Background Wind Research Articles

Different Response of the Ionospheric TEC and EEJ to Ultra‐Fast Kelvin Waves in the Mesosphere and Lower Thermosphere

AbstractWe studied the response of ionospheric total electron content (TEC) and equatorial electrojet (EEJ) to the ultra‐fast Kelvin wave (UFKW) at the equator in the mesosphere using zonal wind data obtained from TIMED Doppler Interferometer (TIDI), EEJ data over the monitoring station Jicamarca (12°S, 77°W) and global TEC maps. The least squares fitting method is utilized to perform a spectral analysis of zonal wind, EEJ and TEC. Our analysis results demonstrate that UFKW events can be divided into four categories: (a) UFKW events with both TEC and EEJ response; (b) UFKW events with TEC response but without EEJ response; (c) UFKW events with EEJ response but without TEC response; (d) UFKW events without neither TEC response nor EEJ response. The first type of UFKW events occur the most often and is generally thought to generate a response in EEJ at approximately 105–110 km through the dynamo effect. The polarization electric field associated with EEJ then produces a response in the ionospheric TEC through the fountain effect. The lack of EEJ response in the second type of UFKWs may be due to the influence of eastward background winds. We found that all UFKW events with EEJ response have a response in TEC. The fourth type of UFKWs have smaller amplitudes, shorter vertical wavelengths and longer periods, which make them more likely to dissipate and cannot propagate to higher altitudes. These UFKWs cannot propagate to the altitude of EEJ and produce a response in EEJ, much less in TEC.

Climatology of turbulent kinetic energy dissipation rate in the middle troposphere using the 205 MHz S–T radar at Kochi, India

Turbulent kinetic energy dissipation rate (ɛ) in the mid-troposphere (5–12 km) using data obtained from the S–T wind profiler radar located at Kochi (10.04°N, 76.33°E) is analyzed for a period of 1595 days, ranging from March 2017 to December 2022, at a vertical resolution of 180 m. The spectral width method was employed for the estimation of ɛ after initial data filtering, and corrections for beam and shear broadening. Monthly variations in ɛ exhibited a marginal decrease with height. The background wind conditions, such as horizontal wind speed, vertical shear of horizontal wind, and wind direction, have minimal impact vertically. It is found that turbulence is more significantly affected by wind speed and wind direction. Westerly winds, despite being infrequent in the mid-troposphere, emerged as the primary contributors to elevated turbulence values. This observation was attributed to the unique topographical characteristics, creating an interplay of land–sea contrast and orography, leading to enhanced turbulence during westerly winds. During the monsoon season, enhanced turbulence is observed throughout the altitude. The presence of the tropical easterly jet was identified as a significant contributor to the increased wind speed and shear observed during the monsoon season and this alignment correlates with an increase in turbulence.

Near-Surface Atmospheric Response to Meso- and Submesoscale Current and Thermal Feedbacks

Abstract Current feedback (CFB) and thermal feedback (TFB) have been shown to strongly influence both atmospheric and oceanic dynamics at the oceanic mesoscale (10–250 km). At smaller scales, oceanic submesoscale currents (SMCs; 0.1–10 km) have a major influence on the ocean’s energy budget, variability, and ecosystems. However, submesoscale air–sea interactions are not well understood because of observational and modeling limitations related to their scales. Here, we use a realistic submesoscale-permitting coupled oceanic and atmospheric model to quantify the spatiotemporal variability of TFB and CFB coupling in the northwest tropical Atlantic Ocean. While CFB still acts as a submesoscale eddy killer by inducing an energy sink from the SMCs to the atmosphere, it appears to be more efficient at the submesoscale by approximately 30% than at the mesoscale. Submesoscale CFB affects the surface stress, however, the finite time scale of SMCs for adjusting the atmospheric boundary layer results in a diminished low-level wind response, weakening partial ocean reenergization by about 70%. Unlike at the mesoscale, submesoscale CFB induces stress/wind convergence/divergence, influencing the atmospheric boundary layer through vertical motions. The linear relationship between the surface stress derivative or wind derivative fields and sea surface temperature gradients, widespread at the mesoscale, decreases by approximately 35% ± 7% or 77% ± 10%, respectively, at the submesoscale. In addition, submesoscale TFB induces turbulent heat fluxes comparable to those at the mesoscale. Seasonal variability in meso- and submesoscale CFB and TFB coupling is mostly related to background wind speed. Also, disentangling submesoscale CFB and TFB is challenging because they can reinforce or counteract each other.

