Dynamics of Atmospheres and Oceans最新文献

Precipitation is a crucial component of the water cycle and is essential for the livelihood of people and ecosystems; therefore, understanding precipitation parameters is vital. Stable isotopes in precipitation can provide important information on precipitation sources, atmospheric circulation patterns, and hydrological processes. In this study, stable isotopes in precipitation for four cities in India were analyzed, namely New Delhi, Hyderabad, Shillong, and Calicut, using data from the International Atomic Energy Agency (IAEA) Global Network for Isotopes in Precipitation (GNIP). The GNIP data were supplemented with in-situ measurements. Results showed the correlations between climate-related factors such as surface air temperature and precipitation levels with the stable isotope composition of precipitation. The relationships critically explore interannual variations in the isotope data over the last three decades. The Local Meteoric Water Line (LMWL) for New Delhi and Hyderabad had intercepts less than 10‰, implying a higher evaporation effect over precipitation, consistent with arid and semi-arid regions with increased altitude. The weighted average value of d-excess for southern and Himalayan points were 10.7 and 12.7, respectively, and the average value of δ¹⁸O were − 3.65 and − 5.84, and δ²H were − 16.8 and − 35.8. The d-excess value was significantly lower in the Northern part (New Delhi), with an average weighted value of 6.6. The key values include the isotopic composition of rainfall in different regions of India, the LMWL for different stations, the d-excess value, and the consistency of meteoric water lines with regional and global values. The results of this study provide valuable information on the variability of stable isotopes in precipitation in India. The study's outcomes can be compared with the isotopic composition of surface water and groundwater. This discovery offers more understanding of the isotopic differences that occur on a smaller scale during organized convection and the factors that affect them. As a result, it enhances our ability to decipher the paleoclimate data in arid, semi-arid, and subtropical monsoon regions.

Deforestation in tropical areas is broadly reported to change the climate both locally and regionally. Warmer and drier conditions, as well as changes in precipitation patterns, are linked to deforestation in the Amazon. In this study, we identified two areas of distinct land use in Amazon: a preserved native forest and an increasingly deforested region southward. Due to the scarcity of available ground data, we propose assessing the impacts of deforestation on surface climate using two different datasets: a station-based reference product and the ERA5 reanalysis. However, as ERA5 does not include a recent and dynamic land use map in its development, an additional goal is to evaluate the potential discrepancies in the reanalysis for not accounting for these changes. Despite some consistent and similar patterns in relative humidity and low intensity (9th decile) precipitation, our results show, indeed, different trends among the datasets, with reference trends always more accentuated than in the reanalysis. Despite being broadly used in numerous studies, reanalysis data under intensive land use change and ungauged areas need to be used with caution to avoid inconclusive or misleading findings.

The Sichuan Basin (SCB) and its surrounding mountainous areas have complicated topography, and the "Nocturnal Rainfall in the Basin (NRB)" and "Nocturnal Rainfall in the Mountainous Areas (NRMA)" are frequent. To further clarify the relationship and the interaction between the two types of "nocturnal rainfall" synoptic systems, the characteristics of the synoptic meteorology, thermodynamics, dynamics, and water vapor fields of the nocturnal precipitation process generated by two Mesoscale Convective Systems (MCSs) that originated from the mountainous area on the western side of the SCB on June 4, 2019 were analyzed and diagnosed in this paper. In addition, the WRF-LES model was used to simulate and analyze the macro and micro physical characteristics of two precipitation centers formed by the main system MCS1 in the center of the SCB and the mountainous areas around it. The results showed as follows. (1) Two MCSs originated from the mountainous area on the western side of the SCB were generated by the eastward movement of the low-pressure trough over the Tibetan Plateau (TP) coupling the higher Convective Available Potential Energy (CAPE) value with the unstable circulation of the upper level. They matured in the SCB and matured and split in the western end of Mt. Daba, respectively. (2) After splitting, the southern part of the sub-system MCS2 sank and moved south along the southern foot of Mt. Daba and uplifted the main system MCS1. After its explosive development, two precipitation centers with the characteristics of the NRB and NRMA were formed. (3) The vertical velocity, divergence, thermal helicity, and potential vorticity could be used as the thermodynamics and dynamics diagnostic quantities to indicate the occurrence and development of the two MCSs. The potential vorticity was an obvious precursory parameter compared with the other three. The water vapor flux divergence and moisture helicity could better indicate the vertical transport of water vapor in the systems. (4) The precipitation simulation result of the WRF-LES model on the main system MCS1 in the SCB was better than that on the sub-system MCS2 in the mountainous area on the northern margin of the SCB. In each MCS1 stage, the precipitation of the NRB was mainly induced by the cold cloud process (supplemented by the warm cloud process), while the precipitation of the NRMA was mainly induced by the warm cloud process. The combination of diagnostic analysis and numerical simulation could effectively promote an understanding of the relationship and interaction between the NRB and NRMA.

