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1. Propane Dehydrogenation to Propylene on Ni and Ni-Sn Catalysts

   Jason P. Robbins, Lotanna Ezeonu (June 2022, North American Catalysis Society Meeting (NAM-27) Conference in New York, NY in 2022)

   Jason P. Robbins, Lotanna Ezeonu, Ziyu Tang, Xiaofang Yang, Bruce E. Koel, Simon G. Podkolzin, "Propane Dehydrogenation to Propylene on Ni and Ni-Sn Catalysts", North American Catalysis Society Meeting (NAM-27) Conference in New York, NY in 2022, Presentation number Wed-GRAM-1650, https://nam.confex.com/nam/2022/meetingapp.cgi/Paper/28324 

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2. Acetic Acid Adsorption and Reactions on Pt and Ni

   Lotanna Ezeonu, Jason P. (June 2022, North American Catalysis Society Meeting (NAM-27) Conference in New York, NY in 2022)

   Lotanna Ezeonu, Jason P. Robbins, Ziyu Tang, Xiaofang Yang, Bruce E. Koel, Simon G. Podkolzin, "Acetic Acid Adsorption and Reactions on Pt and Ni", North American Catalysis Society Meeting (NAM-27) Conference in New York, NY in 2022, Presentation number Wed-P-88, https://nam.confex.com/nam/2022/meetingapp.cgi/Paper/28396 

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3. California margin temperatures modulate regional circulation and extreme summer precipitation in the desert Southwest

   https://doi.org/10.1088/1748-9326/acfd43  

   Bhattacharya, Tripti; Feng, Ran; Maupin, Christopher R.; Coats, Sloan; Brennan, Peter R.; Carter, Elizabeth (October 2023, Environmental Research Letters)

   Abstract In August 2022, Death Valley, the driest place in North America, experienced record flooding from summertime rainfall associated with the North American monsoon (NAM). Given the socioeconomic cost of these type of events, there is a dire need to understand their drivers and future statistics. Existing theory predicts that increases in the intensity of precipitation is a robust response to anthropogenic warming. Paleoclimatic evidence suggests that northeast Pacific (NEP) sea surface temperature (SST) variability could further intensify summertime NAM rainfall over the desert southwest. Drawing on this paleoclimatic evidence, we use historical observations and reanalyzes to test the hypothesis that warm SSTs on the southern California margin are linked to more frequent extreme precipitation events in the NAM domain. We find that summers with above-average coastal SSTs are more favorable to moist convection in the northern edge of the NAM domain (southern California, Arizona, New Mexico, and the southern Great Basin). This is because warmer SSTs drive circulation changes that increase moisture flux into the desert southwest, driving more frequent precipitation extremes and increases in seasonal rainfall totals. These results, which are robust across observational products, establish a linkage between marine and terrestrial extremes, since summers with anomalously warm SSTs on the California margin have been linked to seasonal or multi-year NEP marine heatwaves. However, current generation earth system models (ESMs) struggle to reproduce the observed relationship between coastal SSTs and NAM precipitation. Across models, there is a strong negative relationship between the magnitude of an ESM’s warm SST bias on the California margin and its skill at reproducing the correlation with desert southwest rainfall. Given persistent NEP SST biases in ESMs, our results suggest that efforts to improve representation of climatological SSTs are crucial for accurately predicting future changes in hydroclimate extremes in the desert southwest. 

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4. High Latitude Modulation of the Holocene North American Monsoon

   https://doi.org/10.1029/2022GL099772  

   Routson, Cody C.; Erb, Michael P.; McKay, Nicholas P. (August 2022, Geophysical Research Letters)

   Abstract The North American monsoon (NAM) is an important source of rainfall to much of Mexico and southwestern United States. Westerly winds (westerlies) can suppress monsoon circulation and impact monsoon timing, intensity, and extent. Recent Arctic warming is reducing the temperature gradient between the equator and the pole, which could weaken the westerlies; however, the implications of these changes on the NAM are uncertain. Here we present a new composite index of the Holocene NAM. We find monsoon strength reached a maximum circa 7,000 years ago and has weakened since then. Proxy observations of temperature, hydroclimate and upwelling, along with model simulations, show that the NAM was modulated by the westerlies over the Holocene. If the observed Holocene pattern holds for current warming, a weaker meridional temperature gradient and weaker westerlies could lead to a stronger future NAM. 

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5. The North American Monsoon buffers forests against the ongoing megadrought in the Southwestern United States

   https://doi.org/10.1111/gcb.16762  

   Strange, Brandon M.; Monson, Russell K.; Szejner, Paul; Ehleringer, Jim; Hu, Jia (June 2023, Global Change Biology)

   Abstract The US Southwest has been entrenched in a two‐decade‐long megadrought (MD), the most severe since 800 CE, which threatens the long‐term vitality and persistence of regional montane forests. Here, we report that in the face of record low winter precipitation and increasing atmospheric aridity, seasonal activity of the North American Monsoon (NAM) climate system brings sufficient precipitation during the height of the summer to alleviate extreme tree water stress. We studied seasonally resolved, tree‐ring stable carbon isotope ratios across a 57‐year time series (1960–2017) in 17 Ponderosa pine forests distributed across the NAM geographic domain. Our study focused on the isotope dynamics of latewood (LW), which is produced in association with NAM rains. During the MD, populations growing within the core region of the NAM operated at lower intrinsic and higher evaporative water‐use efficiencies (WUE_iand WUE_E, respectively), compared to populations growing in the periphery of the NAM domain, indicating less physiological water stress in those populations with access to NAM moisture. The disparities in water‐use efficiencies in periphery populations are due to a higher atmospheric vapor pressure deficit (VPD) and reduced access to summer soil moisture. The buffering advantage of the NAM, however, is weakening. We observed that since the MD, the relationship between WUE_iand WUE_Ein forests within the core NAM domain is shifting toward a drought response similar to forests on the periphery of the NAM. After correcting for past increases in the atmospheric CO₂concentration, we were able to isolate the LW time‐series responses to climate alone. This showed that the shift in the relation between WUE_iand WUE_Ewas driven by the extreme increases in MD‐associated VPD, with little advantageous influence on stomatal conductance from increases in atmospheric CO₂concentration. 

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