Ian Simmonds

Ian Simmonds
University of Melbourne | MSD · School of Earth Sciences

Doctor of Philosophy

About

313
Publications
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Publications

Publications (313)
Article
The interannual rainfall variability over the southeast Australian state of Victoria is known to be influenced by a number of large scale and regional phenomena, including the Indian Ocean Dipole (IOD), Southern Oscillation Index (SOI), and Southern Annular Mode (SAM). However, the role of ‘upstream’ regional circulation or pressure anomalies has r...
Article
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In recent decades boreal wildfires have occurred frequently over eastern Siberia, leading to increased emissions of carbon dioxide and pollutants. However, it is unclear what factors have contributed to recent increases in these wildfires. Here, using the data we show that background eastern Siberian Arctic warming (BAW) related to summer Russian A...
Article
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In the mid–high latitude atmosphere, the instability of planetary waves characterizes enhanced planetary wave activity or amplified large‐scale waviness leading to increased regional weather extremes. In this paper, a nonlinear Schrödinger equation is derived to describe the evolution of planetary waves. Then the consequences of Arctic amplificatio...
Article
The winter sea ice cover (SIC) over the Bering Sea (BS) and Okhotsk Sea (OS) shows significant co-variability. In particular, a clear seesaw-like variability can be observed on an intraseasonal scale between the two seas. However, the mechanism by which the atmospheric circulation affects them is unclear and further insight is needed. In this study...
Research
34 In this article, the spatiotemporal relationship between winter precipitation over Spain and 35 sea level pressure fields is studied using the Center of Action (COA) approach. The COAs 36 which make up the North Atlantic Oscillation (NAO), i.e., the Azores High (AH) and the 37 Icelandic Low (IL), are considered separately, and we find that inter...
Preprint
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In recent decades wildfires have occurred frequently over eastern Siberia, which favors increased atmospheric carbon dioxide and air pollution. However, it is not well understood what factors have contributed to the recent increase in these wildfires. Here, we analyzed meteorological and satellite data to show that background Arctic warming related...
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Summer heatwaves over Europe, which can cause many deaths and severe damage, have become increasingly frequent over central and eastern Europe and western Russia in recent decades. In this paper, we estimate the contributions of the warming due to increased greenhouse gases (GHG) and nonlinear variations correlated with the Atlantic Multidecadal Os...
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Rebuttal of a critique of the Stern Review
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In this article, the meridional gradient of daily potential vorticity (PV) on the 330 K isentropic surface is used to identify atmospheric blocking events for the period 1979–2019. The associated two‐dimensional index considers not only Rossby wave breaking, but also energy dispersion and nonlinearity of blocking systems, and thus has a solid theor...
Article
In this article, the spatiotemporal relationship between winter (DJF) precipitation over Spain and sea level pressure fields is studied using the Center of Action (COA) approach. The COAs which make up the North Atlantic Oscillation (NAO), i.e., the Azores High (AH) and the Icelandic Low (IL), are considered separately, and we find that interannual...
Article
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Winter Arctic sea-ice concentration (SIC) decline plays an important role in Arctic amplification which, in turn, influences Arctic ecosystems, midlatitude weather and climate. SIC over the Barents-Kara Seas (BKS) shows large inter-annual variations, whose origin is still unclear. Here we find that interannual variations in winter BKS SIC have sign...
Article
Across the winters of 1999–2011, both the frequency of extreme cold events in East Asia and the Arctic Amplification showed an upward trend. Here we constructed regional AA index in the winters of 1979–2019, and examine the atmospheric driver that linked with strong AA scenarios and cold extreme in EA. Results show that the local atmospheric blocki...
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The spatiotemporal characteristics of the near‐surface wind speed (NWS), wind speed at 100 m hub height (HWS), and wind power density (WPD) over China are assessed during 1980–2021. A homogenization process is applied to NWS at 292 basic meteorological stations. A total of 336 breakpoints are recognized, with 122 associated with instrument replacem...
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This study explores the consequences of independent and combined effects of blockings on the northeast Asian cold vortex (NACV) and corresponding cold outbreaks over East Asia (EA) during boreal winters of 1979-2019. The results show that the development of NACV is closely associated with blocking over the Ural Mountains (UB) upstream and eastern S...
Article
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Observations reveal distinct interdecadal winter Eurasian cold anomaly (ECA) centered over central Eurasia (40°–60° N, 60°–120° E), with a more southwestward extension during 1965–1976 than during 2002–2013. In this paper, Ural blockings (UB) in association with the Interdecadal Pacific Oscillation (IPO) and Atlantic Multi-decadal Oscillation (AMO)...
