Local Dust Storms Research Articles

Long-Term Wind and Air Temperature Patterns in the Southeastern Region of Iran through Model Simulation and Ground Observations

Dust storms are one of the important natural hazards that affect the lives of inhabitants all around the world, especially in North Africa and the Middle East. In this study, wind speed, wind direction, and air temperature patterns are investigated in one of the dustiest cities in Sistan Basin, Zahedan City, located in southeast Iran, over a 17-year period (2004–2020) using a WRF model and ground observation data. The city is located near a dust source and is mostly affected by local dust storms. The World Meteorology Organization (WMO) dust-related codes show that the city was affected by local dust, with 52 percent of the total dust events occurring during the period (2004–2021). The city’s weather station reported that 17.5% and 43% were the minimum and maximum dusty days, respectively, during 2004–2021. The summer and July were considered the dustiest season and month in the city. Since air temperature, wind speed, and wind direction are important factors in dust rising and propagation, these meteorological factors were simulated using the Weather Research and Forecasting (WRF) model for the Zahedan weather station. The WRF model’s output was found to be highly correlated with the station data; however, the WRF simulation mostly overestimated when compared with station data during the study period (2004–2020). The model had a reasonable performance in wind class frequency distribution at the station, demonstrating that 42.6% of the wind was between 0.5 and 2, which is in good agreement with the station data (42% in the range of 0.5–2). So, the WRF model effectively simulated the wind class frequency distribution and the wind direction at Zahedan station, despite overestimating the wind speed as well as minimum, maximum, and average air temperatures during the 17-year period.

Investigation of Levar wind by WRF model in Zabol City (Southeast Iran) in 17 years duration (2005-2021)

Dust particles are one of the most important aerosol types with various effects on atmospheric dynamics and thermodynamics, weather phenomena, atmospheric chemistry, air pollution and human health. In this study, both wind speed and direction are simulated by the WRF model in one of the dustiest cities, Zabol City, in east Iran during a 17 years period (2005-2021). The city was chosen because it’s located in a dust source and is mostly affected by local dust storms. The dust frequency is very high and at least one third of the year, dust-related codes are reported at the weather station of the city. Also, a high number of dust events occurs from May to September that is in coincidence with the Levar wind. Since both wind speed and wind direction are one of important factors in dust rising and propagation, especially near the dust sources, these parameters were simulated by WRF model in this study. WRF model well simulated both the wind direction and the wind class frequency distribution at Zabol station, while the model mostly overestimated the wind speed during the 17 years period.

Sub‐Hourly Observations of Dust Storm Growth, Lee Waves, and Lyot Crater, by the EMM Camera EXI

AbstractWe explore a sequence of 13 unique high‐cadence images of a dust storm, from the Emirates Mars Mission (EMM). The Emirates eXploration Imager camera took these images in less than 8 hr on 18 December 2022 (Martian Year 36, solar longitude 356°). Most of these images are separated by a time difference of half an hour. The region of interest extends from Lyot crater to the east. During the morning, the EMM images show lee waves (atmospheric gravity waves). In the late morning, the lee waves rapidly change into clearly distinct dust storm texture/convective features. We track the evolution of both lee waves and a local dust storm between sunrise and mid‐afternoon. Also, we relate our observations to atmospheric dynamics. Our analysis is supported by the Mars Climate Database and radio occultation measurement data.

Cellular patterns and dry convection in textured dust storms at the edge of Mars North Polar Cap

