Cyclonic Systems Research Articles

The impact of spume droplets induced by the bag-breakup mechanism on tropical cyclone modeling

Spume, large-radius seawater droplets that are ejected from the ocean into the atmosphere, can exchange moisture and heat fluxes with the surrounding air. Under severe weather conditions, spume can substantially mediate air-sea fluxes through thermal effects and thus needs to be physically parameterized. While the impact made by spume on air-sea interactions has been considered in bulk turbulent air-sea algorithms, various hypotheses in current models have resulted in uncertainties remaining regarding the effect of spume on air-sea coupling. In this study, we extended a classic bulk turbulent air-sea algorithm with a “bag-breakup” physical scheme of spume generation parameterizations to include spume effects in a complicated numerical model. To investigate the impact of spume on air-sea coupling, we conducted numerical experiments in a simulation of Tropical Cyclone Narelle. We observed a significant improvement in the ability to model minimum central pressure and maximum sustained surface wind speed when including the bag-breakup spume scheme. In particular, the impact of the bag breakup–generated spume is observed in the intensity, structure, and size of the tropical cyclone system through the modulation of local wind speed (U10), wave height (Hs), and sea surface temperature.

Analysis of Fluid Flow in Pipeline and Cyclone Systems for Preduster Coal Mill Indarung V Factory Using Flow Simulation

Cyclone is a tool for selling particulates from fluid streams without a filter. Cyclone in this case is to separate particulates from the air stream so they don't enter the coal mill. This study aims to analyze the effectiveness of the cyclone, pressure drop, and head loss in the system. The particles to be separated from the fluid stream are 9 microns in size. Pipe length for flow distribution is 67.24 m and 7 units of elbows. This analysis uses numerical methods with flow simulation features and compares them with theoretical results. Theoretical results obtained a pressure drop of 4042.74 Pa and a head loss of 607.82 m. This pressure drop is greater than the pressure fan, which is 1333 Pa. The simulation results of the inlet pipe 200 with a pressure drop of 4207.42 Pa, a head loss of 632.58 m, and an efficiency of 43%. At the inlet pipe 100 with a pressure drop of 4146.04 Pa, a head loss of 623.35 m, and an efficiency of 17%. At the inlet pipe 250 with a pressure drop of 4362.61 Pa, a head loss of 655.82 m, and an efficiency of 39%. Best results on pipe inlet 200.
 Cyclone merupakan alat untuk memisahkan partikulat dari aliran fluida tanpa filter. Cyclone dalam hal ini untuk memisahkan partikulat dari aliran udara supaya tidak masuk ke coal mill. Penelitian ini bertujuan untuk menganalisis efektivitas cyclone, pressure drop, dan head loss pada sistem. Partikel yang akan dipisahkan dari aliran fluida berukuran 9 mikron. Panjang pipa untuk distribusi aliran yaitu 67,24 m dan elbow sebanyak 7 unit. Analisis ini menggunakan metode numerik oleh fitur flow simulation dan membandingkannya dengan hasil teoritis. Hasil teoritis didapatkan pressure drop 4042,74 Pa dan head loss 607,82 m. Pressure drop ini lebih besar dari pressure fan yaitu 1333 Pa. Hasil simulasi inlet pipa 200 dengan pressure drop 4207,42 Pa, head loss 632,58 m, dan efisiensi 43%. Pada inlet pipa 100 dengan pressure drop 4146,04 Pa, head loss 623,35 m, dan efisiensi 17%. Pada inlet pipa 250 dengan pressure drop 4362,61 Pa, head loss 655,82 m, dan efisiensi 39%. Hasil terbaik pada inlet pipa 200.

Effects of Surface Wave-Induced Mixing and Wave-Affected Exchange Coefficients on Tropical Cyclones

Surface waves perform a crucial role in modulating tropical cyclone (TC) systems and have proved to be key for numerical TC predictions. In this study, we investigate the effects of wave-induced mixing and wave-affected surface exchange coefficients using a coupled ocean–atmosphere–wave model for two real TC cases: Shanshan (2018) and Megi (2010). The results demonstrate that wave-affected surface exchange coefficients enhance air–sea heat fluxes and have a significantly positive effect on simulated TC intensity, size, and strengthening process. In contrast, the wave-induced mixing has a negative impact on TC intensity and size and is not conducive to TC intensification and maintenance. The net effect of these two factors is a balance between the wave-affected positive contribution and the negative contribution from wave-induced sea surface temperature cooling. We find that the effect of wave-induced mixing on a TC system depends on the local thermal structure of the ocean. When the thermocline is weak and there is warm water at the wave-induced mixing penetration depth, the negative effect of the wave-induced mixing is weak. However, when there is cold subsurface water and a strong thermocline, wave-induced mixing has a significant impact, which exceeds the wave-driven positive feedback.