Impacts of background wind on the interactions between urban breeze circulation and convective cells: Ensemble large‐eddy simulations

AbstractUrban breeze is produced by the temperature difference between urban and surrounding rural areas, and its interactions with other atmospheric phenomena are of great interest. In this study, the impacts of background wind on the interactions between urban breeze circulation (UBC) and convective cells are numerically investigated. For this, a large number of idealized ensemble simulations are performed using the Weather Research and Forecasting‐large‐eddy simulation model, where the initial background wind speed varies from 0 to 5 m·s−1 in 0.5 m·s−1 intervals. As the background wind speed increases, the location of the strongest updraft moves from the urban center to the downwind boundary of the urban area. This is associated with different interactions between the UBC and convective cells under different background wind speeds. For no background wind, the UBC is relatively strong and its center is located at the urban center, producing a strong updraft there. Convective cells are advected toward the UBC center and merge with the strong updraft, further intensifying it. For weak background wind, the UBC is relatively weak and its center is located near the downwind urban boundary. Convective cells passing the urban area merge with each other and intensify, and after they pass the downwind urban boundary, the strong vertical wind shear in the right part of the UBC tilts and weakens them. For strong background wind, the UBC is very weak and convective cells are advected mainly by the strong background wind. These changes in the characteristics of convective cells in and around the urban area with background wind speed may lead to the changes in the preferred location of cloud initiation and cloud development.

Control of Low-Level Wind on the Diurnal Cycle of Tropical Coastal Precipitation

Abstract To understand how coastal precipitation is controlled by the low-level background wind, we performed comprehensive analysis using the 17-yr observations of the TRMM PR over the entire region of the tropics. We classified the data according to the direction (onshore or offshore) and strength of the cross-shore wind. Under weak winds, the contribution of the diurnal cycle to total precipitation is large, indicating that thermally forced precipitation with a symmetrical propagation pattern with opposite sign across the coastline is dominant. As the background wind strengthens, the contribution of the diurnal cycle reduces owing to the predominance of mechanical forcing; however, the effect of the diurnal cycle remains nonnegligible with an asymmetrical propagation pattern across the coastline. Using the linear theory of the sea–land-breeze circulation, we demonstrated that the difference in propagation is attributable to gravity waves excited by the land–ocean surface heating difference. Under weak winds, symmetrical diurnal phase propagation is caused by the two symmetrical modes of landward and seaward gravity waves. Under stronger background winds, in addition to the Doppler-shifted landward and seaward modes, waves propagating toward the upwind side in the flow-relative frame but with slow group velocity are advected to the downwind near the coastline, forming another mode that moves slowly in the downwind direction. The superposition of the three modes leads to asymmetrical propagation of precipitation with varying phase speed depending on the distance from the coastline.

Understanding the Influence of Urban Form on the Spatial Pattern of Precipitation

AbstractUrban areas are known to modify the spatial pattern of precipitation climatology. Existing observational evidence suggests that precipitation can be enhanced downwind of a city. Among the proposed mechanisms, the thermodynamic and aerodynamic processes in the urban lower atmosphere interact with the meteorological conditions and can play a key role in determining the resulting precipitation patterns. In addition, these processes are influenced by urban form, such as the impervious surface extent. This study aims to unravel how different urban forms impact the spatial patterns of precipitation climatology under different meteorological conditions. We use the Multi‐Radar Multi‐Sensor quantitative precipitation estimation data products and analyze the hourly precipitation maps for 27 selected cities across the continental United States from the years 2015–2021 summer months. Results show that about 80% of the studied cities exhibit a statistically significant downwind enhancement of precipitation. Additionally, we find that the precipitation pattern tends to be more spatially clustered in intensity under higher wind speed; the location of radial precipitation maxima is located closer to the city center under low background winds but shifts downwind under high wind conditions. The magnitude of downwind precipitation enhancement is highly dependent on wind directions and is positively correlated with the city size for the south, southwest, and west directions. This study presents observational evidence through a cross‐city analysis that the urban precipitation pattern can be influenced by the urban modification of atmospheric processes, providing insight into the mechanistic link between future urban land‐use change and hydroclimates.

