DO METEOROLOGISTS SUPPRESS THUNDERSTORMS? Radar-Derived Statics and the Behavior of Moist Convection

Most meteorologists are acquainted with the no- tion of a weather hole—that is, a place that receives less exciting weather than does its surroundings. Exciting weather takes many forms, but when people use the term weather hole, they tend to mean a place that thunderstorms often barely miss, or near which approaching storms often dissipate. For this paper, that is the meaning we adopt. In our experience, many meteorologists and lay weather enthusiasts genuinely believe that they live in weather holes, and this belief, almost without fail, seems to stem from countless hours spent gazing at displays of radar reflectivity. We have generally presumed that such people simply relish thunderstorms, are memorably disappointed whenever storms miss them, and erroneously conclude that their locations are subject to some kind of meteorologic disfavor. The recent availability of multiple years\u27 worth of national radar composites from the Weather Surveillance Radar-1988 Doppler (WSR-88D) network makes it possible to address objectively, if not definitively, whether meteorologists appear to live in weather holes and whether such an appearance is physical or artificial

Severe Convective Wind Environments

Nontornadic thunderstorm winds from long-lived, widespread convective windstorms can have a tremendous impact on human lives and property. To examine environments that support damaging wind producing convection, sounding parameters from Rapid Update Cycle model analyses (at 3-hourly intervals) from 2003 were compared with 7055 reports of damaging winds and 377 081 occurrences of lightning. Ground- relative wind velocity was the most effective at discriminating between damaging and nondamaging wind convective environments. Steep surface-based lapse rates (a traditional damaging wind parameter) gener- ally did not discriminate between damaging and nondamaging wind convective environments. Other pa- rameters, such as convective available potential energy, humidity aloft, and lapse rates aloft were moder- ately discriminating. This paper presents a composite damaging wind algorithm in which the two most discriminatory parameters were combined, yielding more skill than any individual parameter. Damaging wind environments are then examined further through a selection of cases that highlight common severe wind ingredients and failure modes. A primary result is that, even in seemingly favorable environments, when the winds at the top of the inflow layer were either parallel to the convective line or blowing from warm to cold over a front, damaging winds were less likely. In the former case, it appears that the downdraft winds and the cold pool’s gust-front-normal flow are not additive. In the latter case, it appears that convection becomes elevated and does not produce downdrafts that reach the surface. Combining the most discriminatory severe wind parameters with knowledge of these severe wind failure modes may help to improve the situational awareness of forecasters

The 6dF Galaxy Survey: Dependence of halo occupation on stellar mass

In this paper we study the stellar-mass dependence of galaxy clustering in the 6dF Galaxy Survey. The near-infrared selection of 6dFGS allows more reliable stellar mass estimates compared to optical bands used in other galaxy surveys. Using the Halo Occupation Distribution (HOD) model, we investigate the trend of dark matter halo mass and satellite fraction with stellar mass by measuring the projected correlation function, $w_p(r_p)$. We find that the typical halo mass ($M_1$) as well as the satellite power law index ($\alpha$) increase with stellar mass. This indicates, (1) that galaxies with higher stellar mass sit in more massive dark matter halos and (2) that these more massive dark matter halos accumulate satellites faster with growing mass compared to halos occupied by low stellar mass galaxies. Furthermore we find a relation between $M_1$ and the minimum dark matter halo mass ($M_{\rm min}$) of $M_1 \approx 22\,M_{\rm min}$, in agreement with similar findings for SDSS galaxies. The satellite fraction of 6dFGS galaxies declines with increasing stellar mass from 21% at $M_{\rm stellar} = 2.6\times10^{10}h^{-2}\,M_{\odot}$ to 12% at $M_{\rm stellar} = 5.4\times10^{10}h^{-2}\,M_{\odot}$ indicating that high stellar mass galaxies are more likely to be central galaxies. We compare our results to two different semi-analytic models derived from the Millennium Simulation, finding some disagreement. Our results can be used for placing new constraints on semi-analytic models in the future, particularly the behaviour of luminous red satellites. Finally we compare our results to studies of halo occupation using galaxy-galaxy weak lensing. We find good overall agreement, representing a valuable crosscheck for these two different tools of studying the matter distribution in the Universe.Comment: 17 pages, 11 figures. arXiv admin note: text overlap with arXiv:1104.2447 by other author

