Vertical Motion Research Articles

Numerical simulations of the interactions between counterflowing density currents

The collision and interactions between counterflowing density currents frequently occur in nature and engineering practices along the coastal regions. However, the mechanisms and implications of these interactions remain an active research area. In this study, we developed a high-resolution numerical model to simulate the hydrodynamic characteristics of symmetric and asymmetric colliding saline density currents. The aim was to understand the interaction mechanisms, quantify collision parameters, and provide baseline physical insights into the implications of such interactions. The direct numerical simulations reveal that when equal height counterflowing saline density currents collide, the dynamic characteristics of the resulting flow depend on the density difference between the colliding currents, collaborating experimental results. The interaction process initiated mixing and significant vertical motion in the resulting mixed fluid, which attained a maximum rise height of approximately twice that of the colliding currents, thereby enhancing the vertical motion of hypersaline fluid in the ambient column. While the extent of mixing at the collision boundary increases with increasing asymmetry between the colliding currents, a relationship is observed between the buoyancy ratio of the colliding currents and the maximum rise height of the vertically displaced fluid. Given that desalination operations require effective dispersion of brine into the marine environment to minimize local impacts, understanding the collision dynamics of counterflowing saline currents would facilitate improved engineering design and implementation of environmentally compliant coastal management strategies.

Ground subsidence in major Philippine metropolitan cities from 2014 to 2020

Land subsidence is recognized as one of the hazards that threaten Metro Manila, Philippines, and other major urban areas worldwide. It has become a significant global issue caused by excessive groundwater extraction, rapid urbanization, and natural sediment compaction, exacerbated by climate change through rising sea levels. This paper presents vertical ground motion rates in Philippine metropolitan cities using Sentinel-1 InSAR time series analysis from 2014 to 2020 through UK COMET’s LiCSAR products and the LiCSBAS package of Morishita et al. (2020). The results revealed a maximum subsidence rate of 109 mm/yr in Bulacan Province in Greater Manila. For the first time, this paper also presents ground motion estimates and the following maximum subsidence rates for other Philippine metropolitan cities: 11 mm/yr in Metro Cebu, 38 mm/yr in Metro Davao, 9 mm/yr in Metro Iloilo, and 29 mm/yr in Legazpi City. Areas with remarkably high subsidence rates are observed as circular to elliptical deformation features in vertical motion maps. Sinking areas mostly coincide with industrial and commercial complexes evident as a contiguous distribution of large and expansive man-made structures with distinct radar reflections. Monitoring this hazard is crucial as it increases the risk of floods, building and infrastructure damage, and economic loss, and exposes residents along the coast to worsening tidal incursions and storm surges due to climate change. InSAR is proposed here as a targeted, long-term deformation monitoring tool, especially related to groundwater usage.

Interdecadal shifts of ENSO influences on Spring Central Asian precipitation

Spring Central Asian precipitation (SCAP) holds significant implications for local agriculture and ecosystems, with its variability mainly modulated by El Niño–Southern Oscillation (ENSO). The ENSO–SCAP relationship has experienced pronounced interdecadal shifts, though mechanisms remain elusive. Based on observations and climate model simulations, these shifts may result from transitions in ENSO-induced meridional circulation and Rossby wave trains triggered by North Atlantic (NA) sea surface temperature (SST) anomalies. During high (low) correlation periods, ENSO induces strong (weak) vertical motion anomalies over Central Asia, while NA SST anomalies exert a weak (strong) counteracting effect, modulated by the Pacific decadal oscillation (PDO). In the positive (negative) phase of PDO, a slow (fast) decaying ENSO triggers a strong (weak) NA horseshoe-like SST anomaly in the post-ENSO spring, affecting the ENSO–SCAP relationship. Our study identifies a strengthening trend in the ENSO–SCAP relationship since the 2000s, indicating improved predictability for SCAP in recent decades.

