Large Vertical Gradients Research Articles

Effect of 2009 Major SSW Event on the Mesospheric CO2 ${\text{CO}}_{2}$ Cooling

AbstractCarbon dioxide (), an important trace species that is gradually increasing in the atmosphere due to anthropogenic activities, causes enhanced warming in the lower atmosphere. The increased concentration of in the upper atmosphere results in enhanced radiative cooling rates leading to the contraction of the upper atmosphere. Due to its long lifetime and large vertical gradient, concentration is also influenced by large dynamic events. We report a startling case of variability in density and its infrared radiative cooling rates in the mesosphere and lower thermosphere during a major sudden stratospheric warming (SSW) event. A counter‐intuitive connection between density and resulting radiative cooling has been observed during the 2009 major SSW event. The behavior of cooling rates during such a dramatic events draws attention to our current understanding of infrared cooling variation and its connection to changes in concentration. The significance of temperature and atomic oxygen variability in the observed cooling patterns despite changes in concentration, is also highlighted.

Mercury Stable Isotopes Reveal the Vertical Distribution and Trophic Ecology of Deep-Pelagic Organisms over the North-East Atlantic Ocean Continental Slope.

Deep-pelagic species are central to marine ecosystems and increasingly vulnerable to global change and human exploitation. To date, our understanding of these communities remains limited mainly due to the difficulty of observations, calling for complementary innovative tools to better characterize their ecology. We used mercury (Δ199Hg, δ202Hg, Δ201Hg, and Δ200Hg), carbon (δ13C), and nitrogen (δ15N) stable isotope compositions to segregate deep-pelagic species caught on the continental slope of the Bay of Biscay (NE Atlantic) according to their foraging depth and trophic ecology. Decreasing fish Δ199Hg values with corresponding depth estimates from the surface to down to 1,800 m confirmed that mercury isotopes are able to segregate deep species over a large vertical gradient according to their foraging depth. Results from isotopic compositions also identified different mercury sources, likely reflecting different trophic assemblages over the continental slope, in particular, the demersal influence for some species, compared to purely oceanic species. Overall, our results demonstrate how mercury stable isotopes can inform the vertical foraging habitat of little-known species and communities feeding in the deep.

Effect of Vertical Shear in the Zonal Wind on Equatorial Electrojet Sidebands: An Observational Perspective Using Swarm and ICON Data

AbstractThe wind dynamo in the ionosphere leads to differential motion of ions and electrons, which in turn sets up electric fields and currents. Observations show that daytime lower thermospheric horizontal winds have large vertical gradients. Numerical modeling conducted approximately 50 years ago demonstrated that the zonal wind shears in the ∼130–180 km altitude range can generate off‐equatorial relative minima (dips) in the daytime height‐integrated eastward current density, appearing as westward sidebands north and south of the equatorial electrojet (EEJ). This study observationally confirms this connection for the first time by combining Ionospheric CONnection explorer zonal wind profiles and Swarm latitudinal zonal currents. We demonstrate observationally that the magnitude of the EEJ sideband current is proportional to the strength of westward turning winds with altitude in the Pedersen conductivity dominated region. Additional numerical experiments explain the importance of wind shear in different altitude regions in generating the sideband current. This study contributes to the better understanding of the neutral wind effect on the local current generation.

The impacts of geothermal gradients on compressed carbon dioxide energy storage in aquifers

