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Adrian Brügger, Christina Demski, and Stuart Capstick

Abstract

The proportion of the world’s population exposed to above-average monthly temperatures has been rising consistently in recent decades and will continue to grow. This and similar trends make it more likely that people will personally experience extreme weather events and seasonal changes related to climate change. A question that follows from this is to what extent experiences may influence climate-related beliefs, attitudes, and the willingness to act. Although research is being done to examine the effects of such experiences, many of these studies have two important shortcomings. First, they propose effects of experiences but remain unclear on the psychological processes that underlie those effects. Second, if they do make assumptions about psychological processes, they do not typically corroborate them with empirical evidence. In other words, a considerable body of research in this field rests on relatively unfounded intuitions. To advance the theoretical understanding of how experiences of climate change could affect the motivation to act on climate change, we introduce a conceptual framework that organizes insights from psychology along three clusters of processes: 1) noticing and remembering, 2) mental representations, and 3) risk processing and decision-making. Within each of these steps, we identify and explicate psychological processes that could occur when people personally experience climate change, and we formulate theory-based, testable hypotheses. By making assumptions explicit and tying them to findings from basic and applied research from psychology, this paper provides a solid basis for future research and for advancing theory.

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Julia Linder and Victoria Campbell-Arvai

Abstract

In the midwestern United States, intensifying impacts from climate change necessitate adaptation by the agricultural sector. Tree fruit agriculture is uniquely vulnerable to climate change due to the long-lived nature of perennial systems, yet very few studies have addressed how fruit growers perceive climate change and are responding to climate risks. For this study, 16 semistructured interviews were conducted with Michigan tree fruit growers to understand how their climate change beliefs, beliefs about adaptive actions, and climate-related risk perceptions influence adaptation behaviors. While there was a great deal of uncertainty about the anthropogenic nature of climate change, growers generally agreed that unprecedented changes in climate and weather patterns were occurring. Because of a perception of little control over future climate impacts, most growers reactively adapted to climate risks that negatively impacted their orchards by implementing measures such as frost protection, irrigation, pesticides, and crop insurance. This study highlighted that while proactive adaptations such as crop diversification, planting new varieties, and improving soil health will be necessary to increase farm resilience in the future, growers were unable to justify making these changes due to their uncertainty about future climate changes. The findings from this study highlight the need for future outreach efforts by university extension agents, private agricultural advisors, and federal and state agency advisors to provide educational information on the long-term impacts of climate change in order to help growers increase the resilience of their farm in the face of future climate impacts.

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Jingyi Li, Fei Li, Shengping He, Huijun Wang, and Yvan J Orsolini

Abstract

The Tibetan Plateau (TP), referred to as the “Asian water tower,” contains one of the largest land ice masses on Earth. The local glacier shrinkage and frozen-water storage are strongly affected by variations in surface air temperature over the TP (TPSAT), especially in springtime. This study reveals that the relationship between the February North Atlantic Oscillation (NAO) and March TPSAT is unstable with time and regulated by the phase of the Atlantic multidecadal variability (AMV). The significant out-of-phase connection occurs only during the warm phase of AMV (AMV+). The results show that during the AMV+, the negative phase of the NAO persists from February to March, and is accompanied by a quasi-stationary Rossby wave train trapped along a northward-shifted subtropical westerly jet stream across Eurasia, inducing an anomalous adiabatic descent that warms the TP. However, during the cold phase of the AMV, the negative NAO cannot persist into March. The Rossby wave train propagates along the well-separated polar and subtropical westerly jets, and the NAO–TPSAT connection is broken. Further investigation suggests that the enhanced synoptic eddy and low-frequency flow (SELF) interaction over the North Atlantic in February and March during the AMV+, caused by the southward-shifted storm track, helps maintain the NAO pattern via positive eddy feedback. This study provides a new detailed perspective on the decadal variability of the North Atlantic–TP connection in late winter to early spring.

