bluuebunny/crossref_metadata_2025_split huggingface dataset:
Kelvin Waves during GOAmazon and Their Relationship to Deep Convection
Authors: Serra Yolande L. , Rowe Angela , Adams David K. , Kiladis George N. 
Published: August 2020

AbstractThe 2014–15 Observations and Modeling of the Green Ocean Amazon (GOAmazon) field campaign over the central Amazon near Manaus, Brazil, occurred in coordination with the larger Cloud Processes of the Main Precipitation Systems in Brazil: A Contribution to Cloud-Resolving Modeling and to the Global Precipitation Measurement (CHUVA) project across Brazil. These programs provide observations of convection over the central Amazon on diurnal to annual time scales. In this study, we address the question of how Kelvin waves, observed in satellite observations of deep cloud cover over the GOAmazon region during the 2014–15 time period, modulate the growth, type, and organization of convection over the central Amazon. The answer to this question has implications for improved predictability of organized systems over the region and representation of convection and its growth on local to synoptic scales in global models. Our results demonstrate that Kelvin waves are strong modulators of synoptic-scale low- to midlevel free-tropospheric moisture, integrated moisture convergence, and surface heat fluxes. These regional modifications of the environment impact the local diurnal cycle of convection, favoring the development of mesoscale convective systems. As a result, localized rainfall is also strongly modulated, with the majority of rainfall in the GOAmazon region occurring during the passage of these systems.
Moisture Source–Receptor Network of the East Asian Summer Monsoon Land Regions and the Associated Atmospheric Steerings
Authors: Cheng Tat Fan , Lu Mengqian 
Published: August 2020

AbstractThis study aims to construct a novel source–receptor (SR) network to study the atmospheric water cycle associated with the East Asian summer monsoon (EASM) circulation. Using a dynamical recycling model (DRM), 68%–74% of the wet season (April–September) precipitation in six EASM land regions is attributed. The results reveal that terrestrial sources can be equally or more competitive than oceans for several sink regions downwind in East Asia. Terrestrial sources, such as the Indian subcontinent, Indochina, Southwest China, and the eastern Tibetan Plateau, are sustained by southwesterly monsoons and contribute to appreciable fractions of precipitation in the East Asian subregions downwind. Further, southwesterly and southeasterly sources for a sink region alternately dominate the moisture supply in the early and late wet season, respectively, referred to as the “SW–SE source swing.” The SR network is found to be largely governed by the zonal oscillation of the western North Pacific subtropical high and tropical cyclones. Knowledge about the coupled circulations might promise more predictability of the strength of the affected SR pairs. Notably, enhanced moisture supplies from regions such as the Indian subcontinent and Tibetan Plateau are well correlated with an upper-level wave train from western Russia. Finally, the preceding wintertime El Niño may favor (suppress) the moisture contribution of southwesterly (southeasterly) sources in the following wet season. The findings offer insights into the EASM water cycle and the governing circulations, and also accentuate the role of upwind terrestrial sources in the downwind precipitation and freshwater resources.
Precipitation–Radiation–Circulation Feedback Processes Associated with Structural Changes of the ITCZ in a Warming Climate during 1980–2014: An Observational Portrayal
Authors: Lau William K. M. , Tao Weichen 
Published: August 2020

