We present a study that is motivated by a population of water ice clouds in the Hellas Basin that has been observed by the MARs Color Imager (MARCI) instrument on the Mars Reconnaissance Orbiter ...(MRO) to persist throughout the majority of Northern Hemisphere (NH) summer. Although water ice clouds are present in Hellas at very low opacities throughout NH spring, they noticeably thicken after Ls 60° and continue to do so until their peak optical thickness is attained at Ls ~120°. They dissipate rapidly from Ls 120° to 150°, and by Ls 150°, the only clouds in Hellas are on the southern side of the basin and are indistinguishable from the polar hood clouds. We use the NASA/Ames Legacy Mars Global Climate Model (GCM), which is supported by the Agency's Mars Climate Modeling Center, to investigate the dynamical and microphysical mechanisms that control the formation and evolution of Hellas water ice clouds. We show that water is transported from the North Polar Residual Cap (NPRC) southward across the equator and into the Hellas region. Water vapor is confined down low by cloud formation in the aphelion cloud belt, thus limiting the effectiveness of transport by the zonal mean overturning circulation (i.e., the Hadley cell). Thus, contrary to the commonly held conceptual understanding that the Hadley cell controls cross-equatorial water transport during this season, we show that the southward transport of water is done primarily in the vapor phase by stationary eddies at nearly all latitudes, including across the equator. Clouds form near the surface in the basin as moist air mixes with cold polar air on the western side of Hellas and are subsequently transported clockwise around the north side of the basin by the low-level cyclonic circulation. The simulated Hellas clouds have small particle sizes (~3–5 μm), are very low, and exist as long as the NPRC is exposed.
•Clouds observed by MRO/MARCI in the Hellas Basin during NH summer form when water vapor travels from the North Polar Residual Cap (NPRC) across the equator and condenses when it mixes with the cold near-surface air in the Hellas basin.•Tropical aphelion clouds confine water vapor to low levels such that the cross-equatorial transport of total water occurs mainly in the vapor phase by stationary eddies rather than the Hadley cell.•The simulated Hellas clouds have small particle sizes (~ 3-5 microns), are very low, and exist as long as the NPRC is exposed.
In the COVID-19 pandemic, children were considered to play a major role in SARS-CoV-2 transmission similar to influenza. Thus, mitigation measures have been focused on children, impacting their ...everyday life severely. Despite this, infectivity in this age group regarding SARS-CoV-2 is not yet clarified. We performed a serology study in households with confirmed SARS-CoV-2 infection to evaluate virus transmission with focus on children and adolescents. Between January and July 2021, 341 minors and 650 adults from 300 households with a confirmed index case participated in the FamilyCoviDD19-study including serological assessment for SARS-CoV-2 antibodies and a questionnaire on demographics, recent and ongoing symptoms, hygiene measures and comorbidities. 45 (16.3%) of all index cases were < 18 years old. Thereof, 55.6% reported COVID-19 associated symptoms, while nearly all adult index cases were symptomatic (94.8%). There was significantly less virus transmission by children and adolescents compared to adult index cases with a secondary attack rate of 0.29 vs. 0.54. With the caveat that the results do not necessarily apply to the Delta and Omicron variants, we conclude that children and adolescents are less susceptible for SARS-CoV-2 infection, more frequently show an asymptomatic course of disease and are less infective than adults.
Nine simulations are used to predict the meteorology and aeolian activity of the Mars 2020 landing site region. Predicted seasonal variations of pressure and surface and atmospheric temperature ...generally agree. Minimum and maximum pressure is predicted at
Ls
∼
145
∘
and
250
∘
, respectively. Maximum and minimum surface and atmospheric temperature are predicted at
Ls
∼
180
∘
and
270
∘
, respectively; i.e., are warmest at northern fall equinox not summer solstice. Daily pressure cycles vary more between simulations, possibly due to differences in atmospheric dust distributions. Jezero crater sits inside and close to the NW rim of the huge Isidis basin, whose daytime upslope (∼east-southeasterly) and nighttime downslope (∼northwesterly) winds are predicted to dominate except around summer solstice, when the global circulation produces more southerly wind directions. Wind predictions vary hugely, with annual maximum speeds varying from 11 to
19
ms
−
1
and daily mean wind speeds peaking in the first half of summer for most simulations but in the second half of the year for two. Most simulations predict net annual sand transport toward the WNW, which is generally consistent with aeolian observations, and peak sand fluxes in the first half of summer, with the weakest fluxes around winter solstice due to opposition between the global circulation and daytime upslope winds. However, one simulation predicts transport toward the NW, while another predicts fluxes peaking later and transport toward the WSW. Vortex activity is predicted to peak in summer and dip around winter solstice, and to be greater than at InSight and much greater than in Gale crater.
