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Likelihood estimates of extreme winds, including those from tropical cyclones (TCs) at certain locations are used to inform wind load standards for structural design. Here, wind speed average recurrence intervals (ARIs) determined from TC climate data dating back to the 1970s in two quantile-quantile adjusted reanalysis datasets (ERA5 and BARRA [1990]), and best-track observations for context, were compared with Standardized ARIs (AS/NZS) across seven tropical and two subtropical Australian inland coastal regions. The novelty of this work lies in determining TC-wind speed ARIs from a range of datasets that are not typically used to evaluate this metric. Inherent differences between the data used to determine the Standard ARIs (large sample size allow for larger extrapolations; GEV function) and TC data ARIs (smaller sample size and less certain data; the more asymptotic Lognormal/Weibull functions are used) led to the use of different extreme value functions. Results indicated that although these are two distinct ways of determining design wind speeds, when they are considered equivalent, there was a moderate reproduction of the ARI curves with respect to the Standard in both reanalysis datasets, suggesting that similar analyses using climate model products can provide useful information on these types of metrics with some caveats. Trends in TC wind strength affecting coastal Australia were also analyzed, indicating a potential slight downtrend in tropical West coast TC wind strength and slight uptrend for tropical East coast TC wind strength, noting considerable uncertainty given the short time period and limitations of data quality including over longer time periods. Such trends are not only limited to the relationship between TC intensity and anthropogenic warming, but also to regional changes in TC frequency and track direction. This could lead to significant trends emerging in regional Australian TC wind gust strength before several decades of warming have occurred. It is hoped that climate models can provide both longer-term and a more homogenous base for these types of evaluations and subsequent projections with respect to climate change simulations., (© 2022. Crown.)

Extreme wildfires have recently caused disastrous impacts in Australia and other regions of the world, including events with strong convective processes in their plumes (i.e., strong pyroconvection). Dangerous wildfire events such as these could potentially be influenced by anthropogenic climate change, however, there are large knowledge gaps on how these events might change in the future. The McArthur Forest Fire Danger Index (FFDI) is used to represent near-surface weather conditions and the Continuous Haines index (CH) is used here to represent lower to mid-tropospheric vertical atmospheric stability and humidity measures relevant to dangerous wildfires and pyroconvective processes. Projected changes in extreme measures of CH and FFDI are examined using a multi-method approach, including an ensemble of global climate models together with two ensembles of regional climate models. The projections show a clear trend towards more dangerous near-surface fire weather conditions for Australia based on the FFDI, as well as increased pyroconvection risk factors for some regions of southern Australia based on the CH. These results have implications for fields such as disaster risk reduction, climate adaptation, ecology, policy and planning, noting that improved knowledge on how climate change can influence extreme wildfires can help reduce future impacts of these events.

An exploratory analysis of lightning-ignited wildfire data for the Warren Region of Western Australia was carried out for the period from April 1976 to December 2016. Temporal patterns in the series were examined in terms of characterizing the seasonal cycle, and detecting long-term trends and changes in seasonality over time. A generalized additive modelling approach was used to ensure that temporal features were determined by the data rather than a priori assumed mathematical forms (e.g. linear or low-order polynomial functions). The spatial organization of the data was evaluated using concepts from the theory of stochastic point processes. Results indicate a strong seasonality in the monthly lightning ignition series, the presence of a long-term trend and an interaction between trend and seasonality. There is also strong evidence of spatial variation in the number of ignitions per unit area in terms of location and distance from nearest ignition. Within the Warren Region, observation platforms for fire detection and reporting protocols have remained stable over the period of record, and changes in land use are unlikely to have altered the pattern of lightning ignition. Thus, the above results might reflect an interplay between: landscape attributes (e.g. vegetation classes, elevation, slope, aspect); changes in rainfall and fuel moisture; changes in fuel management practices; and, perhaps, an increase in the frequency of dry thunderstorms and fire weather conditions., (Copyright © 2018. Published by Elsevier Ltd.)

Phenomena such as cyclones, fronts and thunderstorms can cause extreme weather in various regions throughout the world. Although these phenomena have been examined in numerous studies, they have not all been systematically examined in combination with each other, including in relation to extreme precipitation and extreme winds throughout the world. Consequently, the combined influence of these phenomena represents a substantial gap in the current understanding of the causes of extreme weather events. Here we present a systematic analysis of cyclones, fronts and thunderstorms in combination with each other, as represented by seven different types of storm combinations. Our results highlight the storm combinations that most frequently cause extreme weather in various regions of the world. The highest risk of extreme precipitation and extreme wind speeds is found to be associated with a triple storm type characterized by concurrent cyclone, front and thunderstorm occurrences. Our findings reveal new insight on the relationships between cyclones, fronts and thunderstorms and clearly demonstrate the importance of concurrent phenomena in causing extreme weather.

Thunderstorms are convective systems characterised by the occurrence of lightning. Lightning and thunderstorm activity has been increasingly studied in recent years in relation to the El Niño/Southern Oscillation (ENSO) and various other large-scale modes of atmospheric and oceanic variability. Large-scale modes of variability can sometimes be predictable several months in advance, suggesting potential for seasonal forecasting of lightning and thunderstorm activity in various regions throughout the world. To investigate this possibility, seasonal lightning activity in the world's tropical and temperate regions is examined here in relation to numerous different large-scale modes of variability. Of the seven modes of variability examined, ENSO has the strongest relationship with lightning activity during each individual season, with relatively little relationship for the other modes of variability. A measure of ENSO variability (the NINO3.4 index) is significantly correlated to local lightning activity at 53% of locations for one or more seasons throughout the year. Variations in atmospheric parameters commonly associated with thunderstorm activity are found to provide a plausible physical explanation for the variations in lightning activity associated with ENSO. It is demonstrated that there is potential for accurately predicting lightning and thunderstorm activity several months in advance in various regions throughout the world.

