243 research outputs found
Extreme weather and climate events with ecological relevance : a review
Author Posting. © The Author(s), 2017. This is the author's version of the work. It is posted here under a nonexclusive, irrevocable, paid-up, worldwide license granted to WHOI. It is made available for personal use, not for redistribution. The definitive version was published in Philosophical Transactions of the Royal Society of London.Series B, Biological Sciences, 372 (2017): 2016.0135, doi: 10.1098/rstb.2016.0135.Robust evidence exists that certain extreme weather and climate events, especially daily temperature and precipitation extremes, have changed in regard to intensity and frequency over recent decades. These changes have been linked to human-induced climate change, while the degree to which climate change impacts an individual extreme climate event (ECE) is more difficult to quantify. Rapid progress in event attribution has recently been made through improved understanding of observed and simulated climate variability, methods for event attribution and advances in numerical modelling. Attribution for extreme temperature events is stronger compared with other event types, notably those related to the hydrological cycle. Recent advances in the understanding of ECEs, both in observations and their representation in state-of-the-art climate models, open new opportunities for assessing their effect on human and natural systems. Improved spatial resolution in global climate models and advances in statistical and dynamical downscaling now provide climatic information at appropriate spatial and temporal scales. Together with the continued development of Earth System Models that simulate biogeochemical cycles and interactions with the biosphere at increasing complexity, these make it possible to develop a mechanistic understanding of how ECEs affect biological processes, ecosystem functioning and adaptation capabilities. Limitations in the observational network, both for physical climate system parameters and even more so for long-term ecological monitoring, have hampered progress in understanding bio-physical interactions across a range of scales. New opportunities for assessing how ECEs modulate ecosystem structure and functioning arise from better scientific understanding of ECEs coupled with technological advances in observing systems and instrumentation.Portions of this study were supported by the Regional and Global Climate Modeling Program
(RGCM) of the U.S. Department of Energy's Office of Biological & Environmental Research
(BER) Cooperative Agreement #DE-FC02-97ER62402, and the National Science Foundation
The climate of Myanmar: evidence for effects of the Pacific Decadal Oscillation
We show evidence for the influence of the Pacific Decadal Oscillation (PDO) on Myanmar's monsoonal hydroclimate using both instrumental and 20th century reanalysis data, and a tree-ring width chronology from Myanmar's central Dry Zone. The âregime shiftsâ identified in the instrumental PDO for the past century are clearly evident in the Myanmar teak. The teak record and PDO index correlate most significantly and positively during DecemberâMay, at râ=â0.41 (0.002, n = 109). We generated composite climate anomalies for southern Asia and adjacent ocean areas during negative and positive PDO phases and above/below average teak growth for the MayâSeptember wet monsoon season. They show that negative (positive) PDO phases correspond to dry (wet) conditions, due to reduced (enhanced) moisture flux into central Myanmar. Multitaper Method (MTM) and Singular Spectrum Analysis (SSA) spectral analyses reveal considerable multidecadal variability over the past several centuries of the teak chronology, consistent with the PDO
Southern hemisphere regional precipitation and climate variability : extremes trends and predictability
This PhD thesis investigates the relative importance of oceanic and atmospheric
influences on extremes, long-term trends, and seasonal to interannual variability
of precipitation for different regions in the Southern Hemisphere in observations,
reanalysis data, and output from general circulation models (GCM).
Examination of interannual rainfall extremes over southwest Western Australia
(SWWA) reveals a characteristic dipole pattern of Indian Ocean sea surface temperature anomalies (SSTA). This coincides with a large-scale reorganization of the wind field over the tropical/subtropical Indian Ocean changing SSTA, via anomalous Ekman transport in the tropical Indian Ocean and via anomalous air-sea heat fluxes in the subtropics, and altering moisture advection onto SWWA. The potential impact of these Indian Ocean SSTA in driving modulations of mid-latitude
precipitation across southern and western regions of Australia is assessed in atmospheric GCM simulations. The SSTA give rise to changes in the thermal properties of the atmosphere, meridional thickness gradient, subtropical jet, thermal wind, and baroclinicity over southern regions of Australia, thus modulating precipitation. In addition, links between anomalous wet conditions over East Africa and these characteristic Indian Ocean SSTA are explored during the "short rain" season in October-November.
Interannual extremes m New Zealand rainfall and their modulation by modes
of Southern Hemisphere climate variability, namely the Southern Annular Mode
(SAM) and El Nino-Southern Oscillation (ENSO), are investigated. Late twentieth
Century trends in New Zealand precipitation are examined for the period 19792006
to quantify the relative impact of recent changes in the large-scale atmospheric
circulation related to the SAM and ENSO. Increasingly drier conditions over much
of New Zealand can be partially explained by the SAM and ENSO.