Dynamic response of seabed in wind power of deep-shallow sea induced by internal solitary waves

With the development of offshore wind power projects worldwide, the stability of deep and shallow sea wind power sites has become a crucial concern. Internal solitary waves (ISWs) are nonlinear and large amplitude waves in the stratified ocean. Their strong vertical and horizontal motion and vorticity and turbulence caused by fragmentation have an important impact on the marine environment, seabed sediments, and marine engineering. This study focuses on the interaction between ISWs and the seabed of wind power sites in deep and shallow seas. Specifically, we investigate the interaction between ISWs and monopile foundations or floating fan plate anchor structures in the seabed. Through the simulation of CFD software and Comsol software, a law of seabed pore pressure variation during the effect of ISWs on the structure can be well demonstrated. Our results demonstrate that ISWs induce the accumulation of excess pore water pressure around the structures. The monopile foundation experiences negative excess pore water pressure at its bottom and the plate anchor at its top. The pore water pressure at the bottom of the monopile foundation initially decreases and then increases. In contrast, the pore water pressure at the right side of the monopile foundation increases, decreases, and then increases. This phenomenon promotes the settlement of the structure. At the bottom of the plate anchor, there is a sharp increase in positive excess pore water pressure by ISW. The pore water pressure above the plate anchor structure initially decreases and then increases, while below the plate anchor, it increases and then decreases. This phenomenon leads to the movement of the anchorage structure and instability of the surrounding soil. The influence of ISWs on the seabed bottom intensifies with the obstruction of the structure, resulting in significant positive pressure at the bottom. Between the two anchoring structures, there is increased seepage of pore water, making the seabed more prone to instability. Through the study of this article, we know that ISW has different effects on the force of monopile foundation and plate anchor structure, which provides a favorable basis for its design and maintenance.

Dynamic modelling and experimental validation of a dynamic track stabiliser vehicle–track spatially coupling dynamics system

A dynamic track stabiliser vehicle is an unconventional vehicle for maintaining the quality of ballasted tracks, and its dynamic performance has a significant impact on its working efficiency. For the first time, this paper proposes a comprehensive dynamic track stabiliser vehicle–track coupled vertical and lateral multi-body dynamics model based on classical vehicle–track coupling dynamics theory. In this model, detailed attention is given to the vertical, lateral, roll, yaw, and pitch motions of the components, including the vehicle body, bogies, wheelsets and stabilisers. The Shen–Hedrick–Elkins theory is employed to describe non-linear wheel–rail contact relationships between the bogie wheelsets and the rails, and three various methodologies are adopted to address complicated wheel–rail interaction problems between the stabiliser wheelsets and the rails. This comprehensive multi-body dynamics model enables a detailed investigation of the dynamic performance of the system under complex excitations, such as the lateral excitation of the stabilisers and vertical downward pressure exerted by hydraulic cylinders, especially the dynamic response of the stabilisers in the vibration environment of the complete vehicle. The dynamics model was fully validated by comparing its results with time- and frequency-domain data obtained from field tests. The results indicate that the model is capable of being used for analysis of the dynamic performance of dynamic track stabiliser vehicles.

Atmospheric Teleconnections Responsible for the Dominant Patterns of Interannual Variability in Summer Drought over Northern Asia

Abstract Summer drought over northern Asia (NA) seriously threatens the local fragile ecological environment and social economy development. In this study, using the standardized precipitation evapotranspiration index (SPEI), we first identify the dominant modes of interannual variability in summer drought condition over NA and then explore the atmospheric patterns responsible for the formation of the modes. The results show that the first empirical orthogonal function (EOF1) mode of summer SPEI over NA exhibits a meridional dipole pattern, which is influenced primarily by the polar–Eurasian teleconnection (POL) and circumglobal teleconnection (CGT) patterns. Under the influence of negative POL and positive CGT patterns, there is an anomalous anticyclone (cyclone) over northwestern Siberia (Lake Baikal to Northeast China). Such atmospheric circulations lead to meridional dipole patterns in air temperature, moisture condition, vertical motion, and cloud cover over NA, favoring decreased (increased) precipitation and increased (decreased) potential evapotranspiration over northern (southern) NA, finally contributing to the formation of EOF1. The second EOF (EOF2) shows an approximate zonal dipole pattern, which is influenced by the British–Baikal Corridor (BBC) and Scandinavia (SCA) teleconnection patterns. The positive BBC and SCA patterns can lead to an anomalous anticyclone over the Ural Mountains and a cyclone over Lake Baikal. Such atmospheric circulations result in a zonal dipole pattern in precipitation and potential evapotranspiration over NA through changing the local moisture condition, air temperature, and radiation, consequently favoring the formation of EOF2. Fitting analysis indicates that the aforementioned atmospheric factors can explain 76% (55%) of the interannual variability of EOF1 (EOF2).

