Planetary boundary layer (PBL) schemes parameterize unresolved turbulent mixing within the PBL and free troposphere (FT). Previous studies reported that precipitation simulation over the Amazon in South America is quite sensitive to PBL schemes and the exact relationship between the turbulent mixing and precipitation processes is, however, not disentangled. In this study, regional climate simulations over the Amazon in January-February 2019 are examined at process level to understand the precipitation sensitivity to PBL scheme. The focus is on two PBL schemes, the Yonsei University (YSU) scheme, and the asymmetric convective model v2 (ACM2) scheme, which show the largest difference in the simulated precipitation. During daytime, while the FT clouds simulated by YSU dissipate, clouds simulated by ACM2 maintain because of enhanced moisture supply due to the enhanced vertical moisture relay transport process: 1) vertical mixing within PBL transports surface moisture to the PBL top, and 2) FT mixing feeds the moisture into the FT cloud deck. Due to the thick cloud deck over Amazon simulated by ACM2, surface radiative heating is reduced and consequently the convective available potential energy (CAPE) is reduced. As a result, precipitation is weaker from ACM2. Two key parameters dictating the vertical mixing are identified, p, an exponent determining boundary layer mixing and λ, a scale dictating FT mixing. Sensitivity simulations with altered p, λ, and other treatments within YSU and ACM2 confirm the precipitation sensitivity. The FT mixing in the presence of clouds appears most critical to explain the sensitivity between YSU and ACM2.

Using the Weather Research and Forecasting (WRF) model with two planetary boundary layer schemes, ACM2 and MYNN, convection-permitting model (CPM) regional climate simulations were conducted for a 6-year period at a 15-km grid spacing covering entire South America and a nested convection-permitting 3-km grid spacing covering the Peruvian central Andes region. These two CPM simulations along with a 4-km simulation covering South America produced by National Center for Atmospheric Research, three gridded global precipitation datasets, and rain gauge data in Peru and Brazil, are used to document the characteristics of precipitation and MCSs in the Peruvian central Andes region. Results show that all km-scale simulations generally capture the spatiotemporal patterns of precipitation and MCSs at both seasonal and diurnal scales, although biases exist in aspects such as precipitation intensity and MCS frequency, size, propagation speed, and associated precipitation intensity. The 3-km simulation using MYNN scheme generally outperforms the other simulations in capturing seasonal and diurnal precipitation over the mountain, while both it and the 4-km simulation demonstrate superior performance in the western Amazon Basin, based on the comparison to the gridded precipitation products and gauge data. Dynamic factors, primarily low-level jet and terrain-induced uplift, are the key drivers for precipitation and MCS genesis along the east slope of the Andes, while thermodynamic factors control the precipitation and MCS activity in the western Amazon Basin and over elevated mountainous regions. The study suggests aspects of the model needing improvement and the choice of better model configurations for future regional climate projections.

The percentage of Geoscience students, faculty, and professionals from historically under-represented minority (URM) groups has been largely unchanged for two decades and remains significantly below general population trends. Diversifying Geosciences, and developing an equitable culture in the discipline requires faculty members (irrespective of race/ethnicity) to engage actively in JEDI (Justice-Diversity-Equity-Inclusion) efforts. Previous studies that focused broadly on faculty experiences in academia indicate that restructuring of existing faculty evaluation frameworks to better value JEDI work may help more URM faculty, researchers and students feel valued, thus enhancing diversity at all academic levels. However, such efforts may not be significantly valued in many Geoscience departments. To better understand faculty perspectives and motivations related to JEDI work, including the effects of faculty evaluation systems on behaviors, we are interviewing a range of faculty members across the US. Preliminary interviews suggest <50% of faculty in the Geoscience departments are actively involved in JEDI work and those who are, are more likely to be women and/or early career professionals. To aid to this data collection process, we will also be conducting a nation-wide survey of Geoscience faculty to better understand the value of JEDI activities in current faculty assessment (evaluations/promotion/tenure/raise etc.) frameworks, and identify potential barriers in engaging more faculty in meaningful DEI work. Using data from the interviews and survey results, we aim to develop example evaluation and reward structures that explicitly value JEDI work that can be adopted/adapted by other Geoscience departments, and to produce webinars focused on helping faculty leaders explicitly value JEDI efforts within hiring and evaluation systems.