Jasmine B.D. Jaffrés

Spatial Averaging of HF Radar Data for Wave Measurement Applications

HF radar data are often collected for time periods that are optimized for current measurement applications where, in many cases, very high temporal resolution is needed. Previous work has demonstrated that this does not provide sufficient averaging for robust wave measurements to be made. It was shown that improvements could be made by averaging the radar data for longer time periods. HF radar provides measurements over space as well as in time, so there is also the possibility to average in space. However, the radar data are correlated in space because of the range and azimuth processing. The implications of this are discussed and estimates of the impact on the reduction in variance in the radar Doppler spectral estimates are obtained. Spatial inhomogeneities and temporal nonstationarity in the ocean wave field itself also need to be taken into account. It is suggested that temporal averaging over periods of up to one hour and spatial averaging over 9–25 nearest neighbors may be suitable, and these will be explored in later work.

Wave climate in the Southern Great Barrier Reef, Australia - Evaluation of an ocean HF radar system and WaveWatch3

The impact of waves on the environment (e.g. erosion) and industries (incl. shipping and tourism) can be very significant. Here, we are presenting analysis of coastal wave data in the southern Great Barrier Reef (GBR), Australia, using a combination of observational data (HF radar) and a numerical wave model (WaveWatch3). The modeled significant wave height fields compare reasonably well with those obtained from the radar stations, inducing confidence in the two datasets. The radar-produced wave fields are spatially more variable compared to the model results, linked to the influence of wind stress resolution and currents in accurately determining wave characteristics.

Mixed layer depth seasonality within the Coral Sea based on Argo data

The worldwide deployment of Argo floats has enabled much more detailed studies of global and regional seas over the last decade. Here, the seasonal variability of the mixed layer depth (MLD) within the Coral Sea was examined with CTD profiles from Argo floats. Multiple threshold values for both temperature and density have been employed to determine the most suitable threshold values for the Coral Sea. A threshold value of 0.04 kg/m3 for density and 0.2°C for temperature appear the most fitting for this region. Although MLD and isothermal layer depth (ILD) coincide quite well in most cases, the relatively common presence of temporary, non-seasonal barrier layers induces an ILD that is significantly deeper than the MLD. Consequently, an MLD estimation based on density is more appropriate. A distinct seasonality in the MLD is evident throughout the Coral Sea, but is generally more pronounced in higher southern latitudes (20–30°S). Salinity inversions are rare and mainly occur in the south-eastern Coral Sea, while barrier layers are more commonly associated with the north-eastern Coral Sea, a region characterised by high rainfall. The significance of regional currents is evident in the north-western Coral Sea, where temperature and ocean heat content is relatively low due to a northward moving boundary current. Shallow bathymetry, in turn, is linked to the absence of Argo data on the continental shelf and in the central Coral Sea.

GHCN-Daily: A treasure trove of climate data awaiting discovery

Abstract International collaboration to create and maintain international, freely accessible datasets greatly facilitates research in many scientific fields. The Global Historical Climatology Network (GHCN)-Daily database provides access to a diverse range of daily weather station data, including precipitation and temperature variables. These data are supplied as individual, station-specific files and structured in a non-delimited format. Here, the GHCN-Daily data structure, spatio-temporal content and associated caveats are delineated. The regularly updated collection now features data from over 100 000 stations in 218 countries and territories. While rigorous quality tests are routinely applied for GHCN-Daily, the database excludes the original quality flags from the source agencies. The extraction of climate variables from the GHCN-Daily database can be challenging for novice users and may thus dissuade from the uptake of this valuable dataset. Consequently, a user-friendly toolkit for MATLAB and GNU Octave is also provided to aid data retrieval from all relevant weather stations. The toolkit reformats the extracted GHCN-Daily data into a more accessible structure to facilitate data mining and research on a large scale.

Waves in the Southern Great Barrier Reef

A brief description of three different platforms (WAVEWATCH III, Acoustic Doppler Current Profiler mooring and HF ocean radar) with directional wave measurement capabilities is provided. Initial results of directional wave and wind patterns derived from observations within the southern Great Barrier Reef, Australia, show consistency with the WAVEWATCH III model. These early findings are promising for future wind-wave investigations and validation studies in this region.