Proposal and application of a convective wind gustiness parameterization based on convective available potential energy

Wind gustiness is an effective approach for addressing mesoscale enhancement in estimating air-sea interface fluxes. In this study, an improved convective gustiness parameterization scheme based on convective available potential energy (CAPE) is formulated utilizing reanalysis data and wind observations from moored buoys. This new parameterization was examined by implementing it in the air-sea flux transfer scheme within the National Center for Atmospheric Research Community Earth System Model (NCAR CESM) version 2.1.3 and contrasting it with a previously proposed scheme based on convective precipitation rate. The results indicate a significant reduction in negative biases of surface winds and latent heat fluxes over the tropical Indian Ocean and western Pacific during summer with the implementation of either gustiness scheme, resulting in an average increase in latent heat flux of approximately 9 W·m− 2. Specifically, the CAPE-based scheme shows a more favorable impact in the Indo-Pacific Warm Pool region, whereas the precipitation-based scheme exhibits inferior performance in the western Pacific Intertropical Convergence Zone. Further analysis reveals that the inclusion of the gustiness scheme distinctly alters surface evaporation and latent heat flux, influencing vertical motion in the area with active convective activity and effectively improving precipitation simulations by up to 18%. Moreover, the CAPE-based scheme reduces the bias in summer precipitation simulations by approximately 5% more than the precipitation-based scheme.

Metaheuristic tuned decentralized PID controller based active suspension system for railway vehicle

AbstractA high‐speed railway system is one of the sustainable alternatives to other modes of transportation and may connect the most congested urban cities with minimum carbon emissions. However, the vibration intensity increases as the train's operating speed increases, resulting in deteriorated ride comfort and stability. Hence, this article investigates a 27‐degree‐of‐freedom (DOF) dynamic model of railway vehicles with an improved active suspension system. The decentralized control structure performs the controlling action with five optimized Proportional Integral Derivative (PID) controllers that suppress the vehicle body's vertical, lateral, pitch, roll, and yaw motions. Further, to optimize the PID parameters, three metaheuristic optimization techniques, Genetic algorithm (GA), Grey Wolf Optimization (GWO), and Flower Pollination Algorithm (FPA), are utilized, and their simulated results are compared with the passive system as well as other conventional tuning technique. Moreover, the performance of the proposed control strategy is evaluated in the frequency domain under random track irregularities, and the results are characterized in terms of power spectral densities (PSDs). The simulated results show that among the proposed metaheuristic algorithms, FPA outperforms with a significant reduction in vehicle vibration compared to other tuning methods. The percentage reduction of the vertical, lateral, pitch, rolls, and yaw accelerations is 71.4%, 35.1%, 52.8%, 48.1%, and 38.2%, respectively, ensuring enhanced vehicle ride comfort.

An electrostatically actuated MEMS microgripper with high amplification for precision manipulation

This paper presents a low-voltage electrostatically actuated MEMS microgripper with high amplified displacements. The design incorporates a novel compliant mechanical amplifier that efficiently converts vertical motions into horizontal motions, resulting in a high amplification ratio of 9.25. The design incorporates a capacitive displacement sensor that can accurately measure the microgripper’s jaw movement. Finite Element Analysis (FEA) is utilized to optimize the design parameters, considering the fabrication constraints. The fabrication is based on the standard silicon-on-insulator micromachining process (SOIMUMPs), combined with an in-house etching process. Experimental testing demonstrates a maximum jaw displacement of 26.8 μm at a low applied voltage of 18 V. A successful grasping of a micro-object is demonstrated, which validates the practicality and effectiveness of the proposed design. Such a microgripper can be promising for the growing need for precise micromanipulation in various applications, such as biological cell manipulation and micro assembly.