Investigation of unique Arabian Sea tropical cyclone with GPU-based WRF model: A case study of Shaheen

The recent severe cyclonic storm (SCS) Shaheen was a rare and unique Tropical Cyclone (TC) formed on September 30, 2021, on the Saurashtra coast off Gujrat, from a depression remnant of another cyclone Gulab off the Bay of Bengal. Under the influence of warm waters, this unique storm travelled westwards, skirting Pakistan's Makran coast before making landfall on northern Oman on October 4, 2021. The present study attempts to understand cyclone Shaheen's track, intensity, and synoptic features with the GPU-based WRF-ARW (v-3.8.1) on the google cloud platform (GCP). A 9 km resolution model domain covering the cyclone's track is initiated with an 18 UTC cycle of the Global Forecasting System (GFS) data. The model skilfully captured Shaheen's track and intensity up to 24 h of lead time which was in close agreement with the India Meteorological Department (IMD) estimates. The simulated track showed an overall track error of approximately 73 km compared to IMD. However, the surface wind stress was in close agreement with IMD. The spatial-temporal analysis of the simulated maximum surface wind speed showed the formation of the distinct eye of the cyclone moving away from the Indian coast towards the Gulf of Oman. Results indicated that Shaheen had a strong low-level (850 hPa) relative vorticity of approximately 193.56 10-5s-1 on 2nd October during the matured severe cyclonic stage, which got reduced to 77.88 × 10-5s-1 on 4th October as the system weakened. Comparison of the simulated synoptic parameters of the storm with reanalysis datasets ERA-5 and NGFS datasets indicated that the model simulated a stronger TC. The cyclone system showed significant relative humidity of about 80–90% with the well-delineated eyewall throughout various stages. The study shows the GPU-based WRF model's reliability with the current set of parameterizations for investigating a unique TC, Shaheen, on a public cloud infrastructure.

Subseasonal Prediction of Early-summer Northeast Asian Cut-off Lows by BCC-CSM2-HR and GloSea5

Northeast Asian cut-off lows are crucial cyclonic systems that can bring temperature and precipitation extremes over large areas. Skillful subseasonal forecasting of Northeast Asian cut-off lows is of great importance. Using two dynamical forecasting systems, one from the Beijing Climate Center (BCC-CSM2-HR) and the other from the Met Office (GloSea5), this study assesses simulation ability and subseasonal prediction skill for early-summer Northeast Asian cut-off lows. Both models are shown to have good ability in representing the spatial structure of cut-off lows, but they underestimate the intensity. The skillful prediction time scales for cut-off low intensity are about 10.2 days for BCC-CSM2-HR and 11.4 days for GloSea5 in advance. Further examination shows that both models can essentially capture the initial Rossby wave train, rapid growth and decay processes responsible for the evolution of cut-off lows, but the models show weaker amplitudes for the three-stage processes. The underestimated simulated strength of both the Eurasian midlatitude and East Asian subtropical jets may lead to the weaker local eddy-mean flow interaction responsible for the cut-off low evolution.

Cloud-radiative impact on the dynamics and predictability of an idealized extratropical cyclone