We present a study of textured local dust storms that develop at the northern polar cap boundary on Mars springtime. We have used images obtained with VMC and HRSC cameras onboard Mars Express and MARCI on MRO to analyze dust storms captured from March to July 2019 (Ls = 350° in MY 34–Ls = 54° in MY 35). The textured storms grow in the longitude sector 150°E-210°E centered at latitude ~60°N and exhibit spiral, filamentary and compact shapes that change and evolve rapidly in a daily basis. The storms translate by prevailing east and southeast winds with speeds 15–45 ms−1. In some areas of their interiors they show organized clusters of cells formed typically by 100 elements with sizes ~5–30 km with a length/width ratio ~ 1.2–3 in the wind direction. The cells have elongated downwind tails with lengths 4–8 times the cell size. The cells top altitudes are ~6–11 km above their surroundings. We propose that the spirals grow as baroclinic vortices within a vertically sheared eastward jet present at this epoch in Mars due to the intense meridional temperature gradient at the polar cap edge. We show using a simple one-dimensional model that the cells can be produced by shallow dry convection with dust acting as the heating source to generate the updrafts. These patterns resemble those seen in laboratory experiments and on clouds in Earth's atmosphere and can serve to comparatively elucidate and discern the different mechanisms at work in each case.

Analyses of a Lake Dust Source in the Middle East through Models Performance

Drying lakes have become a new source of dust, causing severe problems in surrounding areas. From 2000 to 2017, a statistical study was conducted on Lake Urmia in Iran in the Middle East. The results indicated a significant increase in the annual number of dusty days in stations around the lake and the mean annual aerosol optical depth (AOD) at 550 nm. The sharp decrease in annual snowfall rate over the Lake Urmia area since 2007 has been linked to the lake’s decreasing water level and drying. During a dust storm event from 27 October to 31 October 2017, a local dust storm originated from Lake Urmia before another large-scale dust storm originated from the An-Nafud desert. According to MODIS true-color images, dust particles were lifted from Lake Urmia and transported eastward to the Caspian Sea and the HYSPLIT model. The comparison of the four models under the Sand and Dust Storm Warning Advisory and Assessment System (SDS-WAS) revealed that the models overestimated surface dust concentrations compared to ground-based PM10 measurements. Nevertheless, the NOAA/WRF-Chem and DREAMABOL models simulated higher dust concentrations during the dust period. More emphasis should be placed on the development of dust models for SDS-WAS models in Lake Urmia.

Atmospheric Changes During 2021 Local Dust Storms of Mars: A Case Study Based on Tianwen-1 Reports, Mcs and Vmc

Atmospheric Changes During 2021 Local Dust Storms of Mars: A Case Study Based on Tianwen-1 Reports, Mcs and Vmc

Long-Term Variability of Dust Events in Southwestern Iran and Its Relationship with the Drought

Dust storms represent a major environmental challenge in the Middle East. The southwest part of Iran is highly affected by dust events transported from neighboring desert regions, mostly from the Iraqi plains and Saudi Arabia, as well as from local dust storms. This study analyzes the spatio-temporal distribution of dust days at five meteorological stations located in southwestern Iran covering a period of 22 years (from 1997 to 2018). Dust codes (06, 07, 30 to 35) from meteorological observations are analyzed at each station, indicating that 84% of the dust events are not of local origin. The average number of dust days maximizes in June and July (188 and 193, respectively), while the dust activity weakens after August. The dust events exhibit large inter-annual variability, with statistically significant increasing trends in all of five stations. Spatial distributions of the aerosol optical depth (AOD), dust loading, and surface dust concentrations from a moderate resolution imaging spectroradiometer (MODIS) and Modern-Era Retrospective analysis for Research and Applications (MERRA-2) retrievals reveal high dust accumulation over southwest Iran and surrounding regions. Furthermore, the spatial distribution of the (MODIS)-AOD trend (%) over southwest Iran indicates a large spatial heterogeneity during 2000–2018 with trends ranging mostly between −9% and 9% (not statistically significant). 2009 was the most active dust year, followed by 2011 and 2008, due to prolonged drought conditions in the fertile crescent and the enhanced dust emissions in the Iraqi plains during this period. In these years, the AOD was much higher than the 19-year average (2000 to 2018), while July 2009 was the dustiest month with about 25–30 dust days in each station. The years with highest dust activity were associated with less precipitation, negative anomalies of the vegetation health index (VHI) and normalized difference vegetation index (NDVI) over the Iraqi plains and southwest Iran, and favorable meteorological dynamics triggering stronger winds.

