Fig. 1. Latitudinal distribution of dust storms as a function of the areocentric longitude of the Sun (L_s=0° corresponds to the spring equinox) from L_s=170°–270° during the first three Mars years: (top) mapping mission (1999), (middle) extended mission (2001), and (bottom) relay mapping mission (2003). The central curve in each plot corresponds to the sub-solar latitude. The top and bottom curves in each plot are the average latitude of the northern and southern polar cap/polar hood edge.

Fig. 2. Distribution of dust storms as a function of L_s, for the three Mars year from 1999–2004, span several latitude bins: (a) 30°–90° N, (b) 30° S–30° N, and (c) 30°–90° S.

Fig. 3. Labeled surface albedo map (simple cylindrical projection) of Mars generated from MOC global wide-angle red camera images.

Fig. 4. Precursory local dust storm activity along the southern season receding cap edge and in Hellas basin: (a) June 11, 2001 (sol 1), (b) June 12, 2001 (sol 2), (c) June 13, 2001 (sol 3), (d) June 14, 2001 (sol 4), (e) June 15, 2001 (sol 5), (f) June 16, 2001 (sol 6), (g) June 17, 2001 (sol 7), (h) June 18, 2001 (sol 8), (i) June 19, 2001 (sol 9), (j) June 20, 2001 (sol 10), (k) June 21, 2001 (sol 11), (l) June 22, 2001 (sol 12), (m) June 23, 2001 (sol 13), (n) June 24, 2001 (sol 14), (o) June 25, 2001 (sol 15). Maps are simple cylindrically projected at 7.5 km pixel⁻¹ from 0.0°–65.5° S, 245°–335° W.

Fig. 5. Evolution of 2001 planet-encircling dust storm during the expansion phase: (a) June 26, 2001 (sol 16), (b) June 27, 2001 (sol 17), (c) June 28, 2001 (sol 18), (d) June 29, 2001 (sol 19), (e) June 30, 2001 (sol 20), (f) July 1, 2001 (sol 21), (g) July 2, 2001 (sol 22), (h) July 3, 2001 (sol 23), (i) July 4, 2001 (sol 24), (j) July 5, 2001 (sol 25), (k) July 6, 2001 (sol 26), (l) July 7, 2001 (sol 27), (m) July 8, 2001 (sol 28), (n) July 9, 2001 (sol 29), (o) July 10, 2001 (sol 30), (p) July 11, 2001 (sol 31), (q) July 13, 2001 (sol 33), (r) July 17, 2001 (sol 37). During this phase, ten baroclinic dust storms developed in the Acidalia and Utopia storm zones (Hollingsworth et al., 1996 and Hollingsworth et al., 1997; Cantor et al., 2001). Of note was their east–southeast propagation at northern mid-latitudes and their possible interaction with the planet-encircling storm. Maps are simple cylindrical projected at 7.5 km pixel⁻¹ from 80.0° S–80.0° N, 0.0°–360.0° W and have been color stretched to enhance dust event contrast.

Fig. 6. MOC wide-angle limb views showing (a) dust reaching altitudes of about 60 km during the planet-encircling dust event at L_s=192.2° in a red-filter image. Water-ice clouds and haze observed in blue-filter observations reached altitudes of about (b) 15 km and (c) 10 km respectively at L_s=142.0° in the southern subtropics.

Fig. 7. Evolution of 2001 planet-encircling dust storm during the decay phase: (a) August 4, 2001 (sol 54), (b) August 24, 2001 (sol 73), (c) September 22, 2001 (sol 101), (d) September 28, 2001 (sol 107), (e) November 1, 2001 (sol 140). Maps are simple cylindrical projections spanning from 80.0° S–80.0° N, 0.0°–360.0° W, projected at 7.5 km pixel⁻¹ and have been color stretched to enhance dust event contrast.

Fig. 8. Areal extent of planet-encircling dust storm as a function of areocentric longitude of the Sun (L_s), from precursory storm activity through to the time the dust storm became planet encircling. The expansion of the event is fit best by a quadratic Gaussian function, shown as a solid line. However, the function is a poor fit to the two contraction–expansion phases observed between L_s=188.8° and L_s=194.6°.

