bluuebunny/crossref_metadata_2025_split huggingface dataset:
Intraseasonal Variations in Atmospheric and Oceanic Excitation of Length‐of‐Day
Authors: Yu Nan , Ray Jim , Li Jiancheng , Chen Gang , Chao Nengfang , Chen Wei 
Published: February 2021

AbstractLike the seasonal and interannual variations in length‐of‐day (LOD), variations on intraseasonal timescales (periods shorter than 183 days) are also predominantly caused by changes in the angular momentum of the zonal winds. But the smaller intraseasonal LOD excitations from atmospheric surface pressure, oceanic currents, and the ocean bottom pressure are less clear. Here sliding window average filtering is applied to isolate intraseasonal signals from both geodetically observed LOD excitation (shorten to geodetic excitation for convenience) and atmospheric and oceanic LOD excitations. Based on careful comparison between these two‐excitation series, we find that during 1993–2018, atmospheric winds reduce the RMS of observed intraseasonal LOD series from 276.1 to 55.6 μs with a correlation coefficient of 0.9795. Including the effect of surface pressure changes with that of the winds reduced the RMS from 55.6 to 43.3 μs, and increased the correlation coefficient with the observations from 0.9795 to 0.9884. Additionally, including the effects of changes in oceanic currents and bottom pressure further reduced the RMS from 43.3 to 33.9 μs, and further increased the correlation coefficient from 0.9884 to 0.9931. Thus, although the impact of oceans is relatively minor, closer agreement with the observations in the intraseasonal frequency band is obtained when the effects of oceanic processes are added to that of atmospheric. The RMS values and correlation coefficients of ESMGFZ and MPIOM residual series are better than NCEP and ECCO in every component, indicating that NCEP model set is generally poorer than ESMGFZ in the intraseasonal band.
Solar or Diesel: A Comparison of Costs for Groundwater‐Fed Irrigation in Sub‐Saharan Africa Under Two Energy Solutions
Authors: Xie Hua , Ringler Claudia , Mondal Md. Alam Hossain 
Published: February 2021

AbstractSub‐Saharan Africa has long been beset with food insecurity and energy poverty. Expanding irrigated agriculture can help boost food production in the region, but this requires energy for accessing water, especially in groundwater‐fed irrigation. This paper compared economic performance of groundwater pumping for irrigation under two energy solutions: solar photovoltaic (PV) and diesel fuel. We estimated the life‐cycle costs of the power units of two pumping systems for a range of crop and irrigation method scenarios and mapped their relative cost‐effectiveness over cropland in sub‐Saharan Africa. As a renewable and clean energy source, solar energy has attracted much attention and there is keen interest in investing in solar PV to support the development of irrigated agriculture. Results of this study provide insights into the prospects of promoting solar irrigation in sub‐Saharan Africa.
Potential Influences of Volcanic Eruptions on Future Global Land Monsoon Precipitation Changes
Authors: Man Wenmin , Zuo Meng , Zhou Tianjun , Fasullo John T. , Bethke Ingo , Chen Xiaolong , Zou Liwei , Wu Bo 
Published: February 2021

AbstractThe global monsoon system is of exceptional socioeconomic importance owing to its impacts on two‐thirds of the globe’s population. Major volcanic eruptions strongly influence global land monsoon (GLM) precipitation change. By using 60 plausible eruption scenarios sampled from reconstructed volcanic proxies over the past 2,500 years, 21st century volcanic influences on GLM precipitation projections are examined with an Earth system model under a moderate emission scenario. The decadal‐scale ensemble spread with realistic eruptions (VOLC) increases by 17.5% and 20.1% compared to no‐volcanic (NO‐VOLC) and constant background‐volcanic (VOLC‐CONST) scenarios, respectively. Compared with NO‐VOLC, the centennial mean VOLC GLM precipitation shows a 10% overall reduction and regionally, Asia is the most impacted. Changes in atmospheric circulation in the aftermath of large volcanic eruptions match the global warming response patterns well with opposite sign, with the North American monsoon precipitation enhanced following large volcanic eruptions, which is in sharp contrast to the robust decrease in Asian monsoon rainfall. Volcanic activity could delay the time of emergence of anthropogenic influence by five years on average over about 60% of the GLM area. Our results demonstrate the importance of statistical representation of potential volcanism for the projections of future monsoon variability. Quantifying volcanic impacts on regional climate projections and their socioeconomic influences on infrastructure planning, food security, and disaster management should be a priority of future work.
Comparing Patterns of Hurricane Washover into Built and Unbuilt Environments
Authors: Lazarus Eli D. , Goldstein Evan B. , Taylor Luke A. , Williams Hannah E. 
Published: February 2021

