Abstract. The term “flash drought” is frequently invoked to describe droughts that develop rapidly over a relatively short timescale. Despite extensive and growing research on flash drought processes, predictability, and trends, there is still no standard quantitative definition that encompasses all flash drought characteristics and pathways. Instead, diverse definitions have been proposed, supporting wide-ranging studies of flash drought but creating the potential for confusion as to what the term means and how to characterize it. Use of different definitions might also lead to different conclusions regarding flash drought frequency, predictability, and trends under climate change. In this study, we compared five previously published definitions, a newly proposed definition, and an operational satellite-based drought monitoring product to clarify conceptual differences and to investigate the sensitivity of flash drought inventories and trends to the choice of definition. Our analyses indicate that the newly introduced Soil Moisture Volatility Index definition effectively captures flash drought onset in both humid and semi-arid regions. Analyses also showed that estimates of flash drought frequency, spatial distribution, and seasonality vary across the contiguous United States depending upon which definition is used. Definitions differ in their representation of some of the largest and most widely studied flash droughts of recent years. Trend analysis indicates that definitions that include air temperature show significant increases in flash droughts over the past 40 years, but few trends are evident for definitions based on other surface conditions or fluxes. These results indicate that “flash drought” is a composite term that includes several types of events and that clarity in definition is critical when monitoring, forecasting, or projecting the drought phenomenon.

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The anti-corrosion action of lemongrass (cymbopogon citratus) extract (LGE) was evaluated for carbon steel in produced oilfield water using weight loss method and electrochemical impedance spectroscopy (EIS).

Three gemini surfactants were synthesized having the same length of terminal chain but differing in the spacer chain length and they were evaluated as corrosion inhibitors for carbon steel in oilfield water using weight loss, EIS, potentiodynamic polarization and open-circuit potential measurements. These measurements revealed that the synthesized materials have served as effective mixed-type corrosion inhibitors. Their adsorption on a carbon steel surface was well described by means of the Langmuir adsorption isotherm. The activation parameters for the dissolution of carbon steel in solutions of oilfield water in the absence and presence of these inhibitors were calculated. The effect of immersion time on the stability and durability of protective films adsorbed on a carbon steel surface was studied using weight loss method. Ex situ inspection, i.e. post-exposure analysis, for the treated carbon steel surface has been performed using SEM, EDX and FT-IR tools.

A precipitation study has been made with nickel ammonium sulphate produced by mixing aqueous solutions of its constituent salts. Rates of nucleation, as indicated by the induction period, were measured for both agitated and non-agitated systems over the temperature range 0-35 "C. The nucleation rate increases with increases in agitation and temperature but supersaturation has the dominant effect, as predicted by classical nucleation theory. However, attempts to analyse the results in accordance with classical theory were not entirely successful, but it is shown how the assumption of (a) a variation of crygtal surface energy with temperature and (b) the influence of heterogeneous nucleation can account for the discrepancies.Die Fallung von Nickelammoniumsulfat durch Vermischung der wiiorigen Losungen der Ausgangssalze wird untersucht. Keimbildungsgeschwindigkeiten, die sich in den Induktionszeiten ausdriicken, wurden in ruhenden und bewegten Systemen im Temperaturbereich von 0 -35 "C gemessen. Die Keimbildungsgeschwindigkeit nimmt mit der Bewegung der Losung und der Temperatur zu, wie es die klassische Keimbildungstheorie voraussagt. Versuche jedoch, die Ergebnisse in obereinstimmung mit dieser Theorie zu analysieren, waren nicht ganz erfolgreich; es wird aber gezeigt, wie die Annahme einer h d e r u n g der Oberfliichenenergia der Kristalle mit der Temperatur und der EinfluB der heterogenen Keimbildung diese Abweichungen erklaren konnte.

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For the corrosion of carbon steel in 1.0 M HCl solution, the new pyrazolone derivatives (PY1 and PY2) have been identified as active corrosion inhibitors.