Vulnerability of suspension bridges to spatially variable vertical ground motions

This study investigates the vulnerability of long-span suspension bridges to spatially variable vertical ground motions (SV-VGMs). While of recognized importance, a comprehensive understanding of this topic has been traditionally limited by the unavailability of an adequate number of arrays of motions. In this work, 10 simulations of a large-magnitude Hayward Fault earthquake are utilized to perform site-specific structural response assessments of a suspension bridge under different load scenarios. A detailed nonlinear model representative of the West San Francisco-Oakland Bay Bridge is employed as the case study structure. Four sets of nonlinear time-history analyses are performed with and without VGMs and with and without the incorporation of spatial variability to offer the basis for a complete comparison of the demand distributions across different load cases. Results indicate that VGMs largely influence the response of the bridge decks in the vertical direction, with an increase in drifts up to 2× for the case of synchronous input and up to 2.5× for the case of asynchronous inputs. The analysis of the bridge response in the time and frequency domain across all load cases reveals a high sensitivity of the decks’ response to minor time lags in input motions of comparable amplitude, which are seen to activate the contribution of higher modes to the structural response. Evidence from this study points to the potential of severely underestimating structural demands if the (even limited) spatial variability of the input motions is not incorporated correctly. For the case study structure, the probability of exceeding the onset of nonlinearity in the short decks at the design earthquake level is seen to increase by a factor of about two when considering SV-VGMs as opposed to synchronous horizontal motions only.

A 3D-Var assimilation scheme for vertical velocity with CMA-MESO v5.0

Abstract. Certain vertical motions associated with meso-microscale systems are favorable for convection development and maintenance. Correct initialization of updraft motions is thus significant in convective precipitation forecasts. A three-dimensional variational-based vertical velocity (w) assimilation scheme has been developed within the high-resolution (3 km) CMA-MESO (the Mesoscale Weather Numerical Forecast System of the China Meteorological Administration) model. This scheme utilizes the adiabatic Richardson equation as the observation operator for w, enabling the update of horizontal winds and mass fields of the model's background. The tangent linear and adjoint operators are subsequently developed and undergo an accuracy check. A single-point w observation assimilation experiment reveals that the observational information is effectively spread both horizontally and vertically. Specifically, the assimilation of w contributes to the generation of horizontal wind convergence at lower model levels and divergence at higher model levels, thereby adjusting the locations of convection occurrence. The impact of assimilating w on the forecast is then examined through a series of continuous 10 d runs. Further assimilation of w, in addition to the assimilation of conventional and radial wind data, significantly improves the forecast accuracy of precipitation, resulting in higher FSS (fractions skill score) values and higher ETS (equitable threat score) skills at higher thresholds (5 and 20 mm h−1). However, it should be noted that further assimilation of w can potentially lead to some false precipitation, resulting in slightly lower ETS values at lower thresholds (1 mm h−1) and a neutral impact on BIAS (bias score) skills. An individual case study conducted within the batch experiments reveals that assimilating w has a beneficial impact on the enhancement of vertical motion across different layers of the model, facilitating the transport of moisture from lower to middle–high model levels, thereby leading to an improvement in forecast skills.

An Attention-Based Deep Learning Model for Phase-Resolved Wave Prediction

Abstract Phase-resolved wave prediction capability, even if only over two wave periods in advance, is of value for optimal control of wave energy converters, resulting in a dramatic increase in power generation efficiency. Previous studies on wave-by-wave predictions have shown that an artificial neural network (ANN) model can outperform the traditional linear wave theory-based model in terms of both prediction accuracy and prediction horizon when using synthetic wave data. However, the prediction performance of ANN models is significantly reduced by the varying wave conditions and buoy positions that occur in the field. To overcome these limitations, a novel wave prediction method is developed based on the neural network with an attention mechanism. This study validates the new model using wave data measured at sea. The model utilizes past time histories of three Sofar Spotter wave buoys at upwave locations to predict the vertical motion of a Datawell Waverider-4 at a downwave location. The results show that the attention-based neural network model is capable of capturing the slow variation in the displacement of the buoys, which reduces the prediction error compared to a standard ANN and long short-term memory model.

