Abstract
The nighttime ocean cool skin signal Δ
T
defined as skin sea surface temperature (SST
skin
) minus depth SST (SST
depth
) is investigated using 103 days of matchups between shipborne ...Infrared SST Autonomous Radiometer (ISAR) SST
skin
and water intake SST
depth
at ~7.1–9.9-m depths, in oceans around Australia. Before data analysis, strict quality control of ISAR SST
skin
data is conducted and possible diurnal warming contamination is carefully minimized. The statistical distribution of Δ
T
, and its dependencies on wind speed, heat flux, etc., are consistent with previous findings. The overall average Δ
T
value is −0.23 K. It is observed that the magnitude of the cool skin signal increases after midnight and a coolest skin offset (with an average value of −0.36 K) is found at around dawn. The dependency of Δ
T
on SST conditions is observed. Direct warm skin events are discovered when the net heat flux direction is from the atmosphere to the ocean, which is more likely to occur at high latitudes when the air is very humid and warmer than the SST. In addition, several cool skin models are validated: one widely used physical model performs best and can capture most skin-effect trends and details; the empirical models only reflect the basic features of the observed Δ
T
values. If the user cannot apply the physical model (due to, e.g., the algorithm complexity or missing inputs), then the empirical parameterization in the form proposed in a 2002 study can be used. However, we recommend using a new set of parameters, calculated in this study, based on much more representative dataset, and with more rigorous quality control.
High-speed planing craft operating in real seaways encounter high impact loads. The extreme motions and accelerations resulting from such impacts adversely affect the structure of the craft and its ...payload as well as pose a risk to the crew on-board. Limiting craft speed according to the sea state using a speed-wave height operational envelope might ensure structural integrity and greatly improve safe navigation. Accurate estimation of motion and acceleration of planing craft in a seaway is a key requirement in developing reliable and usable allowable speed vs. wave height operational curves. In this paper, the Motion Assessment of Planing Craft in a Seaway (MAPCS) tool, a nonlinear time-domain approach vs. several existing approaches based on experimental, empirical and classification societies' formulas for vertical accelerations and speed vs. wave height limit curves are compared. It is found that the MAPCS approach provides more realistic estimations compared to the commonly employed methods.
For the first time, we reconstructed global distribution of both the total electron content disturbance W index and TEC values for eight extreme storms (Dst < −250 nT) occurred before the epoch of ...GNSS observations in solar cycle 22. We created a model based on superposed epoch analysis of the training set of GIM‐W maps of nine SC23 extreme storms. Global GIM‐W index maps are calculated from 15‐min UPC GIM‐TEC (UQRG) as the logarithmic deviation of instantaneous TEC from the monthly median GIM‐MTEC empirical model. We introduced the storm phase metrics for main and recovery phases of the positive ionosphere disturbance (the WU‐index), the negative disturbance (the WL‐index) and the ring current (the Dst‐index). The probabilistic forecasting model (Pmodel) for SC22 GIM‐Wx maps is developed based on GIM‐W maps of the SC23 training set. The storm phase distribution Φx for the eight SC22 extreme storms is calculated from the proxy time shift (lag) of peak WUmax and WLmin relative to Dstmin. Proxy GIM‐TECx maps are calculated by adjusting the GIM‐MTEC median to the GIM‐Wx prediction. Validation of the technique based on data of UPC and JPL for four intense ionospheric storms showed a root‐mean‐square error less than 3 TECU. The proposed technique can be applied for both the past and future forecasting of GIM‐W index and GIM‐TEC maps.
