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  1. Free, publicly-accessible full text available February 1, 2025
  2. Free, publicly-accessible full text available July 1, 2024
  3. Abstract

    The peptide-like molecule cyanoformamide (NCCONH2) is the cyano (CN) derivative of formamide (NH2CHO). It is known to play a role in the synthesis of nucleic acid precursors under prebiotic conditions. In this paper, we present a tentative detection of NCCONH2 in the interstellar medium with the Atacama Large Millimeter/submillimeter Array (ALMA) archive data. 10 unblended lines of NCCONH2 were seen around 3σ noise levels toward Sagittarius B2(N1E), a position that is slightly offset from the continuum peak. The column density of NCCONH2 was estimated to be 2.4 × 1015 cm−2, and the fractional abundance of NCCONH2 toward Sgr B2(N1E) was 6.9 × 10−10. The abundance ratio between NCCONH2 and NH2CHO is estimated to be ∼0.01. We also searched for other peptide-like molecules toward Sgr B2(N1E). The abundances of NH2CHO, CH3NCO and CH3NHCHO toward Sgr B2(N1E) were about 1/10 of those toward Sgr B2(N1S), while the abundance of CH3CONH2 was only 1/20 of that toward Sgr B2(N1S).

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  4. Recent studies have shown that climate change and global warming considerably increase the risks of hurricane winds, floods, and storm surges in coastal communities. Turbulent processes in Hurricane Boundary Layers (HBLs) play a major role in hurricane dynamics and intensification. Most of the existing turbulence parameterizations in the current numerical weather prediction (NWP) models rely on the Planetary Boundary Layer (PBL) schemes. Previous studies (Zhang 2010; Momen et al. 2021) showed that there is a significant distinction between turbulence characteristics in HBLs and regular atmospheric boundary layers (ABLs) due to the strong rotational effects of hurricane flows. Nevertheless, such differences are not considered in the current schemes of NWPs, and they are primarily designed and tested for regular ABLs. In this talk, we aim to bridge this knowledge gap by conducting new hurricane simulations using the Weather Research and Forecasting (WRF) model as well as large-eddy simulations. We investigate the role of the PBL parameterizations and momentum roughness length in multiple hurricanes by probing the parameter space of the problem. Our simulations have shown that the most widely used WRF PBL schemes do not capture the hurricane intensification properly and underestimate their intensity. We will present that decreasing the roughness length close to the values of observational estimates and theoretical hurricane intensity models in high wind regimes (≳ 45 m s-1) led to significant improvements in the intensity forecasts of strong hurricanes. Furthermore, by decreasing the existing vertical diffusion values, on average more than 20% improvements in hurricane intensity forecasts were obtained compared to the default runs. Our results provide new insights into the role of turbulence parameterizations in hurricane dynamics and can be employed to improve the accuracy of real hurricane forecasts. The implications of these results and improvements for coastal resiliency and fluid-structure interactions will also be discussed. 
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    Free, publicly-accessible full text available June 7, 2024
  5. Abstract The momentum roughness length ( z 0 ) significantly impacts wind predictions in weather and climate models. Nevertheless, the impacts of z 0 parameterizations in different wind regimes and various model configurations on the hurricane size, intensity, and track simulations have not been thoroughly established. To bridge this knowledge gap, a comprehensive analysis of 310 simulations of 10 real hurricanes using the Weather Research and Forecasting (WRF) Model is conducted in comparison with observations. Our results show that the default z 0 parameterizations in WRF perform well for weak (category 1–2) hurricanes; however, they underestimate the intensities of strong (category 3–5) hurricanes. This finding is independent of model resolution or boundary layer schemes. The default values of z 0 in WRF agree with the observational estimates from dropsonde data in weak hurricanes while they are much larger than observations in strong hurricanes regime. Decreasing z 0 close to the values of observational estimates and theoretical hurricane intensity models in high wind regimes (≳45 m s −1 ) led to significant improvements in the intensity forecasts of strong hurricanes. A momentum budget analysis dynamically explained why the reduction of z 0 (decreased surface turbulent stresses) leads to stronger simulated storms. 
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  6. Free, publicly-accessible full text available July 1, 2024
  7. Abstract

    Carbon isotope biosignatures preserved in the Precambrian geologic record are primarily interpreted to reflect ancient cyanobacterial carbon fixation catalyzed by Form I RuBisCO enzymes. The average range of isotopic biosignatures generally follows that produced by extant cyanobacteria. However, this observation is difficult to reconcile with several environmental (e.g., temperature, pH, and CO2concentrations), molecular, and physiological factors that likely would have differed during the Precambrian and can produce fractionation variability in contemporary organisms that meets or exceeds that observed in the geologic record. To test a specific range of genetic and environmental factors that may impact ancient carbon isotope biosignatures, we engineered a mutant strain of the model cyanobacteriumSynechococcus elongatusPCC 7942 that overexpresses RuBisCO across varying atmospheric CO2concentrations. We hypothesized that changes in RuBisCO expression would impact the net rates of intracellular CO2fixation versus CO2supply, and thus whole‐cell carbon isotope discrimination. In particular, we investigated the impacts of RuBisCO overexpression under changing CO2concentrations on both carbon isotope biosignatures and cyanobacterial physiology, including cell growth and oxygen evolution rates. We found that an increased pool of active RuBisCO does not significantly affect the13C/12C isotopic discrimination (εp) at all tested CO2concentrations, yielding εpof ≈ 23‰ for both wild‐type and mutant strains at elevated CO2. We therefore suggest that expected variation in cyanobacterial RuBisCO expression patterns should not confound carbon isotope biosignature interpretation. A deeper understanding of environmental, evolutionary, and intracellular factors that impact cyanobacterial physiology and isotope discrimination is crucial for reconciling microbially driven carbon biosignatures with those preserved in the geologic record.

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  8. Abstract

    Marine diatoms are key primary producers across diverse habitats in the global ocean. Diatoms rely on a biophysical carbon concentrating mechanism (CCM) to supply high concentrations of CO2around their carboxylating enzyme, RuBisCO. The necessity and energetic cost of the CCM are likely to be highly sensitive to temperature, as temperature impacts CO2concentration, diffusivity, and the kinetics of CCM components. Here, we used membrane inlet mass spectrometry (MIMS) and modeling to capture temperature regulation of the CCM in the diatomPhaeodactylum tricornutum (Pt). We found that enhanced carbon fixation rates byPtat elevated temperatures were accompanied by increased CCM activity capable of maintaining RuBisCO close to CO2saturation but that the mechanism varied. At 10 and 18 °C, diffusion of CO2into the cell, driven byPt’s ‘chloroplast pump’ was the major inorganic carbon source. However, at 18 °C, upregulation of the chloroplast pump enhanced (while retaining the proportion of) both diffusive CO2and active HCO3uptake into the cytosol, and significantly increased chloroplast HCO3concentrations. In contrast, at 25 °C, compared to 18 °C, the chloroplast pump had only a slight increase in activity. While diffusive uptake of CO2into the cell remained constant, active HCO3uptake across the cell membrane increased resulting inPtdepending equally on both CO2and HCO3as inorganic carbon sources. Despite changes in the CCM, the overall rate of active carbon transport remained double that of carbon fixation across all temperatures tested. The implication of the energetic cost of thePtCCM in response to increasing temperatures was discussed.

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  9. Free, publicly-accessible full text available July 7, 2024