CORRELATING THE SEASONAL BEHAVIOR OF POLAR WARMING
AND O2 IR NIGHTGLOW
A. S. Brecht (amanda.s.brecht@nasa.gov), NASA Ames Research Center, Moffett Field, CA, USA, L.
Gkouvelis, NASA Postdoctoral Program, NASA Ames Research Center, Moffett Field, CA, USA, R. J. Wilson,
C. E. Harman, M. A. Kahre, NASA Ames Research Center, Moffett Field, CA, USA, A. Kling, Bay Area Environmental Research Institute, Moffett Field, CA, USA.

Introduction:
Mars’ meridional circulation impacts the climate
through the transport of heat, water, dust, and trace
gases. The meridional circulation in the middle atmosphere is instrumental in the exchange of water
between hemispheres and the expansion phase of
large regional- and global-scale dust storms. The
overall nature and structure of the mean meridional
circulation (i.e., the Hadley cell) in the Martian atmosphere has been widely studied but the detailed
behavior is still being investigated. To provide a
more detailed examination of the meridional circulation, two features driven by the mean circulation will
be analyzed as proxies. The first feature is polar
warming (PW), which is dynamically induced due to
the compressional heating of air in the descending
branch of the Hadley cell. The second feature is O2
IR nightglow emission in the 1.27 micron band,
which is the result of a three-body recombination
(O+O+CO2-> O2* +CO2) and is largely dependent
on the transport of dayside produced chemistry. By
characterizing their seasonal sensitivities due to
known lower atmosphere circulation drivers and
correlating them, we will advance our knowledge of
the meridional circulation.
Motivation:
Polar warming is characterized by a reversed
(poleward) meridional temperature gradient in the
middle-to-high latitudes all year, except local summer. It usually occurs between ~50 km and 80 km
and ranges in magnitude from several to tens of
Kelvin. It has been observed and discussed since the
early 1970’s (e.g., Conrath et al., 1973; Conrath et
al., 1981; Martin and Kieffer, 1979; Jakosky and
Martin, 1987; Deming et al., 1986; Smith et al.,
2001; Keating et al., 2003; Tolson et al., 2007;
Bougher et al., 2006; McCleese et al., 2007, 2008,
2010; Kleinbohl et al., 2009; McDunn et al., 2013;
Forget et al., 2009). McDunn et al. (2013) provides
the most quantitative set of parameters of observed
PW based upon MRO/MCS-derived atmospheric
temperatures. The study identifies PW trends that
suggest that the structure of the mean meridional
circulation is complex and not fully understood.
Such trends are: (a) the southern hemisphere annual
maximum PW occurs during late local winter of
Martian year (MY) 29 and MY 30, (b) southern
winter and northern winter solstices have similar PW
magnitudes, and (c) the equinoctial seasons demon-

strated hemispheric asymmetry in PW magnitude
(McDunn et al., 2013).
The O2 IR nightglow emission is a product of 3body reaction that occurs in areas of converging
circulation. The nightglow becomes a valid tracer of
circulation due to the chemical sources (atomic oxygen) largely produced on the dayside through photolysis (CO2 and O3). Chemical species (CO2, O3, O,
etc.) are then transported by the circulation (day to
night; equator to pole) to a region of favorable condition for recombination and subsequent de-excitation
(i.e., emission). The O2 IR nightglow emission at
Mars produces a lower intensity compared to Venus
and Earth, however it has been observed by orbital
missions; Mex/OMEGA (Bertaux et al., 2012),
Mex/SPICAM (Fedorova et al., 2012), and
MRO/CRISM (Clancy et al., 2012, 2013). As with
the PW, the nightglow is observed over high northern and southern latitudes between 40 – 60 km in
altitude. The observational trends of the vertically
integrated emission are: (1) the northern winter solstice has more intense emission than the southern
winter solstice, and (2) the lowest peak altitude occurs during northern winter solstice. These trends
seem to support the general concept of the role of the
mean meridional circulation, unlike some of the PW
trends (Clancy et al., 2012).
Past numerical modeling has been focused on either PW or the O2 IR nightglow, but not both. In
general, numerical models seem to under-predict the
PW and over-predict the O2 IR nightglow emission
in comparison to observations (e.g., Haberle et al.,
1982; Barnes and Haberle, 1996; Wilson, 1997;
Forget et al., 1999; Clancy et al. 2012, 2013).
The observations are suggesting these two features, which are driven by the same circulation and
are co-located, respond to the mean meridional circulation differently with respect to seasons. We will
investigate the seasonal behavior of these features
with respect to different atmospheric conditions and
evaluate the trends.
Methods:
The current NASA Ames Mars Global Climate
Model (MGCM), as described in Kahre et al., (this
meeting), is utilized to characterize the seasonal
response of PW and the O2 IR nightglow emission to
different dynamical drivers and their correlations
simultaneously. Examining the drivers of PW and
O2 IR nightglow emission will provide a deeper

The O2 IR nightglow volume emission rate
(VER) is calculated using the following expression:
E(O2*)=(a*k1*[O]*[O]*[CO2]) / (1+t*(kco2*[CO2]))
where a is the total yield of O2*, k1 is the rate coefficient for the three-body recombination reaction, [O]
and [CO2] are concentrations for each specie, t is the
lifetime by radiative relaxation of O2*, kco2 is the
quenching coefficient for CO2. Current values for
this simulation are: a = 0.75, k1 = 2.5*5.2e35*exp(900/T) cm6 s-1, t = 3800 s, kco2 = 2.0e-20
cm3 s-1. Some of these values are not well known, so
sensitivity tests will need to be conducted.
Preliminary Results:
Polar Warming. Figure 1 demonstrates the
nightside polar warming calculated from the
MGCM. For this simulation, Ls = 90 (Fig. 1 top)
has minimal (~15 K in northern hemisphere) to no
PW. The MCS derived PW for Ls=90 was less than
15 K during MY 29 in both hemispheres. However,
MY 30 had a maximum of ~30 K in the southern
hemisphere and ~15-20 K in the northern hemisphere (McDunn et al. 2013).

