Joshua Soderholm

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

Full-text is free to read on publisher website. 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 NiA±o 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 >500 year PDO index of Shen et al. (2006) is highly correlated with inflows to the headwaters of Australias 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. Copyright 2009 by the American Geophysical Union.

Evidence of solar and tropical-ocean forcing of hydroclimate cycles in southeastern Australia for the past 6500 years

Evidence of solar and tropical-ocean forcing of climate cycles has been found in numerous palaeoclimate records. Numerical modelling studies show physical mechanisms by which direct and indirect solar forcing may affect climate, while there is mounting evidence of solar forcing of tropical ocean-atmosphere teleconnections. This study has developed a 6500 year record of dust deposition, a proxy for regional hydroclimate variability for the Snowy Mountains region of Australia. Spectral analysis of the record provides evidence of statistically significant cycles in dust deposition of 35–43 years, 62–73 years, 161 years and 2200 years. These correlate with variability in solar irradiance and the Pacific Decadal Oscillation (PDO). We present evidence to support physical links between variability in solar irradiance and change in the hydroclimate of southeast Australia and suggest that the effects of global warming and solar maxima on atmospheric circulation over extra-tropical regions may exacerbate these impacts.

Observations of Surface Energy Fluxes and Boundary-Layer Structure Over Heron Reef, Great Barrier Reef, Australia

Over warm, shallow coral reefs the surface radiation and energy fluxes differ from those of the open ocean and result in modification to the marine atmospheric boundary layer via the development of convective internal boundary layers. The complex interrelationships between the surface energy balance and boundary-layer characteristics influence local weather (wind, temperature, humidity) and hydrodynamics (water temperature and currents), as well as larger scale processes, including cloud field properties and precipitation. The nature of these inter-relationships has not been accurately described for coral reef environments. This study presents the first measurements of the surface energy balance, radiation budget and boundary layer thermodynamics made over a coral reef using an eddy-covariance system and radiosonde aerological profiling of the lower atmosphere. Results show that changes in surface properties and the associated energetics across the ocean-reef boundary resulted in modification to the marine atmospheric boundary layer during the Austral winter and summer. Internal convective boundary layers developed within the marine atmospheric boundary layer over the reef and were found to be deeper in the summer, yet more unstable during the winter when cold and drier flow from the mainland enhances heat and moisture fluxes to the atmosphere. A mixed layer was identified in the marine atmospheric boundary layer varying from 375 to 1,200 m above the surface, and was deeper during the summer, particularly under stable anticyclonic conditions. Significant cloud cover and at times rain resulted in the development of a stable stratified atmosphere over the reef. Our findings show that, for Heron Reef, a lagoonal platform reef, there was a horizontal discontinuity in surface energy fluxes across the ocean-reef boundary, which modified the marine atmospheric boundary layer.

The Coastal Convective Interactions Experiment (CCIE): Understanding the Role of Sea Breezes for Hailstorm Hotspots in Eastern Australia

AbstractThunderstorm-affected communities develop an awareness of “hotspot” regions that historically experience more frequent or intense storm activity across many years. A scientifically based understanding of this localized variability has significant implications for both the public and industry; however, a lack of sufficiently long and robust observational datasets has limited prior research at the mesogamma spatial scale (2–20 km). This is particularly true for coastal environments, where hotspot activity has been documented in very few locales (e.g., Florida, southern Appalachian coastal plains, and the Iberian Peninsula), despite 45% of the global population living within 150 km of the coast. The Coastal Convective Interactions Experiment (CCIE) focuses on quantifying hailstorm hotspot activity for the coastal South East Queensland (SEQ) region of Australia and understanding the meteorological conditions that result in the spatial clustering of hailstorm activity.An automated thunderstorm identifi...

Global warming in the context of 2000 years of Australian alpine temperature and snow cover

Annual resolution reconstructions of alpine temperatures are rare, particularly for the Southern Hemisphere, while no snow cover reconstructions exist. These records are essential to place in context the impact of anthropogenic global warming against historical major natural climate events such as the Roman Warm Period (RWP), Medieval Climate Anomaly (MCA) and Little Ice Age (LIA). Here we show for a marginal alpine region of Australia using a carbon isotope speleothem reconstruction, warming over the past five decades has experienced equivalent magnitude of temperature change and snow cover decline to the RWP and MCA. The current rate of warming is unmatched for the past 2000 years and seasonal snow cover is at a minimum. On scales of several decades, mean maximum temperatures have undergone considerable change ≈ ± 0.8 °C highlighting local scale susceptibility to rapid temperature change, evidence of which is often masked in regional to hemisphere scale temperature reconstructions.

Diurnal Preconditioning of Subtropical Coastal Convective Storm Environments

AbstractBoundary layer evolution in response to diurnal forcing is manifested at the mesobeta and smaller scales of the atmosphere. Because this variability resides on subsynoptic scales, the potential influence upon convective storm environments is often not captured in coarse observational and modeling datasets, particularly for complex physical settings such as coastal regions. A detailed observational analysis of diurnally forced preconditioning for convective storm environments of South East Queensland, Australia (SEQ), during the Coastal Convective Interactions Experiment (2013–15) is presented. The observations used include surface-based measurements, aerological soundings, and dual-polarization Doppler radar. The sea-breeze circulation was found to be the dominant influence; however, profile modification by the coastward advection of the continental boundary layer was found to be an essential mechanism for favorable preconditioning of deep convection. This includes 1) enhanced moisture in the city...

The convective features within and surrounding severe tropical Cyclone Larry (2006)

A sequence of ground-based radar reflectivity images sampled in the 17 hours prior to, and during the landfall of Severe Tropical Cyclone Larry (2006) are presented and analyzed using Fourier and wavelet analysis techniques. A range of mesoscale convective anomalies were detected, with characteristics and behavior consistent with vortex Rossby wave initiation. Cyclonically propagating eye-wall kinks, elongations and mesoscale reflectivity maxima were all observed throughout the sampling period, along with intense inner spiral bands. Various deep convective maxima propagated within the eye-wall at speeds consistent with predictions derived by linear barotropic wave theory. Three eye-wall breakdown episodes were observed during the study period, along with corresponding increases in storm-core asymmetric wave power and reductions in estimated storm intensity. Vortex Rossby wave initiated radial flows are also suggested by the presence of a possible mesovortex within a broken section of the eye-wall during landfall, and the outward ejection of filaments of deep convection from an adjacent inner spiral band. The possible influence of this wave activity upon the storm intensity and integrity is discussed.