Unloading Uplift Caused by Surface Processes in New Zealand's Southern Alps

AbstractThe Southern Alps experiences rapid bedrock uplift and intense surface processes like erosion and deglaciation. We quantify how the erosion and deglaciation contribute to the ongoing vertical motions using geophysical models. The erosional unloading uplift is found to be 0.5–1.5 mm/yr throughout the central Southern Alps, whereas the recent deglaciation may locally produce uplift up to 1–3 mm/yr. The estimated unloading uplift accounts for 10%–40% of the GNSS‐observed uplift. After correcting the unloading uplift, the GNSS‐observed uplift can be explained by about 4–6 mm/yr dip‐slip motion on the Alpine fault, which is 10%–50% below previous geodetic estimates. Hence, unloading uplift must be evaluated when interpreting geodetic observations in tectonically active mountain ranges subjected to intense surface processes.

Multi-modal evaluation of respiratory diaphragm motion in chronic obstructive pulmonary disease using MRI series and CT images.

Chronic obstructive pulmonary disease (COPD), characterized by airflow limitation and breathing difficulty, is usually caused by prolonged inhalation of toxic substances or long-term smoking habits. Some abnormal features of COPD can be observed using medical imaging methods, such as magnetic resonance imaging (MRI) and computed tomography (CT). This study aimed to conduct a multi-modal analysis of COPD, focusing on assessing respiratory diaphragm motion using MRI series in conjunction with low attenuation volume (LAV) data derived from CT images. This study utilized MRI series from 10 normal subjects and 24 COPD patients, along with thoracic CT images from the same patients. Diaphragm profiles in the sagittal thoracic MRI series were extracted using field segmentation, and diaphragm motion trajectories were generated from estimated diaphragm displacements via registration. Re-sliced sagittal CT images were used to calculate regional LAVs for four distinct lung regions. The similarities among diaphragm motion trajectories at various positions were assessed, and their correlations with regional LAVs were analyzed. Compared with the normal subjects, patients with COPD typically exhibited fewer similarities in diaphragm motion, as indicated by the mean normalized correlation coefficient of the vertical motion component (0.96 for normal subjects vs. 0.76 for severity COPD patients). This reduction was significantly correlated with the LAV% in the two lower lung regions with a regression coefficient of 0.81. Our proposed evaluation method may assist in the diagnosis and therapy planning for patients with COPD.

Measuring Clear‐Air Vertical Motions From Space

AbstractMeasuring vertical velocity in the atmosphere has long been a challenge due to its small magnitude. Taking advantage of the modulation of free tropospheric relative humidity by vertical motions, we derive analytical relationships that allow us to retrieve vertical motions in clear air from geostationary measurements of brightness temperature in the infrared absorption band of water vapor. The new observations have a resolution of 1 hr and 2 km in time and space, respectively. They capture the variability of mesoscale and large‐scale vertical velocity measured during field campaigns. In the mid‐troposphere, clear‐sky vertical motions are mostly subsiding but highly heterogeneous in space and time. Around organized deep convective systems, strong subsidence (>500 hPa·day−1) is observed within a distance of a few hundred kilometers. In contrast, transient upward motions of up to 100 hPa·day−1 can occur at the mesoscale. Vertical motions in the clear‐sky atmosphere appear to be primarily associated with buoyancy and gravity waves at the mesoscale, and with radiative cooling and equatorial waves at larger spatial scales. This new retrieval reveals a rich range of dynamical features that were previously invisible, thus shedding new light on tropical meteorology.

Distinguishing Extreme Precipitation Mechanisms Associated with Atmospheric Rivers and Nonatmospheric Rivers in the Lower Yangtze River Basin