Compressed CO2 energy storage in aquifers (CCESA) is new low-cost large scale energy storage technology. To further improve the energy efficiency of CCESA, we propose to combine the geothermal system with CCESA. In order to study the influence of geothermal energy on CCESA, aquifers with large vertical interval and different geothermal gradients from 0.026–0.07 °C/m are designed. The 3d wellbore-reservoir grid of underground part of CCESA was established. The simulation covering 100 days of intermittent initial gas fill and 50 days of cyclic injection and production was conducted. The hydrodynamic and thermodynamic behaviors and energy efficiency of the system were analyzed, comparatively. In the gas fill period, the higher the geothermal gradient, the farther the front of CO2 plume diffuses in the target aquifer, and thus the smaller the pressure accumulation. The temperature, pressure and energy efficiency of produced CO2 increases with the increase of geothermal gradient, while the density of released fluid decreases. The energy efficiency is greater than 1.0 under 6 geothermal gradients. The average energy efficiency of high- and low-pressure reservoirs can reach 1.282 and 1.061 under the geothermal gradient of 0.07 °C/m, which is 21.79 % and 5.5 % higher than that of 0.026 °C/m. The total energy efficiency of the joint system finally can reach 95.1 %. This research well confirms that the geothermal energy can dramatically improve the efficiency of CCESA and can enhance its application.

Physical quantity characteristics of severe aircraft turbulence near convective clouds over Australia

Using FY–2G satellite data, Aircraft Meteorological Data Relay (AMDAR) downlink data, and the fifth generation European Centre for Medium–Range Weather Forecasts (ECMWF) atmospheric reanalysis of the global climate (ERA5) dataset, we analyzed the circulation, thermal, and dynamic characteristics of the convective aircraft turbulence over Australia in the Southern Hemisphere. The results show that the near-convective clouds turbulence (NCCT) in the Southern Hemisphere mostly occurred in front of deep warm high–pressure ridges in mid–latitude regions and on the left side of the axis of the subtropical westerly jet stream. The isotherms in this area were relatively dense (i.e., large gradients), and the wind speed was high, with strong horizontal and/or vertical cyclonic wind shear. In addition, the NCCT usually occurred near the zero–divergence or zero–vorticity line and in areas with large vertical wind speed gradients. There were also strong vertical and horizontal wind shears in this area, which could easily trigger severe turbulence. Furthermore, the NCCT in the Southern Hemisphere mostly occurred at the intersection of cold and warm temperature advections (i.e., near the zero–temperature advection line), and the turbulence point was located near the high–altitude frontal zone where there was a strong gradient of cold and warm advections. There was temperature inversion with pseudo–equivalent potential temperatures in the middle and lower troposphere on the warmer side of the turbulence point. The unstable stratification of cold air at the top and warm air at the bottom was conducive to triggering convection from the ground, forming strong convective clouds, and causing severe turbulence.

Field Observations of Hydrostatic Pressure Deviations in a Nearshore Sediment Bed

AbstractMomentary liquefaction (ML), an instantaneous loss of effective stress between individual sand grains, is caused by the upward vertical pressure gradient of the excess pore‐water pressure in the sediment during the passage of a wave. Few field experiments have provided detailed observations of vertical pressure gradients within a sediment bed. Here, a novel autonomous pressure‐profiling instrument, the Pressure Stick, was deployed in the surf zone of an ocean beach in Rye, New Hampshire. The Pressure Stick has eight time‐synced absolute pressure sensors distributed over a 70 cm distance to measure absolute pressure in the water column and in the sediment bed. The absence of direct measurements of the sediment‐water interface location and sediment porosity limit direct observations of ML but allow for an examination of the hydrostatic pressure deviations. Observed upward vertical pressure head gradients within the sediment exceed the assumed effective weight of the sediment. Exceedances of two ML thresholds are observed within 16 cm of the sediment‐water interface and consistently occur at the onset of steeper and larger wave crests. Individual waves are characterized with an approximation of the Sleath parameter and the depth normalized wave height. The ML thresholds are exceeded 1%–40% of the time when the Sleath parameter is greater than 0.1 and 1%–33% of the time when the depth normalized wave height is greater than 0.4. These results suggest that wave steepness and nonlinearity may be necessary to induce large vertical pressure gradients that substantially deviate from hydrostatic pressure.

