Abstract
The Turkana Jet plays a pivotal role in the meteorology of East Africa across timescales, and owes its existence to both large-scale dynamics and the representation of intricate local-scale processes. However, much of our understanding of the jet relies on reanalysis, and these along with climate models that produce important projections do not represent these local-scale processes. We systematically investigate the impact of changing model horizontal and vertical resolution in simulating the Turkana Jet, and associated local and large-scale processes. We perform simulations to coincide with the Radiosonde Investigation For the Turkana Jet (RIFTJet) campaign, enabling direct model-sonde comparisons in unprecedented detail. We find that increasing horizontal model resolution significantly increases the strength of the jet throughout the channel by up to 30%, while vertical resolution changes have little impact. Horizontal resolutions finer than 2.2 km produce a nocturnal jet ∼2 m/s stronger than observed but perform better during the day. The elevated inversion, which is strongly tied to the strength of the jet, is much better represented in resolutions as high as 1.1 km, whereas the global model at resolution O(∼10 km) is unable to produce any nocturnal elevated inversion. Predictions of jet strength are improved at higher resolution, indicating an important role of local process given that models inherit the same large-scale state. Despite further improvements at resolutions finer than 4.4 km, we recommend that 4.4 km is the minimum horizontal resolution required to capture realistic interactions between these processes. Underestimation of the Turkana Jet could cause considerable errors in moisture advection into Africa.
Abstract
Energetic electron precipitation (EEP) during substorms significantly affects ionospheric chemistry and lower-ionosphere (<100 km) conductance. Two mechanisms have been proposed to explain what causes EEP: whistler-mode wave scattering, which dominates at low latitudes (mapping to the inner magnetosphere), and magnetic field-line curvature scattering, which dominates poleward. In this case study, we analyzed a substorm event demonstrating the dominance of curvature scattering. Using ELFIN, POES, and THEMIS observations, we show that 50–1,000 keV EEP was driven by curvature scattering, initiated by an intensification and subsequent earthward motion of the magnetotail current sheet. Using a combination of Swarm, total electron content, and ELFIN measurements, we directly show the location of EEP with energies up to ∼1 MeV, which extended from the plasmapause to the near-Earth plasma sheet (PS). The impact of this strong substorm EEP on ionospheric ionization is also estimated and compared with precipitation of PS (<30 keV) electrons.
Abstract
Surface anticyclones connected to the ridge of an upper-tropospheric Rossby wave are the main dynamical drivers of mid-latitude summer heatwaves. It is, however, unclear to what extent an anomalously low zonal phase speed of the wave in the upper troposphere is necessary for persistent temperature extremes at the surface. Here, we use spectral decomposition to separate fast and slow synoptic-scale waves. A composite analysis of ERA5 reanalysis data reveals that, while in some regions heatwaves become more frequent during episodes of weak or no phase propagation, temperature extremes in other regions are commonly associated with more rapidly eastward propagating Rossby waves. Reflected in the mean heatwave duration as well, this relationship is possibly linked to a longitudinal phase preference of slow and fast waves or a meridional storm track shift. These findings open up new questions about the influence of mid-latitude dynamics on temperature extremes.
A clustering-based method for identifying and tracking squall lines
Zhao Shi, Yuxiang Wen, and Jianxin He
Atmos. Meas. Tech., 17, 4121–4135, https://doi.org/10.5194/amt-17-4121-2024, 2024
The squall line is a type of convective system. Squall lines are often associated with damaging weather, so identifying and tracking squall lines plays an important role in early meteorological disaster warnings. A clustering-based method is proposed in this article. It can identify the squall lines within the radar scanning range with an accuracy rate of 95.93 %. It can also provide the three-dimensional structure and movement tracking results for each squall line.
Uncertainties in temperature statistics and fluxes determined by sonic anemometers due to wind-induced vibrations of mounting arms
Zhongming Gao, Heping Liu, Dan Li, Bai Yang, Von Walden, Lei Li, and Ivan Bogoev
Atmos. Meas. Tech., 17, 4109–4120, https://doi.org/10.5194/amt-17-4109-2024, 2024
Using data collected from three levels of a 62 m tower, we found that both the temperature variances and sensible heat flux obtained from sonic anemometers are consistently lower, by a few percent, compared to those from fine-wire thermocouples.