AbstractExtreme geohazard events can change landscape morphology by redistributing huge volumes of sediment. Event‐driven sediment deposition is typically studied in unbuilt settings – despite the ubiquity of occurrence and high economic cost of these geohazard impacts in built environments. Moreover, sedimentary consequences of extreme events in built settings tend to go unrecorded because they are rapidly cleared, at significant expense, from streets and roads to facilitate emergency response. Reducing disaster costs requires an ability to predict disaster impacts, which itself requires comprehensive measurement and study of the physical consequences of geohazard events. Here, using a database of poststorm aerial imagery, we measure plan‐view geometric characteristics of sandy washover deposits in built and unbuilt settings following five different hurricane strikes along the Atlantic and Gulf Coasts of the US since 2011. We identify systematic similarities and differences between washover morphology in built and unbuilt environments, which we further explore with a simplified numerical model. Our findings suggest that spatial characteristics of the built environment (termed “fabric”) – specifically, the built fraction of the depositional zone – exerts a fundamental control on the form of large deposits. Accounting for the influence of built fabric on the morphodynamics of flow‐driven geohazards is a tractable step toward improved forecasts of hazard impacts and disaster risk reduction.
Assessing the Impact of Wildfires on the Use of Black Carbon as an Indicator of Traffic Exposures in Environmental Epidemiology Studies
Authors: Martenies S. E. , Hoskovec L. , Wilson A. , Allshouse W. B. , Adgate J. L. , Dabelea D. , Jathar S. , Magzamen S. 
Published: February 2021

AbstractEpidemiological studies frequently use black carbon (BC) as a proxy for traffic‐related air pollution (TRAP). However, wildfire smoke (WFS) represents an important source of BC not often considered when using BC as a proxy for TRAP. Here, we examined the potential for WFS to bias TRAP exposure assessments based on BC measurements. Weekly integrated BC samples were collected across the Denver, CO region from May to November 2018. We collected 609 filters during our sampling campaigns, 35% of which were WFS‐impacted. For each filter we calculated an average BC concentration. We assessed three GIS‐based indicators of TRAP for each sampling location: annual average daily traffic within a 300 m buffer, the minimum distance to a highway, and the sum of the lengths of roadways within 300 m. Median BC concentrations were 9% higher for WFS‐impacted filters (median = 1.14 μg/m3, IQR = 0.23 μg/m3) than nonimpacted filters (median = 1.04 μg/m3, IQR = 0.48 μg/m3). During WFS events, BC concentrations were elevated and expected spatial gradients in BC were reduced. We conducted a simulation study to estimate TRAP exposure misclassification as the result of regional WFS. Our results suggest that linear health effect estimates were biased away from the null when WFS was present. Thus, exposure assessments relying on BC as a proxy for TRAP may be biased by wildfire events. Alternative metrics that account for the influence of “brown” carbon associated with biomass burning may better isolate the effects of traffic emissions from those of other black carbon sources.
Real‐Time Earthquake Early Warning With Deep Learning: Application to the 2016 M 6.0 Central Apennines, Italy Earthquake
Authors: Zhang Xiong , Zhang Miao , Tian Xiao 
Published: February 2021

AbstractEarthquake early warning (EEW) systems are required to report earthquake locations and magnitudes as quickly as possible before the damaging S wave arrival to mitigate seismic hazards. Deep learning techniques provide potential for extracting earthquake source information from full seismic waveforms instead of seismic phase picks. We developed a novel deep learning EEW system that utilizes fully convolutional networks to simultaneously detect earthquakes and estimate their source parameters from continuous seismic waveform streams. The system determines earthquake location and magnitude as soon as very few stations receive earthquake signals and evolutionarily improves the solutions by receiving continuous data. We apply the system to the 2016 M 6.0 Central Apennines, Italy Earthquake and its first‐week aftershocks. Earthquake locations and magnitudes can be reliably determined as early as 4 s after the earliest P phase, with mean error ranges of 8.5–4.7 km and 0.33–0.27, respectively.
Classifying Oceanographic Structures in the Amundsen Sea, Antarctica
Authors: Boehme Lars , Rosso Isabella 
Published: February 2021