Cool season rainfall variability in southeastern Australia is investigated via a
classification and characterization of the predominant types of synoptic systems
occurring in the region, focusing on frontal and cutoff low systems. Two definitions
of the autumn break developed for northwestern Victoria are employed to produce
a synoptic climatology of the break phenomenon. Trends in characteristics of the
autumn break indicate that the most recent drought in southeastern Australia is
comparable in severity with the two major droughts in the twentieth Century
Intraseasonal rainfall variability in the Bay of Bengal during the Summer Monsoon: coupling with the ocean and modulation by the Indian Ocean Dipole
The Indian Summer Monsoon rainfall exhibits pronounced intraseasonal variability in the Bay of Bengal (BoB). This study examines the intraseasonal rainfall variability with foci on the coupling with sea surface temperatures (SST) and its interannual modulation. The lagged composite analysis reveals that, in the northern BoB, SST warming leads the onset of intraseasonal rainfall by 5âdays. Latent heat flux is reduced before the rain event but is greatly amplified during the rainfall maxima. Further analysis reveals that this intraseasonal rainfall-SST relationship through latent heating is strengthened in negative Indian Ocean Dipole (IOD) years when the bay-wide local SST is anomalously warm. Latent heat flux is further increased during the intraseasonal rainfall maxima leading to strengthened rainfall variability. The moisture budget analysis shows this is primarily due to stronger low-level moisture convergence in negative IOD years. The results provide important predictive information on the monsoon rainfall and its active/break cycles
The role of atmospheric fronts in austral winter precipitation changes across Australia
© The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Lawrence, L., Parfitt, R., & Ummenhofer, C. C. The role of atmospheric fronts in austral winter precipitation changes across Australia. Atmospheric Science Letters, 23(10), (2022): e1117, https://doi.org/10.1002/asl.1117.Over the past few decades, Southeast Australia has experienced severe regional climatic events and some of the most extreme droughts on record, linked in part to influences from both the El Niño Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD). In this article, the extent to which austral winter rainfall anomalies, in years leading into co-occurring ENSO and IOD events, are communicated specifically through variations in atmospheric fronts is quantified. The most extreme wet (dry) conditions occur in winters characterized by sea surface temperature anomaly patterns exhibiting features of La Niña-Negative IOD (El Niño-Positive IOD). It is found that most of these precipitation anomalies are related to changes in the precipitation associated with the passing of atmospheric fronts specifically. Although there is some suggestion that there are accompanying changes in the frequency of atmospheric fronts, the response appears to be dominated by changes in the amount of precipitation per individual atmospheric front. In addition, the distribution in the dynamic strength of individual atmospheric fronts remains relatively unchanged.Rhys Parfitt would like to gratefully acknowledge NSF OCE award number 2023585 and Caroline C. Ummenhofer support from the James E. and Barbara V. Moltz Fellowship for Climate-Related Research at WHOI
Multi-scale drought and oceanâatmosphere variability in monsoon Asia
© The Author(s), 2015. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Environmental Research Letters 10 (2015): 074010, doi:10.1088/1748-9326/10/7/074010.Spatially extensive and persistent drought episodes have repeatedly influenced human history, including the 'Strange Parallels' drought event in monsoon Asia during the mid-18th century. Here we explore the dynamics of sustained monsoon failure using observed and tree-ring reconstructed drought patterns and a 1300-year pre-industrial community earth system model control run. Both modern observational and climate model drought patterns during years with extremely weakened South Asian monsoon resemble those reconstructed for the Strange Parallels drought. Model analysis reveals that this pattern arises during boreal spring over Southeast Asia, with decreased precipitation and moisture flux, while related summertime climate anomalies are confined to the Indian subcontinent. Years with simulated South Asian drying exhibit canonical El Niño conditions over the Pacific and associated shifts in the Walker circulation. In contrast, multi-year drought periods, resembling those sustained during the Strange Parallels drought, feature anomalous Pacific warming around the dateline, typical of El Niño Modoki events.This work was performed with support and funding from the Significant Opportunities in Atmospheric Research and Sciences Program (NSF AGS-1120459), WHOI Academic Programs Office Funds, and NSF AGS-1338734, AGS-1203704, and AGS-1304245
Dynamical and Thermodynamic Elements of Modeled Climate Change at the East African Margin of Convection
We propose a dynamical interpretation of model projections for an end-of-century wetting in equatorial East Africa. In the current generation of global climate models, increased atmospheric moisture content associated with warming is not the dominant process explaining the increase in rainfall, as the regional circulation is only weakly convergent even during the rainy seasons. Instead, projected wetter future conditions are generally consistent with the El Niño-like trend in tropical Pacific sea surface temperatures in climate models. In addition, a weakening in moisture convergence over the adjacent Congo Basin and Maritime Continent cores of convection results in the weakening of near-surface winds, which increases moisture advection from the Congo Basin core toward the East African margin. Overall confidence in the projections is limited by the significant biases in simulation of the regional climatology and disagreement between observed and modeled tropical Pacific sea surface temperature trends to date
The role of the subtropical North Atlantic water cycle in recent US extreme precipitation events