An introduction of Three-Dimensional Precipitation Particles Imager (3D-PPI)
Jiayi Shi, Xichuan Liu, Lei Liu, Liying Liu, and Peng Wang
Atmos. Meas. Tech. Discuss., https://doi.org/10.5194/amt-2024-106,2024
Preprint under review for AMT (discussion: open, 0 comments)
A Three-Dimensional Precipitation Particles Imager (3D-PPI) is introduced as a novel instrument for measuring the three-dimensional shape, size, and fall velocity of the precipitation particles. The field experiment of the 3D-PPI was conducted at Tulihe, China, more than 880,000 snowflakes were recorded during a typical snowfall case lasting for 13 hours. It shows a potential application in atmospheric science, polar research, and other fields.
Characterizing hail-prone environments using convection-permitting reanalysis and overshooting top detections over south-central Europe
Antonio Giordani, Michael Kunz, Kristopher M. Bedka, Heinz Jürgen Punge, Tiziana Paccagnella, Valentina Pavan, Ines M. L. Cerenzia, and Silvana Di Sabatino
Nat. Hazards Earth Syst. Sci., 24, 2331–2357, https://doi.org/10.5194/nhess-24-2331-2024, 2024
To improve the challenging representation of hazardous hailstorms, a proxy for hail frequency based on satellite detections, convective parameters from high-resolution reanalysis, and crowd-sourced reports is tested and presented. Hail likelihood peaks in mid-summer at 15:00 UTC over northern Italy and shows improved agreement with observations compared to previous estimates. By separating ambient signatures based on hail severity, enhanced appropriateness for large-hail occurrence is found.
Consistent point data assimilation in Firedrake and Icepack
Reuben W. Nixon-Hill, Daniel Shapero, Colin J. Cotter, and David A. Ham
Geosci. Model Dev., 17, 5369–5386, https://doi.org/10.5194/gmd-17-5369-2024, 2024
Scientists often use models to study complex processes, like the movement of ice sheets, and compare them to measurements for estimating quantities that are hard to measure. We highlight an approach that ensures accurate results from point data sources (e.g. height measurements) by evaluating the numerical solution at true point locations. This method improves accuracy, aids communication between scientists, and is well-suited for integration with specialised software that automates processes.
STORM v.2: A simple, stochastic rainfall model for exploring the impacts of climate and climate change at and near the land surface in gauged watersheds
Manuel F. Rios Gaona, Katerina Michaelides, and Michael Bliss Singer
Geosci. Model Dev., 17, 5387–5412, https://doi.org/10.5194/gmd-17-5387-2024, 2024
STORM v.2 (short for STOchastic Rainfall Model version 2.0) is an open-source and user-friendly modelling framework for simulating rainfall fields over a basin. It also allows simulating the impact of plausible climate change either on the total seasonal rainfall or the storm’s maximum intensity.
The Ensemble Consistency Test: From CESM to MPAS and Beyond
Teo Price-Broncucia, Allison Baker, Dorit Hammerling, Michael Duda, and Rebecca Morrison
Geosci. Model Dev. Discuss., https//doi.org/10.5194/gmd-2024-115,2024
Preprint under review for GMD (discussion: open, 0 comments)
The Ensemble Consistency Test (ECT) and its Ultra-Fast variant (UF-ECT) have become powerful tools in the development community for the identification of unwanted changes in the Community Earth System Model (CESM). We develop a generalized setup framework to enable easy adoption of the ECT approach for other model developers and communities. This framework specifies test parameters to accurately characterize model variability and balance test sensitivity and computational cost.
Abstract
The fault zone architecture may provide reliable information about the deformations in both on-fault and off-fault media. The outer damage zones of faults may extend for kilometers and exhibit structural anisotropy, which potentially causes electrical anisotropy in rocks. Thus, electrically anisotropic structures may indicate the dimensions and extent of fault damage zones. We investigated the electrical anisotropic structure of the sinistral Altyn Tagh fault (ATF), NW China, using magnetotelluric data collected in and around the Subei Basin. Our three-dimensional resistivity model reveals widespread anisotropic anomalies at depths <∼5 km. The directions of the minimum horizontal resistivity values of the anomalies inside the Qilian Shan southeast of the ATF are dominantly subparallel to the fault traces at the surface. At deeper levels (∼15–19 km and ∼33–43 km), the anisotropic anomalies are mainly concentrated near the northern strand of the ATF (NATF) and the North Yemahe fault (NYMF) in the northeastern Subei area. The mid-lower crust (∼33–43 km) inside the Qilian Shan is characterized by isotropy or weak anisotropy with low resistivities (∼10 Ωm), which deviate significantly from the values along the NATF. Our results indicate the presence of a ∼30 km wide off-fault damage zone along the NATF and NYMF in the shallow crust that thins downward to the lower crust. We propose that the distribution of anisotropic anomalies is influenced primarily by neighboring faults. An independent deformation model could be appropriate for evaluating the relationships between the ATF and thrust faults within the Qilian Shan.