Key Points
Probabilistic Pmodel is developed to produce proxy GIM‐Wx and GIM‐TECx for eight extreme storms of SC22 before the epoch of GNSS observations
The first storm phase metrics is introduced for the ionospheric positive storm WU, negative storm WL and Dst ring current storm indices
Validation of GIM‐TECx with JPL and UPC maps for four extreme storms of SC23 and SC24 yields RMSE less than three TECU
Lakes are hotspots of dissolved organic matter (DOM) degradation and play an active role in carbon cycles. Alpine lakes are under the most immediate impacts of climate change and act as sentinels of ...alpine ecosystem’s response to global warming, yet the primary environmental drivers of DOM variability in alpine lakes remain unidentified. Here, we sampled and analyzed DOM from 25 alpine lakes (>4,000 m above mean sea level) across the Tibetan Plateau. We found that the water residence time (WRT) of lakes and mean annual temperature (MAT) accounted for 30%–59% of the variance in the abundance of chromophoric DOM (CDOM) and fluorescent DOM (FDOM). Both CDOM and FDOM decreased with increasing WRT and MAT. Molecular‐level analysis of selected DOM samples showed that a higher WRT corresponded to DOM with lower molecular intensities, lower proportions of aromatics, lower oxidized compounds, and higher proportions of reduced and nitrogen‐containing compounds. These results indicate that in‐lake DOM processing dominated the regional variability of CDOM and FDOM. Under the scenario of climate warming and lake enlargement due to increasing precipitation and glacier melting, increased amount of DOM could be processed and removed from Tibetan lakes. Our findings are the first that identified WRT as a significant predictor of the amount of various DOM pools in Tibetan lakes and this observation may be broadly applicable to alpine lakes since they share similar DOM source‐sink characteristics. The simple empirical models (DOM vs. WRT + MAT) established here can be integrated into more sophisticated numerical models in predicting changes in the carbon cycle of alpine lakes.
Key Points
Spatial variability of Tibetan lacustrine dissolved organic matter (DOM) is predicted by water residence time and mean annual temperature
The amount of DOM in Tibetan lakes is regulated primarily by in‐lake processing
Climate warming could lead to decreases in DOC, CDOM, and FDOM concentrations in Tibetan lakes
We report that in determining ventilation rates, it is often necessary to combine naturally-driven infiltration, with air flows from mechanical systems. When there are balanced mechanical systems, ...the solution is simple additivity, because a balanced system does not impact the internal pressure of the space or the air flows through the building envelope. Unbalanced systems, however, change internal pressures and therefore can impact natural ventilation non-linearly in such a way as to make it sub-additive. Several sub-additive approaches are found in the literature, but they are not robust across the full spectrum from tight to leaky buildings and ranges of mechanical ventilation air flow rates. There are two approaches for combining natural infiltration with mechanical ventilation that require different solutions. The forward problem is to find the total air flow when adding mechanical ventilation to natural infiltration, and this application has been investigated in previous studies. The inverse problem finds the required mechanical ventilation in order to meet a total ventilation rate given a known amount of natural infiltration. This article presents the results of millions of hours of simulations of the physically correct solution, which span a broad range of climates, air leakage and structural conditions. This large dataset allows for the comparison with three literature models and the development of new robust sub-additivity models. These improved models are for use with unbalanced systems appropriate for consensus standards and guidelines for both the forward and inverse problem. Finally, they reduce errors to 1% or less and work across the air tightness spectrum.
For future human missions to Mars, it is important to study the surface radiation environment during extreme and elevated conditions. In the long term, it is mainly galactic cosmic rays (GCRs) ...modulated by solar activity that contribute to the radiation on the surface of Mars, but intense solar energetic particle (SEP) events may induce acute health effects. Such events may enhance the radiation level significantly and should be detected as immediately as possible to prevent severe damage to humans and equipment. However, the energetic particle environment on the Martian surface is significantly different from that in deep space due to the influence of the Martian atmosphere. Depending on the intensity and shape of the original solar particle spectra, as well as particle types, the surface spectra may induce entirely different radiation effects. In order to give immediate and accurate alerts while avoiding unnecessary ones, it is important to model and well understand the atmospheric effect on the incoming SEPs, including both protons and helium ions. In this paper, we have developed a generalized approach to quickly model the surface response of any given incoming proton/helium ion spectra and have applied it to a set of historical large solar events, thus providing insights into the possible variety of surface radiation environments that may be induced during SEP events. Based on the statistical study of more than 30 significant solar events, we have obtained an empirical model for estimating the surface dose rate directly from the intensities of a power-law SEP spectra.
