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We identify for the first time an Indian Easterly Jet (IEJ) in the mid‐troposphere during the pre‐monsoon using reanalysis data. The IEJ is weaker and smaller than the African Easterly Jet over West Africa, with a climatological location of 10°N, 60–90°E, 700 hPa, and strength 6–7 m s−1 during March–May. The IEJ is a thermal wind associated with low‐level meridional gradients in temperature (positive) and moisture (negative), resulting from equatorward moist convection and poleward dry convection. The IEJ is associated with a negative meridional potential vorticity gradient, therefore satisfying the Charney‐Stern necessary condition for instability. However, no wave activity is detected, suggesting that the potential for combined barotropic‐baroclinic instability is not often realized. IEJ strong (weak) years feature increased (reduced) near‐surface temperatures and drier (wetter) conditions over India. This study provides an introduction to the IEJ's role in pre‐monsoon dynamics, and a platform for further research. Plain Language Summary Jets, or concentrated regions of fast‐moving winds, can form due to temperature gradients working together with the Earth's rotation. Typically these form in the east/west direction, such as the African Easterly Jet, which is well known over tropical West Africa. Using observation‐based data of the atmosphere, we set out to explore whether such a jet exists near India during spring‐time (the “pre‐monsoon”). The Indian Easterly Jet (IEJ), like its counterpart in West Africa, forms in the lower atmosphere between a south‐to‐north increasing low‐level temperature gradient and a reversed temperature gradient at higher altitudes. But unlike in West Africa, the IEJ breaks down once the summer monsoon begins. We use established methods to show that the IEJ winds have the potential to amplify small cyclonic disturbances, which can develop into larger storms. However, we find that this does not occur commonly. Meanwhile, years in which the IEJ is unusually strong tend to be associated with spring‐time conditions in India that are warmer and drier than normal. This first research into the IEJ paves the way for further analysis on its role in the development of heatwaves, severe storms and the monsoon onset. Key Points The Indian Easterly Jet is a thermal wind in the mid‐troposphere over India during the pre‐monsoon, identified in reanalysis data The jet resembles the African Easterly Jet, but is smaller and weaker, and is not associated with significant easterly wave activity Interannual variability in jet state is linked to variability in pre‐monsoon weather, including surface temperature and precipitation

This paper offers a new perspective on the explanation of the poleward mass flux in the stratosphere. This mass flux represents the upper leg of the so-called Brewer–Dobson circulation. This new perspective is based on the following hypothesis. A positive potential vorticity anomaly, centered over the North Pole, exists in the stratosphere during the winter half-year. This positive potential vorticity anomaly is associated with a negative isentropic density anomaly, which forms due to cross-isentropic downwelling associated with radiative cooling. Isentropic potential vorticity mixing due to breaking planetary waves weakens this potential vorticity anomaly while zonal-mean thermal wind balance is maintained. This requires a weakening of the negative Polar cap isentropic density anomaly, which in turn requires a poleward isentropic mass flux. Support for this hypothesis is found in a case study of a major Sudden Stratospheric Warming event, as an example of intense potential vorticity mixing. It is shown that the stratosphere, both before and after this event, is very close to zonal-mean thermal wind balance, despite the disruptive potential vorticity mixing, while mass is shifted poleward during this event. Solutions of the potential vorticity-inversion equation, which is an expression of thermal wind balance, for zonal-mean potential vorticity distributions before and after the Sudden Stratospheric Warming, demonstrate that mass must shift poleward to maintain zonal-mean thermal wind balance when the positive potential vorticity anomaly is eliminated by mixing. This perspective on the reasons for the poleward stratospheric mass flux also explains the observed isobaric warming as well as the Polar cap zonal-mean zonal wind reversal during a major Sudden Stratospheric Warming.

New methods are need to coordinate the conflicting spatial demands through urban design research and strategies from the perspective of multi-scale urban climate analysis. To integrate wind–thermal environment with urban design, we propose three scale levels, namely the district-superblock, superblock-block, and block-building levels, and divide the urban design elements into voids and solids. Thereafter, we establish a multiscale methodological framework in which the urban design contents are clarified by each scale, and the information transmitted between scales is obtained to ensure consistent value propositions and strategic approaches. The microclimate shaping of the urban open space is transformed into guiding strategies and quantitative indicators of the spatial form of the solid space. Information is transmitted between the scales through the wind–thermal indicators of windward side and the morphological indicators of solid space. Subsequently, the methodology was applied to the project in the core area of Suzhou Science and Technology City, and the findings preliminarily verify the effectiveness and feasibility of the methodology. This research influences urban climate studies and urban design practice in three ways: 1) improving understanding of the correlation between scales; 2) facilitating interaction between the two domains; and 3) providing tools for urban design practices.