Abstract. Extratropical cyclones drive midlatitude weather, including extreme events, and determine midlatitude climate. Their dynamics and predictability are strongly shaped by cloud diabatic processes. While the cloud impact due to latent heating is much studied, little is known about the impact of cloud radiative heating (CRH) on the dynamics and predictability of extratropical cyclones. Here, we address this question by means of baroclinic life cycle simulations performed at a convection-permitting resolution of 2.5 km with the ICON model. The simulations use a newly implemented channel setup with periodic boundary conditions in the zonal direction. Moreover, the simulations apply a new modeling technique for which only CRH interacts with the cyclone, which circumvents changes in the mean state due to clear-sky radiative cooling that has complicated the interpretation of previous work. We find that CRH increases the kinetic energy of the cyclone system. The impact is most prominent at upper levels. To understand the CRH impact on the upper-tropospheric circulation, we diagnose the evolution of differences in potential vorticity between a simulation with and without CRH, and we quantify through which processes these differences grow over the course of the cyclone's life cycle. According to this diagnostic, CRH affects the cyclone mostly via the intensification of latent heating from cloud microphysical processes. Near the tropopause, direct diabatic modification of potential vorticity by intensified latent heat release precedes further changes in the tropopause by the upper-tropospheric divergent flow, which represents an indirect impact of latent heat release. Subsequently, differences in the tropopause structure amplify with the rotational flow during the highly nonlinear stage of the baroclinic wave. Our results show that although CRH is comparably small in magnitude, it can affect extratropical cyclones by changing cloud microphysical heating and subsequently the large-scale flow. The CRH impact follows a previously identified mechanism of multi-stage upscale error growth. At the same time, simulations in which CRH is disabled after certain days show that the CRH impact operates throughout the entire intensification phase of the cyclone. This means that CRH does not merely provide an arbitrary initial perturbation to the cyclone, from which differences grow in a generic way. Instead, our results suggest that uncertainties associated with the representation of CRH in numerical models have a more systematic impact and may more fundamentally influence model predictions of extratropical cyclones.

Evaluation of separation performance for eggshell-based reversed-phase HPLC columns by controlling particle size and application in quantitative therapeutic drug monitoring.

Eggshell-based reversed-phase packing materials were applied to an analytical column for high-performance liquid chromatography. Commercially available eggshell powder was classified by a cyclone system to obtain three types of particles with different diameters (arithmetic mean ± standard deviation: 4.3 ± 3.8, 5.6 ± 3.3, and 9.5 ± 5.5 μm). Sedimentation separation removed tiny particles from each sample, resulting in particles with arithmetic means of 6.6 ± 5.5, 7.3 ± 4.5, and 10.2 ± 5.0 μm, respectively. The unclassified particles and three particle types treated with sedimentation separation were subsequently packed into analytical columns (150 mm × 4.6 mm I.D.), and their separation efficiencies were evaluated by comparing their height equivalent to a theoretical plate (HETP). The column without sedimentation separation exhibited the highest HETP, whereas the columns with sedimentation separation showed better separation efficiency and lower back pressure. The column with the best separation efficiency was applied for the separation of 10 alkylbenzenes and 5 steroids, and all peaks were observed with complete separation (peak resolution: RS > 1.5). Finally, the column was used for quantitative analysis of voriconazole, an azole antifungal agent, and imatinib, a first-generation molecularly targeted drug for cancer treatment, in spiked whole blood. Excellent accuracy (99.1-102.8%) and precision (0.6-1.9%) were observed for the spiked drugs and long-term stability (>3000 column volumes of mobile phase flow) indicated good applicability of the developed eggshell-based column as an analytical column for routine analyses of therapeutic drugs in blood.

Revisiting the Precursors of Cyclonic Systems in the CORDEX RCM REMO2009 Simulations

Revisiting the Precursors of Cyclonic Systems in the CORDEX RCM REMO2009 Simulations

Forest Damage by Extra-Tropical Cyclone Klaus-Modeling and Prediction

Windstorms may have negative consequences on forest ecosystems, industries, and societies. Extreme events related to extra-tropical cyclonic systems remind us that better recognition and understanding of the factors driving forest damage are needed for more efficient risk management and planning. In the present study, we statistically modelled forest damage caused by the windstorm Klaus in south-west France. This event occurred on 24 January 2009 and caused severe damage to maritime pine (Pinus pinaster) forest stands. We aimed at isolating the best potential predictors that can help to build better predictive models of forest damage. We applied the random forest (RF) technique to find the best classifiers of the forest damage binary response variable. Five-fold spatial block cross-validation, repeated five times, and forward feature selection (FFS) were applied to the control for model over-fitting. In addition, variable importance (VI) and accumulated local effect (ALE) plots were used as model performance metrics. The best RF model was used for spatial prediction and forest damage probability mapping. The ROC AUC of the best RF model was 0.895 and 0.899 for the training and test set, respectively, while the accuracy of the RF model was 0.820 for the training and 0.837 for the test set. The FFS allowed us to isolate the most important predictors, which were the distance from the windstorm trajectory, soil sand fraction content, the MODIS normalized difference vegetation index (NDVI), and the wind exposure index (WEI). In general, their influence on the forest damage probability was positive for a wide range of the observed values. The area of applicability (AOA) confirmed that the RF model can be used to construct a probability map for almost the entire study area.