Extinction in Lotka-Volterra model

Competitive birth-death processes often exhibit an oscillatory behavior. We investigate a particular case where the oscillation cycles are marginally stable on the mean-field level. An iconic example of such a system is the Lotka-Volterra model of predator-prey competition. Fluctuation effects due to discreteness of the populations destroy the mean-field stability and eventually drive the system toward extinction of one or both species. We show that the corresponding extinction time scales as a certain power-law of the population sizes. This behavior should be contrasted with the extinction of models stable in the mean-field approximation. In the latter case the extinction time scales exponentially with size.Comment: 11 pages, 17 figure

Climate-driven regime shifts in a mangrove-salt marsh ecotone over the past 250 years.

Climate change is driving the tropicalization of temperate ecosystems by shifting the range edges of numerous species poleward. Over the past few decades, mangroves have rapidly displaced salt marshes near multiple poleward mangrove range limits, including in northeast Florida. It is uncertain whether such mangrove expansions are due to anthropogenic climate change or natural climate variability. We combined historical accounts from books, personal journals, scientific articles, logbooks, photographs, and maps with climate data to show that the current ecotone between mangroves and salt marshes in northeast Florida has shifted between mangrove and salt marsh dominance at least 6 times between the late 1700s and 2017 due to decadal-scale fluctuations in the frequency and intensity of extreme cold events. Model projections of daily minimum temperature from 2000 through 2100 indicate an increase in annual minimum temperature by 0.5 °C/decade. Thus, although recent mangrove range expansion should indeed be placed into a broader historical context of an oscillating system, climate projections suggest that the recent trend may represent a more permanent regime shift due to the effects of climate change

Migration Strategies Vary in Space, Time, and Among Species in the Smallfish Metacommunity of the Everglades

Spatial ecology and movement strategies of aquatic organisms may limit their response to human-caused drying of wetland habitats. We characterized the movement strategies of the most abundant species of fish in the wetlands of the Everglades (USA) to better understand how they cope with annual fluctuations in aquatic habitat size. Over a six-year period, we used a sampling method designed to measure the density, activity levels, and movement direction of small fishes. We estimated changes in displacement speed and directional bias to identify patterns of movement that different fishes use to disperse over the gradient of disturbance in this environment. Movement of fishes ranged from highly active and directed to passive and random, and varied with hydrological condition (water rising, stable, or dropping). Six of the eight species studied displayed directed movement (possibly displaying taxis along environmental gradients) that varied in both speed and directional bias in response to hydrological cues. The remaining two species did not adjust the direction that they moved in response to hydrological cues, but their activity levels increased. Moving with directional bias may improve a fish\u27s chance of early arrival in a newly available habitat or of escaping the risk of desiccation in drying wetlands. Fishes that change activity levels may improve their likelihood of reaching favorable environments by increasing diffusion rates and greater sampling of the environment. Interspecific variation in movement strategies is predicted to play a large role in community structure and may be a primary driver of the dynamics of the Everglades fish metacommunity

Nanopore direct RNA sequencing maps the complexity of Arabidopsis mRNA processing and m6A modification

Understanding genome organization and gene regulation requires insight into RNA transcription, processing and modification. We adapted nanopore direct RNA sequencing to examine RNA from a wild-type accession of the model plant Arabidopsis thaliana and a mutant defective in mRNA methylation (m6A). Here we show that m6A can be mapped in full-length mRNAs transcriptome-wide and reveal the combinatorial diversity of cap-associated transcription start sites, splicing events, poly(A) site choice and poly(A) tail length. Loss of m6A from 3’ untranslated regions is associated with decreased relative transcript abundance and defective RNA 30 end formation. A functional consequence of disrupted m6A is a lengthening of the circadian period. We conclude that nanopore direct RNA sequencing can reveal the complexity of mRNA processing and modification in full-length single molecule reads. These findings can refine Arabidopsis genome annotation. Further, applying this approach to less well-studied species could transform our understanding of what their genomes encode