Rederiva(on of MGS radio occulta(on s temperature with the considera(on of CO 2 condensa(on in the Mar(an atmosphere

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1 Data analysis of Mars orbiters: Rederiva(on of MGS radio occulta(on s temperature with the considera(on of CO 2 condensa(on in the Mar(an atmosphere Katsuyuki Noguchi and Sayaka Ikeda (Nara Women s University) Takeshi Kuroda (Tohoku University) Mar>n Pätzold and Silvia Tellmann (Köln University) Noguchi et al. [2014, JGR]: Es>ma>on of changes in the composi>on of the Mar>an atmosphere caused by CO2 condensa>on from GRS Ar measurements and its applica>on to the rederiva>on of MGS radio occulta>on measurements

2 Summary Mar>an atmospheric composi>on: CO 2 and other gases (N 2, Ar, etc ) Radio occulta>on, which can probe temperature profiles, needs the informa>on of composi>on rate Problem: CO 2 condensa>on at polar night causes change of composi>on rate (CO 2 deple>on and other non- condensa>on species increase), which affects radio occulta>on measurements But no observa>on of the seasonal change of (all the) composi>on rate available We show how to es>mate the change of composi>on rate and Radio occulta>on rederiva>on using the es>mated rate

3 Mar(an (neutral) atmosphere Composi>on Observed by Viking lander (1970 s) Main species: CO 2 95% Other main species: N %, Ar 1.6% Pressure à less than 1/100 of Earth Large seasonal change (20-30%) caused by condensa>on of CO 2 in polar nights

4 Dras(c pressure change by CO 2 condensa(on Ls summer autumn winter spring summer Pressure decreasing due to condensa>on of CO 2 Pressure [hpa] Snyder [1979, JGR] Sol ader landing

5 Time on Mars Sol: One day on Mars ( 24 hours) MY(Mars Year): Year on Mars ( 2 Earth years) Ls(Solar Longitude): Seasons of Mars Northern hemisphere (NH) Sothern hemisphere (SH) Mars Spring / Autumn Ls=0 Summer / Winter Mars Sun Winter / Summer Mars Ls=90 Ls180 Mars Autumn / Spring Ls=270 Ellip>cal orbità Seasons in the SH are more extreme (i.e., hoker summer and colder winter) in the NH.

6 Condensa(on of CO2 in the Mar(an atmosphere Frequently observed in the mesosphere and polar nights IR obs. (20um) by Viking orbiter Pathfinder s decent Nightside Wavy structures with CO2 satura>on temperature in the mesosphere Polar night 140K Dayside 240K Below CO2 condensa>on temperature in the polar night

7 Radio occulta(on (RO) measurement Probes temperature profiles (T precision<1k, alt. resolu>on<1km) U>lizes radio waves transmiked from spacecrad to receiver on Earth, which pass through planetary atmosphere Records radio waves frequency changes according to ver>cal distribu>on of atmospheric refrac>vity Provides refrac>vity number density of air à temperature Mars Receiver on Earth

8 Data flowchart Time series of frequency changes of radio waves Abel transform Ver>cal profile of refrac>vity μ f [Hz] z [km] t [s] ionosphere Electron number density Ver>cal profile of air number density N Ver>cal profile of pressure P Using composi>on rate! Hydrosta9c equilibrium Using composi>on rate! ideal gas law Ver>cal profile of temperature T z [km] z [km] 1 neutral atmosphere μ P [Pa] T [K]

9 Temperature retrieval by RO Needs atmospheric composi>on ra>o when 1. Conver>ng refrac>vity μ to number density of air n gases κ:factors specific for 2. Using mean molecular weight to retrieve temperature from number density, assuming hydrosta>c equilibrium However, previous studies did not consider the change of atmospheric composi>on ra>o caused by CO 2 condensa>on

10 Purpose of study This study Es>mates the change of composi>on rate including CO 2 Rederives the MGS RO temperature to discuss CO 2 condensa>on (satura>on) and ver>cal distribu>on of mixing ra>o - About 70 profiles of MGS- RO in the southern polar night region, where the effect of CO2 condensa>on is strongest.

11 Method: es(ma(on of seasonal change of composi(on rate Main three cons>tuents: CO 2, Ar, N 2 Only Ar s mixing ra>o can be available from observa>ons (Gamma Ray Spectrometer of Mars Odyssey [Sprague et al., 2012]) à how to obtain N 2 and CO 2? N 2 : Ra>o of Ar and N2 (2.7% : 1.6%) should be kept because N 2 and Ar do not condensate. N 2 =2.7/1.6 Ar CO 2 =100 - (N 2 +Ar)[%] à Empirical model of seasonal changes of the three gases mixing ra>o obtained! Note: Constant ver>cal profiles assumed in this step (We will discuss this point later).

12 Results Rederived temperature of MGS- RO u>lizing the newly es>mated composi>on rate Sample: Rederiva>on with 78% CO 2 Overes>ma>on of temperature without considera>on of CO 2 condensa>on Rederived profile CO2 satura>on curve Original profile We u>lize the updated MGS- RO temperature and pressure data to calculate the degree of CO 2 supersatura>on Increasing - frequency of supersatura>on and - degree of supersatura>on

13 Discussion: ver(cal profiles of gases Problem: there is no direct measurements of ver>cal structures of atmospheric composi>on during CO2 condensa>on in polar nights. Results when applying ver>cal distribu>on of MCD Ar for MGS- RO rederiva>on: Result rederived looks realis(c Looks unrealis(c P [Pa] P [Pa] CO2 VMR CO2 VMR - Needs good es>ma>on of ver>cal profiles (especially in the lower layer) - Other way around, we might be able to obtain the informa>on on the mixing ra>o if we adjust temperature to CO2 satura>on temperature (or 35% supersatura>on temperature) à future work!

14 Conclusion We rederive MGS- RO temperature and pressure profiles with the considera>on of CO 2 condensa>on in the Mar>an atmosphere Overes>ma>on of RO temperature occurs if we do not consider CO 2 condensa>on Uncertainty of the ver>cal profiles of the cons>tuents causes large errors of temperature Adver(sement: A symposium on radio science for Earth and planetary atmospheres will be held at Nara Women s university on June 1, Please join!!