Meteorological Instruments Research Articles

Atmospheric footnotes: Ada Lovelace on climate

This article brings to light correspondence between Augusta Ada King, Countess of Lovelace (1815–1852) and Sir John Frederick William Herschel (1792–1871) from the Royal Society archives. The 1848 letters reveal the extent of her contribution to an article authored by her husband, William King, Lord Lovelace (1805–1893), on the role of climate on crop growth. This involvement uncovers little-known facets of her scientific pursuits: her interest in the application of photography to meteorological instrumentation, her budding study of astronomy, and her development of mathematical treatments to model the environmental conditions required for plants to grow. The exchange situates Ada Lovelace in the larger context of Victorian science and reflects more widely on the complicated access of women to institutional science.

Assessing Downburst Kinematics Using Video Footage Analysis

Measurements of downburst outflows using standard meteorological instruments (e.g., anemometers) are rare due to their transient and localized nature. However, video recordings of such events are becoming more frequent. This short communication (Technical Note) study presents a new approach to estimating the kinematics of a downburst event using video footage recordings of the event. The main geometric dimensions of the event, such as downdraft diameter, cloud base height, outflow depth, and the radius of the outflow at a given moment in time, are estimated by sizing them against reference structures of known dimensions that are present in the video footage. From this analysis, and knowing the frame rate of the video recording, one can estimate the characteristic velocities in the downburst event, such as the mean downdraft velocity and the mean velocity of the radial outflow propagation. The proposed method is tested on an August 2015 downburst event that hit Tucson, Arizona, United States. The diameter of the downburst outflow increased with the time from approximately 1.10 km to 3.35 km. This range of values indicates that the event was a microburst. The mean descending velocity of downburst downdraft was 8.9 m s−1 and the horizontal velocity of outflow propagation was 17.7 m s−1. The latter velocity is similar to the measured wind gust at the nearby weather station and Doppler radar. The outflow depth is estimated at 160 m, and the cloud base height was approximately 1.24 km. Estimating the kinematics of downbursts using video footage, while subject to certain limitations, does yield a useful estimation of the main downburst kinematics that contribute to a better quantification of these localized windstorms.

MAP-IO: an atmospheric and marine observatory program on board Marion Dufresne over the Southern Ocean

Abstract. This article is devoted to the presentation of the MAP-IO observation program. This program, launched in early 2021, has enabled the observation of nearly 700 d of measurements over the Indian and Southern Ocean with the equipment of 17 meteorological and oceanographic scientific instruments on board the ship Marion Dufresne. Several observational techniques have been developed to respond to the difficulties of observations on board the ship, in particular for passive remote sensing data, as well as for quasi-autonomous data acquisition and transfer. The first measurements made it possible to draw up unprecedented climatological data of the Southern Ocean regarding the size distribution and optical thickness of aerosols, the concentration of trace gases and greenhouse gases, UV, and integrated water vapor. High-resolution observations of phytoplankton in surface waters have also shown a great variability in latitude in terms of abundance and community structure (diversity). The operational success of this program and these unique scientific results together establish a proof of concept and underline the need to transform this program into a permanent observatory. The multi-year rotations over the Indian Ocean will enable us to assess the trends and seasonal variability of phytoplankton, greenhouse gases, ozone, and marine aerosols in a sensitive and poorly documented climatic region. Without being exhaustive, MAP-IO should make it possible to better understand and assess the biological carbon pump, to study the variability of gases and aerosols in a region that is remote in relation to the main anthropogenic sources, and to monitor the transport of stratospheric ozone by the Brewer–Dobson circulation. The meteorological MAP-IO data set is publicly available at https://www.aeris-data.fr/catalogue-map-io/ (last access: 26 August 2024) (atmospheric data) and at https://doi.org/10.17882/89505 (Thyssen et al., 2022a) (phytoplankton data).

