Eddy covariance measurements of the surface energy balance associated with a localised coral bleaching event, Heron Reef, Great Barrier Reef, Australia

While their ecological, economical and societal values are irrefutable, an uncertain future exists for coral reefs and numerous studies suggest that the threat of coral bleaching will worsen under global warming. Despite the association between global warming and coral reef health, there is a paucity of data relating to the exchanges of heat, moisture and momentum between the atmosphere and the reef surface during bleaching episodes. Understanding these key reef-atmosphere interactions is essential for identifying the processes which control the thermal environment of water on the reef. In this paper we present new direct in situ measurements of radiation transfers and sensible and latent heat fluxes associated with an observed localised coral bleaching event at Heron Reef, in the southern Great Barrier Reef. Measurements were made during a three day period in February 2009 using the Eddy Covariance method. Under the influence of a weak barometric pressure gradient, clear skies and light north easterly winds, daily net radiation peaked at more than 800 W m2, with up to 95% of the net radiation during the morning being partitioned into heating the water column, substrate and benthic cover. Heating was exacerbated by a midafternoon low tide, and low wind speeds resulted in reduced evaporative cooling of the water surface. As a result, daily maximum water surface temperatures exceeded 34°C and near-bottom temperatures 33°C. Such conditions in conjunction with limited horizontal heat transfer due to the pooling of reef waters at the site meant that the water surface and near-bottom water temperatures exceeded 30°C for 27% and 38% of the duration of the observation period respectively resulting in widespread coral bleaching

High resolution record of the Last Glacial Maximum in eastern Australia

A continuous, high resolution (average ca. 22 year) record encompassing the Last Glacial Maximum (LGM) has been developed using multiple proxies (aeolian sediment flux, grain size, pollen and charcoal) in lake sediment from Tortoise Lagoon (TOR), North Stradbroke Island, Queensland, Australia. The presence of Asteraceae tubilifloreae and spineless Asteraceae (common indicators of glacial conditions in Australia) at TOR indicates significantly cooler temperatures (mean annual temperature up to 6oC lower than today). In addition to the palaeoclimatic reconstruction, a record of palaeodust transport pathways for eastern Australia was developed using ICP-MS trace element analysis and geochemical “fingerprinting” of TOR aeolian sediment to continental dust source areas. Vectors between dominant dust source areas and North Stradbroke Island allowed the reconstruction of the position and intensity of LGM dust transport pathways. Furthermore, changes in likely synpotic scale conditions can be postulated based on the position of the dust transport corridors. Similarities between the vegetation at TOR during the LGM and that at temperate sites e.g. Caledonia Fen, Victoria (Kershaw et al. 2007), Redhead Lagoon, New South Wales (Williams et al. 2006) and Barrington Tops, New South Wales (Sweller and Martin 2001) suggests that this record reflects regional conditions across southeastern Australia. The TOR record also correlates well with that from nearby Native Companion Lagoon which suggests that the LGM was actually an extended period of ca. 8 – 10 kyr, characterised by 2 periods of increased aridity (ca. 30 – 26.5 kyr and 21 – 19.5 kyr) (Petherick et al. 2008). A growing number of records from across the Southern Hemisphere e.g. New Zealand (Suggate and Almond 2003; Alloway et al. 2007; Newnham et al. 2007), Chile (Denton et al. 1999), Antarctica (Röthlisberger et al. 2002; EPICA 2006) and Australia (Smith 2009) also show evidence that the LGM encompassed a longer period of time than traditionally accepted, and was not uniformly cool and dry

Drivers of precipitation stable oxygen isotope variability in an alpine setting, Snowy Mountains, Australia

Natural archives that preserve a stable isotopic signature are routinely used to reconstruct palaeoenvironmental conditions. Isotopic values of precipitation are known to be influenced by factors such as the amount and type of precipitation, moisture pathway, landscape and terrain factors, and processes associated with precipitation formation and deposition. This study investigates oxygen isotopic variability using real-time rain and snow precipitation data from a moderate altitude

