GRAVITY WAVES AND THEIR EFFECTS DURING QUIET TIMES AND
DUST STORMS
A. S. Medvedev, Max Planck Institute for Solar System Research, Göttingen, Germany (medvedev@
mps.mpg.de), E. Yiğit, George Mason University, Fairfax, USA, E. D. Starichenko, Space Research Institute
(IKI), Moscow, Russia, D. S. Shaposhnikov, Moscow Institute of Physics and Technology, Moscow, Russia, T.
Kuroda, Tohoku University, Japan, P. Hartogh, Max Planck Institute for Solar System Research, Göttingen,
Germany.

Introduction:
Internal gravity waves (GWs) represent an important dynamical mechanism that links atmospheric
layers in all stably stratified planetary atmospheres.
We present recent advances in understanding GWs
and their effects during global dust storms. The results
include satellite observations and global modeling
performed at Max Planck Institute in close cooperation with colleagues at other international institutions.
Gravity Waves in the Lower Atmosphere:
Using temperature profiles retrieved from MCS
observations, Heavens et al (2020, 2022) discovered
a reduction (by a factor 2, in average) of GW activity
in the lower atmosphere (up to 30-40 km) during the
major dust storm of MY34. Simulations with a GWresolving Martian GCM (Kuroda et al, 2020) confirmed a sudden drop of GW activity of the same
magnitude (Figure 1). The analysis shows that it occurred due to the enhanced convective stability of the
background atmosphere (lower temperatures near the
surface and warmer atmosphere above due to stronger
absorption of radiation by airborne dust), which effectively reduced wave generation.

sphere, which is near the top of the model at ~80 km,
despite the reduction of wave sources. The precise
reason is not fully understood, but there are indications that it occurs due to favorable propagation conditions in the middle atmosphere during dust storms.
The first observational evidence for the increase of
the upper-atmosphere GW activity during a global
dust storm was obtained from MAVEN/NGIMS density measurements in the thermosphere (160-220 km)
by Yiğit et al (2021a). The same factor of two increase in the thermospheric GW activity during the
storm has been discovered in observations.
Gravity Waves Throughout the Atmosphere:
Retrievals from the TGO/ACS instruments with
high vertical resolution provided GW profiles and
characteristics in almost the entire atmosphere: from
30 to ~160 km (Starichenko et al., 2021). They
demonstrated how harmonics in broad wave packets
are affected by instability that leads to wave breaking
and/or saturation and to enhanced acceleration/deceleration of the mean flow. The distribution
of the so-called GW drag (wave-induced acceleration/deceleration) along with the simulated zonal
winds averaged over the second half of MY34 are
presented in Figure 2. The maximum of momentum
forcing is located in the middle atmosphere near the
edges of the zonal jets, in full agreement with theoretical expectations. The magnitudes of the wave drag
are consistent with general circulation modeling using
GW parameterizations. The ongoing work includes
data for MY35, which may help to separate the impact of dust storms.

Figure 1. Time-latitude distribution of the wave kinetic
energy simulated with a Martian high-resolution GCM. A
reduction coincides with the onset of the major storm
(blue), and repeats later in the year during a minor storm

Gravity Waves in the Upper Atmosphere:
The same GW-resolving simulations also revealed an unexpected result: the increase of GW activity by the same factor of two in the upper meso-

Figure 2. GW drag derived from ACS temperature profiles
(shaded) and zonal wind (contours) averaged over the
second half of MY34.

Gravity Waves and the Water “Pump”:
GW drag affects not only zonal winds, but also the
meridional flow, thus altering the global meridional
circulation. Changes in the horizontal flow can greatly
alter the vertical motions of air with important implications for the mass transport and thermodynamics of
the atmosphere. The main channels, through which
water enters the upper atmosphere, are collocated
with the regions of air updraft by the meridional circulation: in low latitudes during the northern autumn
equinox and in high southern latitudes during perihelion. We performed simulations with the Max Planck
Institute MAOAM GCM for MY28 and MY34 dust
storms. The model included the water cycle physics
study the impact of non-orographic GWs. The results
show that dust storm-induced global circulation is the
primary mechanism that enables water penetration to
the upper atmosphere, while GW forcing plays a secondary role by shaping the distribution of water and
modulating the timing and intensity of the transport.
Figure 3 illustrates vertical fluxes of water at the
“bottleneck” height of 80 km (a and b), and the differences in the global amount of water simulated with
and without GWs (c and d). Accounting for smallscale GWs contributes to changes in globally averaged high-altitude water abundance of up to 10%–
25%.

Figure 3. (a and b) Latitude-seasonal cross-sections of the
zonally averaged vertical water vapor flux at 80 km (shaded) simulated with gravity waves (GWs) included and the
IR optical dust opacity (black contours). (c and d) Altitudeseasonal cross-sections of the globally averaged differences
of water vapor (shaded) and temperature (contours) between the simulations with and without GWs.

Gravity Waves and Diffusion of Water in the
Thermosphere:
Simulations reveal that water and other tracers are
transported above 80–100 km by the global circulation (advection), with molecular diffusion playing
virtually no role. However, the impact of the latter
grows with height, and starts to dominate above
∼120 km. Figure 4 presents the water photodissociation rate during MY28 and MY34. It is seen that its
maximum occurs between 60 and 90 km, depending
on the storm’s season, while the location largely coincides with the center of the storm (position of the
maximum of dust opacity). This means that above 120
km, the produced hydrogen molecules are transported
to the upper thermosphere primarily by diffusion.
Breaking gravity waves induce additional diffusion
that facilitates the downgradient (upward) transport of

hydrogen. The MAOAM GCM does not extend above
160 km and cannot be used for quantifying the impact
of GWs in the thermosphere above these heights.
However, the observations with NGIMS/MAVEN
(see above) indicate strong GW activity there. This
remains a subject of further studies.

Figure 4. The dependence of the rate of photodissociation
of water vapor in kg/s/km during the year on latitude (a, b)
and altitude (c, d) dust scenarios MY28 (a, c) and MY34
(b, d). The contours show the total dust opacity concentration in ppm (c, d).

Gravity Waves and Hydrogen Escape:
Once hydrogen reaches the exobase, it is subject
to thermal (Jeans) escape. GW-induced variations of
density and temperature modify the escape rate. Since
it nonlinearly depends on these parameters, the net
escape increases. We estimated the escape flux for
20% and 40% relative variations of temperature
(Yiğit et al, 2021b). Figure 5 shows the variation of
the flux as a function of wave phase. The integral over
the phase gives the net flux. The estimated escape
increases by factor 2 for 40% relative GW variations
of temperature (a typical amplitude) are considered. It
can be seen that the net effect of gravity wave variations in temperature is to enhance the atmospheric
escape flux. Instantaneous gravity wave-induced temperature (or density) fluctuations can even exceed
100%. Overall, wave-induced escape is likely to be a
highly variable process.

Figure 5. Relative escape flux as a function of wave phase
for the sinusoidally varying temperature disturbance δT.
Blue and orange lines correspond to 20% and 40% amplitudes of fluctuations of the characteristic exobase temperature (T exo = 250 K), correspondingly. The area under the
curves gives the net (averaged over the entire wave phase)
escape flux. Gray shading shows the net escape flux for
20% amplitude of disturbances.

In light of these modeling and observational results along with scientific reasoning (Yiğit, 2021c),
gravity wave processes, especially during global dust

stroms are expected to play a major role in modulating atmospheric escape of water. Over millions of
years of planet history, this vertical coupling between
the lower and upper atmosphere via waves could
have significantly affected the Martian climate.
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