Two extreme snowfall events associated with extratropical cyclones, one interacting with the western and one with the central Himalaya, are simulated with the Weather Research and Forecasting (WRF) model over 8 days. One event in January 1999 was driven by a longwave trough over west Asia, with the cyclone becoming terrain-locked in the western Himalayan notch. Another event in March 2006 was driven by a trough further south and east, facilitating the passage of two successive cyclones along the entire Himalayan ridge, drawing moisture from warm tropical waters. These flow patterns are typical for extreme winter precipitation in the western and central Himalaya, respectively, but were amplified in these two cases. In the WRF simulations, snowfall is confined to the western Himalaya in the January simulation, while a near-continuous band of accumulated snowfall along the Himalayan ridge forms in the March simulation. Precipitation rate throughout both simulations is largely determined by cross-barrier moisture flux, which is generally greatest wherever the cyclonic winds converge on the mountains at each time. However, the March 2006 simulation evolves in an environment with greater convective instability upwind of and moisture transport toward the mountains than in the January 1999 event. Hence, greater precipitation rates and more solid snowbands are generated in the March than in the January simulation. However, due to the terrain-locking of the cyclone in the January event, individual locations receive more persistent snowfall, so that the greatest 8 day accumulations are similar between the two events, although these accumulations are more widespread in the March event.

Several recent studies have shown the width of the tropical belt has increased over the last several decades. The mechanisms driving tropical expansion are not well known and the recent expansion is underpredicted by state-of-the art GCMs. We use the CAM3 GCM to investigate how tropical width responds to idealized atmospheric heat sources, focusing on zonal displacement of the tropospheric jets. The heat sources include global and zonally restricted lower-tropospheric warmings and stratospheric coolings, which coarsely represent possible impacts of ozone or aerosol changes. Similar to prior studies with simplified GCMs, we find that stratospheric cooling – particularly at high-latitudes – shifts jets poleward and excites Northern and Southern Annular Mode (NAM/SAM)-type responses. We also find, however, that modest heating of the midlatitude boundary layer drives a similar response; heating at high latitudes provokes a weaker, equatorward shift and tropical heating produces no shift. Over 70 % of the variance in annual mean jet displacements across 27 experiments is accounted for by a newly proposed "Expansion Index", which compares mid-latitude tropospheric warming to that at other latitudes. We find that previously proposed factors, including tropopause height and tropospheric stability, do not fully explain the results. Results suggest recently observed tropical expansion could have been driven not only by stratospheric cooling, but also by mid-latitude heating sources due for example to ozone or aerosol changes.

Vasoactive intestinal peptide (VIP) is a 28-amino acid neuropeptide that belongs to the secretin-glucagon superfamily of peptides and has 68 % homology with PACAP. VIP is abundantly expressed in the central and peripheral nervous system and in the gastrointestinal tract, where it exercises several physiological functions. Previously, it has been reported that VIP regulates feeding behavior centrally in different species of vertebrates such as goldfishes, chicken and rodents. Additional studies are necessary to analyze the role of endogenous VIP on the regulation of appetite/satiety, feeding behavior, metabolic hormones, body mass composition and energy balance. The aim of the study was to elucidate the physiological pathways by which VIP regulates appetite/satiety, feeding behavior, metabolic hormones, and body mass composition. VIP deficient (VIP −/−) and age-matched wild-type (WT) littermates were weekly monitored from 5 to 22 weeks of age using a whole body composition EchoMRI analyzer. Food intake and feeding behavior were analyzed using the BioDAQ automated monitoring system. Plasma levels of metabolic hormones including active-ghrelin, GLP-1, leptin, PYY, pancreatic polypeptide (PP), adiponectin, and insulin were measured in fasting as well as in postprandial conditions. The genetic lack of VIP led to a significant reduction of body weight and fat mass and to an increase of lean mass as the mice aged. Additionally, VIP−/− mice had a disrupted pattern of circadian feeding behavior resulting in an abolished regular nocturnal/diurnal feeding. These changes were associated with an altered secretion of adiponectin, GLP-1, leptin, PYY and insulin in VIP−/− mice. Our data demonstrates that endogenous VIP is involved in the control of appetite/satiety, feeding behavior, body mass composition and in the secretion of six different key regulatory metabolic hormones. VIP plays a key role in the regulation of body phenotype by significantly enhancing body weight and fat mass accumulation. Therefore, VIP signaling is critical for the modulation of appetite/satiety and body mass phenotype and is a potential target for future treatment of obesity.