Abstract
We investigate why the North American Multi-Model Ensemble (NMME) upper-level height forecast for December–February (DJF) 2023/24 differs from the expected El Niño response. These atypical height anomalies emerged despite the fact a strong El Niño was forecast. The analysis focuses on diagnosing the NMME forecasts of DJF 2023/24 for SSTs and 200-hPa heights initialized at the beginning of November 2023 relative to other ensemble mean NMME DJF forecasts dating back to 1982. The results demonstrate that forecasts of the 200-hPa height anomalies had a large contribution from warming trends in global SSTs. It is the combination of trends and the expected El Niño teleconnection that results in the forecast height anomalies. Increasingly, for forecasts of geopotential height anomalies during the recent El Niño winters, the amplitude of trends is nearly equal to the signal from El Niño and has implications for the climatological base period selection for seasonal forecasts.
Abstract
The interaction between volcanic activity and flank instability during the Christmas Eve eruption at Mount Etna in 2018 is explored, using a mechanically consistent inverse model fitting high spatial resolution SAR data. Inversions search for fractures that may be curved and can accommodate co-eval pressure and shear stress changes. Displacements associated with the eruption result from the interaction between two intrusion sources: a buried dyke and a curved sheared intrusion that fed the eruption. Moreover, we identify that the sheared magmatic intrusion induced the observed eastward slip on the Pernicana fault, while the Fiandaca fault was undergoing stress accumulation, which was suddenly released during a M5.0 seismic event. The Fiandaca fault is determined to be listric, rooting beneath the mobile eastern flank of the volcano. This study highlights the role of curved fractures, acting as sheared intrusions or as faults, in volcanoes exhibiting flank instabilities.
Abstract
Grabens, or valleys formed during extensional tectonic events, are common but rarely observed during formation. In November 2023, inelastic surface deformation formed abruptly along Iceland's plate boundary in Grindavík. We documented graben formation in real-time through satellite mapping (InSAR), seismicity, GNSS data, repeated lidar surveys, and field mapping. Five normal faults and ∼12 fissures ruptured the surface delineating two grabens separated by a horst, a context not present in other contemporary case studies. The graben normal faults slipped rapidly (over hours) and maximum surface motions coincided with the occurrence of turbulent seismic swarms in both space and time. Although 3 eruptions took place ∼15 km northeast of Grindavík from 2021 to 2023, attributed to magma intrusions (i.e., dikes), none of these also formed grabens. Thus, the Grindavík grabens shows evidence for tectonic origins. Real-time monitoring of these phenomena provide insight into graben formation on Earth and potentially on other planets.
Abstract
State-of-the-art coupled climate models struggle to accurately simulate historical variability and trends of Antarctic sea ice, impacting their reliability for future projections. Increasing horizontal resolution is expected to improve the representation of coupled atmosphere-ice-ocean processes at high latitudes. Here, we examine the historical changes in the Antarctic sea ice area and volume in High Resolution Model Intercomparison Project simulations against satellite data sets and ocean reanalyzes to assess the benefits of increased spatial resolution. Our results do not show considerable benefits when horizontal resolutions up to 0.25° in the ocean and 25 km in the atmosphere. Limited improvements are reported in the simulated historical sea ice trends, which are nevertheless model-dependent, and associated with the use of model components with more complex sea-ice parameterizations. Given the high computational cost of climate-scale simulations at high spatial resolution, we advocate prioritizing enhancements in sea-ice physics and the interactions among model components in coupled climate simulations.
Bridging classical data assimilation and optimal transport: the 3D-Var case
Marc Bocquet, Pierre J. Vanderbecken, Alban Farchi, Joffrey Dumont Le Brazidec, and Yelva Roustan
Nonlin. Processes Geophys., 31, 335–357, https://doi.org/10.5194/npg-31-335-2024, 2024
A novel approach, optimal transport data assimilation (OTDA), is introduced to merge DA and OT concepts. By leveraging OT's displacement interpolation in space, it minimises mislocation errors within DA applied to physical fields, such as water vapour, hydrometeors, and chemical species. Its richness and flexibility are showcased through one- and two-dimensional illustrations.
