J/A+A/585/A53 Horizontal temperature at Venus upper atmosphere (Peralta+, 2016)
Dayside temperatures in the Venus upper atmosphere from Venus Express/VIRTIS
nadir measurements at 4.3µm.
Peralta J., Lopez-Valverde M.A., Gilli G., Piccialli A.
<Astron. Astrophys. 585, A53 (2016)>
=2016A&A...585A..53P 2016A&A...585A..53P (SIMBAD/NED BibCode)
ADC_Keywords: Solar system ; Planets
Keywords: molecular processes - radiation mechanisms: non-thermal -
radiative transfer - instrumentation: spectrographs -
methods: data analysis - planets and satellites: atmospheres
Abstract:
In this work, we analysed nadir observations of atmospheric infrared
emissions carried out by VIRTIS, a high-resolution spectrometer on
board the European spacecraft Venus Express. We focused on the
ro-vibrational band of CO2 at 4.3 microns on the dayside, whose
fluorescence originates in the Venus upper mesosphere and above. This
is the first time that a systematic sounding of these non-local
thermodynamic equilibrium (NLTE) emissions has been carried out in
Venus using this geometry. As many as 143,218 spectra have been
analysed on the dayside during the period 14/05/2006 to 14/09/2009. We
designed an inversion method to obtain the atmospheric temperature
from these non-thermal observations, including a NLTE line-by-line
forward model and a pre-computed set of spectra for a set of thermal
structures and illumination conditions. Our measurements sound a broad
region of the upper mesosphere and lower thermosphere of Venus ranging
from 10-2 to 10-5mb (which in the Venus International Reference
Atmosphere, VIRA, is approximately 100-150km during the daytime) and
show a maximum around 195±10K in the subsolar region, decreasing
with latitude and local time towards the terminator. This is in
qualitative agreement with predictions by a Venus Thermospheric
General Circulation Model (VTGCM) after a proper averaging of
altitudes for meaningful comparisons, although our temperatures are
colder than the model by about 25K throughout. We estimate a thermal
gradient of about 35K between the subsolar and antisolar points when
comparing r data with nightside temperatures measured at similar
altitudes by SPICAV, another instrument on Venus Express (VEx). Our
data show a stable temperature structure through five years of
measurements, but we also found episodes of strong heating/cooling to
occur in the subsolar region of less than two days.
Description:
The dayside atmospheric temperatures in the UMLT of Venus (displayed
in Figure 7A of this article) are listed as a CSV data file. These
values consist of averages in bins of 5° in latitude and
0.25-hours in local time from dayside temperatures covering five years
of data (from 2006/05/14 to 2011/06/05). These temperatures were
inferred from the CO2 NLTE nadir spectra measured by the instrument
VIRTIS-H onboard Venus Express (see article for full description of
the procedure), and are representative of the atmospheric region
between 10^-2 to 10^-5mb. Along with the temperatures, we also provide
the corresponding error and the number of temperatures averaged in
each bin. The format of the CSV file reasonably agrees with the
expected format of the data files to be provided in the future version
of the Venus International Reference Atmosphere (VIRA).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table.dat 59 1314 *Mean temperatures and errors with VEx/VIRTIS-H
(VIRTIS-H20151090S-90N_06h-18h)
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Note on table.dat: Observation date : 2006-134/2011-156.
Longitude not Applicable (zonal averages are done in Local Time)
FOV<10km. Planet radius = 6051.8km.
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Byte-by-byte Description of file (#): table.dat
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Bytes Format Units Label Explanations
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1- 14 A14 --- --- Date (Not applicable)
16- 18 I3 km Alt Height range contributing
20- 21 I2 km e_Alt rms uncertainty on Alt
23- 26 F4.2 mbar Pmax Pressure range contributing (upper value)
28- 33 E6.3 mbar Pmin Pressure range contributing (lower value)
35- 37 I3 deg LAT Latitude bin (degrees North)
39- 41 I3 deg LON ?=- Longitude (Not applicable)
43- 47 F5.2 h Hbin Local solar time Local Hour bin (12 is noon)
49- 51 I3 K Temp Mean atmospheric temperature
53- 54 I2 K e_Temp Temperature associated error (see paper)
56- 59 I4 --- Nsp Number of VIRTIS-H spectra or temperatures averaged
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Acknowledgements:
Javier Peralta, javier.peralta(at)ac.jaxa.jp
History:
* 17-Dec-2015: on-line version
* 03-Mar-2017: correct table with all lines and header
(End) Javier Peralta [ISAS/JAXA, Japan], Patricia Vannier [CDS] 09-Nov-2015