Pressure Measurements and Video Observations Near and Inside Three EF2 Tornadoes

From the spring of 2016 through the spring of 2019, three EF2-rated tornadoes were sampled with in-situ tornado probes as part of the Pressure Acoustics Recordings Inside Tornadoes Experiment. The probe meteorological instrumentation resolved the temperature, humidity, and pressure-deficit characteristics near or inside all three tornadoes. Probe recorded pressure and visual observations during each tornado event show unique attributes, including multiple strong pressure irregularities before and just after the first EF2 tornado, a rotating bowl-shaped cloud feature located some distance ahead of the second EF2 tornado, independent of the tornado core and immediate inflow layer. Pressure measurements of the bowl feature reveal a brief pressure perturbation lasting roughly 4 s as it passed near or directly over the research team before the documentation of a 41 hPa pressure deficit. During the third EF2 near in-situ deployment, pressure trace observations also reveal pressure fluctuations ahead of the tornado core lasting some 65 s before the documentation of a 13 hPa pressure deficit. These pressure measurements and video observations are consistent in location with recent ultra-high-resolution simulations of the Streamwise Vorticity Current (SVC), or more precisely, the related Vertical Vorticity Sheet (VVS) and Pressure Deficit Lobe (PDL) regions. This paper describes the measured pressure deficit traces during three EF2 tornadoes near and in situ, augmented with brief, one-of-a-kind, near and in-situ video observations of a unique bowl feature, tornado inflow, corner-flow, and tornado core regions. The recorded data and instrumentation were analyzed; results are presented and discussed.

A statistical study of precipitation on the eastern Antarctic plateau (Dome-C) using remote sensing and in-situ instrumentation.

Studying precipitation at very high latitudes is a challenge, particularly during the polar winter. Direct monitoring of ice habit and size in high latitude precipitation is crucial for validating the algorithms used to derive precipitation from radar, and for improving the climatological modeling of polar areas. The high plateau lacks long-term direct observations of precipitation. In this work, carried out at Concordia Station (Dome-C (DC), -75°S, 123°E, 3233 m a.m.s.l), the use of a depolarization LIDAR, a flatbed scanner (ICECAMERA), a microwave profiler (HAMSTRAD) and meteorological instrumentation made possible the study, over the period 2014-2021, of shape, size, height and temperature of formation of precipitation. The precipitation sources were classified into four types: ice fogs, liquid fogs, mixed-phase clouds, and cirrus. Ten representative ice habits for Dome-C were chosen. The size distribution for every habit was calculated, allowing for the estimation of the corresponding radar reflectivity. The use of W-band radars, such as CLOUDSAT, with a sensitivity of -28dB, resulted in capturing all the crystals observed in Concordia. A positive trend was observed between grain size and height in ice habits that are typical of cloud precipitation. North West (NW) and North East (NE) winds at cloud height, blowing from coastal regions, caused the majority of precipitation from clouds. The study also examined the height trend of the ice habit composition of precipitation. The ice habit composition for each of the four types of precipitation source was analyzed, and the possibility of determining the source by simply observing the precipitation was explored. This work marks the first comprehensive investigation of precipitation on the eastern Antarctic plateau.

Microphysical Characterization of Boundary Layer Ice Particles: Results from a 3-Year Measurement Campaign in Interior Alaska

Abstract A three-winter study has been conducted to better understand the relationship between atmospheric conditions and ice fog or diamond dust microphysics. Measurements were conducted east of downtown Fairbanks in interior Alaska during nonprecipitating conditions. Atmospheric conditions were measured with several weather stations around the Fairbanks region and two meteorological temperature profiler instruments (ATTEX MTP-5HE and MTP-5PE). Near-surface ice particle microphysical observations were conducted with the Particle Phase Discriminator mark 2, Karlsruhe edition (PPD-2K), instrument, which measures particles from 8 to 112 μm (sphere equivalent). Panoramic camera images were captured and saved every 10 min throughout the campaign for visual assessment of atmospheric conditions. Machine learning was used to classify both cloud particle microphysical characteristics from the PPD-2K data and to categorize boundary layer conditions using the panoramic camera images. For panoramic camera images, data were categorized as cloudy, clear, fog, snowing, and a nearby power plant plume. For the PPD-2K machine learning study, the scattering pattern images were used to identify rough surface, pristine, sublimating, and spherical particles. Three additional categories were used to identify indeterminant or saturated images. These categories and categories derived from weather station data (e.g., temperature ranges) are used to quantify ice microphysical properties under different conditions. For the complete microphysical dataset, pristine plates or columns accounted for 15.5%, 16.3% appeared to be sublimating particles, and 43.4% were complex particles with either rough surfaces or multiple branches. Although the temperature was as warm as −20°C during measurements, only 1.3% of the particles were classified as liquid. Significance Statement Boundary layer ice particles are frequently present in the near-surface atmosphere when surface temperatures drop below −20°C. Substantial human impacts can occur due to visibility degradation and deposition of particles on surfaces. Understanding particle shape, size, and phase (liquid or solid) is important for understanding those impacts. This study presents the results of a 3-yr measurement campaign in Fairbanks, Alaska, in which we relate ice particle characteristics to lower atmospheric conditions. Results should improve weather forecasting and hazard prediction.

