Evaluation of p-y Curves for Group Piles in Cohesive Soil Based on 3D Numerical Analysis

The pile foundation supported on a structure can generate large horizontal loads due to earthquakes, high winds, and wave actions. The behavior of piles when subjected to horizontal load is generally analyzed using the p-y curve and “p-multiplier (Pm),” which is the coefficient of the group pile effect. In this study, the p-y curves and Pm were calculated by analyzing a single pile and group of piles arranged in 3 × 3 installed in cohesive soil using the finite element analysis program, Plaxis 3D. The soil resistance (p) increased as the undrained shear strength of the clay increased and the distance between the pile centers (S/D) increased. In the case of the group pile effect, when Pm was closer to the center of the group pile, the distance between the pile centers was smaller, and Pm was less due to the interference effect of the adjacent individual piles. In conclusion, it was observed that Pm is affected by the location of the individual piles and the distance between the pile centers.

Assessment of CYGNSS Wind Speed Retrievals in Tropical Cyclones

The NASA CYGNSS satellite constellation measures ocean surface winds using the existing network of the Global Navigation Satellite System (GNSS) and was designed for measurements in tropical cyclones (TCs). Here, we focus on using a consistent methodology to validate multiple CYGNSS wind data records currently available to the public, some focusing on low to moderate wind speeds, others for high winds, a storm-centric product for TC analyses, and a wind dataset from NOAA that applies a track-wise bias correction. Our goal is to document their differences and provide guidance to users. The assessment of CYGNSS winds (2017–2020) is performed here at global scales and for all wind regimes, with particular focus on TCs, using measurements from radiometers that are specifically developed for high winds: SMAP, WindSat, and AMSR2 TC-winds. The CYGNSS high-wind products display significant biases in TCs and very large uncertainties. Similar biases and large uncertainties were found with the storm-centric wind product. On the other hand, the NOAA winds show promising skill in TCs, approaching a level suitable for tropical meteorology studies. At the global level, the NOAA winds are overall unbiased at wind regimes from 0–30 m/s and were selected for a test assimilation into a global wind analysis, CCMP, also presented here.

The Northern Drakensberg Cableway: An Unworkable yet Immortal Development

This study explores the proposed ‘Drakensberg Cableway’ in the Northern Drakensberg. This cableway project is mired in ongoing controversy with both the consultation process and feasibility study heavily criticised. The proposed site of the cableway borders a world heritage site, is within a culturally sensitive area and prone to highly variable weather, including thunderstorms and high winds. The purpose of this study was to garner the views of a mountain user group in South Africa regarding the proposed cableway using a questionnaire survey. Respondents were overwhelmingly not in favour of the development. Users noted several serious concerns ranging from economic, environmental, statutory and political impacts. In particular, the proposed cableway appears financially unsustainable due to low tourist numbers. Additionally, the infrastructure required will have a deleterious effect on the natural environment. It appears that lessons from South Africa’s other two cableways, in terms of economic impacts, environmental issues and weather-related risks, have not been considered. While the provincial KwaZulu-Natal government may punt the proposed cableway as a ‘silver bullet’ solution for the development and social issues bedevilling the area; the project may instead even exacerbate already fraught social and environmental conditions, both at the proposed lower cableway and upper cableway station. Government officials touting this project need to recognise that tourism development in peripheral mountain areas has to proceed within a much wider social and cross-sectoral economic development context.

Cyclonic Wave Simulations Based on WAVEWATCH-III Using a Sea Surface Drag Coefficient Derived from CFOSAT SWIM Data

