Äîêóìåíò âçÿò èç êýøà ïîèñêîâîé ìàøèíû. Àäðåñ îðèãèíàëüíîãî äîêóìåíòà : http://www.cosmos.ru/seminar/20100225/evdokimova.pdf Äàòà èçìåíåíèÿ: Tue Mar 23 19:36:40 2010 Äàòà èíäåêñèðîâàíèÿ: Tue Oct 2 11:13:19 2012 Êîäèðîâêà: Ïîèñêîâûå ñëîâà: ï ï ï ï ï ï ï ï ï ï ï

Search for the signs of atmosphere-surface interactions during Martian year from OMEGA/Mars Express data
Evdokimova N. A. 1, Rodin A. V.
1-I

1,3,

Kuzmin R. O.

1,2,

Fedorova A. A.

1

3

KI, Moscow; 2- Vernadsky institute, Moscow; ­ Moscow Institute of Physics & Technology, Moscow

Photo by ESA


NIR OMEGA spectra (1-2.7 µm, C channel)
Observations of the North polar cap during MY27 aphelion campain Water ice microstructure retrievals Tracking its seasonal changes Identification of zonal variations associated with atmospheric processes search for traces of the atmospheric planetary waves


OMEGA ­ mapping spectrometer for visible and near-IR spectral ranges Overview
· 3 detectors: 0.364-1.070 µm (VNIR) /96 channels 0.926-2.695 µm (C) /128 channels 2.527-5.089 µm (L) /128 channels · instantaneous field of view IFOV ~ 4.1 arcmin (1.2 mrad) · Spectral resolution / ~ 70-200 · highest spatial resolution ~ 300 meters (periapsis) · Cross-track swaths are 16, 32, 64 and 128 pixels wide


Typical modes of observations.
Maximum altitude, km "Pixel" size Track width, pixel Track width, km Track length, pixel Track lenght, km Session duration, min 300 <360m 16 5- 7 ~ 7500 ~ 3000 ~ 12 1500 <1.8km 64 60-120 ~ 2000 ~ 3000 ~ 12 4000 <4.8km 128 300-600 ~ 1000 ~ 3000 ~ 24


Methodology
· Mapping spectral features marking ices · Use synthetic indices rather than retrieve abundances: 1.2, 1.5, 2.0 µm · Work with calibrated radiances rather than relative spectra · Ad hoc atmospheric corrections

Spectral index:

S( ABCD) - S1 Index = S( ABCD)


Correction on atmospheric absorption
·MOLA topography ·CO2: p,T ­ from European Mars Climate Database ·H2O column (Ls, ) - from TES observations ·H2O (, l, z) ­ from GFDL MGCM model ·HITRAN(2004) OMEGA DETECTOR C

Wavelength,µm


Errors and uncertainities
Due to the instrument Dark noise Point-spread function error Calibration error Digitalization error Pixel-to-pixel non-linearity Degradation of spectral channels Errors due to models Ones due to solar spectrum model Due to atmospheric model


Errors and uncertainities
Due to the instrument Dark noise ~0.3% Point-spread function error -> atm. model error Calibration error ~1% Digitalization error ~0.3% Pixel-to-pixel non-linearity ~0.5% Degradation of spectral channels ? Errors due to models Ones due to solar spectrum model ~0.5% Due to atmospheric model ~0.2% Wide adsorption bands, µm 1.2 2.1 1.5 1.45 2 1.5

Index error, %


Sublimation process of the North polar cap. Aphelion season, MY 27
Ls=93°-97° Ls=113°-115° Ls=127°-136°

1.25 µm

1.5 µm


North polar cap, 1.25 µm, Ls ~113º


North polar cap, 1.25 µm, Ls ~113º
A B


North polar cap, 1.25 µm, Ls ~113º
A B (A) (B) (A)


North polar cap, 1.25 µm, Ls ~113º
A Ray-tracing simulation results: B (incidence zenith angle = 0ºand 60º) .7
10 µm, 0 0.6 30 µm, 0 0.5 su r face r eflect ivit y
o o

0

10 µm, 60
o

30 µm, 60 100 µm, 0

o o o

(A) (B) (A)
o o o

0.4

100 µm, 60 300 µm, 0
o

0.3

300 µm, 60 1000 µm, 0

0.2

1000 µm, 60

0.1

0

1

1.2

1.4

1.6

Wavelength, µm

1.8 2 , µm

2.2

2.4

2.6

2.8


Index 1.25 µm calibration Index value vs. mean grain size

55º < SZA < 80º


Index 1.25
Ls=93°-97°

m

mode 3: polar cap sublimation
Ls=113°-115° Ls=127°-136°


Index 1.25
Ls=93°-97°

m m ode 2 and 3: polar cap sublimation
Ls=113°-115° Ls=127°-136°

MGCM water vapor column, pr

m


Index 1.25
Ls=93°-97°

m

mode 3: polar cap sublimation
Ls=113°-115° Ls=127°-136°

Reflectivity ~1 m

During summer reflectivity is decreasing -> defrosting


What causes index and albedo variations across terrace?

Zonal (circum polar) wind

HiRISE imagery analysis

Meridional (catabatic?) wind


Conclusions:
Microphysical structure of frost at the North polar cap reveals the signature of stationary atmospheric waves with the leading wavenumber changing from 2 to 3 Evolution in time and phase of these patterns coincide with waver vapor distribution predicted by GCM Hence, we conclude that North polar cap sublimation is strongly affected by mesoscale wind systems At the local scale, there is an evidence of changing wind direction across spiral terraces ­ probably a contribution of catabatic winds