Concrete self-healing performance using surface roughness parameters: Metrological approach

Traditional test methods for evaluating concrete self-healing performance, such as scanning electron microscopy, ultrasonic waves including velocity pulse and emissions and x-ray imaging have limited accuracy resulting from the damages during the sample preparation and capability of the instruments. Very limited work has been performed to date to conduct non-destructive evaluations using non-contact test methods, hence obtaining three-dimensional images that can evaluate the self-healing performance in cementitious materials. This study meteorological instruments to obtain three-dimensional surface profiles without any external impacts that could potentially cause damage to the concrete surface has been used. The study aims evaluate the healing efficiency and performance of the crack at different time intervals for 28 days by using different healing agents such as microcapsules, cellulose fibre and applying sodium silicate directly on the developed crack. Healing efficiency and performance assessment is conducted through the maximum visualisation featuring, crack width, depth healed product from the contact angle. Metrological selective roughness parameters such as Sa, Sq, Vvv and Smr2 values are also used to evaluate the self-healing performance at various time intervals. A comparison of the numerically obtained data, both individually and from different surface roughness parameters, indicates that crack healing occurrences can be observed when utilizing different healing agents.

A Stereo Camera Simulator for Large‐Eddy Simulations of Continental Shallow Cumulus Clouds Based on Three‐Dimensional Path‐Tracing

AbstractThe complex spatial and temporal structure of cumulus clouds complicates their representation in weather and climate models. Classic meteorological instrumentation struggles to fully capture these features. Networks of multiple high‐resolution hemispheric cameras are increasingly used to fill this data gap, and provide information on this missing multi‐dimensional spatial information. In this study, a path‐tracing algorithm is used to generate virtual camera images of resolved clouds in large‐eddy simulations (LES). These images are then used as a camera network simulator, allowing reconstructions of three‐dimensional cloud edges from the model output. Because the actual LES cloud field is fully known, the combined path‐tracing and reconstruction method can be statistically analyzed. The method is applied to LES realizations of summertime shallow cumulus at the Jülich Observatory for Cloud Evolution (JOYCE), Germany, which also routinely operates a camera network. We find that the path‐tracing method allows accurate reconstruction of up to 70% of the visible cloud edges. Additional sensitivity tests show that the method is robust for changes in its hyperparameters. The sensitivity to cloud optical thickness is also investigated, finding a cloud boundary placement error of approximately 182 m. This error can be considered typical for cloud boundary reconstruction using real stereo camera imagery. The results provide proof of principle for future use of the method for evaluating LES clouds against camera network imagery, and for further optimizing the configuration of such camera networks.

New airborne research facility observes sensitivity of cumulus cloud microphysical properties to aerosol regime over the great barrier reef

The new research aircraft, Cessna 337, is equipped with a meteorological, aerosol, and cloud microphysical instrumentation. A case study from its first campaign is presented showing the sensitivity of cumulus cloud microphysical properties to the aerosol regime over the Great Barrier Reef.