Impacts of Multi-Source Microwave Satellite Radiance Data Assimilation on the Forecast of Typhoon Ampil

This study investigates the impacts of the joint assimilation of microware temperature sensor, Advanced Microwave Sounding Unit-A (AMSUA), and microware humidity sensors, Microwave Humidity Sounder (MHS) and Microwave Humidity Sounder-2 (MWHS2), on the analyses and forecasts for the tropical cyclone (TC) system. Experiments are conducted using a three-dimensional variation (3DVAR) algorithm in the framework of the weather research and forecasting data assimilation (WRFDA) system for the forecasting of Typhoon Ampil (2018). The results show that the assimilation of MWHS2 radiance data improves the analyses better in terms of TC’s structure and moisture conditions than those of the MHS experiment. To some extent, the experiment with only AMSUA radiance delivers some positive impacts of the precipitation, track, and intensity forecast than the other two experiments do. In addition, the skill of the precipitation forecast is notably enhanced with higher equitable threat score (ETS) by the simultaneous assimilation of the MHS, MWHS2, and AMSUA radiance. Generally, assimilation of radiance from all sources of MHS, MWHS2, and AMSUA could combine the advantages of assimilating each type of sensors rather than individually. The consistent improvement is also confirmed for the TC’s track forecast with reduced error on average, whereas the improvement of intensity forecast is not obvious.

Water Vapor Transport by an Equivalent-Barotropic Cyclonic Anomaly Corresponding to Extreme Austral Late Summer Precipitation in Southeast Australia during 2021

Abstract Southeast Australia (SEA) experienced a wet February as well as an extremely wet March accompanied by devastating floods during 2021. Regional water vapor balance analysis at different levels indicates the leading role of water vapor inflow through zonal boundaries during February, and the dominant contribution of water vapor input through meridional boundaries during March, providing adequate anomalous moisture for abnormal precipitation. The horizontal distribution of vertically integrated water vapor flux is characterized as an anomalous cyclonic circulation pattern around the Tasman Sea and SEA, responsible for the intensified water vapor transport along northwesterlies from the tropical Indian Ocean and along anomalous onshore easterlies from the Tasman Sea during both months. Partition of the contributions of dynamic and thermodynamic processes to the anomalous atmospheric water vapor flux reveals the dominant role of the anomalous wind field, but the anomalous variation in the moisture field also plays a part in the water vapor convergence for SEA. The presence of upper and lower large-scale atmospheric circulations ascertains that cyclonic water vapor flux is attributed to a dominant equivalent-barotropic cyclone system over SEA. The plausible joint impacts of internal forcing from the positive southern annular mode (SAM) oscillation, and external forcing from La Niña, are further confirmed by composite analysis; a La Niña–induced low pressure system dominates the lower level over the Australian continent, and the SAM-caused anomalous cyclonic disturbance propagating from higher latitudes governs the higher level above southern Australia, leading to the important equivalent-barotropic cyclonic circulation just above the region of interest.

Co‐Occurrence of Surface O3, PM2.5 Pollution, and Tropical Cyclones in China

AbstractExtreme weather events are on the rise against the backdrop of climate change. Impact of tropical cyclone (TC) system, one of the extreme weather events, on air pollution remain poorly understood. A total of 103 recorded TCs (tropical storms and stronger) together with the surface air quality data collected from over 2000 observational sites in mainland China in 2014–2020 were utilized to examine the co‐occurrence of TC with continental ozone (O3) and fine particulate matters (PM2.5) pollution. TCs exhibit cleaning effects on PM2.5 within its coverage (typically ∼650 km), but enhance the co‐occurrence of O3 and PM2.5 in an extended region. The co‐occurrence frequencies are greater than 30% for any two co‐occurring events, and ∼8% for TC + PM2.5 + O3. We observed superregional trans‐boundary transportation of air pollutants driven by TC, led to ubiquitous spatial offsets and temporal lags of O3, PM2.5 pollution and TC, which are often inconsistent with traditional mechanisms such as accelerated chemical reactions for O3 formation. O3 pollution tends to occur 1∼2 days after PM2.5 pollution moved west. In contrast, PM2.5 pollution usually occur 4–12 hr following O3 pollution within a day over most regions except the southeast of China. Such spatial and temporal offsets vary with the paths of TCs. Composite analysis shows that temperature, wind field and large pressure systems are the key factors for air pollution formation and transportation over TC periphery. Our results have implications for understanding the interactions between TCs and air pollution, particularly for coastal areas where there are recurring TCs.