Addressing issues such as insufficient transient stability and reduced transmission capacity in wind‐thermal bundled systems during DC blocking faults, this paper proposes a coordinated control strategy for wind‐thermal unit tripping under sequential filter removal. This strategy is based on the principle that retaining partial filters can enhance system stability and aims to improve system stability while reducing total unit tripping. By establishing a grid architecture model for a southwestern region, introducing static stability constraints, transient stability constraints, and filter capacity constraints as stability criteria, the study seeks to minimize the total wind‐thermal unit tripping under DC blocking faults. Simulation results demonstrate that when the filter removal amount is 2610 MVar, the total wind‐thermal unit tripping in this model is minimized to 3480 MW. This further proves that sequential filter removal can reduce unit tripping, enhance system stability, and improve transmission capacity. These findings provide an important basis for system operation optimization. This paper proposes a coordinated control strategy for wind and thermal unit scheduling under filter ordered removal based on the principle that retaining part of the filter can enhance system stability. By establishing a grid architecture model, introducing static stability constraints, transient stability constraints, and filter capacity constraints, etc., the minimum wind and thermal unit curtailment under DC outage fault is sought. It is proved that the ordered removal of filters can further reduce the curtailment volume, enhance system stability and transmission capacity, and optimize system operation.

To improve the management of limited real power resources, the controller parameters of flexible alternating current transmission systems (FACTs) and energy storage systems (ESS) may be simultaneously tuned to optimize the frequency regulation in a two‐area thermal power system penetrated by wind power. In this regard, superconducting magnetic energy storage (SMES) and static synchronous series compensator (SSSC), are operated together in different combinations in a two‐area power system. The controller parameters of SMES and SSSC placed in the system are optimized by means of Cuckoo Search Algorithm (CSA). Among the two, SMES is found to provide the best dynamic performance. The performance of coordinated controllers of SMES in both the areas supported by wind power from a double‐fed induction generator (DFIG), is also tested. In the event of any load perturbation, the dynamic performance of the controllers is analyzed with the sole participation of the DFIG and with the simultaneous operation of DFIG and SMES in both areas. Finally, time and frequency domain performance indices are reported and discussed. To improve the management of limited real power resources, flexible AC Transmission systems devices, along with energy storage devices coordinated controllers, may be successfully implemented for Automatic Generation Control of hybrid wind thermal power systems. In this work, energy storage devices, like Superconducting Magnetic Energy Storage System (SMES) and Static Synchronous Series Compensator, are operated together in different combinations in an interconnected two‐area T‐T system.

The synoptic environment around tropical cyclones plays a significant role in vortex evolution. To capture the environment, the operational and research communities calculate diagnostic quantities. To aid with applications and research, the Tropical Cyclone Precipitation, Infrared, Microwave, and Environmental Dataset (TC PRIMED) combines disparate data sources. A key part of TC PRIMED is the environmental context. Often, environmental diagnostics come from multiple sources. However, TC PRIMED uses the European Centre for Medium-Range Weather Forecasts fifth-generation reanalysis (ERA5) product to provide a more complete representation of the storm environment from a single source. Reanalysis products usually poorly resolve tropical cyclones and their surrounding environment. To understand the uncertainty of large-scale diagnostics, ERA5 is compared to the Statistical Hurricane Intensity Prediction Scheme developmental dataset and the National Oceanic and Atmospheric Administration Gulfstream IV-SP dropwindsondes. This analysis highlights biases in the ERA5 environmental diagnostic quantities. Thermodynamic fields show the largest biases. The boundary layer exhibits a cold temperature bias that limits the amount of convective instability; also, the upper troposphere contains temperature biases and shows a high relative humidity bias. However, the upper-troposphere large-scale kinematic fields and derived metrics are low biased. In the lower troposphere, the temperature gradient and advection calculated from the thermal wind suggest that the low-level wind field is not representative of the observed distribution. These diagnostics comparisons provide uncertainty so that users of TC PRIMED can assess the implications for specific research and operational applications.

In a transient warming scenario, the North Atlantic is influenced by a complex pattern of surface buoyancy flux changes that ultimately weaken the Atlantic meridional overturning circulation (AMOC). Here we study the AMOC response in the CMIP5 experiment, using the near-geostrophic balance of the AMOC on interannual time scales to identify the role of temperature and salinity changes in altering the circulation. The thermal wind relationship is used to quantify changes in the zonal density gradients that control the strength of the flow. At 40°N, where the overturning cell is at its strongest, weakening of the AMOC is largely driven by warming between 1000- and 2000-m depth along the western margin. Despite significant subpolar surface freshening, salinity changes are small in the deep branch of the circulation. This is likely due to the influence of anomalously salty water in the subpolar intermediate layers, which is carried northward from the subtropics in the upper limb of the AMOC. In the upper 1000m at 40°N, salty anomalies due to increased evaporation largely cancel the buoyancy increase due to warming. Therefore, in CMIP5, temperature dynamics are responsible for AMOC weakening, while freshwater forcing instead acts to strengthen the circulation in the net. These results indicate that past modeling studies of AMOC weakening, which rely on freshwater hosing in the subpolar gyre, may not be directly applicable to a more complex warming scenario.

