reliable ATLANT™ attribution results to date. This combined data set yielded an enhancement effect of 18.5 per cent and a confidence level of 99 per cent.