Martian M2 peak behavior in the dayside near-terminator ionosphere during interplanetary coronal mass ejections

The interplanetary coronal mass ejections (ICMEs) can pose significant impacts on the Martian ionosphere, resulting in plasma depletion, variability, and escape to space. However, the connections between the ICMEs and the associated responses of the dayside near-terminator Martian ionospheric primary peak (M2) are not well understood. The present study primarily investigates the behavior of the ionospheric peak density (Nm) and height (hm) during the passage of ICMEs using observations from the Radio Occultation Science Experiment (ROSE) aboard MAVEN spacecraft. We have selected 8 such ICMEs (during 2017–2022) at Mars from the existing catalogs and studied the ROSE electron density profiles during quiet and disturbed time (ICMEs) for identical solar zenith angle range. We observed the elevation of the M2 peak (hm ∼ 4–16 km) during disturbed time (ICMEs) with a decrease in Nm (0.41–2.8 × 1010 m−3) in comparison to the quiet time. The present study, for the first time, addressed the influence of ICMEs on the M2 peak parameters (Nm and hm). We have proposed that the development of large vertical pressure gradient and electron temperature enhancement are plausible causes for ionospheric variability. Therefore, the present study provides new insights to understand peak plasma behavior in the dayside near-terminator ionosphere during ICMEs.

Low Blind Zone Atmospheric Lidar Based on Fiber Bundle Receiving

Atmospheric constituents feature a large vertical gradient in concentration, especially at the first few hundred meters over the earth’s surface. Atmospheric lidar usually cannot cover this range due to the incomplete overlap effect or the limited dynamic range of detectors. This drawback is well known as the blind zone effect, which hinders the application of atmospheric lidars in many aspects. In this work, a method based on an optical fiber bundle was proposed to mitigate the blind zone effect. An optical fiber head with several stages, installed at the focal plane of the telescope, is used to receive backscatter light from different range levels. The design of the optical fiber head is analyzed with the ray-tracing technique. The optical fiber installed at the highest stage of the fiber head can collect far-range light like a small aperture, and all the other optical fibers are bundled into a near-range detection channel to receive backscatter light from the first few hundred meters. This special design can avoid the near-range light loss in conventional lidar systems, usually equipped with a small aperture. Different optical attenuations are then applied to near-range and far-range channels to suppress the overall signal dynamic range. This light-receiving method was applied in a 1030 nm elastic lidar, in which a fiber bundle with a three-stage fiber head was fabricated and installed. A test experiment was performed to verify this approach. A good agreement between simulations and in-system results was found. Based on this design, the blind zone of the lidar system is less than 50 m, and the detectable range can be over 10 km along the lidar’s line of sight with a single telescope receiver. This approach brings a new way of designing atmospheric lidar with a low blind zone and can strengthen our ability to monitor urban pollution and promote land-atmosphere interaction research.

A comparison of FORMOSAT-3/COSMIC radio occultation and ionosonde measurements in sporadic E detection over mid- and low-latitude regions

The investigation of sporadic E or Es layers typically relies on ground-based or satellite data. This study compares the Es layers recorded in ionograms with those detected using GNSS L1 signal-to-noise ratio data from FORMOSAT-3/COSMIC radio occultation at mid and low latitudes. GPS radio occultation measurements of Es layers, during an 11-year time span of 2007–2017, within a 2° latitude × 5° longitude grid around each ionosonde site are compared to the Es recordings of the ionosonde. By comparing multi-year radio occultation data with recordings from six ionosonde stations at mid and low latitudes, it was discovered that at least 20% of the Es layer detection results between each ionosonde and its crossing GPS radio occultation measurements did not agree. The results show that the agreement between the two methods in Es detection is highly dependent on the season and local time. This study suggests that Es layer recordings from ground-based ionosonde observations have the best agreement with the Es layers detected by radio occultation data during daytime and local summers. The difference in the Es detection mechanisms between the two methods can explain the inconsistency between Es events measured by these two methods. The detection of Es layers in ionograms relies on the high plasma concentration in the E region, whereas signal scintillations caused by a large vertical gradient of the plasma density in the E region are considered a sign of Es occurrence in satellite techniques.

