Reducing the uncertainty in projections of future ice shelf basal melting

Simulations of ice-shelf basal melting in future climate scenarios from the IPCC’s Fourth Assessment Report (AR4) have revealed a large uncertainty and the potential of a rapidly increasing basal mass loss particularly for the large cold-water ice shelves in the Ross and Weddell Seas. The large spread in model results was traced back to uncertainties in the freshwater budget on the continental shelf, which is governed by sea-ice formation. Differences in sea-ice formation, in turn, were shown to follow the regional differences between the atmospheric heat fluxes imprinted by the climate models. A more recent suite of FESOM model experiments was performed with output from two members of the newer generation of climate models engaged in the IPCC’s Fifth Assessment Report (AR5). Comparing simulations forced with output from the AR5/CMIP5 models HadGem2 and MPI-ESM, we find that projected heat fluxes and thus sea-ice formation over the Southern Ocean continental shelves have converged to an ensemble with a much smaller spread than between the AR4 experiments. For most of the modeled ice shelves, a gradual but accelerating increase of basal melt rates during the 21st century is a robust feature. Both with HadGem2 and with MPI-ESM forcing, basal melt rates for the Filchner–Ronne Ice Shelf in FESOM increase by a factor of two by the end of the 21st century in the RCP85 scenario. For the smaller, warm-water ice shelves, inter-model differences in ice-shelf basal mass loss projections are still slightly larger than differences between the scenarios RCP45 and RCP85; compared with AR4 projections, however, the model-dependent spread has been strongly reduced. Current work aims at further reducing the uncertainties arising from atmospheric forcing by using output from the regional climate model RACMO. The effect of a varying cavity geometry and the response of the grounded ice are being adressed by coupling to the RIMBay ice shelf / ice sheet model

Zenith Propulsion

Launch Vehicle Design for the FAR-Mars Competition The Zenith Propulsion team took on the challenge put forth by the Friends of Amateur Rocketry (FAR), to build and launch a rocket propelled by a liquid rocket engine. In 2018-2019, a capstone team called Tiber Designs successfully designed and tested a 1,000 lbf-thrust rocket engine, named Janus, that uses liquid oxygen and jet-A (aviationgrade kerosene) as propellants. Zenith Propulsion would design a vehicle – 21 ft long, 6 in diameter, 170 lbm loaded – that uses the Janus rocket engine to fly to a target altitude of 30,000 ft above ground level. The vehicle requires propellant tanks, an internal structure to support the tanks, a propellant feed system to direct fuel and oxidizer to the engine, an aeroshell with fins to passively stabilize the rocket in flight, a ground support system to control the launch sequence, and a parachute system to recover the rocket. The vehicle was designed and constructed and reached 82% completion in March 2020 when vehicle testing began. A simulated launch was to be performed with the vehicle in a captive vertical orientation in order to qualify all systems for launch. Due to the onset of COVID-19 related closures, the ability to perform the vehicle test, or to travel to the FAR launch site in California, became impossible. Current plans call for testing and launch efforts to resume in the Fall 2020 semester, with the support of additional funds from the URI

Launch Vehicle Design for the FAR-Mars Competition

Zenith Propulsion is constructing a launch vehicle, named Altair, to compete in a competition hosted by the Friends of Amateur Rocketry (FAR) and the Mars Society. The objective for Zenith Propulsion is to design, build and launch Altair to a qualifying altitude of 30,000 feet in the FAR-Mars competition. Altair will utilize a rocket engine that has been in development at Embry-Riddle Aeronautical University’s Prescott campus since late 2018. This engine, named Janus, uses liquid oxygen and Jet-A and is designed to deliver 1000 lbf of thrust. Altair will be launched from the FAR launch site, in Mojave, CA, on April 18th, 2020. POSTER PRESENTATION EAGLE PRIZE AWAR

The Fate of the Southern Weddell Sea Continental Shelf in a Warming Climate

Warm water of open ocean origin on the continental shelf of the Amundsen and Bellingshausen Seas causes the highest basal melt rates reported for Antarctic ice shelves with severe consequences for the ice shelf/ice sheet dynamics. Ice shelves fringing the broad continental shelf in the Weddell and Ross Seas melt at rates orders of magnitude smaller. However, simulations using coupled ice–ocean models forced with the atmospheric output of the HadCM3 SRES-A1B scenario run (CO2 concentration in the atmosphere reaches 700 ppmv by the year 2100 and stays at that level for an additional 100 years) show that the circulation in the southern Weddell Sea changes during the twenty-first century. Derivatives of Circumpolar Deep Water are directed southward underneath the Filchner–Ronne Ice Shelf, warming the cavity and dramatically increasing basal melting. To find out whether the open ocean will always continue to power the melting, the authors extend their simulations, applying twentieth-century atmospheric forcing, both alone and together with prescribed basal mass flux at the end of (or during) the SRES-A1B scenario run. The results identify a tipping point in the southern Weddell Sea: once warm water flushes the ice shelf cavity a positive meltwater feedback enhances the shelf circulation and the onshore transport of open ocean heat. The process is irreversible with a recurrence to twentieth-century atmospheric forcing and can only be halted through prescribing a return to twentieth-century basal melt rates. This finding might have strong implications for the stability of the Antarctic ice sheet