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Stern H.,University of Melbourne | Davidson N.E.,Center for Australian Weather and Climate Research Bureau of Meteorology Melbourne
Quarterly Journal of the Royal Meteorological Society | Year: 2015

Unique, multi-year datasets of weather observations and official and experimental predictions are used to document trends in weather forecast accuracy and the current level of forecast skill specifically for Melbourne, Australia. The data are applied to quantify prediction skill out to Day-14 for maximum and minimum temperature, and for precipitation amount and probability. An innovative statistical analysis is applied to the data. This analysis clearly demonstrates the need for long time series of forecasts in order to reliably assess long-term trends. The accuracy of the current official Day 5-7 forecasts is found to be similar to that of Day-1 forecasts from 50 years ago. The accuracy of experimental Day 8-10 forecasts is comparable to that of the Day 5-7 forecasts, when they were first officially provided 15 years ago. Some overall skill, albeit limited, is evident out to Day-14 and significance testing indicates that it is unlikely that this apparent skill arose by chance. The results provide evidence of deterministic weather forecast skill out to the hypothesised 15 day limit on such predictions. However, in so doing, the results raise the possibility that the limit may be breached at some stage in the future. © 2015 John Wiley & Sons, Ltd. Source

Shadwick E.H.,Virginia Institute of Marine Science | Trull T.W.,University of Tasmania | Tilbrook B.,University of Tasmania | Sutton A.J.,University of Washington | And 2 more authors.
Global Biogeochemical Cycles | Year: 2015

The Subantarctic Zone (SAZ), which covers the northern half of the Southern Ocean between the Subtropical and Subantarctic Fronts, is important for air-sea CO2 exchange, ventilation of the lower thermocline, and nutrient supply for global ocean productivity. Here we present the first high-resolution autonomous observations of mixed layer CO2 partial pressure (pCO2) and hydrographic properties covering a full annual cycle in the SAZ. The amplitude of the seasonal cycle in pCO2 (∼60μatm), from near-atmospheric equilibrium in late winter to ∼330μatm in midsummer, results from opposing physical and biological drivers. Decomposing these contributions demonstrates that the biological control on pCO2 (up to 100μatm), is 4 times larger than the thermal component and driven by annual net community production of 2.45±1.47molCm-2yr-1. After the summer biological pCO2 depletion, the return to near-atmospheric equilibrium proceeds slowly, driven in part by autumn entrainment into a deepening mixed layer and achieving full equilibration in late winter and early spring as respiration and advection complete the annual cycle. The shutdown of winter convection and associated mixed layer shoaling proceeds intermittently, appearing to frustrate the initiation of production. Horizontal processes, identified from salinity anomalies, are associated with biological pCO2 signatures but with differing impacts in winter (when they reflect far-field variations in dissolved inorganic carbon and/or biomass) and summer (when they suggest promotion of local production by the relief of silicic acid or iron limitation). These results provide clarity on SAZ seasonal carbon cycling and demonstrate that the magnitude of the seasonal pCO2 cycle is twice as large as that in the subarctic high-nutrient, low-chlorophyll waters, which can inform the selection of optimal global models in this region. ©2015. American Geophysical Union. Source

Fujii Y.,Meteorological Research Institute Japan Meteorological Agency Tsukuba Japan | Cummings J.,U.S. Navy | Xue Y.,Climate Prediction Center NCEP College Park | Schiller A.,CSIRO | And 10 more authors.
Quarterly Journal of the Royal Meteorological Society | Year: 2015

The drastic reduction in the number of observation data from the Tropical Atmospheric Ocean (TAO)/Triangle Trans-Ocean Buoy Network (TRITON) array since 2012 has given rise to a need to assess the impact of those data in ocean data assimilation (DA) systems. This article provides a review of existing studies evaluating the impacts of data from the TAO/TRITON array and other components of the Tropical Pacific Observing System (TPOS) on current ocean DA systems used for a variety of operational and research applications. It can be considered as background information that can guide the evaluation exercise of TPOS. Temperature data from TAO/TRITON array are assimilated in most ocean DA systems which cover the tropical Pacific in order to constrain the ocean heat content, stratification, and circulation. It is shown that the impacts of observation data depend considerably on the system and application. The presence of model error often makes the results difficult to interpret. Nevertheless there is consensus that the data from TAO/TRITON generally have positive impacts complementary to Argo floats. In the equatorial Pacific, the impacts are generally around the same level or larger than those of Argo. We therefore conclude that, with the current configuration of TPOS, the loss of the TAO/TRITON data is having a significant detrimental impact on many applications based on ocean DA systems. This conclusion needs to be kept under review because the equatorial coverage by Argo is expected to improve in the future. © 2015 Royal Meteorological Society. Source

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