EXAMPLES OF LAT-ALT DISTRIBUTION OF O2(∆) EMISSION OBSERVED AT THE LIMB BY VIRTIS/Venus Express AT NIGHTIME [5]

First ground-to-thermosphere

Venus GCMAn improved and extended version of the Venus

LMD-GCM described in [3] is currently operational up to 150 km. It includes:

• Main processes contributing to the thermal balance of the upper atmosphere of Venus

• Coupling with a photochemical model [4] • Gravity waves parametrisation following [2].

All these improvements make the LMD-VGCM the only existing full self-consistent

ground-to-thermosphere Venus 3D model [1].

Non-orographic GW parametrization

• Stochastic approach formalism following [2]

• Large ensemble of monochromatic GW launched just above the convective layer (at 55 km)

• At each time step, the effect of a few waves is added to that of the waves launched before

• Source of the GW is chosen uniform (no latitudinal variation)

• Waves characteristics chosen randomly, with arbitrarily fixed probability distribution.

IMPACT ON TEMPERATURE AND WINDS

Introduction: Gravity waves (GW) are believed to play a major role in Venus upper atmosphere dynamics and commonly invoked in the literature to explain density, temperature and cloud structure variation. Supposed to be generated above the thick convective layer, in the middle cloud region (50-60 km), GW propagate upwards and break in the thermosphere, providing a significant source of momentum and energy. A GW parameterisation is implemented for the first time in the Venus General Circulation Model (GCM) developed at the Laboratoire de Meteorologie Dynamique (LMD) [1] following the formalism developed for the Earth [2]. A preliminary study of the impact of the GW parameter uncertainties on the main fields predicted by the LMD-VGCM is presented here.

INPUT basic INPUT basic GW parameters: GW parameters:

Saturation (Sc), Dissipation (Rdis), Launching altitude

Wave characteristics:

● RUWMAX: Vertical flux momentum (at launching altitude)

● CMIN, CMAX: Min/Max relative phase velocity amplitude

KMIN/KMAX: Min/Max Horizontal wavenumber

Conclusions: The large variability of the zonal winds in the region between 90 and 120 km (so-called « transition region ») is usually attributed to changing nature of the GW breaking. This work indicates that our GCM is potentially able to reproduce latitudinal and time variations produced by small-scale dynamics processes as observed [5]. However, theoretical and observational uncertainties prevent current GCMs to use an unique set of parameters to match measurements. In addition, our model does not fully reproduce the observed thermal structure: it might affect the propagation of the GW to the Venus upper atmosphere. Further modeling efforts are foreseen (i.e improvements of NIR cooling/heating rates, a mesoscale model, fine-tuning of the GW parameters).

IMPACT OF A NON-OROGRAPHIC GRAVITY WAVES IMPACT OF A NON-OROGRAPHIC GRAVITY WAVES PARAMETERISATION IN THE VENUS UPPER ATMOSPHEREPARAMETERISATION IN THE VENUS UPPER ATMOSPHERE

BY THE LMD-VGCM BY THE LMD-VGCM

G. Gillia, S. Lebonnoisa, F. Lotta, F. Lefèvreb , A. Stolzenbachb

(a) LMD, CNRS/UPMC/IPSL, Paris, France (b) LATMOS, CNRS/UPMC/UVSQ, Paris, France

0 LT6 LT 18 LT

O2(∆) Brigthness kR * km-1

O2(∆) Brigthness kR * km-1

Wave characteristics:

RUWMAX = 0.005 [kg m-1 s-2]

CMIN, CMAX = 1, 60 [m/s]

KMAX, KMIN = 2.e-5, 1.e-6 (300 km <ʎ < 1000 km)

Cold region between 2-5 LT at mid latitudes: produced by strong equatorial jets and vertical ascending flux from the lower to the upper atmosphere

EXAMPLES OF GW-PARAMETERS FINE-TUNING ON GLOBAL CIRCULATION

These jets are noticeably reduced after the non-orographic GW implementation. Both zonal and vertical winds are smoothed at mid-high latitudes by the GW propagation. The formation of the upwelling cold pool is either linked to angular momentum transport by the thermal tides, or to planetary scale waves propagation from the lower mesosphere.

Pressure level = 1 Pa (about 105 km)

TE

MP

ER

AT

UR

EZ

ON

AL

WIN

DS

VE

RT

ICA

L W

IND

S

Pressure level = 1 Pa (about 105 km)

z = 1 Pa (about 105 km)

z = 1 Pa (about 105 km)z = 1 Pa (about 105 km)

Other inputs parameters:

Sc = 0.85

Rdis = 0.1

latit

ude

latit

ude

latit

ude

Other inputs parameters:

Sc = 0.85

Rdis = 0.1

Wave characteristics:

RUWMAX = 0.005 [kg m-1 s-2]

CMIN, CMAX = 1, 60 [m/s]

KMAX, KMIN = 1.e-4, 1.E-5 (50 km <ʎ < 600 km)

longitude

longitude

With GWWithout GW

After GW implementation:● Differences between morning terminator (MT) and evening terminator(ET) reduced .● O bulge closer to the anti-solar point (0 LT, 0 LAT), as expected.

Better agreement with observations

References:

[1] Gilli et al. (2016), submitted to Icarus; [2] Lott et al.(2012) GRL, 39, L06807; [3] Lebonnois et al.(2010), JGR, 115,E06006; [4] Stolzenbach et al. (2014) in EGU 2014; [5] Gerard et al. 2014, Icarus, 236, 92-103

latitude latitudelatitude

altit

ude

3 LT 1 LT 0 LT

Simulated O2(∆) Limb integrated intensity [MR]

1 LT 0 LT 23 LT

Simulated O2(∆) Limb integrated intensity [MR]

0 LT6 LT 18 LT

LT : 1-3 LT : 23-0.1 LT : 19-3

GW routine simplified scheme

Initialisation

Waves characteristics

INPUTS

OUTPUTS

Evaluation of background flow

Calculation of tendencies

Computation of flux

From the GCM: p(lon,lat),T(lon,lat),winds(lon,lat), physical time step

TENDENCIES on winds (du,dv,dw)