Abstract This study investigates the disparity in quantitative moisture contribution and synoptic-scale vertical motion in the lower reaches of the Yangtze River basin (LYRB) for different extreme precipitation (EP) types, which are categorized as EP associated with atmospheric river (AR&EP) or EP associated with nonatmospheric river (non-AR&EP). To analyze moisture contribution, backward tracking using the Water Accounting Model-2layers is performed. In general, the remote moisture contribution is 9.7 times greater than the local contribution, with the ocean contribution being 1.67 times stronger than the land contribution. However, terrestrial and oceanic contributions obviously increase in the EP types, especially for oceanic contribution being double in magnitude. Notably, the west Pacific (WP) contribution emerges as the dominant differentia between the EP types, playing a crucial role in the AR formation. By solving the quasigeostrophic omega equation, the upper-level jet (ULJ) stream acts as the primary dynamic forcing for transverse vertical motion in AR&EP, while the baroclinic trough exhibits a relatively weaker influence. However, both systems have a nearly equal impact on vertical velocity in non-AR&EP. The enhanced shearwise elevation in the non-AR&EP type is the response of the stronger upper-level ridge over the Tibetan Plateau (TP), which induces enhanced Q vector, the divergence pointing toward the LYRB. However, the main dynamic difference is the location of ULJ, which serves as the trigger role although weak. Diabatic forcing proves to be the decisive factor for vertical motion development, the difference attributed to the released excessive latent heating with excess moisture contribution from the WP in AR&EP with enhanced precipitation. Significance Statement The main objective of this study is to investigate quantitative moisture contribution by applying Water Accounting Model-2layers and vertical motion attribution using the quasigeostrophic omega equation for extreme precipitation types based on the presence or absence of atmospheric river. Our findings reveal excessive moisture from the west Pacific serving not only as key in atmospheric river formation but also as the primary trigger for intensified diabatic vertical motion, inducing enhanced precipitation. The direction of strong winds in the north of the Tibetan Plateau holds crucial forecasting implications, which determine the location of the upper-level jet stream downstream. The transverse vertical motion, induced by the upper-level jet stream, plays the dominant dynamic role in both extreme precipitation (EP) types.

Shear-imposed falling film on a vertical moving plate with disrupted time-reversal

We propose a mathematical model to study the stability and dynamics of a shear-imposed thin film flow on a vertical moving plate, incorporating the influence of odd viscosity. This odd viscosity effect is vital in conventional fluids when there is a disruption in time-reversal symmetry. Our motivation to study the dynamics with odd viscosity arises from recent studies (Kirkinis & Andreev, vol. 878, 2019, pp. 169–189; Chattopadhyay & Ji, vol. 455, 2023, pp. 133883) where the odd viscosity effectively reduces flow instabilities under different scenarios. Utilizing a long wave perturbation method, we derive a nonlinear evolution equation at the liquid–air interface, which is influenced by the motion of the vertical plate, imposed shear, odd viscosity, and inertia. We first perform a linear stability analysis of the model to get firsthand information on various flow parameters. Three distinct conditions for the vertical plate, quiescent, upward-moving, and downward-moving, are considered, accounting the imposed shear and odd viscosity. Additionally, employing the method of multiple scales, we conduct a weakly nonlinear stability analysis for the traveling wave solution of the evolution equation and explore its bifurcation analysis. The bifurcation analysis reveals the existence of subcritical unstable and supercritical stable zones for crucial flow parameters: odd viscosity, imposed shear, and motion of the vertical plate. Both linear and weakly nonlinear stability analyses demonstrate that the destabilizing effect induced by the upward motion of the vertical plate can be alleviated by applying uphill shear, while the destabilizing effect of downhill shear can be mitigated when the vertical plate is in a downward motion. Moreover, we define an eigenvalue problem that mirrors the Orr–Sommerfeld (OS) model for analyzing normal modes and identifying the critical Reynolds number. We investigate the dynamics of surface waves through numerical solutions of the OS eigenvalue problem using the Chebyshev spectral collocation method. We observe the consistent enhancement of stabilization in the presence of odd viscosity. In the low to moderate Reynolds number range, vertical plate motion and odd viscosity show similar behavior in OS analysis, while imposed shear exhibits distinct changes. The Benney-type model does not agree with the OS problem when the Reynolds number is moderate with or without the three key parameters: vertical plate motion, imposed shear, and odd viscosity. However, when the Reynolds number is low with or without the three key parameters: vertical plate motion, imposed shear, and odd viscosity, the Benney-type model agrees with the OS. Further, numerical simulations of the evolution equation corroborate the results obtained from linear stability, weakly nonlinear stability, and OS analyses. Finally, the Hopf bifurcation analysis of the fixed point reveals that the wave speed is influenced by both the motion of the plate and the imposed shear while it remains independent of odd viscosity.