Observations by the Compact Reconnaissance Imaging Spectrometer (CRISM) onboard the Mars Reconnaissance Orbiter (MRO) over the range 440–2920 nm of the very dusty Martian atmosphere of the 2007 ...planet‐encircling dust event are combined with those made by both Mars Exploration Rovers (MERs) to better characterize the single scattering albedo (ω0) of Martian dust aerosols. Using the diagnostic geometry of the CRISM emission phase function (EPF) sequences and the “ground truth” connection provided at both MER locations allows one to more effectively isolate the single scattering albedo (ω0). This approach eliminates a significant portion of the type of uncertainty involved in many of the earlier radiative transfer analyses. Furthermore, the use of a “first principles” or microphysical representation of the aerosol scattering properties offers a direct path to produce a set of complex refractive indices (m = n + ik) that are consistent with the retrieved ω0 values. We consider a family of effective particle radii: 1.2, 1.4, 1.6, and 1.8 μm. The resulting set of model data comparisons, ω0, and m are presented along with an assessment of potential sources of error and uncertainty. We discuss our results within the context of previous work, including the apparent dichotomy of the literature values: “dark” (solar band ω0 = 0.89–0.90) and “bright” (solar band ω0 = 0.92–0.94). Previous work suggests that a mean radius of 1.8 μm is representative for the conditions sampled by the CRISM observations. Using the m for this case and a smaller effective particle radius more appropriate for diffuse dust conditions (1.4 μm), we examine EPF‐derived optical depths relative to the MER 880 nm optical depths. Finally, we explore the potential impact of the resulting brighter solar band ω0 of 0.94 to atmospheric temperatures in the planetary boundary layer.
Abstract
The dust cycle is the dominant driver of meteorology and climate on present-day Mars. Despite this, few studies have investigated the impact of dust interacting with incoming stellar ...radiation on the climate, habitability, and potential spectral signature of Mars-like exo-land planets. Dust availability is positively correlated with increasing soil aridity and therefore dust has significant potential to modify dynamics on dry land planets. In this work, we use an advanced Mars general circulation model to study the coupling between radiatively active dust and land planet climate at different stellar heating rates or planetary orbits. We find that radiatively active dust can significantly modify land planet climate. At Earth orbit, dust with optical properties similar to present-day Mars warms the planetary surface above 273 K and augments both the zonal mean circulation and the thermal tide, and in particular the semidiurnal component. As dust accumulates, peak heating rises off the planetary surface and the most active regions of dust lifting shift from the summer to winter hemisphere. Simulated spectra are nearly featureless across all wavelengths. We find that in order to accurately assess the climate and habitability of land planets it is critical to carefully consider that potential atmospheric dust budget and its radiative impact.
We describe and document the physics packages in the legacy NASA/Ames Mars Global Climate Model, present simulations of the seasonal water cycle and how it compares with observations, assess the role ...of radiatively active clouds on the water cycle and planetary eddies, and discuss the strengths and weakness of the model and the implication for future efforts. The physics packages we describe include the treatment of surface properties, the ground temperature model, planetary boundary layer scheme, sublimation physics, cloud microphysics, the use of a moment method for tracer transport, a semi-interactive dust tracking scheme, and a two-stream radiative transfer code based on correlated-k's. With virtually no tuning of the water cycle and assuming the north polar residual water ice cap is the only source of water we find the model gives a reasonably good simulation of the present seasonal water cycle. No persistent clouds form over the residual cap, seasonal variations in column vapor abundances are similar to those observed, the aphelion cloud belt has about the right opacity, and surface and air temperatures are in reasonably good agreement with observations. The radiative effect of clouds does not significantly alter the seasonal and spatial variation of the moisture fields, though the clouds are thicker and the atmosphere somewhat wetter. As others have found cloud radiative forcing amplifies the mean meridional circulation, transient baroclinic eddies, and global thermal tides. However, it also changes the characteristics of forced stationary waves in ways that are not straightforward to understand. The main weakness of the model, we believe, is sluggish vertical mixing. Water is not transported high enough in the model and as a consequence the water cycle is too dry, the aphelion cloud belt is too low, and the mean meridional circulation is too shallow. These, we feel, could be remedied by some combination of non-local mixing, deep mountain-induced circulations, better horizontal and vertical resolution, and/or gravity wave drag. Efforts are now underway to study these issues as we are transitioning away from our legacy code to one with a more modern dynamical core.
•Full documentation of the NASA/Ames Legacy Mars Global Circulation Model is provided.•Simulations of the present water cycle are in reasonable agreement with available observations.•The radiative effects of clouds on each of major component of the global circulation are assessed.•The overall dryness of the model may be caused by weak vertical transport.
•Feedbacks between the dust and water cycles play a key role in Mars’ climate.•Feedbacks result in the redistribution of dust and increased polar warming.•The enhanced polar warming is more ...consistent with MRO/MCS observations.
Mars Global Climate Model (MGCM) simulations are carried out with and without cloud radiative forcing to investigate feedbacks between the dust and water cycles that contribute to the middle-atmosphere polar warming during northern hemisphere summer. Compared to the simulation without clouds, the simulation with clouds produces stronger polar warming, which is in better agreement with observations. The enhanced polar warming in the presence of cloud formation is caused by a radiative-dynamic feedback between a strengthened circulation due to cloud radiative effects, vertical dust transport, and further circulation intensification.
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