Investigation of Mesosphere and Lower Thermosphere Dynamics over Central and Northern Peru Using SIMONe Systems

Abstract One year of Spread spectrum Interferometric Multistatic meteor radar Observing Network (SIMONe) measurements are analyzed and compared for the first time between two low-latitude locations in Peru: Jicamarca (12°S, 77°W) and Piura (5°S, 80°W). Investigation of the mean horizontal winds and tides reveals that mesosphere and lower thermosphere (MLT) planetary-scale dynamics are similar between these two locations, although differences can be seen in some tidal components, e.g., the diurnal tide. On the other hand, 28-day median values of the momentum fluxes obtained with 4-h, 4-km time–altitude bins indicate that the mesoscale dynamics differ significantly between Jicamarca and Piura, places separated by approximately 850 km. From the middle of July until October 2021, a strong acceleration of the background zonal wind by westward-propagating gravity waves (GWs) is observed above ∼90 km at both locations, although with larger amplitudes over Jicamarca. From the middle of January until April 2022, a second strong acceleration of the background zonal wind, again by westward-propagating GWs, is observed, but this time with larger amplitudes over Piura. The latter is further supported by the dominance of negative vertical gradients of the zonal momentum flux above 89 km of altitude. Thus, these results observationally confirm the previous studies based on general circulation model simulations indicating that the directions of the zonal GW drag and the zonal background wind coincide in the low-latitude MLT. The weak correlations between the horizontal wind gradients over Jicamarca and Piura reinforce the fact that the mesoscale dynamics are different at these two locations.

Planetary Wave Modulation of Gravity Waves Over the Andes in 2016

AbstractThe Andes account for the largest source of orographic gravity waves (GWs) in the middle atmosphere. This results from persistent, strong zonal winds at the surface encountering the north‐south mountain chain, producing strong orographic lift, and resulting GWs. Here, we consider GWs in the stratosphere and mesosphere above the Andes as observed by the Cloud Imaging and Particle Size instrument, the Solar Occultation for Ice Experiment on the AIM satellite, and the Sounding of the Atmosphere using Broadband Emission Radiometry instrument onboard the Thermosphere Ionosphere Mesosphere Energetics and Dynamics satellite. GW variability is considered in the context of the location of the stratospheric wintertime westerly jet and planetary wave (PW) amplitude and phase. The occurrence of GWs in the middle and upper atmosphere depends not only on tropospheric sources, like the Andes, but also on the background winds through which they propagate. Results suggest that the propagation of GWs into the mesosphere is well correlated with winds throughout the middle and upper stratosphere. PWs cause the westerly jet to move over the Andes, resulting in an increase in GW amplitude throughout the middle and upper stratosphere. The evolution and variability of GWs are tied closely to the phase of the PW‐1 and are linked to PW‐2 when the PW amplitudes are sufficiently large. GW amplitude, as observed by all three data sets, increases in the upper stratosphere and lower mesosphere when the trough of the PW‐1 in the stratosphere is over the Andes.