In the present study, we focused on the heat waves (HW) associated with the quasi-biweekly (QBW, 10–20-day period) variability (QBW-HW) over Southern China (SC, 102º–120ºE, 21º–30ºN) in the Flexible Global Ocean–Atmosphere–Land System Model, GridPoint version 3 (FGOALS-g3), and the HW-associated structures and surface air temperature budget investigated by using model outputs from historical experiment of Coupled Model Intercomparison Project Phase 6 (CMIP6). We found that the anomalous circulations related to the QBW-HW events over SC are closely linked to the southeastward propagation of the wave train from mid-high latitudes and the northwestward-propagating disturbances from the tropics. The results also showed that adiabatic and diabatic heating play a key role in the QBW-HW over SC. These results are in good agreement with observations from previous studies. In addition, QBW-HWs are dry in the FGOALS-g3 model, while observed humid HWs occur over SC. The difference is mainly due to the new boundary layer scheme incorporated in the FGOALS-g3 model, which overestimates the entrainment process at the top of the boundary layer during the QBW-HW over SC, resulting in more and drier air into the boundary layer, and thus less moisture. It implies that the entrainment equation at the top of the boundary layer in the FGOALS-g3 model does need to be improved to be suitable for humid HW processes, although the boundary layer scheme can improve the model precipitation and radiative forcing.

The absence of robust quantitative evaluation methods has led to insufficient knowledge of models capability on the rapid intensification (RI) prediction of tropical cyclones (TCs). In this study, we propose a method and define some indicators aiming to evaluate model capability on predicting RI in a more accurate manner. An assessment of model predictive capability on RI of TCs based on 10 years of operational forecasts has been conducted using different RI criteria. The Tropical Regional Atmosphere Model for the South China Sea of China Meteorological Administration (CMA-TRAMS) and the European Centre for Medium-Range Weather Forecasts (ECMWF) high resolution (HRES) operational forecasts were used. Analysis results revealed that the criterion of 6-hour sea level pressure (SLP) change is more appropriate to be used in RI operational forecast. The maximum lead time (MLT) of CMA-TRAMS and HRES was 72 and 78 h, and the maximum deviation of RI occurrence time of CMA-TRAMS and HRES was 48 h delay and 24 h ahead, respectively. Overall results suggest that the model predictive capability of RI is currently limited, and both models have inadequate capability in providing sufficient heat and energy to support RI in the long run. A tendency of CMA-TRAMS to have a lag in RI occurrence time was also demonstrated due to an air-sea interaction lag resulting from the fixed skin sea surface temperature used. Results of the present study provide insights and could be the basis for future efforts on improving parametrization schemes for properly describing RI process of TCs.

The issue of stability of a thin couple-stress liquid layer flows on an inclined plane was inspected. The thin-film approximation was employed to obtain a Benney-like differential equation, that described the time record of the interface profile The linear transition state and reduction ratio of maximum classical (Newtonian) growth-rate were discussed. The complete evolution equation was solved numerically using the method of lines in order to support the novelty of the work. The linear stability could be enhanced by increasing the couple-stress coefficient and surface tension as well as reducing the inclination. However, the ordinary viscosity played an irregular role. The linear results predicted conditions (windows) in which the non-Newtonian film was more stable than its Newtonian counterpart. The nonlinear stimulation anticipated the existence of sock waves in certain situations. The appearance of instability through the linear subcritical region as well as irregular influences with respect to surface tension and couple-stress property was revealed. The nonlinear approach was more accurate in describing the stability issue than the linear one. Such results could be employed to attain the optimum statuses with regard to the film stability, and control the shock waves. They would not only enable accurate practical implementation in the design of inertial confinement fusion capsules and supernova explosions and implosions modeling, but also would allow for precise numerical simulation.