It is well known that numerical models are powerful methods for wave simulation of typhoons, where the sea surface drag coefficient is sensitive to strong winds. With the development of remote sensing techniques, typhoon data (i.e., wind and waves) have been captured by optical and microwave satellites such as the Chinese-French Oceanography SATellite (CFOSAT). In particular, wind and wave spectra data can be simultaneously measured by the Surface Wave Investigation and Monitoring (SWIM) onboard CFOSAT. In this study, existing parameterizations for the drag coefficient are implemented for typhoon wave simulations using the WAVEWATCH-III (WW3) model. In particular, a parameterization of the drag coefficient derived from sea surface roughness is adopted by considering the terms for wave steepness and wave age from the measurements from SWIM products of CFOSAT from 20 typhoons during 2019–2020 at winds up to 30 m/s. The simulated significant wave height (Hs) from the WW3 model was validated against the observations from several moored buoys active during three typhoons, i.e., Typhoon Fung-wong (2014), Chan-hom (2015), and Lekima (2019). The analysis results indicated that the proposed parameterization of the drag coefficient significantly improved the accuracy of typhoon wave estimation (a 0.49 m root mean square error (RMSE) of Hs and a 0.35 scatter index (SI)), greater than the 0.55 RMSE of Hs and >0.4 SI using other existing parameterizations. In this sense, the adopted parameterization for the drag coefficient is recommended for typhoon wave simulations using the WW3 model, especially for sea states with Hs < 7 m. Moreover, the accuracy of simulated waves was not reduced with growing winds and sea states using the proposed parameterization. However, the applicability of the proposed parameterization in hurricanes necessitates further investigation at high winds (>30 m/s).

Characterizing Buoy Wind Speed Error in High Winds and Varying Sea State with ASCAT and ERA5

Buoys provide key observations of wind speed over the ocean and are routinely used as a source of validation data for satellite wind products. However, the movement of buoys in high seas and the airflow over waves might cause inaccurate readings, raising concern when buoys are used as a source of wind speed comparison data. The relative accuracy of buoy winds is quantified through a triple collocation (TC) exercise comparing buoy winds to winds from ASCAT and ERA5. Differences between calibrated buoy winds and ASCAT are analyzed through separating the residuals by anemometer height and testing under high wind-wave and swell conditions. First, we converted buoy winds measured near 3, 4, and 5 m to stress-equivalent winds at 10 m (U10s). Buoy U10s from anemometers near 3 m compared notably lower than buoy U10s from anemometers near 4 and 5 m, illustrating the importance of buoy choice in comparisons with remote sensing data. Using TC calibration of buoy U10s to ASCAT in pure wind-wave conditions, we found that there was a small, but statistically significant difference between height adjusted buoy winds from buoys with 4 and 5 m anemometers compared to the same ASCAT wind speed ranges in high seas. However, this result does not follow conventional arguments for wave sheltering of buoy winds, whereby the lower anemometer height winds are distorted more than the higher anemometer height winds in high winds and high seas. We concluded that wave sheltering is not significantly affecting the winds from buoys between 4 and 5 m with high confidence for winds under 18 ms−1. Further differences between buoy U10s and ASCAT winds are observed in high swell conditions, motivating the need to consider the possible effects of sea state on ASCAT winds.

Technical Report: Monitoring and Communicating Changes in Disturbance Regimes (Version 1.0)

Shifts in disturbance patterns across the Northeast are of increasing concern as the climate continues to change. In particular, changes in patterns of frequency, severity and extent of disturbance event may have detrimental cascading impacts on forest ecosystems and human communities. To explore how changing disturbance regimes might impact future forest health and management it is necessary to understand the historical trends and impacts of disturbance in the region. Although individual types of disturbance have already been analyzed, there is a need for a consolidated overview of the current state of disturbance in northeastern forests. To address this need, the Forest Ecosystem Monitoring Cooperative (FEMC) developed the FEMC: Tracking Shifts in Disturbance Regimes web portal for users to explore changes over time of key disturbance drivers, identify important disturbance responses, and discover where monitoring is happening for both drivers and responses. In collaboration with our advisory committee, we identified key disturbance drivers—flood, high winds, fire, drought, pests—and responses—macroinvertebrates, cold-water fisheries, invasive plants—that are of particular concern in the region. For each of the drivers we identified a suitable regional dataset and analyzed changes over time in frequency, severity, and extent. We also created a structured framework to catalogue programs across the region that are monitoring for these disturbance drivers and responses. Version 1.0 of the FEMC: Tracking Shifts in Disturbance Regimes (https://uvm.edu/femc/disturbance) web portal, first released in October 2021, contains 272 data programs, 11 drivers and three responses. Through the web portal users can browse programs by state, driver type or response type, and explore where monitoring is happening across the region. Driver-specific analyses allow users to quickly see the trends in severity, frequency and extent of selected disturbances and compare the impacts in selected states to regional data. We hope that this collection of programs and the analysis of trends provide researchers and land managers with an easy way to understand the current state of disturbance in northeastern forests that enables them to analyze and plan for future impacts.