Vertical distribution of dust in the martian atmosphere: OMEGA/MEx limb observations

The OMEGA spectrometer on board Mars Express acquired several observations of the Martian limb that are still largely unexploited. Here, we explore the information content of these data in terms of abundance and size of the Martian atmospheric dust. We approach the dust retrievals by applying a full spherical multiple scattering Monte Carlo 1D radiative transfer code to model the 0.5–2.5 μm spectral range (VNIR and SWIR OMEGA channels), in order to derive dust effective radius and number density variation with altitude, between approx. 8 and 50 km. This is the first time this approach is applied to OMEGA limb data; therefore, we only present three study cases where water ice is below the detectability level, in order to focus on the methodological issues, assumptions, and performances before future more extensive applications. The model fully includes multiple scattering effects, which are known to be responsible for the coupling between the limb spectra taken at different altitudes and the surface. An extended three-dimensional modelling of the surface reflectance, acting as surface-shine for limb spectra, is developed. The VNIR channel is found useful in reducing the degeneracy of the radiative transfer solutions. The derived dust vertical distributions, yielding dust effective radii of the order of 0.85 ± 0.15 μm (corresponding to a modal radius rm of ~0.3 μm) between 15 and 30 km are quite in agreement with Global Circulation Models (GCMs), but the abundances lie about one order of magnitude above model predictions, as previously reported from comparison between models and Mars Climate Sounder (MCS) data. An overall agreement is in fact found with MCS data, and in one case the OMEGA-retrieved dust is compatible with a local storm rising from the Hellas basin. Such storms are not well represented in the Mars Climate Database, which provides monthly mean statistics. Our results demonstrate the capability of OMEGA limb data to quantitatively contribute to Martian dust studies, despite the complex and slow radiative transfer computation scheme required to accurately model multiple scattering in the probed spectral range. The desirable application of the retrieval method to the whole OMEGA limb dataset, also expected to help assess the occurrence of local dust storms, requires further work aimed to include water ice aerosols and possibly thermal emission. Being the first attempt to use a Monte Carlo modelling approach to OMEGA limb data, this work represents a useful benchmark for validating faster, although less accurate, radiative transfer models.

Martian water loss to space enhanced by regional dust storms

Mars has lost most of its initial water to space as atomic hydrogen and oxygen. Spacecraft measurements have determined that present-day hydrogen escape undergoes large variations with season that are inconsistent with long-standing explanations. The cause is incompletely understood, with likely contributions from seasonal changes in atmospheric circulation, dust activity and solar extreme ultraviolet input. Although some modelling and indirect observational evidence suggest that dust activity can explain the seasonal trend, no previous study has been able to unambiguously distinguish seasonal from dust-driven forcing. Here we present synoptic measurements of dust, temperature, ice, water and hydrogen on Mars during a regional dust event, demonstrating that individual dust events can boost planetary H loss by a factor of five to ten. This regional storm occurred in the declining phase of the known seasonal trend, establishing that dust forcing can override this trend to drive enhanced escape. Because similar regional storms occur in most Mars years, these storms may be responsible for a large fraction of Martian water loss and represent an important driver of Mars atmospheric evolution. Multi-spacecraft observations of temperature, dust and water ice opacities, water vapour abundances, and thermospheric hydrogen in the atmosphere of Mars during a local dust storm show that even such regional events, much more frequent than global dust storms, can boost global atmospheric escape by a factor of five to ten.

