The first year (December 2015 to November 2016) of IR2 after Akatsuki's successful insertion to an elongated elliptical orbit around Venus is reported with performance evaluation and results of data acquisition. The single-stage Stirlingcycle cryo-cooler of IR2 has been operated with various driving voltages to achieve the best possible cooling under the given thermal environment. A total of 3091 images of Venus (1420 dayside images at 2.02 μm and 1671 night-side images at 1.735, 2.26, and 2.32 μm) were acquired in this period. Additionally, 159 images, including images of stars for calibration and dark images for the evaluation of noise levels, were captured. Low-frequency flat images (not available in pre-launch calibration data) have been constructed using the images of Venus acquired from near the pericenter to establish the procedure to correct for the IR2 flat-field response. It was noticed that multiple reflections of infrared light in the PtSi detector caused a weak but extended tail of the point-spread function (PSF), contaminating the night-side disk of Venus with light from the much brighter dayside crescent. This necessitated the construction of an empirical PSF to remove this contamination and also to improve the dayside data by deconvolution, and this work is also discussed. Detailed astrometry is performed on star-field images in the H-band (1.65 μm), hereby confirming that the geometrical distortion of IR2 images is negligible.
Abstract. We investigated diurnal variations of water-ice clouds in the Tharsis region of Mars in the three apparitions from 1995 to 1999. The Tharsis morning cloud, centered near a point (120• W, 10• N) between Olympus Mons and Tharsis Montes, was the brightest among the morning clouds in Tharsis. Its optical thickness was about 0.6 near 9.5 h Martian local time and reduced to a minimum of about 0.2 around local noon in 1995. The minimum optical thickness was 0.4 in 1997, which also appeared around local noon. The optical thickness of the Tharsis morning cloud increased again in the early or mid afternoon in 1995 and 1997. In the late morning when the brightness of the morning cloud declined, bright afternoon clouds appeared over the major volcanoes in Tharsis. The optical thickness of the afternoon cloud over Olympus Mons was about 0.7 in the early afternoon in early summer, 1997. The Olympus afternoon cloud seems to be more active in early summer than in the first half of late spring. Those morning and afternoon clouds repeat the diurnal variation from late spring to at least early summer every Martian year.
Abstract. We conducted imaging observations of Mars in
This is a brief report on the Martian climate, based on our observations in 2001 as well as those in 1997 and 1999. The focus is the dissipating behavior of the low-latitude cloud belt appearing around the aphelion, the behavior of which has never been explicitly examined. We derive the optical thickness of water ice clouds (WICs) as $ \tau_{\mathrm{WIC}} \approx 0.1$ ($ \lambda \simeq 4400\,{Å}$) at the solar longitude $ L_{\mathrm{s}} = 174^\circ$ in 2001. The latitudinal coverage of the cloud belt is approximately $ L_{\mathrm{s}}$-independent just until its end. The cloud belt divides into a “semi-encircling” cloud band and discrete WICs before its dissipation (over $ L_{\mathrm{s}} \sim 100^\circ \hbox{--} 110^\circ$) in many cases. We suggest that this cloud division should embody localization of the cross-equatorial Hadley circulation.
We have two networks for cooperative Mars observations in Japan: Nishi-Harima Astronomical Observatory Mars Cooperative Observation and Association of Lunar and Planetary Observers in Japan. This paper is a summary of 3515 images collected by the two networks during the first half of the last apparition from 2002 October 18 through 2003 August 31, corresponding to the period of $L_{\mathrm{s}} \sim {83{}^{\mathrm {\circ }}} \hbox{--} {252{}^{\mathrm {\circ }}}$ ($L_{\mathrm{s}}$ is the areocentric longitude of the Sun). During this period, many interesting phenomena were observed. (1) Two local dust storms appeared about $L_{\mathrm{s}} = {214{}^{\mathrm {\circ }}}$ and $L_{\mathrm{s}} = {231{}^{\mathrm {\circ }}}$. (2) Hellas was obscured just before the occurrence of the first dust storm. This may be relevant to the dust storm. (3) Blue clearings were observed. The phenomena in this apparition may be attributed to the optical properties of the ground for the scattering of light. (4) Dark markings in the south polar cap (SPC) developed as the SPC receded in mid-spring of the southern hemisphere. Also, some bright spots appeared on the SPC. (5) The south polar hood receded polewards and SPC began to be observed at about $L_{\mathrm{s}} \sim {185{}^{\mathrm {\circ }}}$ (mid-May). (6) The north polar hood was not detected until $L_{\mathrm{s}} \sim {180{}^{\mathrm {\circ }}}$ in this apparition. (7) The low-latitude cloud belt had been observed until mid-May. In the dissipation phase, a less cloud area appeared in longitudes of 170${{}^{\mathrm {\circ }}}$-200${{}^{\mathrm {\circ }}}$ W.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.