Indian Ocean Dipole (IOD) is the major interannual ocean-atmosphere interaction phenomena in the Indian Ocean (IO) and is influenced by external forcing such as El Nino Southern Oscillation (ENSO). Meanwhile, its co-occurrence and stronger relationship with ENSO have decreased during recent decades. The IOD variability also reduced after 2000, accompanied by a shift of the western pole to central IO extending further southward. The study reports that the boreal fall (SON, September, October, November) season IOD has an intensified relationship with the previous winter Subtropical Indian Ocean dipole (SIOD) and spring season equatorial north tropical Atlantic (NTA) SST anomalies., while the ENSO relationship is reduced from its pre-2000 value. It is found that the persistent warming (cooling) in the western side of positive (negative) SIOD during the previous winter induces easterly (westerly) wind anomalies in the equatorial IO during the following summer and fall, leading to positive (negative) IOD events. These IOD events have the western pole shifted to south-central IO instead of the canonical northwestern warming. The spring season NTA SST anomalies induce stronger summer season circulation and SST gradient in the equatorial Pacific, like ENSO. During the SON season, this pattern is associated with cooling and easterly wind anomalies in the tropical eastern IO and IOD. These two patterns explain the major mode of IOD variability after 2000. While the IOD associated with NTA have co-occurring ENSO during summer and fall, the SIOD-induced IOD events are independent of ENSO in the Pacific. Thus, these two predictors provide long-lead predictability (2–3 seasons ahead) of IOD for both ENSO co-occurring and non-ENSO IOD events. However, the IOD predictability of seasonal prediction models mainly depends on the ENSO-IOD relationship, resulting in reduced IOD skills for many of them after 2000. The models such as COLA-CCSM4, which has improved skill have stronger than observed ENSO-IOD relationship than the pre-2000 period. A linear regression model including SIOD and NTA SST indices of the previous winter and spring season respectively as predictors simulates IOD with a skill of around 0.65 during the recent period, indicating the necessity of seasonal prediction models to capture the variability in the southern IO and NTA and their teleconnections for better prediction of IOD in the recent period of reduced ENSO skill.

The study investigates the characteristics of Extraordinary Atmospheric Rivers (EARs), including large-scale atmospheric patterns, structure, effective sources, and precipitation in the Middle East. For this purpose, ARs with maximum Vertically Integrated Water Vapor Transport (IVT) ≥ 1000 kg m⁻¹ s⁻¹ were extracted from 1981 to 2020. ERA5 and PERSIANN-CCS-CDR data were used to analyze the characteristics of the EARs. The latter was applied to show the precipitation risk level. Atmospheric patterns indicated the state of the merging cyclones. Sudan's low pressure was the more recurrent system in all the patterns and alternately integrated with one or two cyclonic tongues over the Mediterranean, the Black Sea, the Caspian Sea, and then the polar vortex. Atmospheric blocking was present in all events, affecting the lifetime of the EARs and the maximum IVT anomaly, which averaged 4.5 days and 622 kg m⁻¹ s⁻¹, respectively. The EARs are the result of the simultaneous feeding of several moisture pathways from different sources. Both regional (mainly below 850 hPa) and trans-regional (above 700 hPa, except for the western Mediterranean) water sources played a crucial role in their formation. Dynamically, most events were characterized by merging the subtropical and polar jets, with maximum central speeds between 70 and 85 m s⁻¹. EARs were also accompanied by strong near surface wind gusts up to 28 m s⁻¹. In the IVT core wind structure, the low-level jet with a speed of 30 m s⁻¹ deepened to a maximum of 925 hPa. There were also intense upward velocities between − 3 and − 5 Pa s⁻¹ near the precipitation maxima areas in the EARs. The spatial character of the precipitation was of a continuous or intermittent nature, and a considerable part of it fell in short periods (up to 286 mm in 3 h). The daily maximum was 390 mm. Accordingly, the importance of using high-resolution data was represented for such events with devastating hydrological effects.

The northern Gulf of Mexico is facing high rates of wetland loss due to subsidence and sea level–rise, which has encouraged the application of various wetland restoration techniques. Marsh terracing is a restoration technique that has been implemented since the early 1990 s in Texas and Louisiana, yet few studies have been conducted to evaluate its effectiveness. Marsh terraces are segmented berms of soil built in coastal ponds that were once vegetated marshes. Marsh terracing is hypothesized to dissipate wind waves, encourage marsh expansion, and reduce shoreline erosion. This study (1) assessed the effectiveness of the most common terrace shapes (linear, chevron, and square) and spacing (100, 110, and 120 m) at reducing significant wave height (Hs), (2) assessed the effectiveness of alternative terrace designs for reducing Hs during different wind conditions, and 3) estimated the construction costs of alternative terrace designs. The Simulating WAves Nearshore (SWAN) model was used to simulate wind–driven waves in ponds with real and hypothetical terrace designs. Results revealed that: (1) The chevron shape provided the greatest reduction in Hs during all wind conditions, reducing Hs by up to 54%. (2) Hs reduction was not affected by terrace spacings. (3) Based on wave attenuation, the chevron design with a 120 m terrace spacing provided the optimal outcome with an estimated construction cost/ha of $6332 in a 250,000 m² site compared to the terrace shapes and spacings evaluated in this study. This study will help coastal managers design marsh terraces to address wetland erosion in the Gulf of Mexico and other coastal areas facing similar environmental problems.