AbstractIn this study, long-term structural changes in the intertropical convergence zone (ITCZ) and associated precipitation–radiation–circulation feedback processes are examined using multiple sources of reanalysis data for temperature, winds, moisture, and observed precipitation and outgoing longwave radiation (OLR) during 1980–2014. Consistent with CMIP5 climate model projections of the “deep tropical squeeze” under greenhouse warming, this period witnessed a warming and wetting (increased specific humidity) global trend, characterized by a narrowing of the ITCZ core with increased precipitation, coupled to widespread tropospheric drying (deficient relative humidity), increased OLR in the subtropics and midlatitudes, a widening of the descending branches of the Hadley circulation, and a poleward shift of the jet streams in both hemispheres. The widespread tropospheric drying stems from 1) a faster rate of increased saturated water vapor with warming, relative to the increase in ambient moisture due to convective and large-scale transport, and 2) enhanced anomalous subsidence, and low-level moisture divergence in the subtropics and midlatitudes. The long-term trend in enhanced precipitation (latent heating) in the ITCZ core region is strongly coupled to increasing OLR (radiative cooling to space) in the expanding dry zones, particularly over land regions in the subtropics and midlatitudes, arguably as a necessary condition for global thermodynamic energy balance. Analyses of the trend patterns in vertical profiles of p velocity, temperature, and relative humidity with respect to ITCZ precipitation rate and OLR reveal that the contrast between the wet and dry regions in the troposphere has been increasing globally, with the ITCZ core getting wetter and contracting, while the marginal convective and dry zones are getting drier and expanding.
Evaluating the Suitability of Century-Long Gridded Meteorological Datasets for Hydrological Modeling
Authors: Massmann Carolina 
Published: August 2020

AbstractRecent advances in climate reanalyses have led to the development of meteorological products providing information from the beginning of the last century or even before. As these data sources might be of interest to practitioners in the event of missing data from meteorological stations, it is important to assess their usefulness for different applications. The main objective of this study is to investigate the ability of two long-term reanalysis datasets (CERA-20C and 20CR) and one long-term interpolated dataset (Livneh) for supporting hydrological modeling. The precipitation and temperature data of the three datasets were first compared, downscaled, and then used as inputs to the conceptual hydrological model HBV in 168 basins in the United States. The findings suggest that the quality of all three datasets decreases the further we go back in time. Models calibrated at the beginning of the time series, where the data quality is worse, are only able to capture the general properties of the time series and thus do not show a decrease in performance as the period between calibration and validation becomes larger. The opposite is true for models calibrated at the end of the time series, which show a clear decrease in performance toward the beginning of the century. While the hydrological model driven with the interpolated datasets achieved the best performance, the results obtained with the reanalysis datasets were still informative (i.e., better than the long-term monthly mean), and they matched the performance of the interpolated dataset in a few catchments in the northwestern United States.
Missing Data Imputation for Multisite Rainfall Networks: A Comparison between Geostatistical Interpolation and Pattern-Based Estimation on Different Terrain Types
Authors: Oriani Fabio , Stisen Simon , Demirel Mehmet C. , Mariethoz Gregoire 
Published: August 2020

AbstractMissing rainfall data are a major limitation for distributed hydrological modeling and climate studies. Practitioners need reliable approaches that can be employed on a daily basis, often with too limited data in space to feed complex predictive models. In this study we compare different automatic approaches for missing data imputation, including geostatistical interpolation and pattern-based estimation algorithms. We introduce two pattern-based approaches based on the analysis of historical data patterns: (i) an iterative version of K-nearest neighbor (IKNN) and (ii) a new algorithm called vector sampling (VS) that combines concepts of multiple-point statistics and resampling. Both algorithms can draw estimations from variably incomplete data patterns, allowing the target dataset to be at the same time the training dataset. Tested on five case studies from Denmark, Australia, and Switzerland, the algorithms show a different performance that seems to be related to the terrain type: on flat terrains with spatially homogeneous rain events, geostatistical interpolation tends to minimize the average error, while in mountainous regions with nonstationary rainfall statistics, data mining can recover better the rainfall patterns. The VS algorithm, requiring minimal parameterization, turns out to be a convenient option for routine application on complex and poorly gauged terrains.
Large-Scale Influences on Atmospheric River–Induced Extreme Precipitation Events along the Coast of Washington State
Authors: Collow Allison B. Marquardt , Mersiovsky Haiden , Bosilovich Michael G. 
Published: August 2020

