Eric W. Schulz

Observation of wind-waves from a moored buoy in the Southern Ocean

The Southern Ocean is an important component in the global wave climate. However, owing to a lack of observations, our understanding of waves is poor compared to other regions. The Southern Ocean Flux Station (SOFS) has been deployed to fill this gap and represents the first successful moored air-sea flux station at these southern hemisphere latitudes. In this paper, we present for the first time the results from the analysis of the wave measurements, focused on statistics and extremes of the main wave parameters. Furthermore, a spectral characterization is performed regarding the number of wave systems and predominance of swell/wind-sea. Our results indicate a high consistency in terms of wave parameters for all deployments. The maximum significant wave height obtained in the 705 days of observation was 13.41 m. The main spectra found represent unimodal swell dominated cases; however, the dimensionless energy plotted against dimensionless peak frequency for these spectra follows a well-known relation for wind-sea conditions. In addition, the Centre for Australian Weather and Climate Research wave hindcast is validated with the SOFS data.

The impact of the assimilation of scatterometer winds on surface wind and wave forecasts

Recent work has demonstrated that surface marine winds from the Bureau of Meteorologys operational Numerical Weather Prediction (NWP) systems are typically underestimated by 5 to 10%. This is likely to cause significant bias in modelled wave fields that are forced by these winds. A simple statistical adjustment of the wind components is shown to reduce the observed bias in Significant Wave Height considerably. The impact of increasing the vertical resolution of the NWP model and assimilating scatterometer data into the model is assessed by comparing the resulting forecast wind and waves to observations. It is found that, in general, the inclusion of scatterometer observations improves the accuracy of the surface wind forecasts. However, most of the improvement is shown to arise from the increased number of vertical levels in the atmospheric model, rather than directly from the use of the observations. When the wave model is forced with surface winds from the NWP model that includes scatterometer data, it...

An Assessment of Marine Surface Winds from the Australian Bureau of Meteorology Numerical Weather Prediction Systems

Abstract A method for routinely verifying numerical weather prediction surface marine winds with satellite scatterometer winds is introduced. The marine surface winds from the Australian Bureau of Meteorology’s operational global and regional numerical weather prediction systems are evaluated. The model marine surface layer is described. Marine surface winds from the global and limited-area models are compared with observations, both in situ (anemometer) and remote (scatterometer). A 2-yr verification shows that wind speeds from the regional model are typically underestimated by approximately 5%, with a greater bias in the meridional direction than the zonal direction. The global model also underestimates the surface winds by around 5%–10%. A case study of a significant marine storm shows that where larger errors occur, they are due to an underestimation of the storm intensity, rather than to biases in the boundary layer parameterizations.

Air‐sea interaction regimes in the sub‐Antarctic Southern Ocean and Antarctic marginal ice zone revealed by icebreaker measurements

This study analyzed shipboard air-sea measurements acquired by the icebreaker Aurora Australis during its off-winter operation in December 2010 – May 2012. Mean conditions over 7 months (October-April) were compiled from a total of 22 ship tracks. The icebreaker traversed the water between Hobart, Tasmania and the Antarctic continent, providing valuable in situ insight into two dynamically important, yet poorly sampled, regimes: the sub-Antarctic Southern Ocean and the Antarctic marginal ice zone (MIZ) in the Indian Ocean sector. The transition from the open water to the ice-covered surface creates sharp changes in albedo, surface roughness, and air temperature, leading to consequential effects on air-sea variables and fluxes. Major effort was made to estimate the air-sea fluxes in the MIZ using the bulk flux algorithms that are tuned specifically for the sea-ice effects, while computing the fluxes over the sub-Antarctic section using the COARE3.0 algorithm. The study evidenced strong sea-ice modulations on winds, with the southerly airflow showing deceleration (convergence) in the MIZ and acceleration (divergence) when moving away from the MIZ. Marked seasonal variations in heat exchanges between the atmosphere and the ice margin were noted. The monotonic increase in turbulent latent and sensible heat fluxes after summer turned the MIZ quickly into a heat loss regime, while at the same time the sub-Antarctic surface water continued to receive heat from the atmosphere. The drastic increase in turbulent heat loss in the MIZ contrasted sharply to the non-significant and seasonally invariant turbulent heat loss over the sub-Antarctic open water.