Fatality and Operational Specificity of Helicopter Accidents on the Ground

INTRODUCTION: Accidents with aircraft standing are more likely with helicopters than fixed-wing aircraft due to the common presence of off-airport landings and the possibility of the rotor system to strike objects in its immediate surroundings.METHODS: A total of 115 accidents involving helicopters characterized as standing as a broad phase of flight were selected from the NTSB online database for the period 1998 until 2018.RESULTS: Accidents reporting fatal (8.7) or serious injuries (7.8) were significantly less likely to occur when the aircraft was substantially damaged (84.3) or destroyed (5.2). The majority of the cases occurred after off-airport landings (57.4), which were reported significantly more often in Alaska (N= 15). A main rotor strike with an individual was at the basis of each of the 10 fatal accidents in the dataset and in 8 of these cases the cause of the accident was attributed to the victim. None of the accidents occurred in instrument meteorological conditions, but, in particular, high winds and gusts proved a main cause of accident (18.3).CONCLUSION: Pilot, passengers, and crew endangered themselves when they were outside the aircraft while the rotors were still turning. Helicopter operating manuals should highlight the limitations and dangers for wind and wind gusts not only during takeoff and flight, but specifically when standing.de Voogt AJ, Hummel C, Kalagher H. Fatality and operational specificity of helicopter accidents on the ground. Aerosp Med Hum Perform. 2021; 92(7):593596.

Stratified shear instabilities in diurnal warm layers

In low winds (≲2 m s−1), diurnal warm layers form but shear in the near-surface jet is too weak to generate shear instability and mixing. In high winds (≳8ms−1), surface heat is rapidly mixed downward and diurnal warm layers do not form. Under moderate winds of 3–5 m s−1, the jet persists for several hours in a state that is susceptible to shear instability. We observe low Richardson numbers of Ri ≈ 0.1 in the top 2 m between 10:00 and 16:00 local time (from 4 h after sunrise to 2 h before sunset). Despite Ri being well below the Ri = 1/4 threshold, instabilities do not grow quickly, nor do they overturn. The stabilizing influence of the sea surface limits growth, a result demonstrated by both linear stability analysis and two-dimensional simulations initialized from observed profiles. In some cases, growth rates are sufficiently small (≪1 h−1) that mixing is not expected even though Ri < 1/4. This changes around 16:00–17:00. Thereafter, convective cooling causes the region of unstable flow to move downward, away from the surface. This allows shear instabilities to grow an order of magnitude faster and mix effectively. We corroborate the overall observed diurnal cycle of instability with a freely evolving, two-dimensional simulation that is initialized from rest before sunrise.

Potential low bias in high-wind drag coefficient inferred from dropsonde data in hurricanes

Understanding momentum exchange at the air-sea interface is important for accurate hurricane predictions and understanding fundamental storm dynamics. One method for estimating air-sea momentum transfer in high winds is the flux-profile method, which infers surface momentum fluxes and the corresponding drag coefficient from mean velocity profiles obtained from either dropsondes or meteorological towers, under the assumption that the boundary-layer wind profile at low altitudes exhibits a logarithmic profile with height. In this study, we use dropsonde data from reconnaissance aircraft, as well as “virtual sondes” from a turbulence-resolving simulation of an intense tropical cyclone, to critically analyze the diagnosis of drag coefficient CD at hurricane-force wind speeds. In particular, the “roll-off” of the drag coefficient, where CD decreases at 10-m wind speeds ¿ 35 m s−1, is called into question based on uncertainty due to relatively low sample size and a lack of robustness of the flux-profile at high winds. In addition, multiple factors appear to favor an underestimate of CD at hurricane-force winds relative to their true values, including uncertainty in the height of recorded dropsonde data, violation of Monin-Obukhov similarity theory near the eyewall, and the short vertical extent of the logarithmic layer. Due to these and other related sources of uncertainty, it is likely that a quantitative limit has been reached in inferring the specific values of u* and CD using the flux-profile method, while at the same time the potential for underestimation may cast doubt on the CD–U10 relationship inferred from this method at high winds.