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Andrew J. White and N. Robb McDonald

Abstract

This work examines the dynamics of point vortices in a two-layer fluid near large-amplitude, sharply varying topography like that which occurs in continental shelf regions. Topography takes the form of an infinitely long step change in depth, and the two-layer stratification is chosen such that the height of topography in the upper layer is a small fraction of the overall depth, enabling quasigeostrophic theory to be used in both layers. An analytic expression for the dispersion relation of free topographic waves in this system is found. Weak vortices are studied using linear theory and, if located in the lower layer, propagate mainly because of their image in the topography. Depending on their sign, they are able to produce significant topographic wave radiation in their wakes. Upper-layer vortices propagate much slower and produce relatively small amplitude topographic wave radiation. Contour dynamics results are used to investigate the nonlinear regions of parameter space. For lower-layer vortices, linear theory is a good approximation, but for upper-layer vortices complicated features evolve and linear theory is only valid for weak vortices.

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Danielle Newport, David B. Lobell, Balwinder-Singh, Amit K. Srivastava, Preeti Rao, Maanya Umashaanker, Ram K. Malik, Andrew McDonald, and Meha Jain

ABSTRACT

Climate change is predicted to negatively impact wheat yields across northern India, primarily as a result of increased heat stress during grain filling at the end of the growing season. One way that farmers may adapt is by sowing their wheat earlier to avoid this terminal heat stress. However, many farmers in the eastern Indo-Gangetic Plains (IGP) sow their wheat later than is optimal, likely leading to yield reductions. There is limited documentation of why farmers sow their wheat late and the potential constraints to early sowing. Our study uses data from 256 farmers in Arrah, Bihar, a region in the eastern IGP with late wheat sowing, to identify the socioeconomic, biophysical, perceptional, and management factors influencing wheat-sowing-date decisions. Despite widespread awareness of climate change, we found that farmers did not adopt strategies to adapt to warming temperatures and that wheat-sowing dates were not influenced by perceptions of climate change. Instead, we found that the most important factors influencing wheat-sowing-date decisions were irrigation type and cropping decisions during the monsoon season prior to the winter wheat growing season. Specifically, we found that using canal irrigation instead of groundwater irrigation, planting rice in the monsoon season, transplanting rice, and transplanting rice later during the monsoon season were all associated with delayed wheat sowing. These results suggest that there are system constraints to sowing wheat on time, and these factors must be addressed if farmers are to adapt wheat-sowing-date decisions in the face of warming temperatures.

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Greg M. McFarquhar, Chris Bretherton, Roger Marchand, Alain Protat, Paul J. DeMott, Simon P. Alexander, Greg C. Roberts, Cynthia H. Twohy, Darin Toohey, Steve Siems, Yi Huang, Robert Wood, Robert M. Rauber, Sonia Lasher-Trapp, Jorgen Jensen, Jeff Stith, Jay Mace, Junshik Um, Emma Järvinen, Martin Schnaiter, Andrew Gettelman, Kevin J. Sanchez, Christina S. McCluskey, Lynn M. Russell, Isabel L. McCoy, Rachel Atlas, Charles G. Bardeen, Kathryn A. Moore, Thomas C. J. Hill, Ruhi S. Humphries, Melita D. Keywood, Zoran Ristovski, Luke Cravigan, Robyn Schofield, Chris Fairall, Marc D. Mallet, Sonia M. Kreidenweis, Bryan Rainwater, John D’Alessandro, Yang Wang, Wei Wu, Georges Saliba, Ezra J. T. Levin, Saisai Ding, Francisco Lang, Son C.H. Truong, Cory Wolff, Julie Haggerty, Mike J. Harvey, Andrew Klekociuk, and Adrian McDonald

Abstract

Weather and climate models are challenged by uncertainties and biases in simulating Southern Ocean (SO) radiative fluxes that trace to a poor understanding of cloud, aerosol, precipitation and radiative processes, and their interactions. Projects between 2016 and 2018 used in-situ probes, radar, lidar and other instruments to make comprehensive measurements of thermodynamics, surface radiation, cloud, precipitation, aerosol, cloud condensation nuclei (CCN) and ice nucleating particles over the SO cold waters, and in ubiquitous liquid and mixed-phase cloudsnucleating particles over the SO cold waters, and in ubiquitous liquid and mixed-phase clouds common to this pristine environment. Data including soundings were collected from the NSF/NCAR G-V aircraft flying north-south gradients south of Tasmania, at Macquarie Island, and on the RV Investigator and RSV Aurora Australis. Synergistically these data characterize boundary layer and free troposphere environmental properties, and represent the most comprehensive data of this type available south of the oceanic polar front, in the cold sector of SO cyclones, and across seasons.

Results show a largely pristine environments with numerous small and few large aerosols above cloud, suggesting new particle formation and limited long-range transport from continents, high variability in CCN and cloud droplet concentrations, and ubiquitous supercooled water in thin, multi-layered clouds, often with small-scale generating cells near cloud top. These observations demonstrate how cloud properties depend on aerosols while highlighting the importance of confirmed low clouds were responsible for radiation biases. The combination of models and observations is examining how aerosols and meteorology couple to control SO water and energy budgets.

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