Figure 3.4 Wind vectors collected in the Arctic during the northern spring.76 Figure 3.5 Circulation patterns derived for each panel in figure. With the exception of the global dust storm in the second year of MGS mapping (2001), Martian weather is highly repeatable.
Martian Clouds Observed by Mars Global Surveyor Mars Orbiter
Abstract
Two distinct periods of storms in late summer precede the formation of the northern and southern circumpolar hoods. The south polar cap has less cumulus and cumulus clouds than the north polar cap.
Introduction
Storm life cycles and the seasonal distribution of clouds can be easily monitored due to the systematic coverage. We will describe the development and decay of the tropical cloud band and polar hoods, the cloud morphology within the tropical cloud band and polar hoods, the evolution of the band clouds, the distribution of polar waves and spiral clouds, and the "aster Clouds associated with volcanoes .
Data processing
In addition to the geometric effect, variations in camera response can also cause brightness variations in the global map areas. We use a weighted average to mosaic the global map strips, that is, the pixel with smaller angles of incidence and phase and which is further from the angles of view makes a larger contribution to the value in the overlap region, and vice versa.
Tropical cloud distribution
- General features
- Non-uniform decay of the tropical cloud belt
- Cloud morphology of the tropical cloud belt
- Aster clouds above the volcanoes
In the Viking era, low latitude streak clouds (fibrous clouds) were more frequently observed during Ls 45º~130º, while wave clouds and cloud streets (convective clouds) were mainly observed during Ls 80º~130º [Kahn, 1984]. This indicates a change in cloud type in the tropical cloud belt and is consistent with the MOC observations.
North polar clouds
- North polar hood formation (L s 160º~185º)
- North polar streak clouds
- North polar lee waves
- Spiral clouds
Although the Ls ~163º regional storm causes an apparent increase in both the total clouds and the thick dust and condensate clouds (see Plate 1.3), the Ls ~183º storm is mainly associated with an increase in the thick clouds because the total cloud cover is already large before Ls. The dashed lines in (a) and (b) are scaled from the solid lines by the area outside the terminator circles. c) The solid line is the scaled time sequence for the arctic region, the same as the dashed line in (a).
South polar clouds
- Development of the south polar hood
- South polar clouds from mid winter to mid summer
- South polar lee waves
Faint circumpolar striae can be seen in the south polar hood (Plate 1.6 (j-l)), but the number of striae occurs much less than in the northern polar region during the northern dip. Despite the general lack of condensate clouds in the Southern Hemisphere, many lee waves are still observed in the southern polar region. There are 2998 lee waves observed in the south polar region, and 4573 lee waves observed in the north polar region.
The number of south polar lee waves in the second Martian year increases suddenly around Ls ~5º and peaks around Ls ~30º.
Conclusion
These peaks are not only larger than the early fall peak in the Antarctic, but they are also larger than the early fall peak in the Arctic. A wave number two standing wave structure shows clearly in the north but not in the south. Perhaps because of the low abundance of water vapor in the south, cirrus clouds and cumulonimbus clouds are less abundant in the south than in the north.
In both polar regions, fur waves are mainly observed in autumn and winter, and the number of white waves shows a peak in early autumn.
Acknowledgments
Both the north polar cap and the south polar cap begin to develop in late summer about 20º Ls before the equinoxes. Both experience two stormy periods before the formation of circumpolar clouds in early autumn. Condensate clouds appear to be common during the development of the north polar cap, but appear to be rare during the development of the south polar cap.
Southern polar lee waves appear about 15º-25º Ls later than northern polar lee waves and show a maximum peak in late winter.
Wilson, Dynamical properties of Martian water ice clouds and their interactions with atmospheric dust and radiation, Adv.
Cyclones, Tides, and the Origin of a Cross-Equatorial Dust Storm
- Abstract
- Introduction
- Analysis with GCM
- Discussion
- References
Camera (MOC) has provided an unprecedented view of the Martian atmosphere [Cantor et al., 2001; Wang and Ingersoll, 2002]. This is consistent with general circulation model (GCM) simulations, which suggest that the accumulation of dust in the Hadley convergence zone will lead to atmospheric warming and intensification of global circulation [Haberle et al. The Hadley convergence zone appears to be the key to the development of the largest dust storm of the first MGS mapping year.
Ingersoll, Interannual variability of Martian global dust storms - Simulations with a low-order model of the general circulation, Icarus.
Cloud-tracked winds for the first Mars Global Surveyor mapping
Abstract
The latitudinal distribution of zonal winds within 50°N–75°N from mid-northern summer to early northern autumn indicates that winds at higher latitudes are generally weaker than those at lower latitudes, but the rate of increase with time is faster at higher latitudes. There are large-scale waves in the weekly mean meridional wind and in the biweekly mean eddy momentum flux and eddy kinetic energy fields in the northern polar region from mid to late summer. The cloud-tracked winds in the north are generally consistent with winds calculated by a general circulation model at the water condensation level derived from MGS Thermal Emission Spectrometer (TES) observations, but appear to be stronger than the gradient winds derived from TES assuming no flow at the surface.