Quantitative estimation of provenance contributions to loess deposits in Eastern China and implication for paleo-dust storm activity

Improvement in the current knowledge regarding the provenance of loess deposits could clarify complex depositional processes, as well as provide new insights into the paleo-dust storm history in dust source areas. In this study, a comprehensive analysis of the size-differentiated geochemical compositions and zircon UPb ages of the examined loess deposits assisted in deepening the provenance identification of the Xiashu loess in Eastern China. It was first reported that the fine-grained components of the Xiashu loess were mainly derived from the arid region of the Asian interior via the paleo-dust storms, as supported by consistent geochemical compositions of <5 μm components between the Xiashu loess and the Luochuan loess. It has been demonstrated that the geochemical compositions of the 10–20 μm and 20–50 μm components and the zircon (> 40 μm) UPb age distributions of the Xiashu loess were very similar to the Yangtze River sediments, revealing that the >10 μm components of the Xiashu loess were sourced from the local floodplains of the Yangtze River's downstream regions. Furthermore, a new method of combination of provenance results of the size-differentiated fractions and quartz grain-size contents was proposed to quantitatively estimate the Xiashu loess sources. Results of the quantitative evaluations showed that at least 82.43% of the components in the Xiashu loess were the result of nearby-source transport processes and approximately 9.64% were from distant-source transport processes. We thus conclude that the activities of local ancient dust storms dominated the aeolian deposition system in the eastern plain of the Yangtze River Delta. However, it was determined that the long-range transported dust via ancient sandstorms in Asian inland cannot be ignored because fine-grained dust has important impacts on climate, ecological environment, and human health.

Storm dust source fingerprinting for different particle size fractions using colour and magnetic susceptibility and a Bayesian un-mixing model.

In the context of the continued increased global uptake of fingerprinting procedures to explore fluvial sediment sources, far less attention has been paid to dust source tracing and especially using different particle size fractions and low-cost tracers such as colour and magnetic susceptibility. The objective of this study, therefore, was to apportion local dust storm source contributions for the < 63-μm and 63-125-μm fractions of dust samples in a case study in central Iran. Colour and magnetic susceptibility properties were measured on 62 source samples and six dust storm samples. Statistical methods were used to select four different composite fingerprints for discriminating the dust sediment sources. These statistical approaches comprised (1) the Kruskal-Wallis H test (KW-H), (2) a combination of KW-H and discriminant function analysis (DFA), (3) a combination of KW-H and principal components and classification analysis (PCCA), and (4) a combination of KW-H and a general classification and regression tree model (GCRTM). Local dust source contributions were ascribed using a Bayesian un-mixing model using the final composite fingerprints. For both the < 63- and 63-125-μm fractions, the different composite signatures consistently suggested that alluvial fan material was the dominant source of the dust samples. The root mean square differences between the apportionment results using the different fingerprints ranged from 0.5 to 1.6% for the < 63-μm fraction and from 1.8 to 5.8% for the 63-125-μm fraction. The Wald-Wolfowitz runs test was used to compare the posterior distributions of the predicted source proportions created using the alternative final composite fingerprints and the results indicated that most of the pairwise comparisons were significantly different (p ≤ 0.05). For the < 63-μm fraction, the RMSE and MAE estimates of divergence between the modelled and known virtual source mixtures using the different final composite signatures ranged between 1.5 and 23.4% (with a corresponding mean value of 9.4%). The equivalent estimates for the 63-125-μm fraction were 1.2-20.1% (8.3%). The findings clearly demonstrate that colour and magnetic susceptibility tracers offer low-cost options for apportioning dust sources.

Variations in the Ionospheric Peak Altitude at Mars in Response to Dust Storms: 13 Years of Observations From the Mars Express Radar Sounder

AbstractPrevious observations have shown that, during Martian dust storms, the peak of the ionosphere rises in altitude. Observational studies of this type, however, have been extremely limited. Using 13 years of ionospheric peak altitude data from the Mars Advanced Radar for Subsurface and Ionosphere Sounding instrument on Mars Express, we study how the peak altitude responded to dust storms during six different Mars years (MY). The peak altitude increased ∼10–15 km during all six events, which include a local dust storm (MY 33), three regional dust storms (MYs 27, 29, and 32), and two global dust storms (MYs 28 and 34). The peak altitude's orbit‐to‐orbit variability was exceptionally large at the apexes of the MY 29 and MY 32 dust seasons and dramatically increased during the MY 28 and MY 34 global dust storms. We conclude that dust storms significantly increase upper atmospheric variability, which suggests that they enhance dynamical processes that couple the lower and upper atmospheres, such as upward propagating gravity waves or atmospheric tides.