Impacts of regional uplift of the Tibetan Plateau on local summer precipitation and downstream moisture budget: A simulation study

AbstractUsing the Weather Research and Forecasting (WRF) model, a series of sensitivity experiments were conducted to study the individual and overall effects of the various topographic uplifts of the Tibetan Plateau (TP) on regional climate variability. The presence of the southern slope of the TP facilitates the maintenance and development of the South Asia High (SAH), which produces a positive cyclic response between local precipitation and SAH, so that the northern branch of the South Asian summer monsoon (SASM) maintains the water vapor supply. At the same time, the southern slope of the TP has a positive effect on the mid‐latitude tropospheric anomalous cyclone and anticyclone systems which promotes the downstream advancement of the East Asian summer monsoon (EASM) and is favourable for the transfer of water vapor and convective clouds downstream. The role of the TP platform is mainly due to the lifting of moisture generated by its local heating, which favours the formation of local convective clouds and precipitation while causing nonadiabatic warming of the troposphere. Water vapor transported from the TP could affect precipitation in central‐eastern China (CEC). However, the supply of water vapor in Southern East China (SEC) mainly comes from the southeast coast of China. The Tibetan Plateau sensitive areas (TPSA) have impacts on the water vapor transport path. Removing the TPSA favours an increase in precipitation and convective clouds in SEC. The removal of topographic disturbances favours the convergence and dispersion of water vapor at mid‐latitudes. The mid‐latitude dynamical anomaly may form a standoff with the low‐latitude dynamical system. This leads to inefficient precipitation and convective generation processes, a weakened monsoon advance over land, and a southward shift in the rainfall belt.

Characterization of Elemental Composition and Valence State of Cyclone-collected Aerosol Particles Using EDXRF and XAFS at Three Sites in Japan

The valence state and concentration of metallic pollutants are important factors contributing to the health effects of respirable particulate matter (PM); however, they have not been well studied. In this study, coarse and fine powder samples of atmospheric PM were collected using a cyclone system at Kanagawa (KO), Saitama (SA), and Fukuoka (FU) in Japan in 2017. Energy dispersive X-ray fluorescence spectroscopy (EDXRF) was used to measure the concentrations of nine metallic elements (Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, and Pb), and X-ray absorption fine structure (XAFS) spectroscopy was used to analyze the valence states of target elements (Cr, Mn, Fe, Cu, and Zn). The EDXRF results indicated that the average contents of Fe, Ti, and Zn were much higher than those of the other six elements in all samples. The XAFS results showed that the major valence states of the elements were Cr(III), Mn(II), Fe(III), Cu(II), and Zn(II). The percentages of Mn(IV), Fe(II), and Cu(0) were higher in KO and SA samples than in FU samples. Mn(0) and Zn(0) were detected in some samples only, and Cu(I) was not detected in any samples. Correlation analysis, principal component analysis, and cluster analysis were performed on the EDXRF and XAFS data of the target elements. The source identification results showed that the sources of metal contaminants in the samples varied considerably between sampling sites and depended on the industrial structure and geographical location of the sampling area. Our findings on the different valence states of the elements may be important for determining the toxicity of PM at different locations.

The tempest: Geoarchaeological examinations of tropical cycle/hurricane signatures in a submerged, formerly coastal shell midden site, Econfina Channel, Florida, U.S.A.

The nature of preservation potential for submerged cultural landscapes on continental shelves remains varied and not easily defined. This is due to two factors: First, relatively few sites have been discovered offshore, creating a small sample size. Second, excavation and analysis of such submerged sites have only begun to mature during the past few decades. We present here results from an exploratory study of one such site that examines impacts from two tropical cyclone systems in successive years. The main feature of this site is a specific type of archaeological feature: a shell midden. These sites are excellent indicators for coastal occupations globally and can retain evidence for major developments in cultural evolution, including reactions to climate change and sea-level rise from the Pleistocene into the Holocene. Further, they are found worldwide. The degree to which middens have been impacted by past and present marine forces, including tropical cyclones, is a key factor in their potential to preserve such evidence. We used a geoarchaeological methodology that quantifies particle size fractions from sediments taken from various zones within the site to compare them before and after each storm. Results have significant implications for preservation of submerged, formerly coastal archaeological sites globally.