Introduction
If we miss the true positions of the cloud features by four pixels, we will. Cloud-following wind errors can be reduced by tracking the same cloud feature in two frames separated by many orbits, but this depends on the lifetime of the identifiable features and the path traveled by the cloud. Due to the small overlap of bands in the equatorial region, we only track clouds in the northern and southern polar regions (45°-90°N/S).
The program and fronts can be followed in a perpendicular direction, but the elements along them are difficult to identify.
Cloud-tracked winds
- North polar region during L s 135°-195°
- North polar region during L s 20°-55°
- South polar region during L s 337°-10°
Since most good candidates for cloud tracking in the south are dust clouds that show up most clearly through the red filter, each panel here contains measurements from 84 red images taken over the course of a week. The number of measurements is much smaller than in the northern polar region, reflecting the relative lack of clouds and water vapor in the southern hemisphere. As summer approaches, dust storm activities in the south polar maps decrease greatly, and the only mobile features are the arcuate cap edge clouds near the terminator [ Wang and Ingersoll , 2002 ].
The movement of these clouds indicates winds outside the cap in the early evening before the southern summer solstice.
Zonal mean winds
- North polar region during L s 135°-195°
- North polar region during L s 25°-55°
- South polar region during L s 337°-10°
However, it should be noted that TES retrievals are uncertain in the lower atmosphere [ Smith et al ., 2001 ], and errors in the derived wind field are likely to be significant. Many vectors in early northern autumn are derived from streak clouds which are the most representative features in the polar cap [ Wang and Ingersoll , 2002 ]. Winds from the wind in the eastern part of the coil generally have a higher velocity than winds from the wind in the western part of the nacelle, resulting in an average northward flow.
This height corresponds to the water vapor condensation level of <10 km near the northern polar ice cap in early northern spring [Smith, 2002].
Latitudinal distribution of zonal wind
A cross section of the zonal wind between latitude and height for Ls 0°-23° simulated by the NASA Ames GCM shows that winds of 10-15 m/s occur within ~3 km of the surface in the southern high latitudes [ Haberle et al., 1993]. Most of the data before Ls ~180° are roughly consistent with solid body rotation (Figure 3.8b), with an apparent increase in angular velocity between Ls 150°-180°. In summary, dQ dy changes sign somewhere between 60°N-70°N between Ls, indicating possible barotropic instabilities in this region.
If the curvature of the vertical profile u is large, the vertical shear can become the dominant factor in the potential vorticity (P) and change the sign of the slope dP/dy.
Eddy winds
- Fourier wave components
- Eddy momentum flux and eddy kinetic energy
A negative value (blue on the left side of panel 3.1) indicates poleward momentum transfer to the west or equatorward momentum transfer by the wave. The eddy kinetic energy maps for the four periods are shown in the right columns of Panel 3.1. Regions of large eddy kinetic energy correspond to regions of large positive or negative eddy flux.
However, the observed positive-negative-positive eddy momentum flow pattern is not visible in Plate 3.2.
Summary
Smith [2002] estimated the height of the water vapor condensation level to be in the range of 5–10 km during the season of our north polar measurements. The measured winds are much weaker than the GCM-simulated winds at the level of water vapor condensation (∼10 km). The observed zonal mean wind increases from late summer to early autumn in both hemispheres and decreases in spring in the northern polar region.
In the north, the increase in zonal wind from late summer to early autumn appears larger at higher latitudes.
Our measured winds are stronger than the gradient winds at the condensation level of the water vapor flowing from the TES.
Acknowledgements
Martian Clouds Observed by the Mars Global Surveyor Mars
Introduction
The 2001 global dust storm
- Effects on photometric processing
- Storm evolution
- Effects on surface albedo
- Effects on polar clouds
- Global dust storm initiation
Global condensate cloud distribution
Recurrent phenomena
- Aster clouds
- Polar clouds
- Spiral clouds
Summary
Image processing and daily global map
The spatial distribution of lee waves in the north polar maps (45ºN-90ºN) is shown in fig. The number of lee waves observed in the north polar maps as a function of Ls is shown in fig. All the spiral clouds occur in the north polar region from mid-spring to early autumn.
The fact that no spiral clouds are observed in the south indicates different conditions of the two polar regions during the corresponding season (see Section 5). Condensate clouds can be seen just east of the leading (eastern) dust arm in the 0º- 45ºW sector. 2 weeks, the accompanying warming of the atmosphere, and the increase in the amplitudes of thermal tides.
The brightness variations in the images are functions of the observational geometries (incident angles, emission angles and phase angles), the camera response function [Caplinger, 1997] and the albedo of Mars. The phase angles tend towards 0 in the interior of the image and increase outward (Fig. 5.2c).
Representative north polar stereographic maps
Spiral clouds in the north polar region during Ls 160°~185°
Representative south polar stereographic maps