Contribution of Iraqi and Syrian dust storms on particulate matter concentration during a dust storm episode in receptor cities: Case study of Tehran

Frequent dust storms originated from Middle Eastern deserts impact major cities in Iran, including Tehran. Previous studies identified Iraqi and Syrian deserts as the main cross-border contributors to Tehran Particulate Matter (PM) levels. In this study, the contribution of Iraqi and Syrian dust storms to Tehran's PM10 and PM2.5 concentration were assessed during a dust storm episode. Initially, a dust storm event was identified through the statistical analysis of the recorded air pollution data at Tehran's monitoring stations and the visual inspection of the satellite images. A combination of CMAQ/WRF/SMOKE modeling systems was used to simulate PM concentrations from Tehran local sources and dust storms formed in Iraq and Syria. An emission inventory of Tehran anthropogenic and biogenic pollutant sources was also developed and distributed throughout the city. In order to obtain the contribution of the different sources to Tehran PM10 and PM2.5 concentration, several sets of simulations were performed using different emission groups including local sources, Iraqi dust storms, Syrian dust storms and both Iraqi-Syrian dust storms. The results showed local emissions comprised most of the PM concentrations, however cross-border dust sources heavily influenced PM levels at all monitoring stations during the dust event. Nearly 28% of the average PM concentrations were dust particles formed in Iraq and Syria. The simulation of the dust event showed Iraqi's desert were responsible for nearly twice amount of observed PM concentrations in Tehran compared to Syria's desert during the episode. The results of this study could be used for planning effective measures to reduce dust related pollution problems in Tehran.

Characterization of a local dust storm on Mars with REMS/MSL measurements and MARCI/MRO images

The REMS instrument on board the Curiosity rover has been collecting meteorological data from Gale crater on Mars since August 2012. A dust storm that developed north of Gale crater in sol 852 of the Mars Science Laboratory (MSL) mission spread above the location of the Curiosity rover during sols 853–855 (December 30, 2014 to January 1, 2015, areocentric solar longitude Ls 263°, MY32). The storm was observed by the MARCI imaging instrument on the Mars Reconnaissance Orbiter and its effects in the local meteorology were recorded in situ by the REMS instrument on MSL. Here we present a detailed report of the effects of the storm at Gale crater. Using MARCI images, we measured the size and altitude of the dust storm, which reached a size of 482,000 km2, attained an altitude of 19 km above the ground, and dispersed through the Gale crater and its surrounding area the next sol. The dispersion of the dust from the storm was roughly in agreement with the expected values of the winds on Ls 263° from climatological values in the Mars Climate Database (MCD). REMS data show that the storm produced the following effects when the dust arrived at Gale: (1) An increase in the daily amplitude of the atmospheric pressure variation (~15 ± 3 Pa) mainly through a reduction of the daily minimum pressure (~12 Pa) in the late afternoon hours. (2) A decrease of the UV signal (~30%). (3) An unexpected increase in the temperature of the air close to the surface (~14 ± 4 K) in the early afternoon (LT~14–15). (4) A cooling of the surface near noon (~6 ± 4.5 K). The warming of local air was contrary to previous observations of effects of dust storms on the Martian surface. This could be due to the vertical distribution of dust when the storm arrived at Gale crater, which was less vertically extended than in the previous sol. However, the data does not allow for a quantitative evaluation of this hypothesis. Although the storm could be observed from orbit only over one single sol above Gale crater its effects over the local meteorology lasted longer and dissipated in a time-scale of 3 sols.

An Observational Overview of Dusty Deep Convection in Martian Dust Storms.