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Weixin Xu, Steven A. Rutledge, and Kyle Chudler

Abstract

Using 17-yr spaceborne precipitation radar measurements, this study investigates how diurnal cycles of rainfall and convective characteristics over the South China Sea region are modulated by the boreal summer intraseasonal oscillation (BSISO). Generally, diurnal cycles change significantly between suppressed and active BSISO periods. Over the Philippines and Indochina, where the low-level monsoon flows impinge on coast lines, diurnal cycles of rainfall and many convective properties are enhanced during suppressed periods. During active periods, diurnal variation of convection is still significant over land but diminishes over water. Also, afternoon peaks of rainfall and MCS populations over land are obviously extended in active periods, mainly through the enhancement of stratiform precipitation. Over Borneo, where the prevailing low-level winds are parallel to coasts, diurnal cycles (both onshore and offshore) are actually stronger during active periods. Radar profiles also demonstrate a pronounced nocturnal offshore propagation of deep convection over western Borneo in active periods. During suppressed periods, coastal afternoon convection over Borneo is reduced, and peak convection occurs over the mountains until the convective suppression is overcome in the late afternoon or evening. A major portion (>70%) of the total precipitation over the Philippines and Indochina during suppressed periods falls from afternoon isolated to medium-sized systems (<10 000 km2), but more than 70% of the active BSISO rainfall is contributed by nocturnal (after 1800 LT) broad precipitation systems (>10 000 km2). However, offshore total precipitation is dominated by large precipitation systems (>10 000 km2) regardless of BSISO phases and regions.

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Matthew D. Flournoy, Michael C. Coniglio, and Erik N. Rasmussen

Abstract

Although environmental controls on bulk supercell potential and hazards have been studied extensively, relationships between environmental conditions and temporal changes to storm morphology remain less explored. These relationships are examined in this study using a compilation of sounding data collected during field campaigns from 1994 to 2019 in the vicinity of 216 supercells. Environmental parameters are calculated from the soundings and related to storm-track characteristics like initial cell motion and the time of the right turn (i.e., the time elapsed between the cell initiation and the first time when the supercell obtains a quasi-steady motion that is directed clockwise from its initial motion.). We do not find any significant associations between environmental parameters and the time of the right turn. Somewhat surprisingly, no relationship is found between storm-relative environmental helicity and the time elapsed between cell initiation and the onset of deviant motion. Initial cell motion is best approximated by the direction of the 0–6-km mean wind at two-thirds the speed. This is a result of advection and propagation in the 0–4- and 0–2-km layers, respectively. Unsurprisingly, Bunkers-right storm motion is a good estimate of post-turn motion, but storms that exhibit a post-turn motion left of Bunkers-right are less likely to be tornadic. These findings are relevant for real-time forecasting efforts in predicting the path and tornado potential of supercells up to hours in advance.

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Seth P. Howard, Kim E. Klockow-McClain, Alison P. Boehmer, and Kevin M. Simmons

Abstract

Tornadoes cause billions of dollars in damage and over 100 fatalities on average annually. Yet, an indirect cost to these storms is found in lost sales and/or lost productivity from responding to over 2000 warnings per year. This project responds to the Weather Research and Forecasting Innovation Act of 2017, H.R. 353, which calls for the use of social and behavioral science to study and improve storm warning systems. Our goal is to provide an analysis of cost avoidance that could accrue from a change to the warning paradigm, particularly to include probabilistic hazard information at storm scales. A survey of nearly 500 firms was conducted in and near the Dallas–Fort Worth metropolitan area asking questions about experience with tornadoes, sources of information for severe weather, expected cost of responding to tornado warnings, and how the firm would respond to either deterministic or probabilistic warnings. We find a dramatic change from deterministic warnings compared to the proposed probabilistic and that a probabilistic information system produces annual cost avoidance in a range of $2.3–$7.6 billion (U.S. dollars) compared to the current deterministic warning paradigm.

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Samuel Smith, Paul W. Staten, and Jian Lu

Abstract

Models disagree on how much the hydrologic cycle could intensify under climate change. These changes are expected to scale with the Clausius–Clapeyron relation but may locally diverge due in part to the uncertain response of the general circulation, causing the hydrologic cycle to inherit this uncertainty. To identify how the circulation contributes, we link circulation changes to changes in the higher moments of the hydrologic cycle using the novel dynamical framework of the local hydrologic cycle, the portion of the hydrologic cycle driven by moist or dry intrusions. We expand this dynamical framework, developing a closed budget that diagnoses thermodynamic, advective, and overturning contributions to future hydrologic cycle changes. In analyzing these changes for the Community Earth System Model Large Ensemble, we show that overturning is the main dynamic contributor to the tropical and subtropical annual response, consistent with a weakening of this circulation. In the extratropics, we show that advective contributions, likely from storm track changes, dominate the response. We achieve a cleaner separation between dynamic and thermodynamic contributions through a semiempirical scaling, which reveals the robustness of the Clausius–Clapeyron scaling for the local hydrologic cycle. This scaling also demonstrates the slowing of the local hydrologic cycle and how changing subtropical dynamics asymmetrically impact wave breaking and suppress meridional moisture transport. We conclude that dynamic changes in the subtropics are predominantly responsible for the annual, dynamic response in the extratropics and thus a significant contributor to uncertainty in future projections.

