1977 Global Dust Storm B (Viking Era, Second Storm)

A second planet-encircling storm developed just weeks after the first 1977 event cleared, reaching global scale by early September. Viking instruments captured the storm's rapid expansion and decay, and the back-to-back occurrence of two global storms within a single Martian year was unexpected — it demonstrated that global storms can cluster temporally and is still not fully explained by global circulation models. Together the two 1977 storms remain the most systematically studied pair of global Mars dust events in the pre-Mars Global Surveyor era.