The Thunderstorms With the Greatest Lightning Densities on Earth

AbstractThe most intense thunderstorms on Earth were surveyed using the comprehensive meteorological instrumentation on the Tropical Rainfall Measuring Mission (TRMM) satellite. Expansive land‐based Mesoscale Convective Systems (MCSs) were consistently identified among the Earth's most intense thunderstorms, with their organization into many convective cells spanning a large areal extent permitting exceptional overall flash rates for these storms. In this study, we identify a new class of extreme thunderstorm. Lightning‐dense thunderstorms are relatively compact convective storms whose concentrated lightning activity hinders our ability to accurately measure their flash rates. The top storms have a flash rate of one flash spanning many seconds, as there is insufficient separation to distinguish one flash from another. While any particularly active convective cell could be capable of producing high lightning densities, we find that thunderstorms with the greatest lightning densities on Earth are found in maritime thunderstorms that have not been appreciated in prior work due to the inaccurate flash rate measurements. These storms that are mostly found throughout the Gulf of Mexico and east of South Africa (among other coastal and oceanic regions) have measured TRMM proxies for convective intensity that rival the top MCS thunderstorms, but their horizontal and vertical dimensions are small by comparison. Thus, the necessary microphysical elements for electrification processes are more highly concentrated, enabling the observed extreme lightning densities.

Atmospheric and surface observations during the Saint John River Experiment on Cold Season Storms (SAJESS)

Abstract. The amount and the phase of cold-season precipitation accumulating in the upper Saint John River (SJR) basin are critical factors in determining spring runoff, ice jams, and flooding. To study the impact of winter and spring storms on the snowpack in the upper SJR basin, the Saint John River Experiment on Cold Season Storms (SAJESS) was conducted during winter–spring 2020–2021. Here, we provide an overview of the SAJESS study area, field campaign, and data collected. The upper SJR basin represents 41 % of the entire SJR watershed and encompasses parts of the US state of Maine and the Canadian provinces of Quebec and New Brunswick. In early December 2020, meteorological instruments were co-located with an Environment and Climate Change Canada station near Edmundston, New Brunswick. This included a separate weather station for measuring standard meteorological variables, an optical disdrometer, and a micro rain radar. This instrumentation was augmented during an intensive observation period that also included upper-air soundings, surface weather observations, a multi-angle snowflake camera, and macrophotography of solid hydrometeors throughout March and April 2021. During the study, the region experienced a lower-than-average snowpack that peaked at ∼ 65 cm, with a total of 287 mm of precipitation (liquid-equivalent) falling between December 2020 and April 2021, a 21 % lower amount of precipitation than the climatological normal. Observers were present for 13 storms during which they conducted 183 h of precipitation observations and took more than 4000 images of hydrometeors. The inclusion of local volunteers and schools provided an additional 1700 measurements of precipitation amounts across the area. The resulting datasets are publicly available from the Federated Research Data Repository at https://doi.org/10.20383/103.0591 (Thompson et al., 2023). We also include a synopsis of the data management plan and a brief assessment of the rewards and challenges of conducting the field campaign and utilizing community volunteers for citizen science.

High‐Density Integrated GNSS and Hydrologic Monitoring Network for Short‐Scale Hydrogeodesy in High Mountain Watersheds

AbstractWe installed a purpose‐built network of co‐located Global Navigation Satellite System (GNSS) stations and meteorological instrumentation to investigate water storage in a high‐mountain watershed along the Idaho‐Montana border. Twelve GNSS stations are distributed across the Selway‐Lochsa watersheds at approximately 30–40 km spacing, filling a critical observational gap between localized point measurements and regional geodetic and satellite data sets. The unique coupling of geodetic and hydrologic observations in this network enables direct comparison between co‐located GNSS measurements of the elastic response of the solid Earth and local changes in measured water storage. This network is specifically designed to address questions of hydrologic storage and movement at the mountain watershed scale. Here, we describe technical details of the network and its deployment; introduce new hydrologic, meteorologic, and geodetic data sets recorded by the network; process and analyze the source data (e.g., time series of daily three‐dimensional GNSS site positions, removal of non‐hydrologic signals); and characterize basic empirical relationships between water storage, water movement, and GNSS‐inferred surface displacement. The network shows preliminary evidence for spatial differences in displacement resulting from a range of snow loads across elevations, but longer and more complete data records are needed to support these initial findings. We also provide examples of additional scientific applications of this network, including estimations of snow depth and snow water equivalent from GNSS multipath reflectometry. Finally, we consider the challenges, limitations, and opportunities of deploying GNSS and weather stations at high elevations with heavy snowpack and offer ideas for technical improvements.

