Baroclinic Pressure Oscillations in the Martian Atmosphere Observed from Surface Platforms

Baroclinic waves are large-scale atmospheric disturbances driven by meridional temperature
gradients. While they typically form in mid-latitudes, previous studies have shown their presence
even at equatorial latitudes in the Martian atmosphere. These eastward-propagating waves have
periods of 2-10 sols and are most prevalent during the fall, winter, and spring seasons, when
temperature gradients are strongest. Surface pressure measurements offer a valuable tool for
detecting these oscillations, as they produce distinctive pressure patterns that reflect the presence,
propagation, and intensity of baroclinic waves.

In this study, we analyze in-situ surface pressure data collected by Viking Lander 1 (VL1; 22.5°N),
Viking Lander 2 (VL2; 48°N), the Mars Phoenix Lander (68.2°N), the Mars Science Laboratory
(MSL) Curiosity rover (4.6°S), and the InSight lander (4.5°N). The periods and amplitudes of
pressure oscillations over multiple Martian years were determined using spectral analysis with an
iterative mode removal method.

VL2 observed significant wave activity with periods of 2-4 sols during the northern fall, winter, and
spring. Amplitudes generally increased as the season progressed, with particularly high values (>30
Pa) during northern spring of Mars Year (MY) 13, peaking at a period of 2.23 sols. In addition,
wave activity was detected at longer periods between 5 and 12 sols.

During MY 35, InSight detected wave activity with periods of 2-3 sols during the northern fall,
winter, and spring, with the highest amplitudes during the winter season. The period gradually
increased from 2.1 sols to 2.25 sols, and then to 2.35 sols. Additionally, a clear peak with a period
of approximately 6.5 sols was observed during northern winter. In late northern spring, waves with
periods around 3.8-4.3 sols dominated, while in early northern summer, waves with periods near 3.2
sols were most prevalent. In late northern summer, waves with periods ranging from 3.9 to 4.6 sols
were most common. Similar wave activity was observed by the MSL during MY 35, although MSL
waves show some year-to-year variation. These waves detected by MSL and InSight during the
northern fall, winter, and spring exhibit periods similar to those observed by VL2 in mid-latitudes,
though with lower amplitudes, and may be associated with northern hemisphere mid-latitude
baroclinic waves. In contrast, waves detected during the northern summer are likely associated with
baroclinic waves from the southern mid-latitudes.

The wave activity observed at VL1 differs slightly from that observed at MSL and InSight. Waves
with periods of 2-3 sols exhibit higher amplitudes at VL1 during northern hemisphere fall through
spring. Additionally, waves with periods of 6-9 sols tend to have higher amplitudes at VL1
compared to those at MSL and InSight. However, amplitudes are generally similar during the winter
season. The observed differences between these locations may be attributed to VL1’s higher
latitudinal position.

Phoenix observed pressure only during the northern hemisphere summer season. Waves with
periods of 5-10 sols, 3.25-3.5 sols, 7.5-9 sols, and 5.2-5.7 sols were detected. These periods are
somewhat similar to those observed by VL2 during the same season.