The dynamic response of the adrenal cortex to ACTH infusion is analyzed by simulating the distribution, binding, and metabolism of cortisol and aldosterone in a multicompartmental model. The model includes the effects of temperature and cortisol concentration on aldosterone binding in plasma and the distribution between plasma and red blood cells, as verified by new observations. The secretion rates of cortisol and aldosterone were computed from serial measurements of plasma concentrations of endogenous steroids and infused tracers. The model was validated by observations after iv injection of a bolus of cortisol. Nineteen normal volunteers were studied on the fourth day on a diet containing 10 meq sodium. Endogenous ACTH was suppressed by dexamethasone, and alpha-1-24ACTH was infused at two different rates in various sequences over a 4-h period. During each hour of constant ACTH infusion, plasma cortisol continued to increase, while plasma aldosterone rose quickly, reaching a plateau within 20--30 min. Cortisol secretion approached a maximim rate after 20--30 min of ACTH infusion; the continued increase of plasma cortisol resulted from the slow equilibrium with other compartments. Aldosterone secretion rose quickly to a peak and then declined to a lower level after 20 min of ACTH infusion; the lower rate of secretion was maintained for the duration of the constant infusion of ACTH, falling abruptly within a few minutes after stopping the infusion. The characteristic differences in plasma steroid responses to various sequences of ACTH infusions can be explained by the more rapid changes in aldosterone secretion and the different clearance rates of cortisol and aldosterone, which vary with plasma cortisol concentration. The temperature at which blood is separated significantly affects plasma aldosterone measurements.

Aldosterone enters red blood cells (RBC) to a greater extent at 37 C than at lower temperatures. The ratio of 3H-aldosterone concentration in RBC to that in plasma increases from 0.2 at 4 C to 0.7 at 37 C when cortisol concentration is low. Increasing plasma cortisol increases the RBC/plasma aldosterone ratio. When plasma transcortin (CBG) is saturated with cortisol, the RBC/plasma ratio of 3H-aldosterone approaches 0.93, the ratio observed in RBC incubated in 4% albumin solution. The effects of plasma cortisol and temperature on the RBC/plasma ratio reflect an affinity of aldosterone for plasma CBG greater than the affinity for plasma albumin or RBC. Hepatic extraction averages 92% of plasma and RBC aldosterone. Neither hepatic extraction nor renal extraction (less than or equal to 20%) is significantly altered by changing plasma cortisol concentration. Whole blood MCR of aldosterone is unaffected by redistribution of aldosterone from plasma to RBC when plasma cortisol increases, but both plasma cortisol and the temperature at which blood is separated affect the RBC/plasma ratio of 3H-aldosterone and thus change the calculated plasma MCR. The RBC transport of aldosterone, and its dependence on temperature and plasma cortisol, must be taken into account in the evaluation of plasma aldosterone concentration.

During ACTH or cortisol infusion in ten recumbent normal men taking dexamethasone, the metabolic clearance rate of aldosterone increased by 50% as plasma cortisol was raised from low (2 mug/dl) to high concentration (50 mug/dl). Since splanchnic blood flow did not change, a greater efficiency of removal of aldosterone must have occurred, by means of displacement of aldosterone from high-affinity sites on plasma protein. At 37 C, equilibrium dialysis of low-cortisol plasma showed one-third of plasma aldosterone bound to albumin, and 24 to 28% bound to higher-affinity sites on other protein. As plasma cortisol increased, a progressively smaller fraction was tightly bound, approaching zero as transcortin was saturated with cortisol. The addition of large amounts of aldosterone to low-cortisol plasma displaced 14C-cortisol from transcortin binding sites. The results support earlier evidence that a significant fraction of plasma aldosterone is bound to transcortin, from which it is readily displaced by cortisol, resulting in an increased metabolic clearance rate of aldosterone by making a larger fraction available for removal from plasma.

Among 25 patients with benign, essential hypertension, and an equal number with other benign forms of hypertension, without serious cardiac, renal, or cerebrovascular impairment, 41 cases failed to reduce aldosterone excretion rates into the normal range (less than 5 mug/day) on a daily intake of 300 mEq of sodium. The hypertensive patients excreted slightly less than the normal fraction of labeled aldosterone as acid-hydrolyzable conjugate. Secretion rates were significantly higher in the hypertensive patients than in normotensive controls taking the high-sodium intake. On a 10 mEq sodium intake, the increase in excretion and secretion rates of aldosterone in the hypertensive patients could be correlated with plasma renin activity (PRA). The patients with the least increase in PRA had subnormal increase in aldosterone secretion and excretion, while unusually large rises in aldosterone secretion accompanied high PRA, especially in the cases with increased plasma angiotensinogen induced by oral contraceptives. The persistence of inappropriately high aldosterone secretion in most hypertensive patients during sodium loading could be related to a higher PRA than that found in normotensive controls under comparable conditions. In other hypertensives, whose PRA was unresponsive to sodium depletion, there was no significant correlation between PRA and aldosterone output, and no known stimulus to aldosterone production was detected. Five obvious cases of hyperaldosteronism were found among the 16 low-renin patients. The cause of the nonsuppressible aldosterone production in the other low-renin cases remains to be determined.