Showing papers by "Ian R. Young published in 2014"

The large-scale influence of the Great Barrier Reef matrix on wave attenuation

Abstract: Offshore reef systems consist of individual reefs, with spaces in between, which together constitute the reef matrix. This is the first comprehensive, large-scale study, of the influence of an offshore reef system on wave climate and wave transmission. The focus was on the Great Barrier Reef (GBR), Australia, utilizing a 16-yr record of wave height from seven satellite altimeters. Within the GBR matrix, the wave climate is not strongly dependent on reef matrix submergence. This suggests that after initial wave breaking at the seaward edge of the reef matrix, wave energy that penetrates the matrix has little depth modulation. There is no clear evidence to suggest that as reef matrix porosity (ratio of spaces between individual reefs to reef area) decreases, wave attenuation increases. This is because individual reefs cast a wave shadow much larger than the reef itself; thus, a matrix of isolated reefs is remarkably effective at attenuating wave energy. This weak dependence of transmitted wave energy on depth of reef submergence, and reef matrix porosity, is also evident in the lee of the GBR matrix. Here, wave conditions appear to be dependent largely on local wind speed, rather than wave conditions either seaward, or within the reef matrix. This is because the GBR matrix is a very effective wave absorber, irrespective of water depth and reef matrix porosity.

Changes in ocean surface wind with a focus on trends in regional and monthly mean values

Abstract: Data collected from ships and satellites has frequently been used to estimate trends in surface wind speed. Although these data sets consistently show an increase in global average wind speed over recent decades, the magnitude of this increase varies depending on the data source used. Observations of the ocean surface by satellites, namely altimeter and SSM/I, provide reasonably long datasets with global coverage. These well calibrated and validated datasets are analysed for linear trends of regional mean monthly time series and mean time series for each calendar month over the period from 1991 to 2008. Differences between the resulting trends are investigated and discussed. The data indicate that the observed global trend is not uniformly distributed and can be linked to a significant positive trend in regional average time series across equatorial regions and the Southern Ocean. When trends for each calendar month are considered, the Southern Ocean showed a consistent increase for at least three continuous months. Although altimeter trends are consistently stronger than trends from SSM/I, the two datasets share similarities. For example, for some regions the trends are up to 2.0 times the global average trend. The data also show that the month of May exhibits one of largest positive trends and this was found across the North Indian Ocean which may indicate a shift in the onset time of the monsoon season.