Forecasting pressure drop and maximum sustained wind speed associated with cyclonic systems over Bay of Bengal with neuro-computing

The current research anticipates developing a model based on adaptive neuro-computation to foresee the minimum pressure drop (PD) at the centre as well as the maximum sustained wind speed (MSWS) accompanying with cyclonic systems over Bay of Bengal (BOB). The cyclonic systems taken in this work contain systems of different ranges starting from deep depression to extreme severe cyclones. For predicting PD and MSWS, suitable predictors have been sorted using factor analysis and it is observed that low-level vorticity (LLV), mid-tropospheric relative humidity (MRH) and vertical wind velocity at 850, 500 and 200 hPa pressure levels are appropriate parameters to create input matrix of neural network (NN). The adaptive NN representations are skilled with the data from 1990 to 2015 to estimate the PD as well as MSWS over BOB for 47 cyclonic systems. The outcome divulges that the multi-layer perceptron (MLP) NN model delivers decent precision at 6- and 30-h lead time in foretelling the PD. But the lowest error has been found at 6-h lead time in forecasting the central PD during mature stage of cyclonic systems. The result also illustrates that the MLP model is the utmost capable in forecasting the MSWS during mature stage of cyclonic structures with the lowest prediction error at 60-h lead time. The model results were validated and compared with the operational forecast by IMD for the 10 cyclonic systems from 2016 to 2019.

Study of an Arctic blowing snow-induced bromine explosion event in Ny-Ålesund, Svalbard

Bromine explosion events (BEEs) are important processes that influence the atmospheric oxidation capacity, especially in the polar troposphere during spring. Although sea ice surface is thought to be a significant bromine source, bromine release mechanisms remain unclear. High-resolution ground-based observations of reactive bromine, such as BrO, are important for assessing the potential impacts on tropospheric ozone and evaluating chemical models. However, previous model studies paid little attention to Svalbard, which is surrounded by both open ocean and sea ice. In this paper, we present continuous BrO slant column densities and vertical column densities derived by Multi-Axis Differential Optical Absorption Spectroscopy deployed at Ny-Ålesund (78.92°N, 11.93°E) in March 2017. We focused on one BEE in mid-March, during which the vertical column densities of BrO surged from 4.26 × 1013 molecular cm−2 to the peak at 1.23 × 1014 molecular cm−2 on March 17, surface ozone depleted from a background level of 46.25 parts per billion by volume (ppbv) to 13.9 ppbv. This case study indicates that the BEE was strongly associated with blowing snow induced by the cyclone systems that approached Svalbard from March 14 to 18. By considering meteorological conditions, sea ice coverage, and airmass trajectory history, we demonstrate that sea salt aerosols (SSAs) from blowing snow on sea ice, rather than from open ocean, are attributed to the occurrence of this BEE. Model results from a parallelized-tropospheric offline model of chemistry and transport (p-TOMCAT) indicate that this BEE was mainly triggered by a blowing snow event associated with a low-pressure cyclone system. The concentration of blowing-snow-sourced SSAs surged to peak when the airmass pass across the sea-ice-covered area under high wind speed, which is a critical factor in the process of bromine explosion observed in Ny-Ålesund. Due to the coarse resolution, the possible delayed timing of bromine release from SSA and the model-data discrepancies still exist.

Climate Change Impact on the Offshore Wind Energy Over the North Sea and the Irish Sea

The impact of climate change on the environment and human activities is one of the biggest concerns for the international community. Wind energy represents one of the most reliable and promising technology to achieve the target reduction of emissions. Though more intense and uniform resources characterize offshore areas, climate change may alter the environmental conditions and thus Levelized Cost of Energy evaluation. In this study, we analyze the impact of climate change on the offshore wind energy sector over the North Sea and the Irish Sea, where the majority of the European investments are located. To this aim, seven regional climate model simulations from the EURO-Cordex project are first evaluated. The ERA5 reanalysis product is considered the historical reference information after its validation against in-situ records and it is used to analyze the climate simulations by assessing their performance to reproduce weather types. Several statistics are calculated to assess the skill of each model in reproducing past climatology for the reference period (1985-2004). Since no significant differences between simulations are highlighted, an ensemble of all the seven simulations is used to characterize future changes in the offshore climate. Weather types under the representative concentration path scenario RCP8.5 for the future period 2081-2100 are then analyzed to describe the changes in climatological mean and extreme events. Regional climate model simulations are bias-corrected by applying the empirical quantile mapping technique. Then, future changes in six wind energy climate indicators (i.e. mean and extreme wind speed, wind power density, operation hours, gross energy yield, and capacity factor) are estimated for seven operating offshore wind farms. Results indicate a slight decrease in wind energy production, particularly in the northwest of the domain of study, testified by a reduction of all the climate indicators. However, large uncertainties in the projected changes are found at the wind farms located close to the south coast of the North Sea. Extreme wind conditions show a modest rise in the southeastern part of the region, related to an increase of the weather types dominated by cyclonic systems off Scotland shores.