Spatial heterogeneity of air-sea energy fluxes over a coral reef-Heron Reef, Australia

The thermal environment of a coral reef is moderated by complex interactions of air-sea heat and moisture fluxes, local to synoptic-scale weather and reef hydrodynamics. Measurements of air-sea energy fluxes over coral reefs are essential to understanding the reef-atmosphere processes that underpin coral reef environmental conditions such as water temperature, cloud, precipitation, and local winds (such as during coral bleaching events). Such measurements over coral reefs have been rare, however, and the spatial heterogeneity of surface-atmosphere energy exchanges due to the different geomorphic and biological zones on coral reefs has not been captured. Accordingly, the heterogeneity of coral reefs with regard to substrate, benthic communities, and hydrodynamic processes has not been considered in the characterization of the surface radiation budget and energy balance of coral reefs. Here, the first concurrent in situ eddy covariance measurements of the surface energy balance and radiation transfers over different geomorphic zones of a coral reef are presented. Results showed differences in radiation transfers and sensible and latent heat fluxes over the reef, with higher Bowen ratios over the shallow reef flat zone. The energy flux divergence between sites increased with wind speed and during unstable, southeasterly trade winds with the net flux of heat being positive and negative over different geomorphic zones. The surface drag coefficient at measurement height ranged from 1 x 10(-3) to 2.5 x 10(-3), with no significant difference between sites. Results confirm that spatial variation in radiation and air-reef-water surface heat and moisture fluxes occurs across a lagoonal platform reef in response to local meteorological conditions, hydrodynamics, and benthic-substrate cover

Evidence of increased tropical moisture in southeast Australian alpine precipitation during ENSO

An understanding of past atmospheric variability during El Ni�o–Southern Oscillation (ENSO) events is critical for informing debate on current and future changes in precipitation in a warming world. Here we show that atmospheric moisture content over much of Australia during inflow-generating precipitation days (≥10 mm d) associated with La Ni�a (El Ni�o) events has increased (decreased) over the period 1958–2015. This is most notable in tropical latitudes which are the source of moisture of most precipitation ≥ 10 mm in southeast Australia (SEA). These trends are consistent with climate model projections and increases in tropical sea surface temperatures since the 1950s. They confirm that enhanced tropical ocean forcing of interannual climate variability through ENSO due to global warming is changing the hydroclimate of midlatitudes and in-turn will require major changes to water resource use and management

Identification of optimum temperatures for photosynthetic production in subtropical coastal ecosystems – implications for CO2 sequestration in a warming world

Terrestrial ecosystems are often thought to be effective sinks of anthropogenic CO2 emissions with biosphere greening considered unequivocal evidence of this process. Increasing atmospheric concentrations of CO2 along with other greenhouse gases are however, responsible for global warming. As temperature increases, the rate at which biomes sequester CO2 may decline as the optimum temperature for photosynthetic production is exceeded, thereby reducing their potential to sequester CO2. Here we present evidence from three years of direct measurements of CO2 exchanges over subtropical coastal ecosystems in eastern Australia, that the optimum temperature range for photosynthesis of 24.1 to 27.4 °C is routinely exceeded. This causes a rapid decline in photosynthetic production made worse when soil water content decreases. As climate change continues, both rising temperatures and predicted decline in rainfall will see these coastal ecosystems ability to sequester CO2 decrease further rapidly. We suggest similar research is needed urgently over other terrestrial ecosystems

The Coastal Convective Interactions Experiment (CCIE): understanding the role of sea breezes for hailstorm hotspots in Eastern Australia