AbstractThe remote and often ice‐covered Amundsen Sea Embayment in Antarctica is important for transporting relatively warm modified Circumpolar Deep Water (mCDW) to the Western Antarctic Ice Sheet, potentially accelerating its thinning and contribution to sea level rise. To investigate potential pathways and variability of mCDW, 3809 CTD profiles (instrumented seal and ship‐based data) are classified using a machine learning approach (Profile Classification Model). Five vertical regimes are identified, and areas of larger variability highlighted. Three spatial regimes are captured: Off‐Shelf, Eastern and Central Troughs. The on‐shelf profiles further show a separation between cold and warm modes. The variability is higher north of Burke Island and at the southern end of the Eastern Trough, which reflects the convergence of different mCDW pathways between the Eastern and the Central Trough. Finally, a clear but variable clockwise circulation is identified in Pine Island Bay.
Atmospheric River Precipitation Contributed to Rapid Increases in Surface Height of the West Antarctic Ice Sheet in 2019
Authors: Adusumilli Susheel , A. Fish Meredith , Fricker Helen Amanda , Medley Brooke 
Published: February 2021

AbstractEstimating the relative contributions of the atmospheric and dynamic components of ice‐sheet mass balance is critical for improving projections of future sea level rise. Existing estimates of changes in Antarctic ice‐sheet height, which can be used to infer changes in mass, are only accurate at multiyear time scales. However, NASA's Ice, Cloud, and land Elevation Satellite‐2 (ICESat‐2) laser altimetry mission now allows us to accurately measure changes in ice‐sheet height at subannual time scales. Here, we use ICESat‐2 data to estimate height changes over Antarctica between April 2019 and June 2020. These data show widespread increases in surface height over West Antarctica during the 2019 austral winter. Using climate reanalysis data, we show that 41% of increases in height during winter were from snow accumulation via extreme precipitation events—63% of these events were associated with landfalling atmospheric rivers (ARs) which occurred only 5.1% of the time.
Periodic Rising and Falling Tone ECH Waves From Van Allen Probes Observations
Authors: Shen Xiao‐Chen , Li Wen , Ma Qianli 
Published: February 2021

AbstractElectron cyclotron harmonic (ECH) waves are known to precipitate plasma sheet electrons into the upper atmosphere and generate diffuse aurorae. In this study, we report quasiperiodic rising (3 events) and falling tone (22 events) ECH waves observed by Van Allen Probes and evaluate their properties. These rising and falling tone ECH waves prefer to occur during quiet geomagnetic conditions over the dusk to midnight sector in relatively high‐density (10–80 cm−3) regions. Their repetition periods increase with increasing L shell at L < 6, ranging from ∼60 to 110 s. The wave element duration varies from 10 to 130 s peaking at ∼40 s and the chirping rate peaks at ∼50 (∼−50) Hz/s for rising (falling) tones. Our findings reveal intriguing features of the ECH wave properties, which provide new insights into their generation and potential effects on electron precipitation.
Arctic Ozone Depletion in 2019/20: Roles of Chemistry, Dynamics and the Montreal Protocol
Authors: Feng Wuhu , Dhomse Sandip S. , Arosio Carlo , Weber Mark , Burrows John P. , Santee Michelle L. , Chipperfield Martyn P. 
Published: February 2021

AbstractWe use a three‐dimensional chemical transport model and satellite observations to investigate Arctic ozone depletion in winter/spring 2019/20 and compare with earlier years. Persistently, low temperatures caused extensive chlorine activation through to March. March‐mean polar‐cap‐mean modeled chemical column ozone loss reached 78 DU (local maximum loss of ∼108 DU in the vortex), similar to that in 2011. However, weak dynamical replenishment of only 59 DU from December to March was key to producing very low (<220 DU) column ozone values. The only other winter to exhibit such weak transport in the past 20 years was 2010/11, so this process is fundamental to causing such low ozone values. A model simulation with peak observed stratospheric total chlorine and bromine loading (from the mid‐1990s) shows that gradual recovery of the ozone layer over the past 2 decades ameliorated the polar cap ozone depletion in March 2020 by ∼20 DU.
Projecting Global Mean Sea‐Level Change Using CMIP6 Models
Authors: Hermans Tim H. J. , Gregory Jonathan M. , Palmer Matthew D. , Ringer Mark A. , Katsman Caroline A. , Slangen Aimée B. A. 
Published: February 2021

