On Mars, heat from the Sun drives daily changes in temperature, wind, and pressure in the atmosphere. Known as atmospheric tides, these regular patterns play a major role in shaping the planet’s weather.
Atmospheric tides exist on Earth as well, but they have a much greater influence in Mars’s thin atmosphere. The details and drivers of atmospheric tides on Mars have remained unclear, however. Now Forbes et al. present new spacecraft data and model simulations that deepen our understanding of tidal patterns in the middle and upper atmosphere of Mars.
The new observations came from NASA’s Mars Climate Sounder (MCS), an instrument mounted on the Mars Reconnaissance Orbiter, which has circled the Red Planet since 2006. The researchers analyzed about 9 years of MCS-captured temperature data for the middle atmosphere, revealing how tidal patterns shift as the north–south angle at which Mars faces the Sun changes over the course of each year.
Key patterns emerged from the MCS data, including eastward and westward propagating tidal pulses that repeat daily or twice daily. Some of these tidal patterns match the path of sunlight as it sweeps across the planet, while others are out of sync with the Sun but still follow a regular schedule.
The MCS observations aligned well with predictions of tidal patterns from the Laboratoire de Météorologie Dynamique’s Global Climate Model, as captured in the Mars Climate Database. The model predictions also showed how these middle-atmosphere tidal patterns could give rise to longitudinal variations in density that have been observed in the upper atmosphere by the Mars Global Surveyor.
In addition, the researchers used the model predictions to explore how certain atmospheric processes could drive tidal patterns that result in variations in atmospheric density at different altitudes and latitudes, and at different times of the year.
The findings support the use of the Mars Climate Database to study atmospheric tides and could boost scientists’ ability to predict the planet’s weather. The researchers say they next plan to compare model predictions with observations from additional spacecraft, and that future work may examine discrepancies between predictions and observations. (Journal of Geophysical Research: Space Physics, https://doi.org/10.1029/2020JA028140, 2020)
—Sarah Stanley, Science Writer