To advance our knowledge of the response of midlatitude westerlies to various external forcings, we investigate the meridional shift of midlatitude westerlies over arid central Asia (ACA) during the past 21 000 years, which experienced more varied forcings than the present day based on a set of transient simulations. Our results suggest that the evolution of midlatitude westerlies over ACA and driving factors vary with time and across seasons. In spring, the location of midlatitude westerlies over ACA oscillates largely during the last deglaciation, driven by meltwater fluxes and continental ice sheets, and then shows a long-term equatorward shift during the Holocene controlled by orbital insolation. In summer, orbital insolation dominates the meridional shift of midlatitude westerlies, with poleward and equatorward migration during the last deglaciation and the Holocene, respectively. From a thermodynamic perspective, variations in zonal winds are linked with the meridional temperature gradient based on the thermal wind relationship. From a dynamic perspective, variations in midlatitude westerlies are mainly induced by anomalous sea surface temperatures over the Indian Ocean through the Matsuno–Gill response and over the North Atlantic Ocean by the propagation of Rossby waves, or both, but their relative importance varies across forcings. Additionally, the modeled meridional shift of midlatitude westerlies is broadly consistent with geological evidence, although model–data discrepancies still exist. Overall, our study provides a possible scenario for a meridional shift of midlatitude westerlies over ACA in response to various external forcings during the past 21 000 years and highlights important roles of both the Indian Ocean and the North Atlantic Ocean in regulating Asian westerlies, which may shed light on the behavior of westerlies in the future.

Understanding the diurnal variation of horizontal wind in the atmospheric boundary layer is important for weather and climate research and wind energy applications. Here we analyze the hourly data from 91 wind profiler radar sites in China and observe that the power spectral density of horizontal wind in lower troposphere approximately follows the −5/3 power law in the mesoscale range over the ocean and coastal areas. However, in inland areas, the slopes of the power spectra are significantly greater than −5/3. We characterize the temporal and spatial variations of maximum wind speed and low level jets and find that the thermal wind effect may partially contribute to the high percentage of low‐level jets observed in the southeastern coast of China and Hainan Island. While the ERA5 reanalysis reproduces wind spectrum well for time scales >1 day, its spectrum diverges significantly from that of profiler data at shorter time scales. Plain Language Summary Understanding how the horizontal wind changes throughout the day in the lower part of the atmosphere is important for studying weather and climate and using wind energy. In this study, we looked at data from 91 radar sites in China that measure wind every hour. We found that the pattern of how the wind changes follows a specific mathematical relationship, called a power law, where the wind decreases in a particular way with decreasing spatial and temporal scales. This pattern holds true mostly over the ocean and coastal areas, but in areas further inland, the wind behaves a bit differently. We also studied how the low‐level jet (LLJ), which are fast winds at low altitudes, change over time and space. We discovered that the difference in temperature across the region contributes to the occurrence of these LLJs in coastal areas in southeast China and Hainan Island. Finally, we compare our findings with the ERA5 reanalysis, which demonstrates excellent agreement in reproducing the wind spectrum for time scales greater than 1 day. However, the spectrum derived from the ERA5 reanalysis diverges significantly from the profiler data at shorter time scales. Key Points Wind spectrum density from wind profiler radars over China shows a less negative slope over inland sites than the −5/3 power law over ocean Temporal and spatial variation of maximum wind speed in the lower troposphere and low level jets are characterized Wind spectrum from ERA5 reanalysis is realistic (deficient) for time scales >1 day (<1 day) compared with profiler data

Low-level jets (LLJs), in which the wind speed attains a local maximum at low altitudes, have been found to occur in the U.S. mid-Atlantic offshore, a region of active wind energy deployment as of 2023. In contrast to widely studied regions such as the U.S. southern Great Plains and the California coastline, the mechanisms that underlie LLJs in the U.S. mid-Atlantic are poorly understood. This work analyzes floating lidar data from buoys deployed in the New York Bight to understand the characteristics and causes of coastal LLJs in the region. Application of the Hilbert–Huang transform, a frequency analysis technique, to LLJ case studies reveals that mid-Atlantic jets frequently occur during times of adjustment in synoptic-scale motions, such as large-scale temperature and pressure gradients or frontal passages, and that they do not coincide with motions at the native inertial oscillation frequency. Subsequent analysis with theoretical models of inertial oscillation and thermal winds further reveals that these jets can form in the stationary geostrophic wind profile from horizontal temperature gradients alone—in contrast to canonical LLJs, which arise from low-level inertial motions. Here, inertial oscillation can further modulate the intensity and altitude of the wind speed maximum. Statistical evidence indicates that these oscillations arise from stable stratification and the associated frictional decoupling due to warmer air flowing over a cold sea surface during the springtime land–sea breeze. These results improve our conceptual understanding of mid-Atlantic jets and may be used to better predict low-level wind speed maxima.