Deep convection, as used in meteorology, refers to the rapid ascent of air parcels in the Earth's troposphere driven by the buoyancy generated by phase change in water. Deep convection undergirds some of the Earth's most important and violent weather phenomena and is responsible for many aspects of the observed distribution of energy, momentum, and constituents (particularly water) in the Earth's atmosphere. Deep convection driven by buoyancy generated by the radiative heating of atmospheric dust may be similarly important in the atmosphere of Mars but lacks a systematic description. Here we propose a comprehensive framework for this phenomenon of dusty deep convection (DDC) that is supported by energetic calculations and observations of the vertical dust distribution and exemplary dusty deep convective structures within local, regional, and global dust storm activity. In this framework, DDC is distinct from a spectrum of weaker dusty convective activity because DDC originates from pre-existing or concurrently forming mesoscale circulations that generate high surface dust fluxes, oppose large-scale horizontal advective-diffusive processes, and are thus able to maintain higher dust concentrations than typically simulated. DDC takes two distinctive forms. Mesoscale circulations that form near Mars's highest volcanoes in dust storms of all scales can transport dust to the base of the upper atmosphere in as little as two hours. In the second distinctive form, mesoscale circulations at low elevations within regional and global dust storm activity generate freely convecting streamers of dust that are sheared into the middle atmosphere over the diurnal cycle.

Quantifying the atmospheric impact of local dust storms using a martian global circulation model

We investigate the modelled impact on the global atmosphere of local dust storm simulations on the martian atmosphere. The investigation utilises existing observations from Mars Global Surveyor’s Mars Orbiter Camera and the Thermal Emission Spectrometer instruments, and the UK version of the LMD Mars Global Circulation Model. A typical example investigated here is a local dust storm in the Terra Sirenum region centred at (40∘S, 146.5∘W), with lateral coverage of ∼2.1E+5 km2 and peak optical depth of 0.7. We find atmospheric cooling, initially mainly restricted to the planetary boundary layer, by up to 8% (-14 K) during the night of the first sol with a consequential abrupt rise (+15 K) on the following sol, compared to the pre-storm diurnal range of 175–210 K at this location. Divergent wind currents, with a high-pressure centre, develop on the first day of the storm resulting in changes in both wind components up to three times their base values (±10m∕s). Atmospheric densities above 15 km altitude exhibit a peak increase of +9% from pre-storm values, while surface pressures show less change ±3%. Dynamical changes triggered by a local dust storm are quantified and their importance are thus considered in the context of potential future Mars spacecraft missions.

Effects of Local Dust Storms on the Upper Atmosphere of Mars: Observations and Simulations

AbstractThe effects of a local dust storm on the upper atmosphere of Mars are researched through the observations of the lower and upper Martian atmosphere in the MGS (Mars Global Surveyor) radio occultation experiments. The ionosphere profiles in the high‐latitude region of northern hemisphere are thought to be under the influence of a local dust storm occurring in the low‐latitude areas during Ls 135–150°, Mars Year (MY) 27. A method to estimate the Martian upper neutral densities via the heights of ionospheric main peak is presented. Through the method, the 130‐km atmospheric neutral densities (or CO2 densities) of the area during the dust storm were calculated. MCD V4.3 (Mars Climate Database, Version 4.3) is used to derive the normal (or dust‐storm‐free) neutral densities of the same region and period. By analyzing the differences between the calculated densities and MCD (V4.3) simulated ones, the influence of the local dust storm on the upper atmosphere densities can be quantitatively derived. Based on the variation of the upper atmosphere densities, the behavior of regional ionospheric main peak under the dust storm can be simulated by a photochemical equilibrium model. The simulated ionosphere parameters are compared with the MGS‐observed ones, and it is found that two profile data sets are consistent with one another, thus indicating that the method employed to estimate the upper neutral densities is accurate.

