Abstract
Altitude-triggered lightning provides favorable conditions for the research of bidirectional leader system. In the summer of 2023, altitude-triggered lightning experiment was conducted on the Field Experiment Base on Lightning Sciences, China Meteorological Administration. The multifrequency radiation characteristics of bidirectional leaders and the interactions of both ends during the propagation are analyzed. Specifically, the discharge processes that produce LF-MF magnetic radiations from bidirectional leaders are revealed by high-speed images, and these LF-MF radiations correspond to the VHF radiations generated by bidirectional leaders well. Unlike the strong correlation between LF-MF radiation strengths and discharge intensities, the VHF radiation strengths exhibit significant variation even among similar-intensity discharge events, as VHF radiations correspond to the random and microscopic discharge processes associated with streamers. Furthermore, the changes in leader speed and channel brightness before and after the initiation of bidirectional leaders indicate that the development of the two ends of bidirectional leaders is mutually reinforcing.
Abstract
Satellite imagery provides a global perspective for studying river hydrology and water quality, but clouds remain a fundamental limitation of optical sensors. Explicit studies of this problem were limited to specific locations or regions. In this study, we characterize the global severity of this limitation by analyzing 22 years of daily satellite cloud cover data and modeled river discharge for a global sample 21,642 river reaches of diverse sizes and climates. Our results show that the bias in observed river discharge is highly organized in space, particularly affecting Tropical and Arctic rivers. Given the fundamental nature of this cloud limitation, optical satellites will always provide a biased representation of river conditions. We discuss several strategies to mitigate bias, including modeling, data fusion, and temporal averaging, yet these methods introduce their own challenges and uncertainties.
Abstract
During active geomagnetic periods both electrons and protons in the outer radiation belt have been frequently observed to penetrate to low L (<4). Previous studies have demonstrated systematic differences in the deep penetration of the two species of particles, most notably that the penetration of protons is observed less frequently than for electrons of the same energies. A recent study by Mei et al. (2023, https://doi.org/10.1029/2022GL101921) showed that the time-varying convection electric field contributes to the deeper penetration of low-energy electrons and that a radial diffusion-convection model can be used to reproduce the storm-time penetration of lower-energy electrons to lower L. In this study, we analyze and provide physical explanations for the different behaviors of electrons and protons in terms of their penetration depth to low L. A radial diffusion-convection model is applied for the two species with coefficients that are adjusted according to the mass-dependent relativistic effects on electron and proton drift velocity, and the different loss mechanisms included for each species. Electromagnetic ion cyclotron (EMIC) wave scattering losses for 100s of keV protons during a specific event are modeled and quantified; the results suggest that EMIC waves interacting with protons of lower energies than electrons can contribute to prevent the inward transport of the protons.
Abstract
Marine-terminating glacier fjords play a central role in the transport of oceanic heat toward ice sheets, regulating their melt. Mixing processes near glacial termini are key to this circulation but remain poorly understood. We present new summer measurements of circulation and mixing near a marine-terminating glacier with active sub-glacial discharge. 65% of the fjord's vertical overturning circulation is driven by the buoyant plume, however we newly report intense vertical and horizontal mixing in the plume's horizontal spreading phase, accounting for the remaining 35%. Buoyant plume theory supports 2%–5% of total glacial melt. Thus, most of the heat associated with vertical overturing short-circuits the glacial front. We find however that turbulence in the horizontal spreading phase redistributes the short-circuited heat back into the surface waters of the near-glacial zone. Our findings highlight the need for further research on the complex mixing processes that occur near the glacier terminus.
Abstract
We report an Arase-all sky imager (ASI) conjugate event in which the pulsating aurora (PsA) has a one-to-one correspondence with chorus bursts. Wavelet analysis displayed three peaks at ∼0.3 Hz, 4 Hz, and >10 Hz, corresponding to the main pulsation, internal modulation, and fast modulation, respectively. These correspond to the old terms of ∼5–15 s pulsations, chorus risers/elements and subelements/subpackets, respectively. Electron “microbursts” correspond to the 4-Hz peak. The internal and fast modulations are further verified by the analysis based on fast Fourier transform analyses. Moreover, the spatial distributions of the Fourier spectral amplitude show that the internal and fast modulations are well-structured within auroral patches. The above results indicate a paradigm shift away from quasilinear theory which implicitly assumes diffuse wave generation. The three time-scale modulations are consistent with coherent chorus which has been theoretically argued to lead to pitch angle transport three orders of magnitude faster.
Implementation of a brittle sea ice rheology in an Eulerian, finite-difference, C-grid modeling framework: impact on the simulated deformation of sea ice in the Arctic
Laurent Brodeau, Pierre Rampal, Einar Ólason, and Véronique Dansereau
Geosci. Model Dev., 17, 6051–6082, https://doi.org/10.5194/gmd-17-6051-2024, 2024
A new brittle sea ice rheology, BBM, has been implemented into the sea ice component of NEMO. We describe how a new spatial discretization framework was introduced to achieve this. A set of idealized and realistic ocean and sea ice simulations of the Arctic have been performed using BBM and the standard viscous–plastic rheology of NEMO. When compared to satellite data, our simulations show that our implementation of BBM leads to a fairly good representation of sea ice deformations.