Observations and modelling of the winter thunderstorm on 4 February 2022 at the Milešovka meteorological observatory

AbstractThe study analyses a winter thunderstorm that passed over the Milešovka meteorological observatory on 4 February 2022, between 2300 and 2330 UTC. Lightning was recorded directly over the observatory by both the observer and the EUCLID lightning network at 2320 UTC. To analyse the state of the atmosphere at the time when the lightning occurred, we used data from the X‐band Doppler polarimetric radar and the Ka‐band Doppler polarimetric vertical profiler, both located at the observatory. We also applied data from the Meteosat Second Generation satellite, and data from standard meteorological instruments located at the observatory. In addition, we run our cloud electrification model to simulate cloud electrification of the winter thunderstorm to find out whether the model develops conditions suitable for the occurrence of lightning and if so, under what circumstances. Our results show that the lightning appeared at the very end of the storm passage defined by high radar reflectivity. At the same time, it is clear from the radar observations that before lightning occurred, the cloud contained hydrometeors (graupel, cloud or rain water, and ice or snow) which are commonly associated with charge separation by collisions. Our analysis of the radar data also suggests that in at least several parts of the cloud the electric field was strong. Although the cloud top height was very low compared to summer storms, the model results indicate conditions suitable for lightning occurrence. However, uncertainty remains on how to properly formulate the initial conditions for model simulations for this type of storm which was shallow and occurs rarely in winter.

Extinction of high-power laser radiation under adverse weather conditions.

The propagation of laser radiation over long distances can be significantly affected by atmospheric extinction due to precipitation as well as aerosol particles and molecules. The knowledge of the contribution of precipitation is critical to the operation of a variety of laser-based systems. The study of high-power laser transmission around 1µm is of particular interest because several atmospheric transmission windows are located in this region. To investigate the effect of adverse weather conditions on laser transmission, free-space laser transmission experiments are conducted on the DLR test range in Lampoldshausen, Germany. A high-power laser with a wavelength of 1.03µm is used for the transmission measurements in combination with calibrated power monitors. Local weather conditions are continuously monitored by meteorological instruments during the experiments. Extinction coefficients are derived from transmission measurements showing that the extinction for snow is 7 times higher than for rain, and the extinction for drizzle/rain is 4 times higher than for rain at a given precipitation rate of 1mm/h. For a mixture of rain and snow, the extinction is comparable to that of rain, indicating that the water content strongly influences the optical properties and thus the extinction of laser radiation in mixed precipitation. A good relationship is found between the measured extinction coefficient and visibility for drizzle and rain and a slightly larger scatter of the data for snow. Furthermore, measured extinction coefficients are compared to the extinction coefficients based on the experimental size distributions of precipitation particles and geometric optics. A reasonable agreement is obtained for rain, with no improvement taking the forward-scattering into the detector aperture into account, and a much better agreement is obtained for snow when the forward-scattering contribution is included.

Heat budget of lake ice during a complete seasonal cycle in lake Hanzhang, northeast China

The seasonal cycle of ice formation and breakup in Lake Hanzhang, China, was monitored during the winter of 2020–2021 using a float equipped with meteorological, hydrological, and optical instruments. This lake is located in mid-latitude cold and dry climate zone. We categorized the ice season into growth, equilibrium, and melting stages. The thickness of ice increased by an average of 0.7 cm day−1 at the bottom of the ice during the growth stage, and during the equilibrium stage it was stable at 35.0 ± 0.5 cm. During the melting stage, the internal melting dominated the ice ablation (1.0 cm day−1), followed by bottom melting (0.45 cm day−1) and surface melting (0.25 cm day−1). The net short-wave and long-wave radiative fluxes dominated the heat budget throughout the seasonal cycle. Sublimation was 1.1 cm, 73% of that in the growth stage. During the melting stage, the absorbed short-wave radiative flux promoted internal melting, enlarged the porosity, and enhanced further surface melting. The frequent negative air temperature during nighttime hindered the phase changes of the lake ice surface layer. In addition, the upward sensible heat flux in the lake water body increased from 7.8 to 14.5 W m−2 due to the increased light transmittance by lake ice. The heat balance and heat fluxes in ice-covered lakes in mid-latitude dry climate have rarely been explored. The results increase the knowledge of lake ice geophysics and are also useful for calibration and validation of lake ice models.