This paper describes a program of centrifuge model tests on the uplift behaviour of suction caisson foundations. The parameters considered were the loading rate, caisson diameter (D), soil strength ...profile, and type of footing (i.e., mono-caisson and tetra-caissons group). The loading responses were examined in terms of total uplift resistance, suction beneath the caisson lid, and the vertical displacements of the caisson and at the soil surface. There exists a critical uplift displacement, approximately 0.02D and 0.01D for the mono-caisson and the tetra-caissons groups, respectively, at which a turning point can be identified in the load–displacement curve. This was found to be attributed to the adhesion on the caisson–soil interface reaching a peak response and then dropping. Of interest is that the tetra-caissons group exhibits much greater normalized uplift resistance than the mono-caisson group before reaching an uplift displacement of about 0.02D, suggesting superiority of the former in term of serviceability. However, a reversed trend was observed at greater displacement, and accordingly an empirical model was derived to quantify the shadowing effect of caisson groups. Regarding the cyclic response, several cycles of large-amplitude loading are sufficient to reduce the ultimate bearing capacity of caisson(s) to below the self-weight of the inner soil plug(s), indicating a transition of failure mechanism.
An original method for analyzing the influence of the meteorological, as well as physical-geographical conditions on the flooding of stormwater in small urban catchment areas is proposed. A ...logistical regression model is employed for the identification of the flooding events. The elaborated model enables to simulate the stormwater flooding in a single rainfall event, on the basis of the rainfall depth, duration, imperviousness of the catchment and its spatial distribution within the analyzed area, as well as the density of the stormwater network. The rainfall events are predicted considering the regional convective rainfall model for 32 rain gauges located in Poland, based on 44 years of rainfall data. In the study, empirical models are obtained to calculate the rainfall duration conditioning the flooding of stormwater in a small urban catchment area depending on the characteristics of the examined urban basins. The empirical models enabling to control the urbanization process of catchment areas, accounting for the local rainfall and meteorological characteristics are provided. The paper proposes a methodology for the identification of the areas especially sensitive to stormwater flooding in small urban catchment areas depending to the country scale. By employing the presented methodology, the regions with most sensitive urban catchments are identified. On this basis, a ranking of towns and cities is determined from the most sensitive to flooding in small urban catchment areas to the regions where the risk of flooding is lower. Using the method developed in the paper, maximum impervious catchment area are determined for the selected regions of the country, the exceedance of which determines the occurrence of stormwater flooding.
The flow characteristics of a pintle injector element were studied by theory and experiments. A spray angle model was firstly proposed based on our previous work, and then a model on the discharge ...coefficient of the orifice was also derived. Then, experiments were conducted by a pintle injector element which was simplified from pintle injectors with discrete radial orifices. Snapshots of the sprays were captured by using backlit photography technique. Results show that the pintle injector forms an arched cloak-like spray. The spray pattern and breakup are heavily related to the local momentum ratio and Reynolds numbers of jet and film. The spray angles obtained from the snapshots coincide with theory well. Meanwhile, a semi-empirical model of discharge coefficient of the orifice was proposed based on the experiments. It is found that the spray angle and discharge coefficient are dominated by the local momentum ratio. The spray angle and discharge coefficient increase along with local momentum ratio and tend to be stable for large local momentum ratios. Besides, discharge coefficient of the orifice is also found to be slightly affected by the ratio of jet diameter to film thickness.
•A theoretical spray angle model was proposed and validated.•A semi-empirical model on the discharge coefficient of the orifice was proposed.•TMR dominates the spray angle and discharge coefficient of the orifice.
This paper presents a comparative study between Bayesian Neural Network (BNN), classical Neural Network (NN) and empirical models for estimating the daily global solar irradiation (DGSR). An ...experimental meteorological database from 1998 to 2002 at Al-Madinah (Saudi Arabia) has been used. Four input parameters have been employed: air temperature, relative humidity, sunshine duration and extraterrestrial irradiation. Automatic relevance determination (ARD) method has investigated in order to select the optimum input parameters of the NN. Results show that the BNN performs better that other NN structures and empirical models.
► Comparative study between Bayesian NN, classical NN and empirical models for estimating of global solar irradiation. ► The Bayesian Neural Network performs better that other NN structures and empirical models. ► Based on ARD technique, it has been proven that the sunshine duration is the most relevant input parameter. ► Bayesian approach offers the possibility by using of the evidence framework to select the optimal number of hidden units.
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