AbstractThe effective climate sensitivity (EffCS) of models in the Coupled Model Intercomparison Project 6 (CMIP6) has increased relative to CMIP5. We explore the implications of this for global mean sea‐level (GMSL) change projections in 2100 for three emissions scenarios. CMIP6 projections of global surface air temperature are substantially higher than in CMIP5, but projections of global mean thermal expansion are not. Using these projections as input to construct projections of GMSL change with IPCC AR5 methods, the 95th percentile of GMSL change at 2100 only increases by 3–7 cm. Projected rates of GMSL rise around 2100 increase more strongly, though, implying more pronounced differences beyond 2100 and greater committed sea‐level rise. Intermodel differences in GMSL projections indicate that EffCS‐based model selection may substantially alter the ensemble projections. GMSL change in 2100 is accurately predicted by time‐integrated temperature change, and thus requires reducing emissions early to be mitigated.
F Region Electric Field Effects on the Intermediate Layer Dynamics During the Evening Prereversal Enhancement at Equatorial Region Over Brazil
Authors: Santos A. M. , Batista I. S. , Brum C. G. M. , Sobral J.H.A. , Abdu M. A. , Souza J. R. 
Published: February 2021

AbstractUsing ionograms from the Brazilian equatorial site of São Luís (SL, 2° S; 44° W, I = −3.8°), the relationship between the uplift of the intermediate layers (ILs) at sunset and the prereversal enhancement of the zonal electric field (PRE) is investigated. The ILs were studied during the solar maximum (2003) and minimum activity (2009) periods. The presence of the ILs during the PRE occurrence time was very low during both years. In 2003, six ILs’ events were observed, being four of them in the summer solstice and one in the March equinox. In 2009, only a single event was registered and occurred during the December month. The results show that depending on the height at which the ILs are located, their upward movement at sunset can be in some way related to the normal F layer rise at sunset due to the PRE. The initial altitude at which such ascending ILs were observed was higher than their normal height near sunset. Additionally, the eastward prompt penetration electric fields (PPEFs) during weak magnetic storms can also contribute to the IL’s rise. An interesting case of uplift of a sporadic‐E layer from ∼120 to 290 km probably due to the PPEF is also investigated.
Modeling of the Lower Ionosphere During Solar X‐Ray Flares of Different Classes
Authors: Bekker S. Z. , Ryakhovsky I. A. , Korsunskaya J. A. 
Published: February 2021

AbstractThis study presents the results obtained from modeling the lower ionosphere response to C‐, M‐ and X‐class solar X‐ray flares. This model is based on a 5‐component scheme for the ionization‐recombination cycle of the ionospheric D‐region. Input parameters for the plasma‐chemical model under different heliogeophysical conditions corresponding to selected X‐ray flares were determined by using data received from the AURA, SDO, and GOES satellites. Verification of the obtained results was carried out with use of ground‐based radiophysical measurements taken at the geophysical observatory Mikhnevo. The results obtained from a comparison of the calculated and experimental radio wave amplitude variations along six European very low frequency (VLF) paths show that the average normalized root mean square error is ∼7%, 14%, and 18% for C‐, M‐, and X‐class flares, respectively. Qualitative and quantitative analysis of the verification results for the VLF signal amplitude show good predictive capability of the model built for describing weak and moderate ionospheric disturbances.
Meteor‐Ablated Aluminum in the Mesosphere‐Lower Thermosphere
Authors: Plane John M. C. , Daly Shane M. , Feng Wuhu , Gerding Michael , Gómez Martín Juan Carlos 
Published: February 2021

