Factors Contributing to Record-Breaking Heat Waves over the Great Plains during the 1930s Dust Bowl

Record-breaking summer heat waves were experienced across the contiguous United States during the decade-long “Dust Bowl” drought in the 1930s. Using high-quality daily temperature observations, the Dust Bowl heat wave characteristics are assessed with metrics that describe variations in heat wave activity and intensity. Despite the sparser station coverage in the early record, there is robust evidence for the emergence of exceptional heat waves across the central Great Plains, the most extreme of which were preconditioned by anomalously dry springs. This is consistent with the entire twentieth-century record: summer heat waves over the Great Plains develop on average ~15–20 days earlier after anomalously dry springs, compared to summers following wet springs. Heat waves following dry springs are also significantly longer and hotter, indicative of the importance of land surface feedbacks in heat wave intensification. A distinctive anomalous continental-wide circulation pattern accompanied exceptional heat waves in the Great Plains, including those of the Dust Bowl decade. An anomalous broad surface pressure ridge straddling an upper-level blocking anticyclone over the western United States forced substantial subsidence and adiabatic warming over the Great Plains, and triggered anomalous southward warm advection over southern regions. This prolonged and amplified the heat waves over the central United States, which in turn gradually spread westward following heat wave emergence. The results imply that exceptional heat waves are preconditioned, triggered, and strengthened across the Great Plains through a combination of spring drought, upper-level continental-wide anticyclonic flow, and warm advection from the north

Natural hazards in Australia: heatwaves

As part of a special issue on natural hazards, this paper reviews the current state of scientific knowledge of Australian heatwaves. Over recent years, progress has been made in understanding both the causes of and changes to heatwaves. Relationships between atmospheric heatwaves and large-scale and synoptic variability have been identified, with increasing trends in heatwave intensity, frequency and duration projected to continue throughout the 21st century. However, more research is required to further our understanding of the dynamical interactions of atmospheric heatwaves, particularly with the land surface. Research into marine heatwaves is still in its infancy, with little known about driving mechanisms, and observed and future changes. In order to address these knowledge gaps, recommendations include: focusing on a comprehensive assessment of atmospheric heatwave dynamics; understanding links with droughts; working towards a unified measurement framework; and investigating observed and future trends in marine heatwaves. Such work requires comprehensive and long-term collaboration activities. However, benefits will extend to the international community, thus addressing global grand challenges surrounding these extreme events

A Recent Class of Chemosensory Neurons Developed in Mouse and Rat

In most animal species, the vomeronasal organ ensures the individual recognition of conspecifics, a prerequisite for a successful reproduction. The vomeronasal organ expresses several receptors for pheromone detection. Mouse vomeronasal type-2 receptors (V2Rs) are restricted to the basal neurons of this organ and organized in four families. Family-A, B and D (family ABD) V2Rs are expressed monogenically (one receptor per neuron) and coexpress with either Vmn2r1 or Vmn2r2, two members of family-C V2Rs. Thus, basal neurons are characterized by specific combinations of two V2Rs. To investigate this issue, we raised antibodies against all family-C V2Rs and analyzed their expression pattern. We found that six out of seven family-C V2Rs (Vmn2r2-7) largely coexpressed and that none of the anti-Vmn2r2-7 antibodies significantly stained Vmn2r1 positive neurons. Thus, basal neurons are divided into two complementary subsets. The first subset (Vmn2r1-positive) preferentially coexpresses a distinct group of family-ABD V2Rs, whereas the second subset (Vmn2r2-7-positive) coexpresses the remaining group of V2Rs. Phylogenetic reconstruction and the analysis of genetic loci in various species reveal that receptors expressed by this second neuronal subset are recent branches of the V2R tree exclusively present in mouse and rat. Conversely, V2Rs expressed in Vmn2r1 positive neurons, are phylogenetically ancient and found in most vertebrates including rodents. Noticeably, the more recent neuronal subset expresses a type of Major Histocompatibility Complex genes only found in murine species. These results indicate that the expansion of the V2R repertoire in a murine ancestor occurred with the establishment of a new population of vomeronasal neurons in which coexists the polygenic expression of a recent group of family-C V2Rs (Vmn2r2-7) and the monogenic expression of a recent group of family-ABD V2Rs. This evolutionary innovation could provide a molecular rationale for the exquisite ability in individual recognition and mate choice of murine species