Fig. 9. Wind speed vectors obtained from the propagation of baroclinic storm activity and the planet-encircling dust event from L_s=175.0°–199.0° over plotted against the MOC red-filter geodesy simple cylindrical map (Caplinger and Malin, 2001). General circulation is to the east with wind speeds ranging from 3 to 32 m s⁻¹. The most northern derived wind speeds are from baroclinic storm activity moving eastward along the Acidalia and Utopia storm tracks, with speeds ranged from 5 to 15 m s⁻¹.

Fig. 10. Local wind streak and surface albedo changes observed in Syrtis Major (4.0–6.0° N, 295.0°–297.0° W) with the wide-angle red-filter MOC at full-resolution (230 m pixel⁻¹), during a two Mars year period from L_s=183.8° in 2001 to L_s=180.8° in 2003. (a) Just prior to the onset of the 2001 planet-encircling dust event on June 24, 2001, the Minnaert albedo (A_m) of the monitoring site was 0.15. The direction of the bright wind streaks in the lee of the craters indicates that the dominant near-surface wind direction was flowing to the west–southwest. (b) The dust event had ended by November 1, 2001 and atmospheric dust has already begun to settle covering the region in a uniform layer of dust, removing albedo features and raising the albedo to A_m=0.27. (c) Dark albedo features between craters started to reappear as the surface was beginning to be swept clean of dust by winds blowing to the west–southwest, lowering the local albedo to A_m=0.23 on January 14, 2003. (d) The monitoring site quickly darkened and by January 28, 2003 had reached A_m=0.17, almost returning to its pre-event albedo state. Bright wind streaks in the lees of craters suggest that the dominant local surface winds were to the west–southwest most of the day. Wind streaks in the lees of craters suggest that local surface winds were from the east–northeast most of the day. (e) A slight change in wind streak patterns was noted for a few weeks around March 21, 2002, signaling a change in the dominant wind direction to the southwest, but that quickly returning to the west–southwest. (f) By the following southern spring, May 5, 2003 the surface albedo had returned to A_m=0.15 and the bright wind streaks extended to the west–southwest.

Fig. 11. Visible (600 nm) wavelength atmospheric dust opacities during the 2001 planet-encircling storm as a function of the areocentric longitude of the Sun (L_s) for several regions across the planet: Elysium (30° N, 230° W), the Viking I Landing site in Chryse (22.5° N, 48° W), Claritas (20° N, 110° W), and Hellas basin (42° S, 300° W). Maximum dust opacities reached 3.7–5.0, which were higher than the visible and thermal infrared opacities observed for the 1977a planet-encircling dust storm but consistent with those observed for the 1977b storm (Pollack et al., 1979, Martin et al., 1979, Thorpe, 1981 and Zurek, 1981).

Fig. 12. Estimated exponential decay constants for the 2001 storm at the four monitoring sites.

Fig. 13. Minnaert surface albedo maps using (k=0.7) were obtained from MOC wide-angle red-filter observations well before the onset of the 2001 planet-encircling dust storm (a) February 3–22, 2000, to just prior to (b) June 1–8, 2001, to after the atmospheric dust had mostly settled (c) January 1–10, 2002. Maps show large-scale albedo changes across much of the southern hemisphere, while in the northern hemisphere changes were observed in Syrtis Major and the dark albedo feature northwest of Elysium Mons. Albedo changes are the result of the redistribution of surface dust by mass movement and by atmospheric fall-out. Maps are simple cylindrical projections with a resolution of 7.5 km pixel⁻¹.

Fig. 14. Spatial distribution of the measured surface albedo changes observed between L_s=169.0° and L_s=306° resulting from the 2001 planet-encircling dust storm, which is overlaid on an MOC red-filter global simple cylindrical albedo map from April 2002. Bin sizes range from 2° to 10°.

Fig. 15. Syrtis Major large-scale regional Minnaert albedo (k=0.7) changes observed during a one Mars year period with the red-filter wide-angle MOC at a resolution of 7.5 km pixel⁻¹: (a) June 11, 2001, (b) November 10, 2001, (c) January 1, 2002, (d) February 19, 2002, (e) November 4, 2002, (f) May 3, 2003. It took approximately one martian year for the regional surface albedo to return to approximately pre-planet-encircling dust storm state, though small-scale albedo variations still remained. The white box in (a) corresponds to the albedo monitoring site at 4.0°–6.0° N, 295.0°–297.0° W.

