It has been hypothesized that black carbon (BC) influences mixed‐phase clouds by acting as an ice‐nucleating particle (INP). However, the literature data for ice nucleation by BC immersed in supercooled water are extremely varied, with some studies reporting that BC is very effective at nucleating ice, whereas others report no ice‐nucleating ability. Here we present new experimental results for immersion mode ice nucleation by BC from two contrasting fuels (n‐decane and eugenol). We observe no significant heterogeneous nucleation by either sample. Using a global aerosol model, we quantify the maximum relative importance of BC for ice nucleation when compared with K‐feldspar and marine organic aerosol acting as INP. Based on the upper limit from our laboratory data, we show that BC contributes at least several orders of magnitude less INP than feldspar and marine organic aerosol. Representations of its atmospheric ice‐nucleating ability based on older laboratory data produce unrealistic results when compared against ambient observations of INP. Since BC is a complex material, it cannot be unambiguously ruled out as an important INP species in all locations at all times. Therefore, we use our model to estimate a range of values for the density of active sites that BC particles must have to be relevant for ice nucleation in the atmosphere. The estimated values will guide future work on BC, defining the required sensitivity of future experimental studies.

Sumatra Squalls are common weather phenomena which have a very large impact affecting 85 million people throughout equatorial South East Asia, and many more through trade links with other regions; however, current comprehension behind Sumatra Squalls is not well studied and interpretation is insufficient. The aim of this article is to raise the community interest on Sumatra Squalls and underline the need for increased research. Twenty‐two years of observational data has been collated and analysed to create climatologically general features of Sumatra Squalls. These squalls have a clear diurnal cycle and commonly make landfall in the west coast of the Malay Peninsula and Singapore during the pre‐dawn and early morning. Additionally, these squalls commonly form during the intermonsoon season (April‐May and October‐November) and Southwest monsoon (June‐September) seasons with average frequencies of 8 and 6 occurrences per month respectively.

Sumatra squalls are commonly occurring, vigorous and deep convective systems that emanate over Sumatra, sweeping eastwards across the strategically important Malacca Strait shipping route and affecting the population of 85 million people who live in the region. Despite their disruptive potential, there is a paucity of literature on the structure and dynamics of Sumatra squalls. In this article, the structure of the 12 July 2016 Sumatra squall was studied using a high‐resolution Weather Research and Forecasting Model simulation (version 3.7.1). After comparing the reflectivity patterns of both the simulated and actual Sumatra squalls, we showed the large‐scale features of the Sumatra squall: the rear‐inflow jet, ascending front‐to‐rear flow, wind shear and cold pool generation. Following that, we took advantage of the high resolution of the simulation to examine the detailed features of this Sumatra squall and the signs that the conventional squall line propagation mechanism is responsible for Sumatra squall propagation.