Characteristic features of latitudinal manifestations of the 23–24 April 2023 geomagnetic storm
Leonid Chernogor
Ann. Geophys. Discuss., https//doi.org/10.5194/angeo-2024-9,2024
Revised manuscript under review for ANGEO (discussion: final response, 6 comments)
Ground-based magnetometer observations show that part of the near-Earth cross-tail current closed itself via the ionosphere, to which it was linked by the substorm current wedge, and manifested itself in the magnetograms acquired at high and equatorial latitude stations on the night side of the Earth. Observations suggest that the Bz interplanetary magnetic field component threshold for the formation of the substorm current wedge lies in the –(22–30) nT interval.
Abstract
Temperatures and pressures from high explosive detonations far exceed atmospheric conditions in typical combustion reactions, and consequently, detonation soot forms with physiochemical properties distinct from soot formed by combustion. In this study, samples of detonation soot from two high explosives, PBX 9502 and Composition B-3, were analyzed. Ice nucleation experiments on soot collected after controlled detonations were conducted in the laboratory to probe immersion and contact mode freezing. Samples nucleated ice at temperatures warmer than commercially available nanodiamonds, which has a mean nucleation temperature of −20.7°C. Ice nucleation rate coefficients increase rapidly by two to three orders of magnitude below −20°C for every sample. Size-selected 137 μm diameter particles produced during detonation in an ambient air atmosphere yield bimodal distributions of freezing temperature with primary and secondary nucleation modes centered at −20°C and −13°C, respectively. The presence of a secondary mode allows for enhanced ice nucleation rate coefficients (one to two orders of magnitude greater than samples without a secondary mode) at temperatures outside the influence of the primary mode (>−17°C). Given the observed onset nucleation temperatures of −9.2°C, our results imply that detonation soot of the type studied here would only need to reach an altitude of approximately 4 km to facilitate ice formation.
Abstract
The Atmospheric InfraRed Sounder (AIRS) aboard Aqua provides essential long-term data on vertical cloud fraction, particularly valuable in the Arctic region. This study offers a comprehensive assessment of Arctic vertical cloud fraction derived from AIRS through a comparison with independent ground- and space-based radar and lidar observations. In comparison to the measurements at the North Slope Alaska site, results reveal a significant underestimation of low-level cloud cover by AIRS, especially for near-surface clouds, while mid- and high-level cloud fractions show better consistency. In comparison to the satellite-based product from 3S-GEOPROF-COMB, the accuracy varies across different underlying surfaces (land vs. sea) and seasons. AIRS shows significant positive biases in mid-level cloud fraction over sea surfaces with sea ice concentration below 15%, indicating potential limitations in the cloud retrieval algorithm in regions with large sea ice variations. The issue of low-level clouds identification is primarily caused by the limited penetrating capability of infrared hyperspectral sensing and the accuracy of preceding surface and atmospheric state products, which diminish the accuracy of AIRS low-level cloud fraction.
Abstract
The Stratospheric Total Aerosol Counter (STAC) is a lightweight balloon-borne instrument that utilizes condensational growth techniques to measure the total aerosol concentration. STAC is a miniaturized version of the legacy Wyoming condensation particle counter that operated from 1974 through 2020 in the middle latitudes and polar regions, with a few measurements in the tropics. Here we provide a description of the STAC instrument and the total aerosol measurement record, demonstrating that typical total aerosol profiles exhibit a peak in number mixing ratio, with values between 800 and 2,000 particles per mg of air (mg−1), just below the lapse rate tropopause (LRT). In the tropics and middle latitudes, mixing ratios decrease above the LRT likely due to coagulation and scavenging that results in a transfer of mass to the fewer but larger aerosol particles of the Junge layer. Exceptions to this occur in the spring time in the middle latitudes where a new particle layer between 20 and 25 km is frequently observed. In the poles, total aerosol profiles exhibit two distinct features: new particle formation in austral spring, and an increasing mixing ratio above 17 km likely due to the presence of meteoric smoke that has been concentrated within the polar vortex. High observed stratospheric particle mixing ratios, in excess of 2,000 mg−1, are observed in the polar new particle layer and at the top of polar profiles.