Fig. 16. Local Minnaert albedo (k=0.7) changes observed over Syrtis Major (4.0°–6.0° N, 295.0°–297.0° W) by the wide-angle red-filter MOC at full resolution (230 m pixel⁻¹) during the past two Mars years (2001–2002, 2003–2004) as a function of areocentric longitude of the Sun (L_s). The region went through several periods of darkening in 2001, with the most rapid being a two week period between L_s=313.0° and L_s=318.3°, resulting from either a short period of strong surface winds or the removal of the final microns of surface dust deposits. The small spike in albedo at L_s=355.0° was associated with increased water-ice cloud cover. The 2003–2004 observations showed a Syrtis Major that was darker by 0.075. Syrtis Major showed a gradual darkening from L_s=238.6° through L_s=315.3°, at a rate similar to that observed the previous year between L_s=271.3° and L_s=300.0°. A rapid brightening associated with the December 2003 regional dust event was observed between L_s=319.4° and L_s=341.4°, which raised the surface albedo to levels similar to those observed the previous Mars year. The regional dust event generated a dust veil that encircled the southern hemisphere through most of the month of January 2004.

Fig. 17. The average daily MOC instrument temperature response to changes in Mars' reflectance as a function of time measured in degrees of L_s. The 1999 instrument response follows a general seasonal trend, warming as Mars approaches the Sun and cooling as it moves further away. Temperature changes between L_s=185.0° and L_s=250.0° in 2001 result from increased atmospheric dust loading during the planet-encircling dust storm. As atmospheric dust settles, instrument temperature returns to previous year's levels.

Fig. 18. Regional dust storm activity from L_s=220.0°–229.0° in 1999. Three of the regional storms were cross-equatorial events that moved southward along the Acidalia storm track on (a) L_s=221.0° and (b) L_s=223.0° into Valles Marineris generating a storm that moved into northern Noachis (c) L_s=225.0°. The other two regional storms where observed in (d) Arcadia on L_s=226.0° and (e) along the south polar cap edge in Sirenum on L_s=228.0°. The regional storms generated a diffuse dust veil (τ_dust1.0) that encircled the planet for about two weeks. The simple cylindrical map is a mosaic of MOC wide-angle red-filter observations taken at a resolution of 7.5 km pixel⁻¹.

Fig. 19. Onset of the June–July 2003 dust event was initiated from a north-to-south cross-equatorial dust storm that moved though Isidis and Tyrrhena between L_s=211° and L_s=212°: (a) June 28, 2003, (b) June 29, 2003, and (c) June 30, 2003. Daily global maps show the extend of the regional dust storm and the planet-encircling dust cloud (“haze”) it generated on (d) July 6, 2003, which extend from 180° to 355° W. By (e) July 13, 2003 the storm had dissipated, but the diffuse dust veil it had generated had encircled the southern hemisphere between 30° and 60° S. Maps are generated from wide-angle red-filter MOC global image which are simple cylindrical projected from (a–c) 50° S–50° N, 250°–310° W, (d–e) 60° S–40° N, 0°–360° W at a resolution of 7.5 km pixel⁻¹ and mosaiced together.

Fig. 20. The dust haze generated during December 2003 was initiated by a series of five north-to-south cross-equatorial storms moving southward along the Acidalia storm track between L_s=312.3° and L_s=322.0°. The first two cross-equatorial storms were observed as local activity in Chryse on (a) the 8th of December and (b) 10th of December. (c) The second storm became regional in areal extent crossing into Margaritifer on the 12th of December. (d) By the 15th of December the regional storm covered an area from 64.3° S–20.0° N, 315.0°–132.0° W. At the same time a third storm had developed, this one in Tempe–Acidalia. (e) One sol later on the 16th of December, the new storm had moved southward along the Acidalia storm-track into Xanthe. During the next week two more cross-equatorial storms developed along the Acidalia storm track. (f) The last of these storms crossed into the southern hemisphere from Xanthe on the 25th of December, generating a second regional storm. (g) Both regional storms were quickly dissipating by the 27th of December leaving behind a diffuse dust veil (τ1.0) that would encircled much of the southern hemisphere and cause concerns for the MER-A orbital insertion. Maps are generated from wide-angle red-filter MOC global image which are simple cylindrical projected from (a–c) 30° S–30° N, 10°–70° W, (d–e) 70° S–50° N, 315°–135° W, (f–g) 90° S–30° N, 0°–360° W at a resolution of 7.5 km pixel⁻¹ and mosaiced together.

North polar baroclinic dust storms

Regional albedo changes