How Well Must Surface Vorticity Be Organized for Tornadogenesis?

Abstract This study investigates whether quasi-random surface vertical vorticity is sufficient for tornadogenesis when combined with an updraft typical of tornadic supercells. The viability of this pathway could mean that a coherent process to produce well-organized surface vertical vorticity is rather unimportant. Highly idealized simulations are used to establish random noise as a possible seed for the production of tornado-like vortices (TLVs). A number of sensitivities are then examined across the simulations. The most explanatory predictor of whether a TLV will form (and how strong it will become) is the maximal value of initial surface circulation found near the updraft. Perhaps surprisingly, sufficient circulation for tornadogenesis is often present even when the surface vertical vorticity field lacks any obvious organized structure. The other key ingredient for TLV formation is confirmed to be a large vertical gradient in vertical velocity close to the ground (to promote stretching). Overall, it appears that random surface vertical vorticity is indeed sufficient for TLV formation given adequate stretching. However, it is shown that longer-wavelength noise is more likely to be associated with substantial surface circulation (because it is the areal integral of vertical vorticity). Thus, coherent vorticity sources that produce longer-wavelength structures are likely to be the most supportive of tornadogenesis.

Variability of Vertical Total Electron Content Gradients in the Brazilian Sector

Ground Based Augmentation Systems are designed to meet demanding requirements during airport approach and landing sections of aircraft routes. It computes corrected and smoothed differential corrections and other information. These messages are transmitted to aircraft, which may use the corrections to improve their position estimation. However, residual correction errors remain, due to ionospheric spatial and temporal gradients between Ground Based Augmentation System reference receivers and approaching aircrafts. Large vertical ionospheric delay gradients detected during combinations of extreme geophysical environments indicate that there are problematic conditions for Ground Based Augmentation System operation over the Brazilian region. Motivated by the above conditions, data from Rede Brasileira de Monitoramento Contínuo, the Brazilian public network of dual-frequency Global Navigation Satellite System receivers operated by Instituto Brasileiro de Geografia e Estatística were analyzed to estimate ionospheric vertical Total Electron Content gradients. The effects from different locations (represented by the dip latitude) and geophysical conditions (represented by solar activity, season, and local time) on variations of ionospheric vertical Total Electron Content gradients have been statistically quantified. The results from the present work provide information to more detailed performance assessments of Ground Based Augmentation System procedures under equatorial and low-latitude ionospheric regions, aimed at flexibly delimiting the conditions for feasible operation in such regions.

An Improved One-Dimensional Bending Angle Forward Operator for the Assimilation of Radio Occultation Profiles in the Lower Troposphere

Abstract Under very large vertical gradients of atmospheric refractivity, which are typical at the height of the planetary boundary layer, the assimilation of radio occultation (RO) observations into numerical weather prediction (NWP) models presents several serious challenges. In such conditions, the assimilation of RO bending angle profiles is an ill-posed problem, the uncertainty associated with the RO observations is higher, and the one-dimensional forward operator used to assimilate these observations has several theoretical deficiencies. As a result, a larger percentage of these RO observations are rejected at the NWP centers by existing quality control procedures, potentially limiting the benefits of this data type to improve weather forecasting in the lower troposphere. To address these problems, a new methodology that enables the assimilation of RO data to be extended to the lower moist troposphere has been developed. Challenges associated with larger atmospheric gradients of refractivity are partially overcome by a reformulation that has minimal effect at higher altitudes. As a first step toward this effort, this study presents both the theoretical development of this new methodology and a forecast impact assessment of it using the NCEP NWP system. Though using a conservative approach, benefits in the lower tropical troposphere are already noticeable. The encouraging results of this work open the potential for further exploitation and optimization of RO assimilation.

