Although rain shadows (i.e., leeside reductions of precipitation downwind of orography) are commonly described in textbooks, quantitative climatologies of the rain-shadow effect are rare. To test quantitatively a classic rain-shadow locality of the Peak District, United Kingdom, precipitation from 54 observing stations over 30 years (1981–2010) are examined. Under 850-hPa westerlies, annual and daily precipitation amounts are on average higher in Manchester in the west and the Peak District than in Sheffield in the east. More precipitation falls—and falls more frequently—frequently in Manchester than Sheffield on 197 westerly flow days annually. In contrast, more precipitation falls—and falls more frequently—in Sheffield than Manchester on 28 easterly flow days annually. These bulk precipitation statistics support a climatological rain shadow. However, when individual days are investigated, only 17% of westerly flow days occur where daily rainfall data might exhibit the rain-shadow effect (defined here as Manchester with precipitation and Sheffield with no precipitation). In contrast, only 10% of easterly flow days occur where daily rainfall data might exhibit the rain-shadow effect (Sheffield with precipitation and Manchester with no precipitation). Thus, westerly winds are more likely to exhibit a rain-shadow effect than easterly winds. Although the distribution of precipitation observed across the Peak District can sometimes be explained by the rain-shadow effect, the occurrence of the rain-shadow effect by our admittedly strict definition is not as frequent as one might expect to explain the local precipitation climate for which it has sometimes been previously credited. Thus, an attempt to understand the climatological relevance of the rain-shadow effect from one location reveals ambiguity in the definition of a rain shadow and in its interpretation from real rainfall data.

Abstract. Layers of aerosol at heights between 2 and 11 km were observed with Raman lidars in the UK between 23 and 31 May 2016. A network of these lidars, supported by ceilometer observations, is used to map the extent of the aerosol and its optical properties. Space-borne lidar profiles show that the aerosol originated from forest fires over western Canada around 17 May, and indeed the aerosol properties – weak volume depolarisation (<5 %) and a lidar ratio at 355 nm in the range 35–65 sr – were consistent with long-range transport of forest fire smoke. The event was unusual in its persistence – the smoke plume was drawn into an atmospheric block that kept it above north-western Europe for 9 days. Lidar observations show how the smoke layers became optically thinner during this period, but the lidar ratio and aerosol depolarisation showed little change. The results demonstrate the value of a dense network of observations for tracking forest fire smoke, and show how the dispersion of smoke in the free troposphere leads to the emergence of discrete thin layers in the far field. They also show how atmospheric blocking can keep a smoke plume in the same geographic area for over a week.

No abstract

We analyse the enhanced flow rate of water through nano-fabricated graphene channels that has been recently observed experimentally. Using molecular dynamics simulations in channels of similar lateral dimensions as the experimental ones, our results reveal for the first time a relationship between water structure and the variation of flux in the rectangular graphene channels. The substantial enhancement in the flow rate compared to Poieseuille flow is due to the formation of layered 2D structures in the confined space, which persists up to a channel height of 2.38 nm, corresponding to six graphene layers.The structure of the water shows an intricate crystal of pentagonal and square tiles, which has not been observed before. Beyond six layers we find a sudden drop in flux due to the disordering of the water, which can be understood by classical flow dynamics.

Carbon nanomaterials of differing dimensionality, namely fullerenes, nanotubes and graphene oxide are shown to stabilize the Blue Phases at the expense of the N* phase until its complete disappearance. A BP–N*–SmA* triple point is observed.