Oscillations of GW Activities in the MLT Region over Mid-Low-Latitude Area, Kunming Station (25.6° N, 103.8° E)

Gravity wave (GW) activities play a prominent role in the complex coupling process of wave–wave and wave–background circulation around mid-low-latitude and equatorial areas. The wavelengths are wide, from about 10 m to 100 km, with a period from minutes to hours. However, the oscillations of GW activities are apparently different between the period bands of 0.1 to 1 h (HF) and 1 to 5 h (LF). To further understand the characteristics of GW activities, the neutral winds during 2008–2009 with a resolution of 3 min obtained from a medium-frequency (MF) radar in Kunming (25.6° N, 103.8° E) were analyzed. Using two numerical filters, the HF and LF GWs were estimated. Interestingly, the power spectral density grows larger as the frequency increases. It linearly falls with decreasing frequency when the period is less than 2 h. The seasonal variations in both HF and LF GWs are strongly demonstrated in August–September, November, and February–March with maximum meridional variances of 1100 m2 s−2 and 500 m2 s−2 and maximum zonal variances of 800 m2 s−2 and 350 m2 s−2 in, respectively. The turbulent velocity was also calculated and shows similar oscillations with GW activities. Furthermore, the GW propagation direction exhibits strong seasonal variations, which may be dependent on the location of the motivating source and background wind.

Numerical Modelling of PM10 Propagation in Rustavi City Atmosphere During the Southern Background Wind

Numerical Modelling of PM10 Propagation in Rustavi City Atmosphere During the Southern Background Wind

Interannual and Interhemispheric Comparisons of Q2DW Bimodal and Unimodal Structures During the 2003–2020 Summer Period

AbstractBy analyzing Sounding of the Atmosphere using Broadband Emission Radiometry and the Modern‐Era Retrospective analysis for Research Applications Version 2 reanalysis observations from 2003 to 2020, we found that the structural variation of the westward quasi‐2‐day wave (Q2DW) is related to the mean zonal wind in the background atmosphere, and the zonal wavenumber 3 (W3) is more affected by the background atmosphere than the zonal wavenumber 4 (W4). Our study focuses on the spatial structure of ∼50–95 km and ∼50°S–50°N. The spatial structure of W3 and W4 in the Northern and Southern Hemispheres is unimodal and bimodal, while the bimodal structure of W3 in the Southern Hemisphere is more obvious in some years. In the unimodal structure, W3 has a higher (altitude) peak in the Southern Hemisphere (∼82 km) than in the Northern Hemisphere (∼70 km), while W4 peaks at ∼70 km in both hemispheres. In the bimodal structure, W3 in the Southern Hemisphere fluctuates mostly at ∼82 km, followed by ∼68 km, while W3 in the Northern Hemisphere fluctuates mostly at ∼70 km, followed by ∼82 km. The spatial structure of W4 in both hemispheres fluctuates mainly at ∼70 km, followed by ∼82 km. In addition, W3 is stronger in the Southern Hemisphere than the Northern Hemisphere, W4 is stronger in the Northern Hemisphere than the Southern Hemisphere, and peak amplitudes of both W3 and W4 are larger in a bimodal structure than unimodal structure. The diagnostic analysis shows that the interannual and interhemispheric structure changes of Q2DWs may be due to the larger mean flow instabilities, background winds, and refractive index in the mesosphere, which make the bimodal structure of W3 and W4 obtain larger energy for propagation and amplification, resulting in higher (altitude) and larger amplitudes. This indicates that the background atmosphere of the mesosphere can affect the spatial structure of Q2DWs.

Environmental Controls on the Tropical Island Diurnal Cycle in the Context of Intraseasonal Variability

Abstract The mechanisms regulating the relationship between the tropical island diurnal cycle and large-scale modes of tropical variability such as the boreal summer intraseasonal oscillation (BSISO) are explored in observations and an idealized model. Specifically, the local environmental conditions associated with diurnal cycle variability are explored. Using Luzon Island in the northern Philippines as an observational test case, a novel probabilistic framework is applied to improve the understanding of diurnal cycle variability. High-amplitude diurnal cycle days tend to occur with weak to moderate offshore low-level wind and near to above average column moisture in the local environment. The transition from the BSISO suppressed phase to the active phase is most likely to produce the wind and moisture conditions supportive of a substantial diurnal cycle over western Luzon and the South China Sea (SCS). Thus, the impact of the BSISO on the local diurnal cycle can be understood in terms of the change in the probability of favorable environmental conditions. Idealized high-resolution 3D Cloud Model 1 (CM1) simulations driven by base states derived from BSISO composite profiles are able to reproduce several important features of the observed diurnal cycle variability with BSISO phase, including the strong, land-based diurnal cycle and offshore propagation in the transition phases. Background wind appears to be the primary variable controlling the diurnal cycle response, but ambient moisture distinctly reduces precipitation strength in the suppressed BSISO phase and enhances it in the active phase.