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Pier Luigi Vidale, Kevin Hodges, Benoit Vannière, Paolo Davini, Malcolm J. Roberts, Kristian Strommen, Antje Weisheimer, Elina Plesca, and Susanna Corti

Abstract

The role of model resolution in simulating geophysical vortices with the characteristics of realistic tropical cyclones (TCs) is well established. The push for increasing resolution continues, with general circulation models (GCMs) starting to use sub-10-km grid spacing. In the same context it has been suggested that the use of stochastic physics (SP) may act as a surrogate for high resolution, providing some of the benefits at a fraction of the cost. Either technique can reduce model uncertainty, and enhance reliability, by providing a more dynamic environment for initial synoptic disturbances to be spawned and to grow into TCs. We present results from a systematic comparison of the role of model resolution and SP in the simulation of TCs, using EC-Earth simulations from project Climate-SPHINX, in large ensemble mode, spanning five different resolutions. All tropical cyclonic systems, including TCs, were tracked explicitly. As in previous studies, the number of simulated TCs increases with the use of higher resolution, but SP further enhances TC frequencies by ~30%, in a strikingly similar way. The use of SP is beneficial for removing systematic climate biases, albeit not consistently so for interannual variability; conversely, the use of SP improves the simulation of the seasonal cycle of TC frequency. An investigation of the mechanisms behind this response indicates that SP generates both higher TC (and TC seed) genesis rates, and more suitable environmental conditions, enabling a more efficient transition of TC seeds into TCs. These results were confirmed by the use of equivalent simulations with the HadGEM3-GC31 GCM.

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Kai-Chih Tseng, Nathaniel C. Johnson, Eric D. Maloney, Elizabeth A. Barnes, and Sarah B. Kapnick

Abstract

The excitation of the Pacific–North American (PNA) teleconnection pattern by the Madden–Julian oscillation (MJO) has been considered one of the most important predictability sources on subseasonal time scales over the extratropical Pacific and North America. However, until recently, the interactions between tropical heating and other extratropical modes and their relationships to subseasonal prediction have received comparatively little attention. In this study, a linear inverse model (LIM) is applied to examine the tropical–extratropical interactions. The LIM provides a means of calculating the response of a dynamical system to a small forcing by constructing a linear operator from the observed covariability statistics of the system. Given the linear assumptions, it is shown that the PNA is one of a few leading modes over the extratropical Pacific that can be strongly driven by tropical convection while other extratropical modes present at most a weak interaction with tropical convection. In the second part of this study, a two-step linear regression is introduced that leverages a LIM and large-scale climate variability to the prediction of hydrological extremes (e.g., atmospheric rivers) on subseasonal time scales. Consistent with the findings of the first part, most of the predictable signals on subseasonal time scales are determined by the dynamics of the MJO–PNA teleconnection while other extratropical modes are important only at the shortest forecast leads.

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Brett Chrisler and Justin P. Stachnik

Abstract

Recent studies have examined moist entropy (ME) as a proxy for moist static energy (MSE) and the relative role of the underlying processes responsible for changes in ME that potentially affect MJO propagation. This study presents an analysis of the intraseasonally varying (ISV) ME anomalies throughout the lifetime of observed MJO events. A climatology of continuing and terminating MJO events is created from an event identification algorithm using common tracking indices including the OLR-based MJO index (OMI), filtered OMI (FMO), real-time multivariate MJO (RMM), and velocity potential MJO (VPM) index. ME composites for all indices show a statistically significant break in the wavenumber-1 oscillation at day 0 for terminating events in nearly all domains except RMM phase 6 and phase 7. The ME tendency is decomposed into horizontal and vertical advection, sensible and latent heat fluxes, and shortwave and longwave radiative fluxes using ERA-Interim data. The relative role of each processes toward the eastward propagation is discussed as well as their effects on MJO stabilization. Statistically significant differences occur for all terms by day −10. A domain sensitivity test is performed where eastward propagation is favored for vertical advection given a larger, asymmetric domain for continuing events. A reduced eastward propagation from vertical advection is evident 2–3 days before similar differences in horizontal advection for terminating events. The importance of horizontal advection for the eastward propagation of the MJO is discussed in addition to the relative destabilization from vertical advection in the convectively suppressed region downstream of future terminating MJOs.

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