Analysis of wind shear for the ExoMars mission using ultra-high resolution Large Eddy Simulation T. Bertrand, A. Spiga, A. Colaïtis

Mission context ExoMars ESA mission 2016: - TGO - EDM Landing point: Meridiani Planum ̴ 1.88°S / E

Objectives Evaluate wind shears at ExoMars landing site Definition: A strong wind shear at an atmospheric level results either from large differences of wind amplitude or contrasts in wind direction, or both, over a small vertical extent.

Objectives Wind shear Evaluate wind shears at ExoMars landing site Possible effect of a wind shear on EDM’s landing system: Large Eddy Simulation: 400 levels between 0 and 5 km altitude Vertical resolution =12.5 m LCT = 1 p.m until 1.45 p.m Horizontal resolution = 12 m 400 levels between 0 and 5 km altitude Vertical resolution =12.5 m LCT = 1 p.m until 1.45 p.m Horizontal resolution = 12 m

Wind shear characterization Wind vector U V θ UV (alt = n+1) UV (alt = n) Δ(θ) D(UV) D(UV) enables to evaluate the combined effects of angle and amplitude. It is a good indicator of wind shears. U V

Vertical discretization 12.5 m UV (m/s) Altitude (m) In order to constrain the mission, we are concerned with wind shears occuring over a vertical distance of m

Exemple of wind shears with UV and θ profiles at two different locations (distant from 750m) Exemple of wind profile

with UV and θ profiles Exemple of wind shears Altitude (km) Δ(UV)ΔθΔθ (°) Wind shear with high Δ(UV) Wind shear with high Δθ

Δ(UV) and Δ(θ) at 4 different times and at two different locations (distant from 750m)

for each latitude and longitude, over all time and altitudes Maximal values of D(UV)

Between 0-5 km and 0100PM-0145PM Maximal values of D(UV) D(UV) [ s -1 ]

Δ(UV) ΔθΔθ Extreme cases of wind shear profiles Red curve: sheared case Blue curve: smooth case Altitude (km) D(UV) High Δθ D(UV)= 0.42 s -1 (15.7 m.s -1 over 37,5m)

UV D(UV)Δ(θ) High D(UV) High Δθ Extreme cases of wind shear profiles

Probability of wind shear Considering maximal values of D(UV) only (s -1 ) max

Probability of wind shear Considering all values of D(UV) from LES (s -1 ) max

Conclusions Wind shears diagnostic  D(UV) … combining gradient of wind amplitude and wind direction. Most plausible ExoMars landing profiles have very moderate shears (< 3 m.s -1 over a vertical distance of 37.5 m). A majority of maximal shears are between 0.15 and 0.25 s -1. Extreme wind shears of about 15 m.s -1 are found over a vertical distance of 37.5 m (but low probability: P < 0.01). On the one hand, the probability of having wind shears less than 0.1 s -1 is quite high when considering all times and altitudes available. When considering only maximal wind shears over the same area, a majority of wind shears between 0.15 and 0.25 s -1 are found. In a general way, over a vertical distance of 37.5 m, variations of wind amplitude of 3 m.s -1 combined with angle variation of about 60° are relatively frequent.