The coastal convective interactions experiment (CCIE's) integration of climatological analysis with an intensive field campaign has provided an opportunity for revealing some of the complexities surrounding thunderstorm hotpots in complex physical settings like SEQ. For the CCIE climatological analysis, a continuous 18-yr (July 1997 to June 2015) volumetric reflectivity radar dataset was sourced from the 1.9° S-band weather radar located at Marburg, 50 km west of Brisbane. A cell-based analysis of this archive was performed using a MATLAB implementation of the identification, tracking, and selected analysis algorithms from the Weather Decision Support System-Integrated Information (WDSS-II). The 10-min interval of the Marburg radar volumes creates significant spatial discontinuities between MESH grids from an individual thunderstorm. A preliminary analysis indicates a strong relationship between the presence of the sea breeze and the Boonah hailstorm hotspot, but further analysis is needed to isolate the additional influence of synoptic and topographic drivers. Furthermore, fine-scale field observations of the sea-breeze?thunderstorm interaction events have begun to shed some light on the meteorology of thunderstorm hotspots in South East Queensland (SEQ)

A Radar-Based Hail Climatology of Australia

In Australia, hailstorms present considerable public safety and economic risks, where they are considered the most damaging natural hazard in terms of annual insured losses. Despite these impacts, the current climatological distribution of hailfall across the continent is still comparatively poorly understood. This study aims to supplement previous national hail climatologies, such as those based on environmental proxies or satellite radiometer data, with more direct radar-based hail observations. The heterogeneous and incomplete nature of the Australian radar network complicates this task and prompts the introduction of some novel methodological elements. We introduce an empirical correction technique to account for hail reflectivity biases at C-band, derived by comparing overlapping C- and S-band observations. Furthermore, we demonstrate how object-based hail swath analysis may be used to produce resolution-invariant hail frequencies, and describe an interpolation method used to create a spatially continuous hail climatology. The Maximum Estimated Size of Hail (MESH) parameter is then applied to a mixture of over fifty operational radars in the Australian radar archive, resulting in the first nationwide, radar-based hail climatology. The spatiotemporal distribution of hailstorms is examined, including their physical characteristics, seasonal and diurnal frequency, and regional variations of such properties across the continent.Comment: Revision 1 of manuscript submitted to Monthly Weather Revie

The Effects of Spatial Interpolation on a Novel, Dual-Doppler 3D Wind Retrieval Technique

Three-dimensional wind retrievals from ground-based Doppler radars have played an important role in meteorological research and nowcasting over the past four decades. However, in recent years, the proliferation of open-source software and increased demands from applications such as convective parameterizations in numerical weather prediction models has led to a renewed interest in these analyses. In this study, we analyze how a major, yet often-overlooked, error source effects the quality of retrieved 3D wind fields. Namely, we investigate the effects of spatial interpolation, and show how the common practice of pre-gridding radial velocity data can degrade the accuracy of the results. Alternatively, we show that assimilating radar data directly at their observation locations improves the retrieval of important dynamic features such as the rear flank downdraft and mesocyclone within a simulated supercell, while also reducing errors in vertical vorticity, horizontal divergence, and all three velocity components.Comment: Revised version submitted to JTECH. Includes new section with a real data cas

Reconstructing annual inflows to the headwater catchments of the Murray River, Australia, using the Pacific Decadal Oscillation

The Pacific Decadal Oscillation (PDO) is a major forcing of inter-decadal to quasi-centennial variability of the hydroclimatology of the Pacific Basin. Its effects are most pronounced in the extra-tropical regions, while it modulates the El Nino Southern Oscillation (ENSO), the largest forcing of global inter-annual climate variability. PalaeoPDO indices are now available for at least the past 500 years. Here we show that the \u3e500 year PDO index of Shen et al. (2006) is highly correlated with inflows to the headwaters of Australia\u27s longest river system, the Murray-Darling. We then use the PDO to reconstruct annual inflows to the Murray River back to A.D. 1474. These show penta-decadal and quasi-centennial cycles of low inflows and a possible 500 year cycle of much greater inflow variability. Superimposed on this is the likely influence of recent anthropogenic global warming. We believe this may explain the exceptionally low inflows of the past decade, the lowest of the previous 529 years