Martian mesospheric cloud observations by IUVS on MAVEN: Thermal tides coupled to the upper atmosphere

Abstract

We report observations of Martian mesospheric ice clouds and thermospheric scale heights by the Imaging Ultraviolet Spectrograph on NASA's Mars Atmosphere and Volatile Evolution mission. The clouds are observed between 6 A.M. and 8 A.M. local time using mid‐UV limb observations between 60 and 80 km tangent altitude where ice particles that scatter sunlight can appear as detached layers near the equator. The equatorial longitudinal distribution shows populations of clouds near −110°E and −10°E as well as a population near 90°E, which does not have a clear precedent. The cloud populations indicate a wave 3 pattern near 70 km, which is confirmed by independent mesospheric temperature observations. Scale heights 100 km above the clouds derived from concurrent Imaging Ultraviolet Spectrograph (IUVS) observations also reveal a wave 3 longitudinal structure, suggesting that the temperature oscillations enabling the formation of mesospheric clouds couple to the upper atmosphere.

Detection of Mesospheric CO2 Ice Clouds on Mars in Southern Summer

“…The correlation with these strong, low-harmonic longitude perturbations suggests that nonmigrating tides play a role in formation of the clouds. The measured perturbations appear to be dominated by an m = 3 wave, a common situation on Mars (Forbes et al, 2002;Gröller et al, 2018;Lo et al, 2015;Stevens et al, 2017;Wilson, 2002). Fourier analysis indicates that the longitudinal wave for the -Sco occultations gives amplitudes of 27% and 53% for the m = 2 and m = 3 waves, with lesser contributions from other waves (see Gröller et al, 2018, for a description of the Fourier analysis).…”

“…One cloud occurred near the southern summer solstice ( L s =264°), while the other appeared in late summer ( L s =338°). Equatorial mesospheric CO 2 clouds on Mars were usually observed between L s =0–180° (Clancy et al, ; Montmessin et al, , Montmessin et al, ; ; Stevens et al, ), although Määttänen et al () have reported one daytime equatorial CO 2 cloud at L s =330° in MY29 with MEx/OMEGA observations. Thus, the clouds reported here are the first tropical high‐altitude nighttime clouds to be observed during southern summer.…”

“…The cloud particle effective radius derived from Mie theory ranged from 80 to 130 nm when assuming a pure CO 2 ice composition and spherical particles. More recently, Stevens et al (2017) (González-Galindo et al, 2011) and mesoscale gravity waves (Spiga et al, 2012;Yiggit et al, 2015) have been suggested to be responsible for the generation of supersaturated cold pockets. In addition, the presence of nuclei is necessary for the heterogeneous nucleation of CO 2 ice clouds (Listowski et al, 2014;Määttänen et al, 2010;Plane et al, 2018).…”

Atmospheric Tides at High Latitudes in the Martian Upper Atmosphere Observed by MAVEN and MRO

“…These have been observed at spatial scales ranging from a few tens of kilometers, which have been interpreted as internal gravity waves (e.g., Fritts et al, ), up to planetary scales, where waves including atmospheric tides (e.g., Withers et al, ), Kelvin waves (e.g., Gasperini et al, ), stationary planetary waves (SPWs; e.g., Medvedev et al, ), Rossby waves, and secondary waves generated in tidal‐Rossby wave interactions (e.g., Moudden & Forbes, ) have all been identified. These waves are seen to have significant impacts on the density (e.g., Fritts et al, ), temperature and pressure (e.g., Stevens et al, ; Withers et al, ), energy budget (e.g., Medvedev & Yiğit, ), and composition of this region (e.g., England et al, ).…”

“…Therefore, it is worth looking in more detail at the waves that may create wavenumber‐3 signatures in fixed LT frames in the upper atmosphere, with an emphasis on identifying their propagation direction and periodicity ( n and s in equations and ) from the observations. Observations of atmospheric tides in the Martian upper atmosphere have been reported in both in situ (e.g., England et al, ; Liu et al, ) and remote sensing data (e.g., Lo et al, ; Medvedev et al, ; Stevens et al, ) from the MAVEN spacecraft, and in the middle atmosphere from the MRO spacecraft (e.g., Guzewich et al, ; Moudden & Forbes, ). This study uses a combination of these to examine global‐scale atmospheric waves at high latitudes and identifies a strong wavenumber‐3 signature in the two cases studied.…”