Magnitude and seasonal variation of N2O and CH4 emissions over a mixed agriculture-urban region

Inventory estimates of N2O and CH4 emissions disregard temporal and spatial variabilities, which hinders the search for effective local strategies to lower greenhouse gas emissions. We have quantified the emissions of N2O and CH4 in a mixed agriculture-urban region using two independent approaches, i.e., the vertical gradient method (VGM) and the radon-tracer method (RTM), compared the estimated annual fluxes with the EDGARv6.0 emissions, revealed the seasonal variations of the VGM fluxes, and inferred the sources that most likely cause the seasonal variations based on the footprint analysis even though our methods cannot attribute different sources. We show that the annual RTM estimates represented by the mode of lognormal fit for N2O and CH4 are 0.4 g m−2 yr−1 and 12 g m−2 yr−1, and the VGM estimates are 0.6 ± 0.3 g m−2 yr−1 and 13 ± 4 g m−2 yr−1, respectively. Furthermore, the average EDGARv6.0 emissions constrained by the VGM and the RTM footprints are 1.3 g m−2 yr−1 and 0.9 g m−2 yr−1 for N2O, and 21 g m−2 yr−1 and 18 g m−2 yr−1 for CH4. Compared to our estimated fluxes, EDGARv6.0 N2O and CH4 emissions are both overestimated; for N2O, it is mainly caused by an overestimation of the chemical industry's emission. Moreover, in contrast to EDGARv6.0′s nearly constant monthly emissions throughout the year, the VGM estimates of N2O and CH4 show seasonal variations with relatively high values from March to September, which is most likely caused by agricultural activities. Our study demonstrates that large nighttime vertical gradients of atmospheric N2O and CH4 mole fractions at a tall tower can be used to derive surface fluxes by the VGM; taken together with the RTM fluxes, both the annual means and the temporal variations of N2O and CH4 emissions can be constrained on a regional scale.

A Radar-Based Quantitative Precipitation Estimation Algorithm to Overcome the Impact of Vertical Gradients of Warm-Rain Precipitation: The Flood in Western Germany on 14 July 2021

Abstract The demand of accurate, near-real-time radar-based quantitative precipitation estimation (QPE), which is key to feed hydrological models and enable reliable flash flood predictions, was highlighted again by the disastrous floods following after an intense stratiform precipitation field passing western Germany on 14 July 2021. Three state-of-the-art rainfall algorithms based on reflectivity Z, specific differential phase KDP, and specific attenuation A were applied to observations of four polarimetric C-band radars operated by the German Meteorological Service [DWD (Deutscher Wetterdienst)]. Due to the large vertical gradients of precipitation below the melting layer suggesting warm-rain processes, all QPE products significantly underestimate surface precipitation. We propose two mitigation approaches: (i) vertical profile (VP) corrections for Z and KDP and (ii) gap filling using observations of a local X-band radar, JuXPol. We also derive rainfall retrievals from vertically pointing Micro Rain Radar (MRR) profiles, which indirectly take precipitation gradients in the lower few hundreds of meters into account. When evaluated with DWD rain gauge measurements, those retrievals result in pronounced improvements, especially for the A-based retrieval partly due to its lower sensitivity to the variability of raindrop size distributions. The VP correction further improves QPE by reducing the normalized root-mean-square error by 23% and the normalized mean bias by 20%. With the use of gap-filling JuXPol data, the A-based retrieval gives the lowest errors followed by the Z-based retrievals in combination with VP corrections. The presented algorithms demonstrate the increased value of radar-based QPE application for warm-rain events and related potential flash flooding warnings.