AbstractTransient, narrow plumes of strong water vapor transport, referred to as atmospheric rivers (ARs), are responsible for much of the precipitation along the West Coast of the United States. The most intense precipitation events are almost always induced by an AR on the coast of Oregon and Washington and can result in detrimental impacts on society due to mudslides and flooding. To accurately predict AR events on numerical weather prediction, subseasonal, and seasonal time scales, it is important to understand the large-scale impacts on extreme AR events. Here, characteristics of ARs that result in an extreme precipitation event are compared to typical ARs on the coast of Washington State. In addition to more intense water vapor transport, notable differences in the synoptic forcing are present during extreme precipitation events that are not present during typical AR events. Subseasonal and seasonal teleconnection patterns are known to influence the weather in the Pacific Northwest and are investigated here. The Madden–Julian oscillation (MJO) plays a role in determining the strength of precipitation associated with an AR on the Washington coast. Phase 5 of the MJO (convection centered over the Maritime Continent) is the most common phase during an extreme precipitation event, while phase 2 (convection over the Indian Ocean) discourages an extreme event from occurring. Interactions between El Niño–Southern Oscillation (ENSO) and the propagation speed of the MJO result in extreme events during phase 1 of the MJO and El Niño but phase 8 during neutral ESNO conditions.
Detecting Rain–Snow-Transition Elevations in Mountain Basins Using Wireless Sensor Networks
Authors: Cui Guotao , Bales Roger , Rice Robert , Anderson Michael , Avanzi Francesco , Hartsough Peter , Conklin Martha 
Published: August 2020

AbstractTo provide complementary information on the hydrologically important rain–snow-transition elevation in mountain basins, this study provides two estimation methods using ground measurements from basin-scale wireless sensor networks: one based on wet-bulb temperature Twet and the other based on snow-depth measurements of accumulation and ablation. With data from 17 spatially distributed clusters (178 nodes) from two networks, in the American and Feather River basins of California’s Sierra Nevada, we analyzed transition elevation during 76 storm events in 2014–18. A Twet threshold of 0.5°C best matched the transition elevation defined by snow depth. Transition elevations using Twet in upper elevations of the basins generally agreed with atmospheric snow level from radars located at lower elevations, while radar snow level was ~100 m higher due to snow-level lowering on windward mountainsides during orographic lifting. Diurnal patterns of the difference between transition elevation and radar snow level were observed in the American basin, related to diurnal ground-temperature variations. However, these patterns were not found in the Feather basin due to complex terrain and higher uncertainties in transition-elevation estimates. The American basin tends to exhibit 100-m-higher transition elevations than does the Feather basin, consistent with the Feather basin being about 1° latitude farther north. Transition elevation averaged 155 m higher in intense atmospheric river events than in other events; meanwhile, snow-level lowering was enhanced with a 90-m-larger difference between radar snow level and transition elevation. On-the-ground continuous observations from distributed sensor networks can complement radar data and provide important ground truth and spatially resolved information on transition elevations in mountain basins.
Does Subgrid Routing Information Matter for Urban Flood Forecasting? A Multiscenario Analysis at the Land Parcel Scale
Authors: Cao Xuejian , Ni Guangheng , Qi Youcun , Liu Bo 
Published: August 2020

AbstractThe accessibility of high-resolution surface data enables fine distributed modeling for urban flooding. However, the surface routing processes between nonhomogeneous land cover components remain in most grid units, due to the high spatial heterogeneity of urban surfaces. Limited by the great difficulty in the acquisition, subgrid routing information (SRI) is always ignored in high-resolution urban flood modeling, and more importantly, the potential impacts of missing SRI on flood forecasting are still less understood. In this study, 54 urban-oriented scenarios of subgrid routing schemes are designed at an isolated grid, including three types of land parcels, two routing directions, and nine routing percents. The impacts of missing SRI are evaluated comprehensively under 60 different rainfall scenarios, in terms of the peak runoff (PR) and the runoff coefficient (RC). Furthermore, the influence mechanism is revealed as well to explain the discrepancy of the impacts under different conditions. Results show the missing of the routing process from impervious to pervious areas leads to significant impacts on the simulation of both PR and RC. Overestimated RC is detected, however, the impacts on PR are bidirectional depending on the rainfall intensity. Overestimation of PR due to missing SRI is observed in light rainfall events, but the opposite effect is identified under heavy rainfall conditions. This study highlights the importance of incorporating the SRI for urban flood forecasting to avoid underestimating the hazard risk in heavy rainfall. Simultaneously, it identifies that blindly utilizing infiltration-based green infrastructure is not feasible in urban stormwater management, due to the possible increase in peak runoff.
On the Formation of a Subsurface Weakly Sheared Laminar Layer and an Upper Thermocline Strongly Sheared Turbulent Layer in the Eastern Equatorial Pacific: Interplays of Multiple-Time-Scale Equatorial Waves
Authors: Liu Chuanyu , Wang Xiaowei , Liu Zhiyu , Köhl Armin , Smyth William D. , Wang Fan 
Published: August 2020