Figure 1: Polar warming for cloud case. Night time
(22-2 LT), zonal average, binned 10 Ls, 5 Lat.
understanding of the meridional circulation and how
it impacts transport of other elements (e.g., water,
dust). The work shown here uses a single MGCM
set up. We
use a background dust scenario, which is constructed
from the Montabone scenarios (MY29-34) by identifying the spatially and seasonally varying minimum
value of the multi-year record to filter out the influence of episodic regional dust storms. For this specific application, the dust scenario is zonally averaged. The vertical dust distribution is governed by a
latitudinally and seasonally varying prescription
similar to Forget et al. (1999). The water ice clouds
are radiatively active and solar flux is set for solar
moderate conditions.
Orographic and nonorographic gravity waves are not enabled for this
simulation.
The simulated fields are binned in Ls (10) and
latitude (5), zonally averaged, specifically looking
at nightside (local time = 22-02).
The polar warming magnitude is quantified as
described in McDunn et al., 2013:
△pT(Lat) = [TLat – T2]p; LatT2＜ Lat ≦ T1, where T1 is
the largest bin-averaged temperatures in each hemisphere, T2 is the smallest bin-averaged temperature
between LatT1 and the equator, LatT1 is the latitude of
T1 and LatT2 is the latitude of T2. Following
McDunn et al. (2013) temperature enhancement
larger than 15 K is used to identify PW.

Figure 2: O2 IR nightglow volume emission rate for
cloud case. Night time (22-2 LT), zonal average,
binned 10 Ls, 5 Lat.
The northern winter solstice (Ls= 270; Fig. 1
bottom) has PW magnitudes as large as 70 K in the
northern hemisphere and ~20 K in the southern hemisphere. The MCS derived PW for Ls = 270 was
largest overall in MY 28 with the maximum northern
hemisphere ~ 50 K and southern hemisphere ~30 K.

This Mars year also had a solstitial-season global
dust storm. Both MY 29 and MY 30 resulted in
northern hemisphere PW ~30 K and southern hemisphere PW ~15 K (McDunn et al., 2013).
This general trend of the simulated larger PW
near northern winter solstice compared to southern
winter solstice is consistent with the expected seasonal variation in the strength and extent of the mean
meridional

Figure 3: Maximum values of polar warming and
log O2 IR nightglow volume emission rate with respect to solar longitude (Ls). Night time (22-2 LT),
zonal average, binned 10 Ls, 5 Lat. [Top] Northern
hemisphere and [Bottom] Southern hemisphere.
circulation. However, the simulated behavior of the
northern hemisphere PW at Ls=90 being larger than
the southern hemisphere is not expected.
O2 IR Nightglow Emission. Figure 2 demonstrates the simulated nightside O2 IR nightglow
VER. This simulation demonstrates the nightglow to
be largest in the winter hemisphere with respect to
solar longitude. The maximums are similar in magnitude for the southern winter solstice (Ls=90; Fig.
2, top) and northern winter solstice (Ls=270; Fig. 2,
bottom) which would seem counter to what would be
expected. The mean meridional circulation is observed to be stronger during Ls = 270, as the PW
magnitudes in Figure 1 supports. Further examination and results will be compared to Clancy et al.
2012 and 2013, which discusses the MARCI CRISM
O2 IR nightglow emission observations.
Correlation. As discussed above, these features
are driven by the same circulation and have been
observed in similar spatial regions. Figure 3 shows

how the simulated maximum polar warming and O 2
IR VER vary seasonally; with the top panel representing the northern hemisphere and the bottom
panel representing the southern hemisphere. In the
north, the O2 IR VER has a sinusoidal pattern, with a
minimum near Ls=~100 and a maximum near
Ls=~270. PW has a similar sinusoidal pattern but
with an extra sizable decrease Ls=~205. The southern hemisphere shows the two features trending in
opposite directions around Ls = 90 and then both
trending toward a minimum near Ls = ~290. Clancy
et al. (2012, 2013) presented the correlation between
CRISM observed O2 IR nightglow emission and
MCS temperatures for Ls = 74-137, Lat=70-90 S,
and altitude range of 50-60 km. They found the two
features to be anticorrelated, as did the GCM results
within that study. They claim, based on the southern
hemisphere observations, that the correlation with
adiabatic heating with O2 IR nightglow emission is
not very strong, but it seems to be largely dependent
on the temperature dependent rate constant.
Future Work:
We will examine the behavior of the PW and O2
IR nightglow VER and correlate their seasonal behaviors to provide more knowledge on the
meridional circulation. We will extend the work of
Clancy et al. (2012, 2013) by studying the full Martian year. The thermal and wind field, along with
mass stream functions will also be reviewed. Moreover, several sensitivity cases will be conducted to
investigate the relative importance of thermal
(clouds and dust) and wave-induced forcing on the
correlation between PW and O2 IR nightglow VER,
thus the meridional circulation.
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