Guy Kelman

An Evaluation of the Efficacy of Using Observed Lightning to Improve Convective Lightning Forecasts

AbstractDynamic lightning forecasts [total and cloud to ground (CG)] were produced on a convection-allowing forecast grid with 4-km grid spacing with lightning assimilation (ASML) and without lightning assimilation [control (CNTL)]. A dynamic scheme produces time- and space-dependent potential electrical energy, which then converts this energy into lightning (e.g., number per hour per grid element). The assimilation scheme uses observed, gridded total lightning to determine how much water vapor is added at constant temperature in the mixed-phase region, leading to a convective response. ASML and CNTL lightning forecasts were compared to observed total and CG lightning. Four case studies—each representing a different type of convective regime—demonstrate that the spatial distribution and intensity of forecast lightning were improved when lightning assimilation was used. Over 3 days in March 2012, eight 18-h lightning forecasts quantified the advantages in forecast accuracy. Equitable threat scores for fore...

The Sensitivity of Hurricane Irene to Aerosols and Ocean Coupling: Simulations with WRF Spectral Bin Microphysics

AbstractHurricane Irene (2011) moved northward along the eastern coast of the United States and was expected to cause severe wind and flood damage. However, the hurricane weakened much faster than was predicted. Moreover, the minimum pressure in Irene occurred, atypically, about 40 h later than the time of maximum wind speed. Possible reasons for Irene’s weakening and the time shift between maximum wind and minimum central pressure were studied in simulations using WRF with spectral bin microphysics (WRF-SBM) with 1-km grid spacing and ocean coupling. Both ocean coupling and aerosol distribution/concentration were found to influence Irene’s development. Without ocean coupling or with ocean coupling and uniform aerosol distribution, the simulated maximum wind occurred at about the same time as the minimum pressure. With ocean coupling and nonuniform spatial aerosol distributions caused by aerosols from the Saharan air layer (band) and the continental United States, the maximum wind occurred about 40 h befo...

Gene ORGANizer: linking genes to the organs they affect

Abstract One of the biggest challenges in studying how genes work is understanding their effect on the physiology and anatomy of the body. Existing tools try to address this using indirect features, such as expression levels and biochemical pathways. Here, we present Gene ORGANizer (geneorganizer.huji.ac.il), a phenotype-based tool that directly links human genes to the body parts they affect. It is built upon an exhaustive curated database that links >7000 genes to ∼150 anatomical parts using >150 000 gene-organ associations. The tool offers user-friendly platforms to analyze the anatomical effects of individual genes, and identify trends within groups of genes. We demonstrate how Gene ORGANizer can be used to make new discoveries, showing that chromosome X is enriched with genes affecting facial features, that positive selection targets genes with more constrained phenotypic effects, and more. We expect Gene ORGANizer to be useful in a variety of evolutionary, medical and molecular studies aimed at understanding the phenotypic effects of genes.

Nucleation of Social Groups: The Role of Centrality Inequality and Social Mobility

Even though the heterogeneity of social networks centrality is well documented, its role and effect on network stability, is unclear. It is known that, universally, networks have an “inner” highly-connected nucleus and, in contrast, sparser outer shells. But, to what extent the existence of this nucleus is crucial for the survival of a network? To what extent is the outer shells, much-larger population, essential to the longevity of the network? Furthermore, network structure is very much dependent on the mobility between centrality shells, i.e., social mobility. What is, then, the role of social mobility in the formation of the nucleus-periphery profile and does it have an effect on network lifetime? Here, we explore these questions using data collected of more than 10K networked communities, with more than 134K users, for over a decade. We find that: (i) social mobility is, on average, negative and promotes instability, and (ii) the more positive social mobility is, the more stable the community. Further, (iii) the network is composed of two phases, a large but ephemeral sparsely-connected cloud of actors which nucleates around a highly stable nucleus of core users. Finally, (iv) networked communities which closely maintain a nucleation ratio, i.e., ratio between nucleus size and outer shells size, of 1 to 3, exhibit the best chances of survival. Deviations from this nucleation ratio translates into the collapse of the network, especially for younger communities.

Centralized nucleation in online networks leads to high social inequality

Even though the heterogeneity of centrality in social networks is well documented, its role and effect on network stability in real life remains unclear. The literature roughly suggests that network structure is such that networks have an “inner” highly-connected nucleus and, in contrast, sparse outer shells. But to what extent is the existence of this nucleus crucial for the survival of a network? To what extent is the outer shells’ much larger population essential to the longevity of the network? Furthermore, as a network grows and forms, theoretically speaking, network structure should be dependent on the patterns of change of degree centrality, i.e., social mobility between centrality shells. What is the role of social mobility in the formation of the nucleus-to-periphery profile, and is it related to network lifetime? Here, we explore these questions using data collected covering over a decade of activity from more than 10, 000 networked communities, with more than 134,000 users. We find that: (i) social mobility is, on average, negative but that, (ii) the higher the social mobility of the members of the network, the more stable and long-living the network is. Further, (iii) the network is, indeed, composed of two phases - a large but ephemeral sparsely connected “cloud” of actors, that nucleates around a highly stable nucleus of users. Lastly, (iv) networked communities which maintain a specific nucleus-to-periphery ratio η, i.e., a ratio of the size of the nucleus to periphery of around η=14

Satellite detection of severe convective storms by their retrieved vertical profiles of cloud particle effective radius and thermodynamic phase

\eta =\frac{1}{4}

Dissortative from the Outside, Assortative from the Inside: Social Structure and Behavior in the Industrial Trade Network

, have a greater chance of survival. We find that deviations from this nucleus-to-periphery ratio predict a collapse of network activity, especially in the case of younger communities.

Many-to-one contagion of economic growth rate across trade credit network of firms

Keywords-business networks; communication networks; social interaction; spatial statistics; stationary point processes; economy; industrial firms; Abstract—In this paper we report evidence from the Italian industrial sectors whereby firms that buy and sell are spatially distributed with a pattern that reflects the microeconomic powers at play. The main finding is that firms are neither clustered around population centers nor are they situated at random. Although geography has an important role in shaping the population map of Italy, the reasons for the positional pattern of buyers and sellers appear to be social. Geographic proximity between sellers and their buyers is supported by the excess in short-distance social ties.