AbstractThe first global atmospheric model (WACCM‐Al) of meteor‐ablated aluminum was constructed from three components: The Whole Atmospheric Community Climate Model (WACCM6); a meteoric input function for Al derived by coupling an astronomical model of dust sources in the solar system with a chemical meteoric ablation model; and a comprehensive set of neutral, ion‐molecule and photochemical reactions relevant to the chemistry of Al in the upper atmosphere. The reaction kinetics of two important reactions that control the rate at which Al+ ions are neutralized were first studied using a fast flow tube with pulsed laser ablation of an Al target, yielding k(AlO+ + CO) = (3.7 ± 1.1) × 10−10 and k(AlO+ + O) = (1.7 ± 0.7) × 10−10 cm3 molecule−1 s−1 at 294 K. The first attempt to observe AlO by lidar was made by probing the bandhead of the B2Σ+(v′ = 0) ← X2Σ+(v″ = 0) transition at λair = 484.23 nm. An upper limit for AlO of 60 cm−3 was determined, which is consistent with a night‐time concentration of ∼5 cm−3 estimated from the decay of AlO following rocket‐borne grenade releases. WACCM‐Al predicts the following: AlO, AlOH and Al+ are the three major species above 80 km; the AlO layer at mid‐latitudes peaks at 89 km with a half‐width of ∼5 km, and a peak density which increases from a night‐time minimum of ∼10 cm−3 to a daytime maximum of ∼60 cm−3; and that the best opportunity for observing AlO is at high latitudes during equinoctial twilight.
Crustal Footprint of Mantle Upwelling and Plate Amalgamation Revealed by Ambient Noise Tomography in Northern Vietnam and the Northern South China Sea
Authors: Yang Xuan , Yao Huajian , Huang Bor‐Shouh 
Published: February 2021

AbstractA high‐resolution crustal and uppermost mantle velocity model of northern Vietnam and the northern South China Sea (SCS) is essential for understanding the evolution of the SCS and its relationship to the Hainan plume, which is still controversial. Based on ambient seismic noise analysis, we processed ambient noise data from 65 broadband stations in southwestern China and northern Vietnam to obtain the crustal and uppermost mantle, S‐wave velocity model, through the direct surface‐wave tomography method, with a lateral resolution of 100–150 km. Our results show distinct lateral velocity variation at shallow crustal depths, such as significant low velocity in the Beibu Gulf Basin and the Yinggehai Basin and relatively higher velocity in Hainan Island. We suggest that the low velocity of the lower crust and uppermost mantle beneath the Yinggehai Basin indicates the present upwelling of upper mantle material. However, the observed high‐velocity upheaval feature beneath the Leizhou Peninsula may represent the ancient magmatic underplating, which has a relation to the Hainan plume. Moreover, our results demonstrate different crustal structures of the two flanks of the Red River Fault, that is, in the middle and lower crust, the S‐wave velocity in the region north of the Red River Fault is higher than that in the south. This may be associated with the collision and amalgamation of the South China and Indochina Blocks. In addition, our results also indicate a crustal footprint of the amalgamation of the Yangtze and Cathaysia Blocks.
Magnetic Pulsations Triggered by Microseismic Ground Motion
Authors: Chen Chieh‐Hung , Lin Jing‐Yi , Gao Yongxin , Lin Cheng‐Horng , Han Peng , Chen Chun‐Rong , Lin Li‐Ching , Huang Rong , Liu Jann‐Yenq 
Published: February 2021

AbstractGeomagnetic pulsations with an enhanced amplitude of 0.1–1 nT in a frequency band of 0.1–0.2 Hz were observed by three three‐component magnetometers. The geomagnetic pulsations exhibit slight time difference that is unusually observed within a limited area of ∼5 × 5 km2 at the northern end of Taiwan. The time difference suggests the geomagnetic pulsations are not dominated by global effects but local ones. We compare the seismic signals recorded by the cosited broadband seismometers for investigating potential mechanisms of these geomagnetic pulsations. Results from analysis of both seismic and geomagnetic data exhibit consistent source azimuths from the Pacific Ocean to the northeast of the observation sites with a wave propagation speed of ∼2.9 km/s estimated based on P‐SV‐type microseisms. Polarization and particle motion analyses demonstrate that the geomagnetic pulsations move with an elliptical rotation form, showing a close association with the P‐SV‐type microseisms. The 90° phase difference between the horizontal and vertical components of the geomagnetic signals suggests that the time‐lagged geomagnetic pulsations are possibly caused by the motional induction effect after the arrivals of P‐SV‐type microseisms.