Offshore Migration of Summer Monsoon Low‐Level Jet on a Diurnal Scale

AbstractThis study investigates the diurnal migration of the low‐level jet (LLJ) over the Bay of Bengal in the summer monsoon, which remains understudied despite the well‐documented diurnal offshore propagation of rainfall worldwide. The southwesterly LLJ exhibits maximum strength during the night and morning. The LLJ undergoes a substantial eastward migration of approximately 600 km from the eastern offshore of India at midnight to the center of the Bay of Bengal by afternoon. A linear land‐sea breeze model is effective in capturing the diurnal migration with similar speed and phase. Including background wind offshore extends the migration, rather than confining it to the coast. This migration is driven by inertia‐gravity waves arising from the diurnal land‐sea thermal contrast and is influenced by the westerly upstream wind from the Indian subcontinent. Our results have important implications for understanding diurnal monsoon circulations and their associated precipitation.

Long-Term Observational Characteristics of Different Severe Convective Wind Types around Australia

Abstract Regional understanding of severe surface winds produced by convective processes [severe convective winds (SCWs)] is important for decision-making in several areas of society, including weather forecasting and engineering design. Meteorological studies have demonstrated that SCWs can occur due to a number of different mesoscale and microscale processes, in a range of large-scale atmospheric environments. However, long-term observational studies of SCW characteristics often have not considered this diversity in physical processes, particularly in Australia. Here, a statistical clustering method is used to separate a large dataset of SCW events, measured by automatic weather stations around Australia, into three types, associated with strong background wind, steep lapse rate, and high moisture environments. These different types of SCWs are shown to have different seasonal and spatial variations in their occurrence, as well as different measured wind gust, lightning, and parent-storm characteristics. In addition, various convective diagnostics are tested in their ability to discriminate between measured SCW events and nonsevere events, with significant variations in skill between event types. Differences in environmental conditions and wind gust characteristics between event types suggests potentially different physical processes for SCW production. These findings are intended to improve regional understanding of severe wind characteristics, as well as environmental prediction of SCWs in weather and climate applications, by considering different event types. Significance Statement The purpose of this study is to improve regional understanding of different types of severe wind events in Australia, specifically those associated with atmospheric convection. We did this by constructing a dataset of 413 severe convective wind events, using weather station and radar data within 20 regions around Australia. We then split those events into three different types, based on the environmental conditions that they occur within. We found that each event type tends to occur at different times of the year and in different regions, while also having different wind gust and lightning characteristics. In addition, the atmospheric conditions that are helpful for prediction of severe wind events differs between each type. These results are intended to be useful for prediction of severe wind events associated with convection and assessing their variability, characteristics, and impacts, in both weather forecasting and climate analysis.

Identification of spectrum of secondary acoustic-gravity waves in the middle and upper atmosphere in a high-resolution numerical model

Considerable attention has recently been paid to the study of so-called “secondary” acoustic-gravity waves (AGWs) that arise as a result of instability and nonlinear interactions of “primary” wave modes propagating from atmospheric sources, among themselves, and with the mean flow. In this paper, for the first time, the horizontal spatial spectra of primary and secondary AGWs are separated at fixed altitude levels in the middle and upper atmosphere at different time moments, which are simulated using a three-dimensional nonlinear high-resolution model AtmoSym. It is shown that in a short time after switching on the plane wave source at the lower boundary of the model, the spectrum consists of a peak corresponding to primary AGW and quasi-white noise generated by random atmospheric disturbances and the numerical model. Later, secondary peaks appear in the spectra at horizontal wave numbers, which are multiples of the wave numbers of primary AGW. The proposed separation of the spectra of primary and secondary AGWs makes it possible to estimate the relative contribution of secondary AGW at different altitudes, at different times, and with different stability of background temperature and wind profiles in the atmosphere.

