Each month, Physics Today editors explore the research and design choices that inspired the latest cover of the magazine.
Not a year goes by without hurricanes and other severe storms threatening lives and property. This month’s cover photo, captured from the International Space Station, shows Hurricane Florence as it made landfall in North Carolina on 14 September 2018. The category 1 storm killed 52 people and caused some $24 billion in damage.
To emphasize the voluminous, swirling clouds of Florence on the cover, senior graphic designer Freddie Pagani picked a simple sans-serif font, Helvetica Inserat, for the cover line and staggered the lines of text to trace the hurricane’s curvature. The font’s color and slight transparency contrast with the text’s shadows, which mimic the darker regions of the clouds.
In the May issue of Physics Today, Caroline Muller and Sophie Abramian dive into how clouds form and aggregate in the atmosphere and what advances have been made in observing and simulating cloud dynamics and convective storm systems.
In addition to hurricanes, another example of convective storm systems are squall lines. (The one at right, from 2013, is about 1600 km long and passed across Florida, Georgia, and South Carolina.) They emerge as a belt of thunderstorms, often ahead of a cold front, and are organized by large-scale variations of the atmosphere. Changes in wind speed with altitude create a shearing motion that blocks the movement of a surface-bound, relatively cold mass of air, which then acts as a ramp on which warm, moist air rises and forms clouds. The process is self-reinforcing too: More clouds form in squall lines and other regions that already have clouds.
Although squall lines last on the order of hours and travel thousands of kilometers, the weather phenomena are affected by slower-moving and larger-scale modifications to the atmosphere’s background state brought about by climate change. The new observational campaigns and idealized simulations that Muller and Abramian describe in their article should help to address uncertainties in cloud dynamics by better identifying what the relevant physical processes are and how convective organization will change with global warming.
