Christopher Lee

University of Toronto | U of T · Department of Physics

Crater mapping using neural networks and other automated methods has increased recently with automated Crater Detection Algorithms (CDAs) applied to planetary bodies throughout the solar system. A recent publication by Benedix et al. (2020, https://doi.org/10.1029/2019ea001005) showed high performance at small scales compared to similar automated C...

Crater mapping using neural networks and other automated methods has increased recently with automated Crater Detection Algorithms (CDAs) applied to planetary bodies throughout the solar system. A recent publication by Benedix et al. (2020) showed high performance at small scales compared to similar automated CDAs but with a net positive diameter b...

The Sun drives a semidiurnal (12-hour) thermal tide in Earth's atmosphere. Zahnle and Walker suggested that an atmospheric oscillation with period Pres ≈ 10.5 hours resonated with the Solar driving ≈600 million years ago (Ma), when the length of day (lod) was ≈21 hours. They argued that the enhanced torque balanced the Lunar tidal torque, fixing th...

A planet’s surface conditions can significantly impact its climate and habitability. In this study, we use the 3D general circulation model ExoPlaSim to systematically vary dayside land cover on a synchronously rotating, temperate rocky planet under two extreme and opposite continent configurations, in which either all of the land or all of the oce...

Inferring the climate and surface conditions of terrestrial exoplanets in the habitable zone is a major goal for the field of exoplanet science. This pursuit will require both statistical analyses of the population of habitable planets as well as in-depth analyses of the climates of individual planets. Given the close relationship between habitabil...

The discovery of a large number of terrestrial exoplanets in the habitable zones of their stars, many of which are qualitatively different from Earth, has led to a growing need for fast and flexible 3D climate models, which could model such planets and explore multiple possible climate states and surface conditions. We respond to that need by creat...

A planet's surface conditions can significantly impact its climate and habitability. In this study, we use the 3D general circulation model ExoPlaSim to systematically vary dayside land cover on a synchronously rotating, temperate rocky planet under two extreme and opposite continent configurations, in which either all of the land or all of the oce...

We present inter-annual, seasonal and regional variations in the daytime Martian convective boundary layer (CBL). Martian CBL meteorology is driven both by the effect of diurnal and seasonal cycles as well as complex Martian topography. One of the most important components of the Martian atmosphere is its dust cycle. Here, we develop a novel semi-i...

Large eddy simulation (LES) of the Martian convective boundary layer (CBL) with a Mars‐adapted version of the Weather Research and Forecasting model is used to examine the impact of aerosol dust radiative‐dynamical feedbacks on turbulent mixing. The LES is validated against spacecraft observations and prior modeling. To study dust redistribution by...

The discovery of a large number of terrestrial exoplanets in the habitable zones of their stars, many of which are qualitatively different from Earth, has led to a growing need for fast and flexible 3D climate models, which could model such planets and explore multiple possible climate states and surface conditions. We respond to that need by creat...

Inferring the climate and surface conditions of terrestrial exoplanets in the habitable zone is a major goal for the field of exoplanet science. This pursuit will require both statistical analyses of the population of habitable planets as well as in-depth analyses of the climates of individual planets. Given the close relationship between habitabil...

Crater cataloging is an important yet time-consuming part of geological mapping. We present an automated Crater Detection Algorithm (CDA) that is competitive with expert-human researchers and hundreds of times faster. The CDA uses multiple neural networks to process digital terrain model and thermal infra-red imagery to identify and locate craters...

A large number of studies have responded to the growing body of confirmed terrestrial habitable zone exoplanets by presenting models of various possible climates. However, the impact of the partial pressure of background gases such as N2 has not yet been well-explored, despite the abundance of N2 in Earth’s atmosphere and the lack of constraints on...

The published full paper can be found at https://www.researchgate.net/publication/353603588_Large_Eddy_Simulations_of_the_Dusty_Martian_Convective_Boundary_Layer_With_MarsWRF/stats

For methane emission reduction strategies in urban areas to be effective, large emitters must be identified. Recent studies in U.S. cities have highlighted the contribution of methane emissions from natural gas distribution networks and end use. We present a methane emission source identification and quantification method for the Greater Toronto Ar...

Crater cataloging is an important yet time-consuming part of geological mapping. We present an automated Crater Detection Algorithm (CDA) that is competitive with expert-human researchers and hundreds of times faster. The CDA uses multiple neural networks to process digital terrain model and thermal infra-red imagery to identify and locate craters...

As the number of known exoplanets has climbed into the thousands, efforts by theorists to understand the diversity of climates that may exist on terrestrial planets in the habitable zone have also accelerated. These efforts have ranged from analytical, to simple 0-D, 1-D, and 2-D models, to highly-sophisticated 3D global climate models (GCMs) adapt...

A large number of studies have responded to the growing body of confirmed terrestrial habitable zone exoplanets by presenting models of various possible climates. However, the impact of the partial pressure of background gases such as N$_2$ has been poorly-explored, despite the abundance of N$_2$ in Earth's atmosphere and the lack of constraints on...

Plain Language Summary Studies examining the ability of Earth‐like planets to host life have often used conditions leading to “snowball” events, where sea ice extends all the way to the equator, as a limit to the range of habitable climates. This has been based on the assumption that snowball planets are always below freezing everywhere on their su...