Выделение спектра вторичных акустико-гравитационных волн в средней и верхней атмосфере в численной модели высокого разрешения

Considerable attention has recently been paid to the study of so-called “secondary” acoustic-gravity waves (AGWs) that arise as a result of instability and nonlinear interactions of “primary” wave modes propagating from atmospheric sources, among themselves, and with the mean flow. In this paper, for the first time, the horizontal spatial spectra of primary and secondary AGWs are separated at fixed altitude levels in the middle and upper atmosphere at different time moments, which are simulated using a three-dimensional nonlinear high-resolution model AtmoSym. It is shown that in a short time after switching on the plane wave source at the lower boundary of the model, the spectrum consists of a peak corresponding to primary AGW and quasi-white noise generated by random atmospheric disturbances and the numerical model. Later, secondary peaks appear in the spectra at horizontal wave numbers, which are multiples of the wave numbers of primary AGW. The proposed separation of the spectra of primary and secondary AGWs makes it possible to estimate the relative contribution of secondary AGW at different altitudes, at different times, and with different stability of background temperature and wind profiles in the atmosphere.

Cooperative Standoff Target Tracking using Multiple Fixed-Wing UAVs with Input Constraints in Unknown Wind

This paper investigates the problem of cooperative standoff tracking using multiple fixed-wing unmanned aerial vehicles (UAVs) with control input constraints. In order to achieve accurate moving target tracking in the presence of unknown background wind, a coordinated standoff target tracking algorithm is proposed. The objective of the research is to steer multiple UAVs to fly a circular orbit around a moving target with prescribed intervehicle angular spacing. To achieve this goal, two control laws are proposed, including relative range regulation and space phase separation. On one hand, a heading rate control law based on a Lyapunov guidance vector field is proposed. The convergence analysis shows that the UAVs can asymptotically converge to a desired circular orbit around the target, regardless of their initial position and heading. Through a rigorous theoretical proof, it is concluded that the command signal of the proposed heading rate controller will not violate the boundary constraint on the heading rate. On the other hand, a temporal phase is introduced to represent the phase separation and avoid discontinuity of the wrapped space phase angle. On this basis, a speed controller is developed to achieve equal phase separation. The proposed airspeed controller meets the requirements of the airspeed constraint. Furthermore, to improve the robustness of the aircraft during target tracking, an estimator is developed to estimate the composition velocity of the unknown wind and target motion. The proposed estimator uses the offset vector between the UAV’s actual flight path and the desired orbit, which is defined by the Lyapunov guidance vector field, to estimate the composition velocity. The stability of the estimator is proved. Simulations are conducted under different scenarios to demonstrate the effectiveness of the proposed cooperative standoff target tracking algorithm. The simulation results indicate that the temporal-phase-based speed controller can achieve a fast convergence speed and small phase separation error. Additionally, the composition velocity estimator exhibits a fast response speed and high estimation accuracy.

The Observed Effects of Cold Pools on Convection Triggering and Organization During DYNAMO/AMIE

AbstractCold pools that form from existing convection can generate new clouds nearby, a process that has been suggested to contribute to cloud organization. However, some disagreement exists on the role of cold pools in cloud organization over tropical oceans, and much remains to be understood on how this role depends on the state of large‐scale disturbances such as the Madden‐Julian Oscillation (MJO). This study addresses this question by examining the intraseasonal variability in the properties of cold pools and their effects on convection triggering using observations. The unique set of surface meteorology data and ground‐based radars deployed during the DYNAMO/AMIE field campaign are used to identify cold pools and the associated spatiotemporal evolution of rainfall. The results suggest that cold pools enhance rainfall at their expected speed of 3–8 m s−1, which includes the Doppler‐shifting effect by the background wind. The cold pools also enhance rainfall mainly within a 20 km radius, especially in the direction of boundary‐layer vertical wind shear. However, gravity waves appear to contribute predominantly to the propagation of convection over a wider range of distances due to their faster propagation speeds. The interface of convection triggering and propagation at different speeds of cold pools and gravity waves seems to contribute to cloud organization. The effectiveness of cold pools and gravity waves on cloud organization also depends highly on the MJO due to the combined effects of changes in environmental humidity and boundary to lower‐tropospheric wind.