A simple approach to represent precipitation-derived freshwater fluxes into nearshore ocean models: an FVCOM4.1 case study of Quatsino Sound, British Columbia
Krysten Rutherford, Laura Bianucci, and William Floyd
Geosci. Model Dev., 17, 6083–6104, https://doi.org/10.5194/gmd-17-6083-2024, 2024
Nearshore ocean models often lack complete information about freshwater fluxes due to numerous ungauged rivers and streams. We tested a simple rain-based hydrological model as inputs into an ocean model of Quatsino Sound, Canada, with the aim of improving the representation of the land–ocean connection in the nearshore model. Through multiple tests, we found that the performance of the ocean model improved when providing 60 % or more of the freshwater inputs from the simple runoff model.
TAMS: a tracking, classifying, and variable-assigning algorithm for mesoscale convective systems in simulated and satellite-derived datasets
Kelly M. Núñez Ocasio and Zachary L. Moon
Geosci. Model Dev., 17, 6035–6049, https://doi.org/10.5194/gmd-17-6035-2024, 2024
TAMS is an open-source Python-based package for tracking and classifying mesoscale convective systems that can be used to study observed and simulated systems. Each step of the algorithm is described in this paper with examples showing how to make use of visualization and post-processing tools within the package. A unique and valuable feature of this tracker is its support for unstructured grids in the identification stage and grid-independent tracking.
Global sensitivity analysis of simulated remote sensing polarimetric observations over snow
Matteo Ottaviani, Gabriel Harris Myers, and Nan Chen
Atmos. Meas. Tech., 17, 4737–4756, https://doi.org/10.5194/amt-17-4737-2024, 2024
We analyze simulated polarization observations over snow to investigate the capabilities of remote sensing to determine surface and atmospheric properties in snow-covered regions. Polarization measurements are demonstrated to aid in the determination of snow grain shape, ice crystal roughness, and the vertical distribution of impurities in the snow–atmosphere system, data that are critical for estimating snow albedo for use in climate models.
Drone CO2 measurements during the Tajogaite volcanic eruption
John Ericksen, Tobias P. Fischer, G. Matthew Fricke, Scott Nowicki, Nemesio M. Pérez, Pedro Hernández Pérez, Eleazar Padrón González, and Melanie E. Moses
Atmos. Meas. Tech., 17, 4725–4736, https://doi.org/10.5194/amt-17-4725-2024, 2024
Volcanic eruptions emit significant quantities of carbon dioxide (CO2) to the atmosphere. We present a new method for directly determining the CO2 emission from a volcanic eruption on the island of La Palma, Spain, using an unpiloted aerial vehicle (UAV). We also collected samples of the emitted CO2 and analyzed their isotopic composition. Together with the emission rate the isotopic data provide valuable information on the state of volcanic activity and the potential evolution of the eruption.
Impact and Optimization of Calibration Conditions for Air Quality Sensors in the Long-term Field Monitoring
Han Mei, Peng Wei, Meisam Ahmadi Ghadikolaei, Nirmal Kumar Gali, Ya Wang, and Zhi Ning
Atmos. Meas. Tech. Discuss., https://doi.org/10.5194/amt-2024-130,2024
Preprint under review for AMT (discussion: open, 0 comments)
Long-term field testing across diverse climatic environments is conducted to identify the optimized calibration conditions for NO2, NO, CO, and O3 electrochemical sensors. The results uncovered three factors that influence calibration performance: calibration period, concentration range, and time averaging. We developed a comprehensive framework for the best sensor calibration practices, which serves as a valuable reference for calibrating various sensor types used in air quality monitoring.
A large-scale validation of snowpack simulations in support of avalanche forecasting focusing on critical layers
Florian Herla, Pascal Haegeli, Simon Horton, and Patrick Mair
Nat. Hazards Earth Syst. Sci., 24, 2727–2756, https://doi.org/10.5194/nhess-24-2727-2024, 2024
Snowpack simulations are increasingly employed by avalanche warning services to inform about critical avalanche layers buried in the snowpack. However, validity concerns limit their operational value. We present methods that enable meaningful comparisons between snowpack simulations and regional assessments of avalanche forecasters to quantify the performance of the Canadian weather and snowpack model chain to represent thin critical avalanche layers on a large scale and in real time.
Abstract
Low Earth orbit (LEO) radio occultation|radio occultations (RO) constellations can provide global electron density profiles (EDPs) to better specify and forecast the ionosphere-thermosphere (I-T) system. To inform future RO constellation design, this study uses comprehensive Observing System Simulation Experiments (OSSEs) to assess the ionospheric specification impact of assimilating synthetic EDPs into a coupled I-T model. These OSSEs use 10 different sets of RO constellation configurations containing 6 or 12 LEO satellites with base orbit parameter combinations of 520 or 800 km altitude, and 24° or 72° inclination. The OSSEs are performed using the Ensemble Adjustment Kalman Filter implemented in the data assimilation (DA) Research Testbed and the Thermosphere-Ionosphere-Electrodynamics General Circulation Model (TIEGCM). A different I-T model is used for the nature run, the Whole Atmosphere Model-Ionosphere Plasmasphere Electrodynamics (WAM-IPE), to simulate the period of interest is the St. Patrick's Day storm on March 13–18, 2015. Errors from models and EDP retrieval are realistically accounted for in this study through distinct I-T models and by retrieving synthetic EDPs through an extension Abel inversion algorithm. OSSE assessment, using multiple metrics, finds that greater EDP spatial coverage leading to improved specification at altitudes 300 km and above, with the 520 km altitude constellations performing best due to yielding the highest observation counts. A potential performance limit is suggested with two 6-satellite constellations. Lastly, close examination of Abel inversion error impacts highlights major EDP limitations at altitudes below 200 km and dayside equatorial regions with large horizontal gradients and low electron density magnitudes.