Preprint
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The decline of Arctic sea ice concentration (SIC) plays an important role in Arctic amplification which influences Arctic ecosystem, midlatitude weather and climate. The Arctic SIC shows prominent interannual and interdecadal variability. Although the interdecadal variability of the Arctic SIC fluctuations is mainly linked to Atlantic Multidecadal...
Article
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In recent decades, the winter surface air temperature (SAT) anomaly in the Northern Hemisphere has exhibited a warm Arctic‐cold Eurasia (WACE) dipole pattern and this has undergone significant decadal variation. In this paper, the physical cause of the decadal variability of the WACE pattern is explored, and it is shown to be mediated by the phases...
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In this study, the persistent winter haze that occurred over Beijing during 1980 to 2016 is examined using reanalysis and station data. On both interannual and daily-to-weekly timescales, the winter haze weather in Beijing is found to be associated with a pronounced atmospheric teleconnection pattern from the North Atlantic to Eurasia (Beijing). A...
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This study investigates how El Niño-Southern Oscillation (ENSO) modulates winter cold anomalies over central Eurasia (CE) using reanalysis data during 1950–2019. It is found that ENSO can significantly influence winter air temperature over CE mainly through modulating the strength and location of the cyclonic anomaly of Ural blocking (UB) or long-l...
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We analyze the polar sea ice distribution and the global sea level pressure (SLP) and baroclinicity distributions over the “satellite” period of 1979–2020. In the Arctic, there are statistically significant sea ice extent (SIE) decreases in all calendar months, and the annual mean has lost 2.22 million km² over the four decades. The Antarctic SIE,...
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We investigate linear trends in Antarctic skin temperatures (temperatures from about the top millimeter of the surface) over the four seasons using ERA5 ensemble mean reanalysis data. During 1950–2020, statistically significant warming occurred over East and West Antarctica in spring, autumn and winter, and over the Antarctic Peninsula in autumn an...
Article
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The goal of this study is to advance an automated and objective scheme for the identification of cold fronts over the Mediterranean based on wind‐related criteria, MedFTS, by further incorporating thermal criteria, in order to improve the identification of cold fronts on a climatological basis. These thermal criteria are related to cold advection a...
Preprint
Full-text available
Observations revealed distinct interdecadal winter Eurasian cold anomaly (ECA) centered over central Eurasia (40o-60oN,60o-120oE), with a more southwestward extension during 1965-1976 than during 2002-2013. In this paper, Ural blockings (UB) in association with the Interdecadal Pacific Oscillation (IPO) and Atlantic Multi-decadal Oscillation (AMO)...
Article
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Compound extremes, which involve extremes in two or more meteorological parameters, have received little attention until now. We present a new global climatology of compound events that involve extreme precipitation and extreme wind and that are triggered by low-pressure systems. The analysis employs the 3-hourly ERA5 reanalysis (1979–2018) and two...
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The Antarctic Peninsula of West Antarctica was one of the most rapidly warming regions on the Earth during the second half of the 20th century. Changes in the atmospheric circulation associated with remote tropical climate variabilities have been considered as leading drivers of the change in surface conditions in the region. However, the impacts o...
Article
For the last few decades the Northern Hemisphere midlatitudes have seen an increasing number of temperature extreme events. It has been suggested that some of these extremes are related to planetary wave activity. In this study we identify wave propagation regions at 300 hPa using ERA-Interim dataset from 1980 – 2017 and link them to temperature ex...
Preprint
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The persistent winter haze episodes that occurred in Beijing over the period 1980 to 2016 are examined based on both reanalysis and station data. On both interannual and intra-seasonal timescales, winter haze weather in Beijing is found to be associated with a significant atmospheric teleconnection pattern from the North Atlantic to Eurasia (Beijin...
Article
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Two intense heatwaves of July and early August 2018 are found to be associated with a European blocking (EB) event accompanied by a series of consecutive positive North Atlantic Oscillation (NAO ⁺ ) events. Further analyses show that the collaborative role of an EB event and its upstream NAO ⁺ pattern could increase the frequency, persistence, magn...
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A climatology of the marine atmospheric boundary layer (MABL) and the lower free troposphere over the Southern Ocean (SO) is constructed using 2,186 high‐resolution atmospheric soundings from four recent campaigns conducted in the period of 2016–2018. Relationships between the synoptic meteorology and MABL thermodynamic structure are examined using...