Gamma Scientific Sets High Standards for Light Measurement

Gamma Scientific Sets High Standards for Light Measurement

Correlation analysis between fault frequency and service time of underground fluid instruments

In this paper, we make a statistical analysis of the fault information of the underground fluid instruments of 12 models in China from January 2021 to May 2022 based on the Pearson correlation coefficient, and compare the fault statistics of the meteorological three-element instruments of 3 models during the study period. The results show that: (1) The numbers of faults of the underground fluid instruments of 12 models with different service times are basically positively correlated with the numbers of the corresponding instruments, with good consistency. Moreover, the automatic observation instruments (8 models) with more than 30 units are significantly correlated at a 0.05 significance level (95% confidence level). Even at a 0.01 significance level (99% confidence level), there are 7 models (7/8) with significant correlation. (2) The positive and negative correlations between the monthly average number of faults and the corresponding service times of the underground fluid instruments of 12 models with different service times are random, and there are 9 models (75%) with no significant correlation at a 0.05 significance level (95% confidence level), while 12 models (100%) with no significant correlation at a 0.01 significance level (99% confidence level). (3) The monthly average numbers of faults of the underground fluid instruments of 12 models are basically 0.02–0.05 times/(unit·month), and the overall fault frequency is low. (4) The fault statistics results of the meteorological three-element instruments of 3 models are consistent with the characteristics of the underground fluid instruments of 12 models. In general, there is no significant correlation between the fault frequency and the service time of underground fluid instruments. (5) The results of this paper demonstrate that the service time of underground fluid instruments cannot be taken as the main reason for whether to update the instruments. Similarly, the fault frequency of the instruments cannot be taken as the main reason for the service life of the instruments in the process of formulating the service life standards of underground fluid instruments.

Open-Path Atmospheric Transmission of Diode-Pumped Alkali Lasers in Maritime and Desert Environments.

A tunable diode laser absorption spectroscopy (TDLAS) device has been developed to study long-path atmospheric transmission near diode pumped alkali laser (DPAL) emission wavelengths. By employing a single aperture and retro reflector in a mono-static configuration, the noise associated with atmospheric and platform jitter were reduced by a factor of ∼30 and the open-air path length was extended to 4.4 km and over a very broad spectral range, up to 120 cm-1. Water vapor absorption lines near the rubidium (Rb) and cesium (Cs) variants of the DPAL near 795 and 894 nm, oxygen lines near the potassium (K) DPAL near 770 nm, and water vapor absorption in the vicinity of the neodymium-doped yttrium aluminum garnet (Nd:YAG) laser 1.064 μm and chemical oxygen iodine laser (COIL) 1.3 μm lines were studied. The detection limit for path absorbance increases from ΔA = 0.0017 at 100 m path length to 0.085 for the 4.4 km path. Comparison with meteorological instruments for maritime and desert environments yields agreement for the 2.032 km path to within 1.5% for temperature, 4.5% for pressure, and 5.1% for concentration, while agreements for the 4.4 km path are within 1.4% for temperature, 7.7% for pressure, and 23.5% for concentration. An intra cavity output spectroscopy (ICOS) device was also used as a spectral reference to verify location of atmospheric lines. Implications of TDLAS collection system design on signal-to-noise (S/N) are discussed as well as the effect of path turbulence on baseline noise and inform the selection of the DPAL variant least affected by molecular absorption.

