Effects of the MY34/2018 Global Dust Storm as Measured by MSL REMS in Gale Crater

Abstract

The Rover Environmental Monitoring Station (REMS) instrument that is onboard NASA's Mars Science Laboratory (MSL) Curiosity rover. REMS has been measuring surface pressure, air and ground brightness temperature, relative humidity, and UV irradiance since MSL's landing in 2012. In Mars Year (MY) 34 (2018) a global dust storm reached Gale Crater at L_s ~190°. REMS offers a unique opportunity to better understand the impact of a global dust storm on local environmental conditions, which complements previous observations by the Viking landers and Mars Exploration Rovers. All atmospheric variables measured by REMS are strongly affected albeit at different times. During the onset phase, the daily maximum UV radiation decreased by 90% between sols 2075 (opacity ~1) and 2085 (opacity ~8.5). The diurnal range in ground and air temperatures decreased by 35K and 56K, respectively, with also a diurnal-average decrease of ~2K and 4K respectively. The maximum relative humidity, which occurs right before sunrise, decreased to below 5%, compared with pre-storm values of up to 29%, due to the warmer air temperatures at night while the inferred water vapor abundance suggests an increase during the storm. Between sols 2085 and 2130, the typical nighttime stable inversion layer was absent near the surface as ground temperatures remained warmer than near-surface air temperatures. Finally, the frequency-domain behavior of the diurnal pressure cycle shows a strong increase in the strength of the semidiurnal and terdiurnal modes peaking after the local opacity maximum, also suggesting differences in the dust abundance inside and outside Gale.

Figure 1:

Dust deposition on the UV sensor: comparison between MSL sols 2036 (pre-storm) and 2216 (after the storm), taken by MAHLI. The images were taken at different times of sol, hence with different sun position, as evidenced by the different sun glint locations at the edges of the photodiodes. It can be seen in the zooms for both images of the same photodiode that the sensor is almost blocked by the dust, which highlights the deposition of dust over the rover due to the dust storm.

Figure 2:

Interannual comparison of the intra-seasonal (L_s = 120 – 300º) evolution as a function of solar longitude (MY color-coded) of: (a) normalized values of the daily maximum UV flux measured by the ABC channel, (b) daily mean ground temperature, (c) daily-mean near-surface air temperature, (d) daily maximum RH (generally achieved between 04:00 and 06:00 LTST), (e) water vapor volume mixing ratio inferred at the same time as the RH shown in (d), and (f) daily mean atmospheric pressure. Vertical lines show the start times of the GDS onset (sol 2075), highly dusty (sol 2085) and decay (sol 2100) phases in Gale Crater, as well as the end of the decay phase (sol 2169), as defined in Table 1.

Figure 3:

Evolution of REMS variables (sols 2060–2170) for the period encompassing the onset (sols 2075–2084), highly dusty (sols 2085–2100) and decay phases of the GDS. Daily mean, maximum, and minimum values are shown for pressure (A) and temperatures (B and E), while the relative humidity (C) and water mixing ratio (D) values correspond to values where the RH reaches its maximum (between 4:00–6:00 LTST) and their uncertainty is lower. Finally, the daily maximum UV irradiance (F) is shown normalized to the value on sol 2070. A 20-sol mobile average is also shown for each variable for a better visualization. As in Fig.2, vertical lines show the start times of the GDS onset (sol 2075), highly dusty (sol 2085) and decay (sol 2100) phases in Gale Crater.

Figure 4:

Comparison between the nominal diurnal cycle (blue asterisks) just prior to storm onset (sols 2060–2070) and the highly dusty diurnal cycle (red dots) within the highly dusty phase of the GDS (sols 2085–2095). The values for very low RH (<3%) are considered unreliable and therefore are not shown (see text). Note that the UV radiance after noon in the nominal case is strongly affected by shadows in all sols; i.e., the direct component of the sunlight is fully or partially blocked by the rover’s remote sensing mast during the ~12:00–14:00 period.

Figure 5:

(top-left): Evolution of the diurnal pressure tide amplitude (blue circles), compared to the semidiurnal (green crosses) and the terdiurnal (red points) tide amplitudes; (bottom-left): as in the top-left, but for the diurnal pressure tide phases; (top-right): difference between minimum surface and air temperatures (i.e., the difference at night) at 1.5 m above the surface; (bottom-right): difference between maximum surface and air temperatures. Moving average values are also shown for a better visualization of the trend. Mastcam opacity is included in every plot (black lines) for comparative purposes. The first vertical line indicates the onset of GDS effects in Gale, the second indicates the start of the highly-dusty phase, and the third indicates the start of the decay phase, from the REMS variables perspective.