Doppler Sodar Measured Winds and Sea Breeze Intrusions over Gadanki (13.5° N, 79.2° E), India

Doppler sodar measurements were made at the tropical Indian station, i.e., Gadanki (13.5° N, 79. 2° E). According to wind climatologies, the wind pattern changes from month to month. In July and August, the predominant wind direction during the monsoon season was the southwest. In September, it was the northwest and south. While the winds in November came from the northeast, they came from the northwest and southwest in October. The winds in December were out of the southeast. The diurnal cycle of winds at 60-m above the ground was visible, with disturbed wind directions in September and October. This may be connected to the Indian subcontinent’s southeastern monsoon recession. To better understand the monsoon circulation on a monthly basis, the present work is innovative in that it uses high-resolution winds measured using the Doppler sodar at the atmospheric boundary layer. The convergence of a sea breeze and the background wind might result in a sudden change in wind direction, and forecasting such a chaotic atmospheric event is crucial in the aviation sector. As a result, the wind shear that is produced may pose a serious threat to airplanes that are landing. In the current study, we present a few cases of sea breeze intrusions. The physics underlying these intrusions may help modelers better understand these chaotic wind structures and use them as inputs in their models. Based on surface-based atmospheric characteristics, there have been two reports of deep sea breeze intrusions that we report in this research. The sea breeze days were marked by substantial (moderate) drops in temperature (dewpoint temperatures) and increased wind speed and relative humidity. The India Meteorological Department (IMD) rainfall data showed a rise in precipitation over this location on 23 July (4.8 mm) and 24 July (9.5 mm) when sea breeze intrusions over Gadanki were noticed. Sea breeze intrusions could have brought precipitation (intrusion-laden precipitation) to this area due to conducive meteorological conditions. A simple schematic model is proposed through a diagrammatic illustration that explains how a sea breeze triggers precipitation over adjacent locations to the seacoast. The skew-T log-P diagrams have been drawn using the balloon-borne radiosonde measured atmospheric data over Chennai (a nearby location to Gadanki) to examine the thermodynamic parameters to gain insights into the underlying mechanisms and meteorological conditions during sea breeze intrusion events. It is found that the convective available potential energy (CAPE), which is presented as a thermos diagram, was associated with large values on 23 July and 24 July (898 J/kg and 1250 J/kg), which could have triggered thunderstorms over Chennai.

CFD model for airflow in a subway station compared to on-site measurements: The challenges of as-built environment

Understanding the contribution of piston effect and train-induced airflow to the ventilation of underground subway stations is essential to design efficient ventilation systems. To this aim, numerical models using computational fluid dynamics (CFD) have been used to recreate existing stations with a number of simplifying assumptions. However, the large variety of station configurations as well as types of sources influencing the airflow makes the generalization to other cases difficult. This study intends to predict numerically the train-induced wind affecting the climate of subway stations perceived on the platforms, and a comparison of these numerical predictions with field tests in an actual station is provided and extensively discussed.A simplified geometry of a station, where the ventilation is mainly realized by the piston effect caused by the train movement, is used to implement a scenario of a train passing through the station, with dynamic meshing techniques, and background wind is included in one configuration. Experimental measurements at 9 locations along the station's platform, repeated in order to improve statistical accuracy and the reproducibility of the results, provide data that can be compared with the corresponding numerical simulation. Numerical to experimental comparison is based on quantification of the peaks due to ingoing and outgoing trains through parameters like peak value, skewness and kurtosis. It is found that the main features of the airflow are well captured by the model, but the differences observed also highlight the challenges of simulating the as-build environment. Several non-dimensional metrics proposed in this paper can be used for comparison with other papers, so that a validated numerical model can be a relevant tool to calculate different velocity scenarios for trains and within different station architectures, supporting the design of ventilation systems to improve the comfort and safety of passengers.