Parameterization of Rocket Dust Storms on Mars in the LMD Martian GCM: Modeling Details and Validation

AbstractThe origin of the detached dust layers observed by the Mars Climate Sounder aboard the Mars Reconnaissance Orbiter is still debated. Spiga et al. (2013, https://doi.org/10.1002/jgre.20046) revealed that deep mesoscale convective “rocket dust storms” are likely to play an important role in forming these dust layers. To investigate how the detached dust layers are generated by this mesoscale phenomenon and subsequently evolve at larger scales, a parameterization of rocket dust storms to represent the mesoscale dust convection is designed and included into the Laboratoire de Météorologie Dynamique (LMD) Martian Global Climate Model (GCM). The new parameterization allows dust particles in the GCM to be transported to higher altitudes than in traditional GCMs. Combined with the horizontal transport by large‐scale winds, the dust particles spread out and form detached dust layers. During the Martian dusty seasons, the LMD GCM with the new parameterization is able to form detached dust layers. The formation, evolution, and decay of the simulated dust layers are largely in agreement with the Mars Climate Sounder observations. This suggests that mesoscale rocket dust storms are among the key factors to explain the observed detached dust layers on Mars. However, the detached dust layers remain absent in the GCM during the clear seasons, even with the new parameterization. This implies that other relevant atmospheric processes, operating when no dust storms are occurring, are needed to explain the Martian detached dust layers. More observations of local dust storms could improve the ad hoc aspects of this parameterization, such as the trigger and timing of dust injection.

The cascade from local to global dust storms on Mars: Temporal and spatial thresholds on thermal and dynamical feedback

We use the MarsWRF general circulation model to examine the temporal and spatial response of the atmosphere to idealized local and regional dust storm radiative heating. The ability of storms to modify the atmosphere away from the location of dust heating is a likely prerequisite for dynamical feedbacks that aid the growth of storms beyond the local scale, while the ability of storms to modify the atmosphere after the cessation of dust radiative heating is potentially important in preconditioning the atmosphere prior to large scale storms. Experiments were conducted over a range of static, prescribed storm sizes, durations, optical depth strengths, locations, and vertical extents of dust heating. Our results show that for typical sizes (order 105 km2) and durations (1–10 sols) of local dust storms, modification of the atmosphere is less than the typical variability of the unperturbed (storm-free) state. Even if imposed on regional storm length scales (order 106 km2), a 1-sol duration storm similarly does not significantly modify the background atmosphere. Only when imposed for 10 sols does a regional dust storm create a significant impact on the background atmosphere, allowing for the possibility of self-induced dynamical storm growth. These results suggest a prototype for how the subjective observational categorization of storms may be related to objective dynamical growth feedbacks that only become available to storms after they achieve a threshold size and duration, or if they grow into an atmosphere preconditioned by a prior large and sustained storm.

Textured Dust Storm Activity in NE Amazonis-SW Arcadia, Mars: Phenomenology and Dynamical Interpretation.

Dust storms are Mars's most notable meteorological phenomenon, but many aspects of their structure and dynamics remain mysterious. The cloud-top appearance of dust storms in visible imagery varies on a continuum between diffuse/hazy and textured. Textured storms contain cellular structure and/or banding, which is thought to indicate active lifting within the storm. Some textured dust storms may contain the deep convection that generates the detached dust layers observed high in Mars's atmosphere. This study focuses on textured, local dust storms in a limited area within NE Amazonis and SW Arcadia Planitiae (25°-40° N,155°-165° W) using collocated observations by instruments on board the Mars Global Surveyor (MGS) and Mars Reconnaissance Orbiter (MRO) satellites. In northern fall and winter, this area frequently experiences dust storms with a previously unreported ruffled texture that resembles wide, mixed-layer rolls in the Earth's atmosphere, a resemblance that is supported by high resolution active sounding and passive radiometry in both the near and thermal infrared. These storms are mostly confined within the atmospheric boundary layer and are rarely sources of detached dust layers. The climatology and structure of these storms is thus consistent with an underlying driver of cold air advection events related to the passage of strong baroclinic waves. While the properties of the studied region may be ideal for detecting these structures and processes, the dynamics here are likely relevant to dust storm activity elsewhere on Mars.