Solutions for Tropical Vertical Motion under Convective Quasi-Equilibrium Constraints

Abstract Solutions for tropical convection (vertical motion), including both the first (deep) and the second baroclinic (shallow) modes, subject to convective quasi-equilibrium (CQE) constraints are formulated. Under CQE assumption, tropical convection ω(p, x, y) can be decomposed into a product of height-dependent variable Ωi(p) and space-dependent variable ∇·vi(x, y) with the former constrained by conservation of moist static energy (MSE) or dry static energy (DSE) perturbations, depending on whether the atmospheric column is dominated by ascending or descending motions. We then evaluate the roles of deep and shallow modes of convection in transporting moisture and static energy against observations using the European Centre for Medium-Range Weather Forecasts reanalysis data. The moisture transport by deep mode produces a spatial pattern similar to observations, except for an obvious underestimate of the magnitude over the eastern Pacific convergence zone (EPCZ) and cold tongue areas, where the contribution of shallow mode may account for up to 25% of the total moisture transport. In contrast, the MSE transport by deep mode exhibits a very poor performance, especially over the EPCZ where the observational MSE transport is negative, but a positive value is predicted by deep mode. Including the contribution of shallow mode immediately remedies this deficiency, due to a better representation of the bottom-heavy structure of ascending motions over the EPCZ. These improvements apply to almost the entire tropics, although the correlation tends to decrease away from the convergence zones. Since simple atmospheric models often assume a single heating (forcing) profile to represent the effect of cumulus convection, the present study highlights the importance and feasibility of including both deep and shallow modes in a simple atmospheric model, while at the same time maintaining the simple model framework, to more accurately represent the moisture and MSE transports by convection in the tropics.

Diagnosing drivers of tropical precipitation biases in coupled climate model simulations

In this study, we analyse the large-scale biases in tropical precipitation climatology of two different types of coupled ocean–atmosphere general circulation models (GCMs): the coupled model intercomparison project (CMIP) models and ICON-Sapphire, a global storm-resolving model. We employ the simple globally resolved energy balance (GREB) diagnostic precipitation model to evaluate four drivers of the precipitation biases in the simulations: surface specific humidity, surface relative humidity, tropospheric mean and variability in the vertical motion. The tropical precipitation biases in the CMIP and ICON-Sapphire simulations are surprisingly similar in their patterns and also in the elements forcing them. The results of our analysis using the GREB model show that the precipitation biases result from both biases in the sensitivity to the four forcing fields and biases in the simulated forcing fields themselves. The most significant bias for both, the CMIP and ICON-Sapphire simulations, is a too high sensitivity to the mean vertical circulation (ωmean\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\\omega }_{\ ext{mean}}$$\\end{document}) and bias in the ωmean\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\\omega }_{\ ext{mean}}$$\\end{document} climatology itself. This also holds for specific long-standing biases, such as the double intertropical convergence zone problem. Meanwhile, biases in the climatology of specific and relative humidity play only a minor role but contribute to an overall small increase in precipitation in CMIP models that may be related to the “drizzling” bias. These results can give insights to the modelling community regarding model development, and illustrate that the GREB diagnostic precipitation model applied is a good tool for evaluating the drivers of large-scale tropical precipitation.

Assessing Current Coastal Subsidence at Continental Scale: Insights From Europe Using the European Ground Motion Service

AbstractBeside climate‐change‐induced sea‐level rise (SLR), land subsidence can strongly amplify coastal risk in flood‐prone areas. Mapping and quantifying contemporary vertical land motion (VLM) at continental scales has long been a challenge due to the absence of gridded observational products covering these large domains. Here, we fill this gap by using the new European Ground Motion Service (EGMS) to assess the current state of coastal VLM in Europe. First, we compare the InSAR‐based EGMS Ortho (Level 3) with nearby global navigation satellite systems (GNSS) vertical velocity estimates and show that the geodetic reference frame used to calibrate EGMS strongly influences coastal vertical land velocity estimates at the millimeter per year level and this needs to be considered with caution. After adjusting the EGMS vertical velocity estimates to a more updated and accurate International Terrestrial Reference Frame (ITRF2014), we performed an assessment of VLM in European low elevation coastal flood plains (CFPs). We find that nearly half of the European CFP area is, on average, subsiding at a rate faster than 1 mm/yr. More importantly, we find that urban areas and populations located in the CFP experience a near −1 mm/yr VLM on average (excluding the uplifting Fennoscandia region). For harbors, the average VLM is even larger and increases to −1.5 mm/yr on average. This demonstrates the widespread importance of continental‐scale assessments based on InSAR and GNSS to better identify areas at higher risk from relative SLR due to coastal subsidence.