The Dust Season of
Mars lasts during the Spring and Summer for the planet's Southern Hemisphere. During this time, small regional dust storms can occur across Mars' landscape, particularly where thermal and pressure sublimation prevents soil saturation. These storms tend to to span no more than 2,000 kilometers and last at most a few days before dissipating.
Some of these storms, particularly those that develop in or transition into the Southern Hemisphere, can become regional and last for weeks. The largest of these storms occasionally can encircle Mars' entire Southern Hemisphere. Roughly once a decade, global storms can develop that fully enshroud the planet.
The regional storms that appear fairly regularly are categorized into three types:
Type A Dust Storms
Type A storms form from small Northern Hemisphere dust storms that originate near the North Pole in the Northern Autumn/Southern Spring. Those that transition into the Southern Hemisphere can grow from an influx of solar energy and heat, which boosts wind speeds that in turn unsettles more dust.
Type B Dust Storms
Type B storms, in contrast, originate from near the South pole shortly prior to the Southern Summer Solstace. These are believed to originate from CO2 sublimation from Mars' southern polar ice cap. It is possible that several simultaneous storms fuse into a regional storm to form a Type B storm. The relative decrease in polar mass in the years since Terraformation have made these storms relatively weak compared to 21st century observations.
Type C Dust Storms
Type C storms also occur in the Southern Summer, but originate in the Northern hemisphere shortly after the end of the Type B Storm's life cycle. Type C Storms behave like a Type A, transitioning from the North to the South and gaining strength. Type C Storms differ from Type A in their frequency (only one Type C event per year) and variability, which has yet to be accurately accounted for by climate models. Type C storms can have a wide range of intensities and durations.
Effects on Life and Operations
Martian wind speeds during dust storms are only a moderate threat, with wind speeds ranging from between 60-120 km/h, or no more deadly than a weak Category 1 Hurricane or strong Tropical Storm. Aerial missions are usually ill advised due to the potential for sudden gusts of wind, especially in turbulent geometry like the Mariner Valley Region or Hellas Crater. These storms also produce lightning which can damage sensitive equipment that is not properly grounded, or cause fires to combustible materials.
By far the most impactful aspect of dust storms are the large volumes of fine particulates which can wreak havoc on sensitive equipment. Electrostatic cleaning mechanisms are the best way to mitigate this effect, but this requires periodic cleaning passes which may not always prevent damage in time. Additionally, Martian Dust will severely reduce visibility and may cause radio and telemetry interference depending on the amount of iron in the particulates.
Native Martians who can normally breathe Martian atmosphere can develop respiratory problems associated with the Martian dust, necessitating filtered breating apparatuses.
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