Search for: All records

Abstract Semidiurnal variability of alongshore currents on the inner shelf of the Southern California Bight is investigated using a 7‐year velocity and pressure time series. Analysis reveals that the ‐frequency alongshore current varies significantly over spatial scales of O(10 km), inconsistent with the expected progressive surface tide. Instead, the observed variability is attributed to the influence of a northward‐propagating, superinertial baroclinic coastal trapped wave (CTW) that generates a quasi‐barotropic flow, defined as the portion of the depth‐averaged alongshore current that is not directly driven by the surface tide. A superinertial CTW model, forced by realistic bathymetry and stratification conditions, suggests that the dominant mode of variability is likely a mode‐1 CTW with a wavelength of approximately 40 km. The observations and model also reveal that seasonal changes in stratification modulate the wavelength and phase speed of the CTW, leading to a seasonal pattern in the phasing of the quasi‐barotropic alongshore flow. These findings provide a new perspective on the complex dynamics governing semidiurnal variability of alongshore currents on the inner shelf of the Southern California Bight and highlight the importance of considering the effects of superinertial CTWs when examining coastal dynamics. 

Abstract The drag coefficient, Stanton number and Dalton number are of particular importance for estimating the surface turbulent fluxes of momentum, heat and water vapor using bulk parameterization. Although these bulk transfer coefficients have been extensively studied over the past several decades in marine and large‐lake environments, there are no studies analyzing their variability for smaller lakes. Here, we evaluated these coefficients through directly measured surface fluxes using the eddy‐covariance technique over more than 30 lakes and reservoirs of different sizes and depths. Our analysis showed that the transfer coefficients (adjusted to neutral atmospheric stability) were generally within the range reported in previous studies for large lakes and oceans. All transfer coefficients exhibit a substantial increase at low wind speeds (<3 m s⁻¹), which was found to be associated with the presence of gusts and capillary waves (except Dalton number). Stanton number was found to be on average a factor of 1.3 higher than Dalton number, likely affecting the Bowen ratio method. At high wind speeds, the transfer coefficients remained relatively constant at values of 1.6·10⁻³, 1.4·10⁻³, 1.0·10⁻³, respectively. We found that the variability of the transfer coefficients among the lakes could be associated with lake surface area. In flux parameterizations at lake surfaces, it is recommended to consider variations in the drag coefficient and Stanton number due to wind gustiness and capillary wave roughness while Dalton number could be considered as constant at all wind speeds. 

Abstract The recent IceCube detection of TeV neutrino emission from the nearby active galaxy NGC 1068 suggests that active galactic nuclei (AGNs) could make a sizable contribution to the diffuse flux of astrophysical neutrinos. The absence of TeVγ-rays from NGC 1068 indicates neutrino production in the vicinity of the supermassive black hole, where the high radiation density leads toγ-ray attenuation. Therefore, any potential neutrino emission from similar sources is not expected to correlate with high-energyγ-rays. Disk-corona models predict neutrino emission from Seyfert galaxies to correlate with keV X-rays because they are tracers of coronal activity. Using through-going track events from the Northern Sky recorded by IceCube between 2011 and 2021, we report results from a search for individual and aggregated neutrino signals from 27 additional Seyfert galaxies that are contained in the Swift's Burst Alert Telescope AGN Spectroscopic Survey. Besides the generic single power law, we evaluate the spectra predicted by the disk-corona model assuming stochastic acceleration parameters that match the measured flux from NGC 1068. Assuming all sources to be intrinsically similar to NGC 1068, our findings constrain the collective neutrino emission from X-ray bright Seyfert galaxies in the northern sky, but, at the same time, show excesses of neutrinos that could be associated with the objects NGC 4151 and CGCG 420-015. These excesses result in a 2.7σsignificance with respect to background expectations. 

Abstract While a stimulating effect of plant primary productivity on soil carbon dioxide (CO₂) emissions has been well documented, links between gross primary productivity (GPP) and wetland methane (CH₄) emissions are less well investigated. Determination of the influence of primary productivity on wetland CH₄emissions (FCH₄) is complicated by confounding influences of water table level and temperature on CH₄production, which also vary seasonally. Here, we evaluate the link between preceding GPP and subsequent FCH₄at two fens in Wisconsin using eddy covariance flux towers, Lost Creek (US‐Los) and Allequash Creek (US‐ALQ). Both wetlands are mosaics of forested and shrub wetlands, with US‐Los being larger in scale and having a more open canopy. Co‐located sites with multi‐year observations of flux, hydrology, and meteorology provide an opportunity to measure and compare lag effects on FCH₄without interference due to differing climate. Daily average FCH₄from US‐Los reached a maximum of 47.7 ηmol CH₄m⁻² s⁻¹during the study period, while US‐ALQ was more than double at 117.9 ηmol CH₄ m⁻² s⁻¹. The lagged influence of GPP on temperature‐normalized FCH₄(T_air‐FCH₄) was weaker and more delayed in a year with anomalously high precipitation than a following drier year at both sites. FCH₄at US‐ALQ was lower coincident with higher stream discharge in the wet year (2019), potentially due to soil gas flushing during high precipitation events and lower water temperatures. Better understanding of the lagged influence of GPP on FCH₄due to this study has implications for climate modeling and more accurate carbon budgeting. 

We report a study of the inelasticity distribution in the scattering of neutrinos of energy 80–560 GeV off nucleons. Using atmospheric muon neutrinos detected in IceCube’s sub-array DeepCore during 2012–2021, we fit the observed inelasticity in the data to a parameterized expectation and extract the values that describe it best. Finally, we compare the results to predictions from various combinations of perturbative QCD calculations and atmospheric neutrino flux models. Published by the American Physical Society2025