Article
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Winter surface air temperature (SAT) over North America exhibits pronounced variability on subseasonal, interannual, decadal, and interdecadal time scales. Here, reanalysis data from 1950–2017 are analyzed to investigate the atmospheric and surface ocean conditions associated with its subseasonal to interannual variability. Detrended daily SAT data...
Method
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The University of Melbourne Cyclone Detection and Tracking Algorithm is now available from the following webpage: http://cyclonetracker.earthsci.unimelb.edu.au/
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In this paper, the physical processes underlying recent winter cold anomalies over East Asia (EA) are examined via statistical analysis. It is found that the EA cold anomaly depends on the warming in the North Atlantic, sea ice loss in the Barents–Kara Sea (BKS), and atmospheric teleconnection patterns. Specifically, the sea ice loss in the BKS can...
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The relationship between the Indian Ocean High (IOH) and austral autumn (March–May) precipitation variability over Tasmania during 1951–2016 is described. We present evidence that changes in autumn rainfall are influenced primarily by a strength of the Indian Ocean high pressure (IOH_P) and its longitudinal position (IOH_LN). The variation of the I...
Article
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The objective of this work is the development of an automated and objective identification scheme of cold fronts in order to produce a comprehensive climatology of Mediterranean cold fronts. The scheme is a modified version of The University of Melbourne Frontal Tracking Scheme (FTS), to take into account the particular characteristics of the Medit...
Article
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The relationship between the Indian Ocean High (IOH) and austral autumn (March–May) precipitation variability over Tasmania during 1951–2016 is described. We present evidence that changes in autumn rainfall are influenced primarily by a strength of the Indian Ocean high pressure (IOH_P) and its longitudinal position (IOH_LN). The variation of the I...
Article
This study examines the relationship between midlatitude synoptic activity and variations in the width of the tropics in the Southern Hemisphere for the period 1979–2016. The edge of the tropical belt is defined here in terms of the latitude of the subtropical ridge (STR) of sea level pressure, and eddy activity in the midlatitudes is characterized...
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Australian northwest cloudbands (NWCBs) are continental-scale bands of continuous cloud that stretch from northwest to southeast Australia. In earlier studies, where the characteristics of NWCBs and their relationship with precipitation were identified from satellite imagery, there was considerable uncertainty in the results due to limited quality...
Article
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A winter Eurasian cooling trend and a large decline of winter sea ice concentration (SIC) in the Barents-Kara Seas (BKS) are striking features of recent climate changes. The question arises as to what extent these phenomena are related. A mechanism is presented that establishes a link between recent winter SIC decline and midlatitude cold extremes....
Article
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In this paper, the effects of Eurasian circulation patterns such as high-latitude European blocking (HEB) and Ural blocking (UB) events on winter sea-ice concentration (SIC) in the Barents–Kara seas (BKS) and Eurasian cooling is examined to differentiate the different roles of HEB and UB in association with positive North Atlantic Oscillation (NAO⁺...
Article
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Purpose of Review Dynamic manifestations of climate change, i.e. those related to circulation, are less well understood than are thermodynamic, or temperature-related aspects. However, this knowledge gap is narrowing. We review recent progress in understanding the causes of observed changes in polar tropospheric and stratospheric circulation, and i...
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Winds are one of the major meteorological contributors to deaths, damage and insured losses in Australia. A ‘freak storm’ hit the state of South Australia on 28 September 2016, causing state‐wide blackouts and leaving 1.7 million people without power. In the first part of this two‐part study, we analyse this event and find that it was indeed extrem...
Article
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An extreme extratropical cyclone (ETC) struck South Australia on 28 September 2016, causing state‐wide blackouts and damage. In the second part of this two‐part study, we examine the extreme surface wind producing mechanisms within the ETC. ETCs have been extensively studied in the Northern Hemisphere (particularly in western Europe), highlighting...
Article
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Winter atmospheric blocking circulations such as Ural blocking (UB) have been recognized to play an important role in recent winter Eurasian cooling. Observational analyses performed here reveal that the winter warming in the Barents-Kara Seas (BKS) related to the recent decline of sea ice concentration (SIC) has been accompanied by a large increas...
Article
Fire regimes across the globe have great spatial and temporal variability, and these are influence by many factors including anthropogenic management, climate and vegetation types. Here we utilise the satellite based ‘active fire’ product, from MODIS sensors, to statistically analyse variability and trends in fire activity from the global to region...