Impact of Meteorological Conditions and Human Activities on Air Quality During the COVID-19 Lockdown in Northeast China

During the lockdown implemented to curb the spread of COVID-19, human activities have drastically reduced, providing a valuable opportunity to study and compare the impact of meteorological conditions and human activities on air quality. In this study, large-scale weather circulation, local meteorological conditions, and the impact of human activities are comprehensively considered, and changes in the concentration of major air pollutants in the northeast during this period are systematically studied. The large-scale weather circulation patterns that mainly affect the northeast region are divided into nine types by using the T-mode Principal components analysis objective circulation classification method. It is found that the northeast region is located at the edge of weak high pressure (Types 1, 2, and 7) and at the rear of high pressure (Type 4) and has higher concentrations of PM2.5, NO2, SO2, and CO; in cyclonic weather systems, low vortices (Types 3 and 5) and under the influence of the updraft (Type 6) in front of the trough, the ozone concentration is higher. The changes in the concentrations of PM2.5, NO2, CO, SO2, and O3 in the three cities, namely Shenyang, Changchun, and Harbin, during the lockdown period are compared, and it is found that the concentrations of PM2.5, NO2, CO, and SO2 have a tendency to first decrease and then increase, while the changes of O3 concentration are cyclical and increased significantly during this period. This demonstrates that pollutants such as PM2.5, NO2, CO, and SO2 are more susceptible to human activities and local meteorological conditions, and changes in O3 concentration are more closely related to changes in weather circulation types. Finally, the FLEXPART-WRF model is used to simulate the pollution process of nine circulation types, which confirms that particulate pollution in the northeast is mainly affected by local emissions and local westward sinking airflow.

A climatological-dynamical analysis of tropopause folds over Southwest Asia in the period of 1989–2018

Tropopause folding is believed to be connected to the development of cyclonic systems in midlatitudes as well as the larger-scale, lower-frequency processes in the lower latitudes. To investigate such connections, a statistical and dynamical analysis of tropopause folds occurred in Southwest Asia is carried out for the period of 1989–2018. Tropopause folds are identified using the Era-Interim reanalysis dataset from the European Centre for Medium-Range Weather Forecasts. The spatial–temporal distributions of tropopause folding show that the frequency of folding is higher in the winter hemisphere than in the summer hemisphere and greater values of the frequency are found mostly within an elongated zonal band which is situated between 20 and 40 degrees latitude. Southwest Asia also has strong positive anomalous values of tropopause folding frequency and achieves the values more than five times the average of the Northern Hemisphere in the summer, especially in the northern latitudes of this region including Afghanistan, Iran and the eastern Mediterranean. This can be attributed mainly to the formation of summer monsoon in the subtropical latitudes of the Indian Ocean. In this regard, the examination of the effects of El Niño and La Niña on the spatial–temporal distributions of tropopause folding reveals that the values of 3-month running average of tropopause folding frequency coincident with La Niña tend to be larger than those with El Nino in both the hemispheres and Southwest Asia. This result is consistent with the previous findings on the tendency for higher occurrence of anticyclonic (cyclonic) baroclinic wave life cycles during La Niña (El Niño). Dynamically, the folds occurred in the study area are associated with the formation of waves at 500 hPa level and subsequently the creation of surface cyclones. In areas of high frequency of folding events, strong meridional shear of the zonal winds and jet stream amplification are observed at 200 hPa level. The analysis of wave activity flux and its divergence for the selected month of June 2015 shows two regions of wave propagation, one with a wave-packet like signature of flux divergence/convergence centers in the upper troposphere and one over the lower troposphere. The upper-tropospheric wave packet ends with an area of flux convergence related with the receipt and decay of Rossby waves, while in the lower troposphere, a flux divergence region as a source of stationary waves associated with the Indian monsoon activity is identified.