The diverse meteorology of Jezero crater over the first 250 sols of Perseverance on Mars

NASA’s Perseverance rover’s Mars Environmental Dynamics Analyzer is collecting data at Jezero crater, characterizing the physical processes in the lowest layer of the Martian atmosphere. Here we present measurements from the instrument’s first 250 sols of operation, revealing a spatially and temporally variable meteorology at Jezero. We find that temperature measurements at four heights capture the response of the atmospheric surface layer to multiple phenomena. We observe the transition from a stable night-time thermal inversion to a daytime, highly turbulent convective regime, with large vertical thermal gradients. Measurement of multiple daily optical depths suggests aerosol concentrations are higher in the morning than in the afternoon. Measured wind patterns are driven mainly by local topography, with a small contribution from regional winds. Daily and seasonal variability of relative humidity shows a complex hydrologic cycle. These observations suggest that changes in some local surface properties, such as surface albedo and thermal inertia, play an influential role. On a larger scale, surface pressure measurements show typical signatures of gravity waves and baroclinic eddies in a part of the seasonal cycle previously characterized as low wave activity. These observations, both combined and simultaneous, unveil the diversity of processes driving change on today’s Martian surface at Jezero crater.

Ceiling displacement ventilation system in an experimental theatre: A method to optimize thermal comfort

Compared to traditional theatres, experimental theatres have a lower floor height and the lights are closer to the audience. The large vertical temperature gradient caused by the underfloor air distribution (UFAD) system extremely impairs thermal comfort. Thus, an improved method by introducing the ceiling displacement ventilation (CDV) system was evaluated. CFD models of the experimental theatre were established and verified by field tests. The influence of designing and operation parameters of the CDV systems on thermal comfort was investigated. Effects on energy consumption and air quality were also analyzed to improve application feasibility. The results indicated that the increment of air temperature at the audience head (AHA temperature) was reduced by 51.0% with the help of the CDV system. Thermal comfort was improved as the installation height was extended higher. Furthermore, under constant total air supply rate, the AHA temperature of the last row was decreased with the increase in the air supply ratio of the UFAD to CDV systems (RUtoC), and the total power consumption was declined by 3.1% through adjusting RUtoC compared to the traditional UFAD system. Additionally, the air quality could be significantly improved. The results are helpful to the design and operation of HVAC systems in experimental theatres.

Large scale alignment of alumina platelets en route to porous nacre-like alumina by ice-templating

Ice templating, being a highly versatile technique contributes largely to the development of biomimetic structures. Biomimetic materials are the synthetic materials that possess one or more design and functional aspects of natural materials like abalone nacre, bone, wood. The present research aimed to replicate the inorganic part of nacre, by taking as-synthesized alpha-alumina platelets as primary building blocks. Ice templating was carried out under large vertical temperature gradient in a custom-built setup, that resulted in large-scale ordered lamellar structure; mainly due to the fast and straightforward self-assembly of platelets during directional solidification. The structural wavelength and lamella thickness, the critical parameters to define the ordered lamellar microstructure, were measured to be 16.23 ± 2.0 μm and 2.79 ± 1.0 μm respectively. The resultant green scaffold was subsequently pressed (i.e. cold-compaction) in a direction perpendicular to the ice-front growth and sintered at 1550 °C/4h. Although the nature of the compression response (before and after intermediate cold compaction step) did not change considerably, but large differences in the strength, work of fracture and modulus were obtained. This is mainly due to the large reduction of porosity as well as large-scale alignment of alumina platelets in bulk, resulted from the additional intermediate cold-compaction step. The microstructure of the sintered specimen displayed large-scale parallel alignment of anisotropic alumina platelets, closely resembles to the inorganic counterpart of natural nacre.