AbstractThe origins of an observed weakly sheared nonturbulent (laminar) layer (WSL), and a strongly sheared turbulent layer above the Equatorial Undercurrent core (UCL) in the eastern equatorial Pacific are studied, based mainly on the data from the Tropical Atmosphere and Ocean mooring array. Multiple-time-scale (from 3 to 25 days) equatorial waves were manifested primarily as zonal velocity oscillations with the maximum amplitudes (from 10 to 30 cm s−1) occurring at different depths (from the surface to 85-m depths) above the seasonal thermocline. The subsurface-intensified waves led to vertically out-of-phase shear variations in the upper thermocline via destructive interference with the seasonal zonal flow, opposing the tendency for shear instability. These waves were also associated with depth-dependent, multiple-vertical-scale stratification variations, with phase lags of π/2 or π, further altering stability of the zonal current system to vertical shear. The WSL and UCL were consequently formed by coupling of multiple equatorial waves with differing phases, particularly of the previously identified equatorial mode and subsurface mode tropical instability waves (with central period of 17 and 20 days, respectively, in this study), and subsurface-intensified waves with central periods of 6, 5, and 12 days and velocity maxima at 45-, 87-, and 40-m depths, respectively. In addition, a wave-like feature with periods of 50–90 days enhanced the shear throughout the entire UCL. WSLs and UCLs seem to emerge without a preference for particular tropical instability wave phases. The generation mechanisms of the equatorial waves and their joint impacts on thermocline mixing remain to be elucidated.
Baroclinic Characteristics and Energetics of Annual Rossby Waves in the Southern Tropical Indian Ocean
Authors: Huang Ke , Wang Dongxiao , Feng Ming , Han Weiqing , Chen Gengxin , Sun Chaojiao , Zhang Xiaolin , Xie Qiang , Wang Weiqiang , Liu Qinyan , Yao Jinglong 
Published: August 2020

AbstractThe first baroclinic mode Rossby wave is known to be of critical importance to the annual sea level variability in the southern tropical Indian Ocean (STIO; 0°–20°S, 50°–115°E). In this study, an analysis of continuously stratified linear ocean model reveals that the second baroclinic mode also has significant contribution to the annual sea level variability (as high as 81% of the first baroclinic mode). The contributions of residual high-order modes (3 ≤ n ≤ 25) are much less. The superposition of low-order (first and second) baroclinic Rossby waves (BRWs) primarily contribute to the high energy center of sea level variability at ~10°S in the STIO and the vertical energy penetration below the seasonal thermocline. We have found that 1) the low-order BRWs, having longer zonal wavelengths and weaker damping, can couple more efficiently to the local large-scale wind forcing than the high-order modes and 2) the zonal coherency of the Ekman pumping results in the latitudinal energy maximum of low-order BRWs. Overall, this study extends the traditional analysis to suggest the characteristics of the second baroclinic mode need to be taken into account in interpreting the annual variability in the STIO.
Instability Processes in Simulated Finite-Width Ocean Fronts
Authors: Skyllingstad Eric D. , Samelson Roger M. 
Published: August 2020