Prediction of Indian Summer Monsoon Rainfall: A comparison of SST indices in the Indo-Pacific region

International audienceThe focus of this study is to document and discuss the variability and predictability of the Indian Summer Monsoon (ISM) rainfall at interannual time-scales. Various SST indices have already been proposed in the literature in order to understand the variability of ISM rainfall. However, the forecast skills and dynamics of these different indices have never been compared in detail. The present analysis is based on monthly mean rainfall, SST and atmospheric fields for the period 1979-2007. Four SST indices are computed in different regions of the Indian and Pacific oceans - Nino3.4 SST index in December-January, South East Indian Ocean SST (SEIO) in February-March, the Indian Ocean Basin Mode (IOB) in April-May, the Indian Ocean Dipole (IOD) averaged from September to November - and compared though composite analyses of SST and atmospheric fields, and correlation with ISM rainfall, onset and withdrawal. The results show that SEIO SSTs during late boreal winter or IOB SSTs during boreal spring are significant precursors for both the late ISM (August-September) and withdrawal of the monsoon, while the early part of the monsoon (June-July) and the monsoon onset are mostly influenced by an early ENSO onset and equatorial Pacific variability during spring. Furthermore, correlation and regression analyses show that the IOB index is associated with the decay of ENSO events on one hand, while the SEIO index is linked to developing El Nino/La Nina episodes on the other. Despite different spatio-temporal definitions and relationships with ENSO, IOB and SEIO SSTs can thus both impact ISM rainfall, mainly through air-sea interactions within the Indian Ocean. With comparable predicting skills, the choice of the better index then hinges on SST conditions in the equatorial Pacific Ocean several months before the onset of the monsoon. Hence, this study not only stresses the importance of a proper definition of the summer rainy season, but sheds light on the respective merits of different SST indices for a better long-range prediction of ISM rainfall

Future projections of Australian heatwave number and intensity based on CMIP5 models

Australia is a continent of climatic extremes, experiencing devastating floods, decadal-long droughts and crippling heat waves. Since the late twentieth century, summer heat waves across Australia have been getting progressively longer, hotter and more frequent, with human-induced climate change a major player in the increase. This study utilises global climate models to project how the total number of summer heat waves will change and how hot, on average, they may become (their magnitude) by the end of the twenty-first century. While the models perform well at capturing the heat wave magnitude across Australia, they struggle to simulate the regional variations in the total number of events. The models project a doubling of heat wave events by 2100 across southern Australia, and an almost tripling in the northern-central regions, under a high greenhouse-gas emissions scenario. In the regions where the heat waves are hottest, such as Victoria, South Australia, and south-west Western Australia, the models project an increase of almost 2°C in magnitude by the end of the century. Furthermore, the intensity of these southern Australian heat waves is projected to rise faster than the long-term increase in the background temperature, implying the magnitude of these events may become more extreme in the future

On the use of composite analyses to form physical hypotheses: An example from heat wave - SST associations

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-scale and regional SST conditions observed during summer HWs in Perth, southwest Australia. Composite results initially point to the importance of the subtropical South Indian Ocean, where physically coherent SST dipole anomalies appear to form a necessary condition for HWs to develop across southwest Australia. However, sensitivity tests based on pattern correlation analyses indicate that the vast majority of days when the identified SST pattern appears are overwhelmingly not associated with observed HWs, which suggests that this is definitely not a sufficient condition for HW development. Very similar findings are obtained from the analyses of 15 coupled climate model simulations. The results presented here have pertinent implications and applications for other climate case studies, and highlight the importance of applying comprehensive statistical approaches before making physical inferences on apparent climate associations