© The Author(s), 2017. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Climate Dynamics 50 (2018): 1291â1305, doi:10.1007/s00382-017-3685-y.The role of the oceanic water cycle in the record-breaking 2015 warm-season precipitation in the US is analyzed. The extreme precipitation started in the Southern US in the spring and propagated northward to the Midwest and the Great Lakes in the summer of 2015. This seasonal evolution of precipitation anomalies represents a typical mode of variability of US warm-season precipitation. Analysis of the atmospheric moisture flux suggests that such a rainfall mode is associated with moisture export from the subtropical North Atlantic. In the spring, excessive precipitation in the Southern US is attributable to increased moisture flux from the northwestern portion of the subtropical North Atlantic. The North Atlantic moisture flux interacts with local soil moisture which enables the US Midwest to draw more moisture from the Gulf of Mexico in the summer. Further analysis shows that the relationship between the rainfall mode and the North Atlantic water cycle has become more significant in recent decades, indicating an increased likelihood of extremes like the 2015 case. Indeed, two record-high warm-season precipitation events, the 1993 and 2008 cases, both occurred in the more recent decades of the 66 year analysis period. The export of water from the North Atlantic leaves a marked surface salinity signature. The salinity signature appeared in the spring preceding all three extreme precipitation events analyzed in this study, i.e. a saltier-than-normal subtropical North Atlantic in spring followed by extreme Midwest precipitation in summer. Compared to the various sea surface temperature anomaly patterns among the 1993, 2008, and 2015 cases, the spatial distribution of salinity anomalies was much more consistent during these extreme flood years. Thus, our study suggests that preseason salinity patterns can be used for improved seasonal prediction of extreme precipitation in the Midwest.LL is supported by the Postdoctoral Scholar Program at WHOI, with funding provided by the Oceans and Climate Change Institute. RWS is supported by NASA Grants NNX12AF59G and NNX14AH38G, and NSF Grant OCE-1129646. CCU is supported by NSF Grant AGS-1355339
North Atlantic natural variability modulates emergence of widespread Greenland melt in a warming climate
Author Posting. © American Geophysical Union, 2018. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 45 (2018): 9171-9178, doi:10.1029/2018GL079682.Recordâbreaking melt over Greenland in recent decades is linked not only to climate change but also to natural variability, including persistent atmospheric highâpressure conditions in the negative phase of the North Atlantic Oscillation and warm North Atlantic Ocean temperatures during the positive phase of the Atlantic Multidecadal Oscillation. However, the relative importance of natural variability for Greenland melt under varying degrees of greenhouse forcing is still unclear. Using reanalysis data and a large ensemble of climate model simulations, we find that a negative North Atlantic Oscillation and positive Atlantic Multidecadal Oscillation consistently promote heightened summer melt under various forcing conditions. Moreover, timing of widespread 21st century Greenland melt varies considerably between ensemble members due to different phasing of these modes of natural variability. These results indicate the importance of natural modes of variability across a range of external forcing conditions for interannual melt variability and the emergence of widespread Greenland melt.U.S. National Science Foundation Grant Number: ANSâ1736738;
Woods Hole Oceanographic Institution Summer Student Fellow program Grant Number: AGSâ13553392019-03-1
Impact of surface forcing on Southern Hemisphere atmospheric blocking in the AustraliaâNew Zealand sector
Author Posting. © American Meteorological Society, 2013. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Climate 26 (2013): 8476â8494, doi:10.1175/JCLI-D-12-00860.1.Characteristics of atmospheric blocking in the Southern Hemisphere (SH) are explored in atmospheric general circulation model (AGCM) simulations with the Community Atmosphere Model, version 3, with a particular focus on the AustraliaâNew Zealand sector. Preferred locations of blocking in SH observations and the associated seasonal cycle are well represented in the AGCM simulations, but the observed magnitude of blocking is underestimated throughout the year, particularly in late winter and spring. This is related to overly zonal flow due to an enhanced meridional pressure gradient in the model, which results in a decreased amplitude of the longwave trough/ridge pattern. A range of AGCM sensitivity experiments explores the effect on SH blocking of tropical heating, midlatitude sea surface temperatures, and landâsea temperature gradients created over the Australian continent during austral winter. The combined effects of tropical heating and extratropical temperature gradients are further explored in a configuration that is favorable for blocking in the AustraliaâNew Zealand sector with warm SST anomalies to the north of Australia, cold to the southwest of Australia, warm to the southeast, and cool Australian land temperatures. The blocking-favorable configuration indicates a significant strengthening of the subtropical jet and a reduction in midlatitude flow, which results from changes in the thermal wind. While these overall changes in mean climate, predominantly forced by the tropical heating, enhance blocking activity, the magnitude of atmospheric blocking compared to observations is still underestimated. The blocking-unfavorable configuration with surface forcing anomalies of opposite sign results in a weakening subtropical jet, enhanced midlatitude flow, and significantly reduced blocking.C.C.U.
received support from the Australian Research Council
through funding awarded to the Centre of Excellence
for Climate System Science and the Penzance Endowed
Fund at WHOI. P.C.M., M.J.P., and J.S.R. were funded
by the CSIRO Climate Adaptation Flagship and the
Managing Climate Variability R&D Program.2014-05-0
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