Article
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Extra-tropical cyclones in the subantarctic play a central role in the poleward transport of heat and moisture into Antarctica, with the latter being a key component of the mass balance of the Antarctic ice sheet. As the climate in this region undergoes substantial changes, it is anticipated that the character of these synoptic features will change...
Article
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In this paper, we analyze observational and reanalysis data to demonstrate that the Atlantic Multidecadal Oscillation (AMO) significantly modulates winter Eurasian surface air temperature through its impact on the shape, frequency and persistence of Ural blocking (UB) events that last for 10–20 d. This impact results from changes in mid-high latitu...
Article
The Arctic has been warming faster than elsewhere, especially during the cold season. According to the leading theory, ice-albedo feedback warms the Arctic Ocean during the summer, and the heat gained by the ocean is released during the winter, causing the cold-season warming. Screen and Simmonds (2010; SS10) concluded that the theory is correct by...
Article
Throughout the world fire regimes are determined by climate, vegetation and anthropogenic factors, and they have great spatial and temporal variability. The availability of high-quality satellite data has revolutionised fire monitoring, allowing for a more consistent and comprehensive evaluation of temporal and spatial patterns. Here we utilise a s...
Article
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The impact of winter atmospheric blocking over the Ural Mountains region (UB) coincident with different phases of the North Atlantic Oscillation (NAO) on the sea ice variability over the Barents and Kara Seas (BKS) in winter is investigated. It is found that the UB in conjunction with the positive phase of the NAO (NAO þ) leads to the strongest sea...
Article
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The Southern Ocean (SO) is the region of the world ocean bordering on Antarctica over which significant exchanges between the atmosphere, the ocean and the sea ice take place. Here, the strong and nearly unhindered eastward flow of the Antarctic Circumpolar Current plays an important role in mean global climate as it transmits climate anomalies aro...
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The impact of winter atmospheric blocking over the Ural Mountains region (UB) coincident with different phases of the North Atlantic Oscillation (NAO) on the sea ice variability over the Barents and Kara Seas (BKS) in winter is investigated. It is found that the UB in conjunction with the positive phase of the NAO (NAO⁺) leads to the strongest sea...
Article
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A composite dataset (comprising geopotential height, sea surface temperature, zonal and meridional surface winds, precipitation, cloud cover, surface air temperature, latent plus sensible heat fluxes, and sea ice concentration) has been investigated with the aim of revealing the dominant time scales of variability from 1982 to 2013. Three covarying...
Article
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Part I of this study examines the relationship among winter cold anomalies over Eurasia, Ural blocking (UB) and the background conditions associated with Arctic warming over the Barents-Kara Sea (BKS) using reanalysis data. It is found that the intensity, persistence and occurrence region of UB-related Eurasian cold anomalies depend strongly on the...
Article
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In Part I of this study, it was shown that the Eurasian cold anomalies related to Arctic warming depend strongly on the quasi-stationarity and persistence of the Ural blocking (UB). Our analysis revealed that under weak mean westerly wind (MWW) and vertical shear (VS) (quasi-barotropic) conditions with weak synoptic-scale eddies and large planetary...
Chapter
In this study the synoptic environment and thermodynamic mechanisms of two cases of surface cyclogenesis in the south Ionian and Aegean Seas, associated to strong low-level cold surges, are analyzed. The cases are characteristic examples of two different synoptic categories, affecting the weather in the Greek area. The analysis was performed using...
Chapter
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Mediterranean explosive cyclogenesis is the result of the interaction between upper level baroclinic and low level diabatic processes. This interaction presents significant differences in specific Mediterranean sub-areas and in different cases of rapid deepening, especially regarding the evolution of the diabatic processes. In this study, the regio...
Chapter
A comprehensive climatology of anticyclones affecting the Mediterranean has been assembled employing the objective finding and tracking scheme of the University of Melbourne (MS). The identified anticyclones have been characterized as cold or warm on the basis of their thermal structure at the lower isobaric levels with the aid of an extension modu...
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Scientific Reports 6 : Article number: 29599 10.1038/srep29599 ; published online: 14 July 2016 ; updated: 24 August 2016 This Article contains an error in the legend of Table 1.
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This paper highlights some caveats in using composite analyses to form physical hypotheses on the associations between environmental variables. This is illustrated using a specific example, namely the apparent links between heat waves (HWs) and sea surface temperatures (SSTs). In this case study, a composite analysis is performed to show the large-...