Исследование временной изменчивости параметров вертикальной структуры вод в прибрежной зоне южного Крыма

The issues of the formation and temporal variability of the vertical structure of the Black Sea waters off the coast of the southern Crimea are considered. A large array of instrumental measurement data obtained in the second half of 2013 (June–December) during operational monitoring of the vertical temperature profile in the area of Stationary oceanographic platform of the Marine Hydrophysical Institute in the coastal zone near Cape Kikineiz is used. The measurements were carried out using a thermoline, which is a system of temperature sensors distributed in depth from the surface to the bottom. To study the vertical structure of the temperature field, a model of two-layer stratification is considered, when two quasi-homogeneous layers (the upper one is warmer and the lower one cold) are separated by a layer of large vertical temperature gradients—the thermocline. A number of parameters of the vertical structure of waters were calculated: the vertical temperature gradient, its maximum values and depth of occurrence, the temperature of the thermocline core (if it was recorded) and quasi-uniform layers, the temperature difference between these layers, and the thermocline thickness. The median estimates of the daily values of the listed parameters are analyzed. Specific cases of transformation of the vertical profile of water temperature during the upwelling and downwelling processes are considered. It is shown that the temporal variability of the parameters of the vertical structure is significant, especially in the summer hydrological season. The main contribution to the variability is caused by the seasonal course of the heat flow from the atmosphere through the sea surface and surge processes (upwelling and downwelling) in the summer period caused by abrupt changes in the alongshore wind component. In the autumn hydrological season, the thermocline is recorded sporadically with a slight gradient in the form of the lower boundary of the subsurface layer of daytime heating, or a thin bottom layer.

Radiosonde comparison of ERA5 and ERA-Interim reanalysis datasets over tropical oceans

After the release of the ERA-Interim reanalysis, many changes have been made to the Integrated Forecasting System model and data-assimilation system, resulting in an improved reanalysis, ERA5. One of the changes in the model allows the model version in ERA5 to represent the moisture sensitivity of deep convection more realistically than the model version in ERA-Interim. A previous modeling study showed that this change alone improved the representation of the tropical atmosphere, e.g. tropical variability and precipitation distribution. Here we compare the vertical structures of average temperature and moisture over tropical oceans in ERA5, ERA-Interim and radiosonde observations to see whether ERA5 is also closer to observations for those regions and variables. Our results reveal that at many levels, temperature and relative humidity in ERA5 and ERA-Interim differ from observations, however ERA-Interim is generally closer to observations than ERA5 in the low-to-midtroposphere. Most notably, in many stations, ERA5 is on average colder than observations at ∼550-800 hPa. Large vertical gradients occur in the profile of the mean temperature difference between ERA5 and observations at ∼700-900 hPa, but are absent in ERA-Interim. Relative humidity differences are not as robust as temperature differences, however in many stations ERA5 is on average moister than observations at ∼650-800 hPa while ERA-Interim is closer to observations there. Below the ∼950 hPa-level ERA5 and ERA-Interim are generally colder and moister than observations. Our results indicate that ERA5 deviates more than ERA-Interim from tropical radiosonde observations in the low-to-midtroposphere. It seems plausible that this deviation is, at least partly, due to the newer formulation of organised deep entrainment in ERA5 and the associated mechanism for the moisture sensitivity. However, more extensive model evaluation is needed to understand the reasons for the differences between the reanalyses and radiosonde observations.

Spatiotemporal characteristics of the dam-break induced surge pressure on a vertical wall

ABSTRACT In this study, the impact process on a vertical wall due to the dam-break-induced surge was investigated experimentally. The entire surge impact process is classified into three stages, i.e. the initial impact stage, the reflected stage, and the second impact stage. Meanwhile, the wall is vertically divided into the bottom impact zone and the upper outer zone. In the initial impact stage, the upper turbulent and the lower steady splash-ups occur. Only the steady splash-ups induce horizontal pressures on the wall. In the reflected stage, a pressure oscillation occurs, which can be estimated using the pressure oscillation model. Pressure distribution in the impact zone has a large vertical gradient only in the initial impact stage. Surge force exerting on the bottom impact zone remains large in the entire process, whereas surge force in the outer zone is important only in the reflected stage. The maximum total force is equally contributed by the impact and outer zone components. A modified water wedge model was proposed, which predicts the pressure-rising process reasonably. The solid body assumption is suitable only for the turbulent splash-ups in the outer zone, which however is oversimplified for the steady splash-ups movement in the impact zone.