Assessing the relationship between weather conditions and rockfall using terrestrial laser scanning to improve risk management

Abstract. Since 1987, more than 13 200 rockfalls have been inventoried by the ministère des Transports du Québec (MTQ) as having impacted the national road Route 132 in northern Gaspésie. This natural hazard represents a nearly permanent danger for road users. Traditional mitigation measures can be ineffective on poorly consolidated, deformed and highly fractured rockwalls such as those found in northern Gaspésie. To address this issue, implementing preventive risk management based on the factors that trigger rock instabilities could be the most effective method. Earthquake, rainfall and freeze–thaw cycles are commonly considered to be the main rockfall-triggering factors. This study aims to better understand the climatic conditions conducive to rockfalls in northern Gaspésie in order to provide knowledge to implement an appropriate risk management strategy. Three rockwalls were scanned with terrestrial laser scanning (TLS) instruments during specific pre-targeted weather conditions. Over a period of 18 months, 17 surveys have allowed us to identify 1287 rockfalls with a magnitude above 0.005 m3 on a scanned surface of 12 056 m2. In addition, meteorological instruments and a 550 cm thermistor string have been installed directly on a vertical rockwall. It appears that some weather conditions influence the occurrence, frequency and magnitude of rockfalls. In winter, rockfall frequency is 12 times higher during a superficial thaw than during a cold period in which temperature remains below 0 ∘C. In summer, rockfall frequency is 22 times higher during a heavy rainfall event than during a mainly dry period. Superficial freeze–thaw cycles (< 50 cm) cause mostly a high frequency of small-magnitude events, while deeper spring thaw (> 100 cm) results in a high frequency of large-magnitude events. The influence of weather conditions on rockfall frequency and magnitude is crucial in order to improve risk management, since large-magnitude events represent higher potential hazards. This study provides a classification of weather conditions based on their ability to trigger rockfalls of different magnitudes. This knowledge could be used to implement a risk management strategy.

Enhanced automated meteorological observations at the Canadian Arctic Weather Science (CAWS) supersites

Abstract. The changing Arctic climate is creating increased economic, transportation, and recreational activities requiring reliable and relevant weather information. However, the Canadian Arctic is sparsely observed, and processes governing weather systems in the Arctic are not well understood. There is a recognized lack of meteorological data to characterize the Arctic atmosphere for operational forecasting and to support process studies, satellite calibration/validation, search and rescue operations (which are increasing in the region), high-impact weather (HIW) detection and prediction, and numerical weather prediction (NWP) model verification and evaluation. To address this need, Environment and Climate Change Canada commissioned two supersites, one in Iqaluit (63.74∘ N, 68.51∘ W) in September 2015 and the other in Whitehorse (60.71∘ N, 135.07∘ W) in November 2017 as part of the Canadian Arctic Weather Science (CAWS) project. The primary goals of CAWS are to provide enhanced meteorological observations in the Canadian Arctic for HIW nowcasting (short-range forecast) and NWP model verification, evaluation, and process studies and to provide recommendations on the optimal cost-effective observing system for the Canadian Arctic. Both sites are in provincial/territorial capitals and are economic hubs for the region; they also act as transportation gateways to the north and are in the path of several common Arctic storm tracks. The supersites are located at or next to major airports and existing Meteorological Service of Canada ground-based weather stations that provide standard meteorological surface observations and upper-air radiosonde observations; they are also uniquely situated in close proximity to frequent overpasses by polar-orbiting satellites. The suite of in situ and remote sensing instruments at each site is completely automated (no on-site operator) and operates continuously in all weather conditions, providing near-real-time data to operational weather forecasters, the public, and researchers via obrs.ca. The two sites have similar instruments, including mobile Doppler weather radars, multiple vertically profiling and/or scanning lidars (Doppler, ceilometer, water vapour), optical disdrometers, precipitation gauges in different shielded configurations, present weather sensors, fog monitoring devices, radiation flux sensors, and other meteorological instruments. Details on the two supersites, the suites of instruments deployed, the data collection methods, and example case studies of HIW events are discussed. CAWS data are publicly accessible via the Canadian Government Open Data Portal (https://doi.org/10.18164/ff771396-b22c-4bc3-844d-38fc697049e9, Mariani et al., 2022a, and https://doi.org/10.18164/d92ed3cf-4ba0-4473-beec-357ec45b0e78, Mariani et al., 2022b); this dataset is being used to improve our understanding of synoptic and fine-scale meteorological processes in the Arctic and sub-Arctic, including HIW detection and prediction and NWP verification, assimilation, and processes.