AbstractA simple, isolated front is modeled using a turbulence resolving, large-eddy simulation (LES) to examine the generation of instabilities and inertial oscillations by surface fluxes. Both surface cooling and surface wind stress are considered. Coherent roll instabilities with 200–300-m horizontal scale form rapidly within the front after the onset of surface forcing. With weak surface cooling and no wind, the roll axis aligns with the front, yielding results that are equivalent to previous constant gradient symmetric instability cases. After ~1 day, the symmetric modes transform into baroclinic mixed modes with an off-axis orientation. Traditional baroclinic instability develops by day 2 and thereafter dominates the overall circulation. Addition of destabilizing wind forcing produces a similar behavior, but with off-axis symmetric-Ekman shear modes at the onset of instability. In all cases, imbalance of the geostrophic shear by vertical mixing leads to an inertial oscillation in the frontal currents. Analysis of the energy budget indicates an exchange between kinetic energy linked to the inertial currents and potential energy associated with restratification as the front oscillates in response to the vertically sheared inertial current. Inertial kinetic energy decreases from enhanced mixed layer turbulence dissipation and vertical propagation of inertial wave energy into the pycnocline.
Numerical Investigation of Mechanisms Underlying Oceanic Internal Gravity Wave Power-Law Spectra
Authors: Pan Yulin , Arbic Brian K. , Nelson Arin D. , Menemenlis Dimitris , Peltier W. R. , Xu Wentao , Li Ye 
Published: August 2020

AbstractWe consider the power-law spectra of internal gravity waves in a rotating and stratified ocean. Field measurements have shown considerable variability of spectral slopes compared to the high-wavenumber, high-frequency portion of the Garrett–Munk (GM) spectrum. Theoretical explanations have been developed through wave turbulence theory (WTT), where different power-law solutions of the kinetic equation can be found depending on the mechanisms underlying the nonlinear interactions. Mathematically, these are reflected by the convergence properties of the so-called collision integral (CL) at low- and high-frequency limits. In this work, we study the mechanisms in the formation of the power-law spectra of internal gravity waves, utilizing numerical data from the high-resolution modeling of internal waves (HRMIW) in a region northwest of Hawaii. The model captures the power-law spectra in broad ranges of space and time scales, with scalings ω−2.05±0.2 in frequency and m−2.58±0.4 in vertical wavenumber. The latter clearly deviates from the GM76 spectrum but is closer to a family of induced-diffusion-dominated solutions predicted by WTT. Our analysis of nonlinear interactions is performed directly on these model outputs, which is fundamentally different from previous work assuming a GM76 spectrum. By applying a bicoherence analysis and evaluations of modal energy transfer, we show that the CL is dominated by nonlocal interactions between modes in the power-law range and low-frequency inertial motions. We further identify induced diffusion and the near-resonances at its spectral vicinity as dominating the formation of power-law spectrum.
Baroclinic Modes over Rough Bathymetry and the Surface Deformation Radius
Authors: LaCasce J. H. , Groeskamp Sjoerd 
Published: August 2020

AbstractThe deformation radius is widely used as an indication of the eddy length scale at different latitudes. The radius is usually calculated assuming a flat ocean bottom. However, bathymetry alters the baroclinic modes and hence their deformation radii. In a linear quasigeostrophic two-layer model with realistic parameters, the deep flow for a 100-km wave approaches zero with a bottom ridge roughly 10 m high, leaving a baroclinic mode that is mostly surface trapped. This is in line with published current meter studies showing a primary EOF that is surface intensified and has nearly zero flow at the bottom. The deformation radius associated with this “surface mode” is significantly larger than that of the flat bottom baroclinic mode. Using World Ocean Atlas data, the surface radius is found to be 20%–50% larger over much of the globe, and 100% larger in some regions. This in turn alters the long Rossby wave speed, which is shown to be 1.5–2 times faster than over a flat bottom. In addition, the larger deformation radius is easier to resolve in ocean models.