Engineering topics

Colaprete, A.

Publications and source records attributed to Colaprete, A..

60 records · Page 4

NASA NTRS2004

The Effect of Impacts on the Early Martian Climate

The first images returned by the Mariner 7 spacecraft of the Martian surface showed a landscape heavily scared by impacts. Mariner 9 imaging revealed geomorphic features including valley networks and outflow channels that suggest liquid water once flowed at the surface of Mars. Further evidence for water erosion and surface modification has come from the Viking Spacecraft, Mars Pathfinder, Mars Global Surveyor's (MGS) Mars Orbiter Camera (MOC), and Mars Odyssey's THEMIS instrument. In addition to network channels, this evidence includes apparent paleolake beds, fluvial fans and sedimentary layers. The estimated erosion rates necessary to explain the observed surface morphologies present a conundrum. The rates of erosion appear to be highest when the early sun was fainter and only 75% as luminous as it is today. All of this evidence points to a very different climate than what exists on Mars today. The most popular paradigm for the formation of the valley networks is that Mars had at one time a warm (T average > 273), wetter and stable climate. Possible warming mechanisms have included increased surface pressures, carbon dioxide clouds and trace greenhouse gasses. Yet to date climate models have not been able to produce a continuously warm and wet early Mars. The rates of erosion appear to correlate with the rate at which Mars was impacted thus an alternate possibility is transient warm and wet conditions initiated by large impacts. It is widely accepted that even relatively small impacts (approx. 10 km) have altered the past climate of Earth to such an extent as to cause mass extinctions. Mars has been impacted with a similar distribution of objects. The impact record at Mars is preserved in the abundance of observable craters on it surface. Impact induced climate change must have occurred on Mars.

Colaprete, A.↗

NASA NTRS2003

The NASA/Ames Mars General Circulation Model: Model Improvements and Comparison with Observations

For many years, the NASA/Ames Mars General Circulation Model (GCM) has been built around the UCLA B-grid dynamical core. An attached tracer transport scheme based on the aerosol microphysical model of Toon et al. (1988) provided a tool for studying dust storm transport and feedbacks (Murphy et al., 1995). While we still use a B-grid version of the model, the Ames group is now transitioning to the ARIES/GEOS Goddard C-grid dynamical core (Suarez and Takacs, 1995). The C-grid produces smoother fields when the model top is raised above 50 km, and has a built in transport scheme for an arbitrary number of tracers. All of our transport simulations are now carried out with the C-grid. We have also been updating our physics package. Several years ago we replaced our bulk boundary layer scheme with a level 2 type diffusive scheme, and added a multi-level soil model (Haberle et al., 2000). More recently we replaced our radiation code with a more generalized two-stream code that accounts for aerosol multiple scattering and gaseous absorption. This code gives us much more flexibility in choosing aerosol optical properties and radiatively active gases.

Haberle, R. M.↗

NASA NTRS2003

Obliquity Driven Climate Change in Mars' Recent Past

We use the NASA/Ames grid Mars general circulation model with an updated radiation code and cloud nlicrophysics scheme. To speed up the simulations, we run the model at fairly coarse resolution (7.5" latitude x 22.5" longitude). Radiation Code Fluxes and heating rates are calculated from a radiation code based on the two-stream solution to radiative transfer that fully accounts for multiple scattering in the presence of gaseous absorp- tion. The model has 12 spectral intervals. Dust and water ice scattering properties are included. For dust, we use the Ockert-Bell [9] values in the visible, and Forget [IO] values in the infrared. For ice, we can either compute them online as the cloud evolves, or we can specify them. Gaseous opacities for water vapor and CO2 are calculated from correlated k-distributions taken from full line-by-line models. Cloud Microphysics Our cloud scheme is based on momentlorder scheme in which the mass mixing ratio and number density of the cloud ensemble are the advected species. From these we obtain a mean particle size and an estimate or the particle size distribution assuming a variance) which we then divide into 8 bins. Cloud microphysics is performed in each of these bins and includes nucleation, condensation, and gravitational settling. Dust is treated as a tracer and serves as condensation nuclei. The altered size distribution is then converted back into a mean size, a mixing ratio, and a particle number density.

Haberle, R. M.↗

NASA NTRS2003

Carbon Dioxide Convection in the Martian Polar Night and Its Implications for Polar Processes

Each Martian year nearly 30% of the atmosphere is exchanged with the polar ice caps. This exchange occurs through a combination of direct surface condensation and atmospheric precipitation of carbon dioxide. It has long been thought the amount of condensation within the polar night is maintained by a balance between diabatic processes such as radiative cooling and latent heating from condensing CO2. This assumption manifests itself in Mars General Circulation Models (GCM) in such a way as to never allow the atmospheric temperature to dip below the saturation temperature of CO2. However, observations from Mars Global Surveyor (MGS) Radio Science (RS) and the Thermal Emission Spectrometer (TES) have demonstrated this assumption to be, at best, approximate. Both RS and TES observations within the polar nights of both poles indicate substantial supersaturated regions with respect to CO2. The observed temperature profiles suggest conditionally unstable regions containing planetary significant amounts of potential convective energy. Presented here are estimates of the total planetary inventory of convective available potential energy (CAPE) and the potential convective energy flux (PCEF). The values for CAPE and PCEF are derived from RS temperature profiles and compared to Mars GCM results using a new convective CO2 cloud model that allows for the formation of CAPE.

Colaprete, A.↗

NASA NTRS2003

Obliquity Driven Climate Change in Mars' Recent Past

Mars has a natural mechanism for experiencing significant climate change and redistributing surface ice. Obliquity changes alone are quite capable of moving ice into low latitudes and may provide an explanation for the many geological landforms that strongly indicate recent climate change.

Haberle, R. M.↗

NASA NTRS2002

Effects of Large Impacts on Mars: Implications for River Formation

The Martian crater record provides ample evidence of the impacts of large (> 100 km) objects. These objects create hot global debris layers meters or more in depth, cause long term warming, and are capable of melting and precipitating a significant amount of water globally. Additional information is contained in the original extended abstract.

Segura, T. L.↗