Impact crater cataloging is an important tool in the study of the geological history of planetary bodies in the Solar System, including dating of surface features and geologic mapping of surface processes. Catalogs of impact craters have been created by a diverse set of methods over many decades, including using visible or near infra-red imagery an...

Habitable planetary are commonly imagined to be temperate planets like Earth, with areas of open ocean and warm land. In contrast, planets with colder surfaces and permanent snowball states, where oceans are entirely ice-covered, are believed to be inhospitable. However, we show using a general circulation model that terrestrial habitable zone plan...

Mars exhibits less atmospheric variability at the solstices than it does during periods nearer the equinoxes. Much of this variability in air temperature and dust activity is attributable to a significant decrease in eastward traveling transient wave amplitudes in the lower atmosphere near the solstice. Previous versions of the Mars Weather Researc...

Observations provide increasing evidence of a methane hydrological cycle on Titan. Earth-based and Cassini-based monitoring has produced data on the seasonal variation in cloud activity and location, with clouds being observed at increasingly low latitudes as Titan moved out of southern summer. Lakes are observed at high latitudes, with far larger...

A detailed one-dimensional analysis of the energy balance in Venus atmosphere is proposed in this work, based on the Net Exchange Rate formalism that allows to identify in each altitude region the dominant energy exchanges controlling the temperature. Well-known parameters that control the temperature profile are the solar flux deposition and the c...

The formation, evolution, and structure of Venus remain a mystery more than 50 years after the first visit by a robotic spacecraft. Radar images have revealed a surface that is much younger than those of the Moon, Mercury, and Mars as well as a variety of enigmatic volcanic and tectonic features quite unlike those we are familiar with on Earth. Wha...

We explore possible mechanisms for the generation of warm, wet climates on early Mars as a result of greenhouse warming by both water vapor and periodic volcanic trace emissions. The presence of both water vapor (a strong greenhouse gas) and other trace greenhouse gases (such as SO2) in a predominantly CO2 atmosphere may act, under certain conditio...

In the context of an International Space Science Institute (ISSI) working group, we have conducted a project to compare the most recent General Circulation Models (GCMs) of the Venus atmospheric circulation. A common configuration has been decided, with simple physical parametrization for the solar forcing and the boundary layer scheme. Six models...

We present details of an approach to creating a k-distribution radiative transfer model (KDM) for use in the Martian atmosphere. Such models preserve the accuracy of more rigorous line-by-line models, but are orders of magnitude faster, and can be effectively implemented in 3-D general circulation models. The approach taken here is sufficiently gen...

We investigate the sensitivity of the circulation and thermal structure of the martian atmosphere to numerical model resolution in a general circulation model (GCM) using the martian implementation (MarsWRF) of the planetWRF atmospheric model. We provide a description of the MarsWRF GCM and use it to study the global atmosphere at horizontal resolu...

We investigate the ability of modern general circulation models (GCMs) to simulate transport in the martian atmosphere using measurements of argon as a proxy for the transport processes. Argon provides the simplest measure of transport as it is a noble gas with no sinks or sources on seasonal timescales. Variations in argon result solely from ‘free...

TitanWRF general circulation model simulations performed without sub-grid-scale horizontal diffusion of momentum produce roughly the observed amount of superrotation in Titan’s stratosphere. We compare these results to Cassini–Huygens measurements of Titan’s winds and temperatures, and predict temperature and winds at future seasons. We use angular...

The authors describe a new radiative transfer model of the Venus atmosphere (RTM) that includes optical properties from nine gases and four cloud modes between 0.1 and 260 μm. A multiple-stream discrete ordinate flux solver is used to calculate solar and atmospheric infrared fluxes with a prescribed temperature profiles and calculate radiative–conv...

Mars Odyssey observed that Argon abundance was greatly enhanced during winter solstice at southern pole in Martian atmosphere. The Argon enrichment factor can reach as high as 6-7. Several studies have examined the mechanisms that cause such enrichment. Current Mars GCMs can produce the seasonal variation of Argon enhancement to some degree. Howeve...

Observations from the Thermal Emission Spectrometer (TES) aboard the Mars Global Surveyor (MGS) are being used to constrain the evolution of a General Circulation Model of the Martian atmosphere, MarsWRF, using an ensemble Kalman filter data assimilation framework, DART. We describe the setup of MarsWRF to allow its use within the data assimilation...

With the successful Venus Express mission and future missions planned for Venus exploration in the near future, study of the Venus atmosphere has been rapidly expending in the last few years. The development of General Circulation Models (GCMs) has focused on helping researchers to understand the details of the superrotation mechanism and other int...

A condensing cloud parameterization is included in a super-rotating Venus General Circulation Model. A parameterization including condensation, evaporation and sedimentation of mono-modal sulfuric acid cloud particles is described. Saturation vapor pressure of sulfuric acid vapor is used to determine cloud formation through instantaneous condensati...

The NCAR terrestrial Weather Research and Forecast (WRF) atmospheric model has been converted into a global, planetary model. The model is fully compressible, has Coriolis and curvature treatment and has hydrostratic and non-hydrostatic options. The model has been converted for use on Venus, initally using the linearized forcing and dissipation pa...