Event Days Research Articles

Analysing foodborne illness outbreak severity in the USA, 2009–19

BackgroundIn the USA, one in six Americans have had a foodborne illness, resulting in approximately US$17·6 billion (2018) of losses annually attributed to medical costs, productivity losses, and economic burden due to death. Previous research has characterised these burdens with use of various methods, including disability-adjusted life-years (DALYs), medical care costs, and revenue losses of food retailers. However, these indices assess only the socioeconomic burdens of outbreaks without providing an index to compare the health-related severity of outbreaks regarding geographical spread of transmission, outbreak duration, and the morbidity and mortality of case outcomes. MethodsIn this study, we proposed a data-driven index for evaluating outbreak severity using the publicly available US Centers for Disease Control and Prevention's National Outbreak Reporting System (NORS) database from Jan 1, 2009, to Dec 31, 2019. We identified 67 metrics related to the geographical extent (eg, counties or states where individuals with a foodborne illness resided and were exposed), case severity (eg, primary cases, hospital admissions, emergency room visits, and deaths), duration (eg, days of illness and days of exposure events), and their ratios. We selected 11 metrics to create the index on the basis of completeness and distributional characteristics of these metrics. We generated index scores by normalising natural log-transformed values on a 0–1 scale and averaging all metrics per outbreak. Scores ranged from 0 (lowest severity) to 1 (highest severity). FindingsNORS reported 9407 outbreaks in our 11-year study period. We found that bacterial outbreaks associated with the genera Streptococcus, Listeria, and Salmonella had the highest median severity scores, whereas Bacillus, Staphylococcus, and Clostridium had the lowest scores. Among protozoa, Cryptosporidium and Cyclospora had the lowest median scores, whereas Giardia and Toxoplasma had the highest scores. Hepatitis had the highest median score for virus-associated outbreaks, whereas Norovirus, which had the most outbreaks reported in our study period (n=3088), had the lowest score. InterpretationOur index illustrates the usefulness of publicly reported surveillance data in establishing a data-driven approach for monitoring the severity of foodborne outbreaks regarding their spread, duration, and morbidity and mortality. Differences in outbreak severity by pathogen inform how to best allocate resources for monitoring, tracking, and preventing foodborne disease outbreaks. Being data driven, our index emphasises the importance of improved data quality, integrity, and completeness of surveillance records. Future research should strive to validate this index by use of longitudinal cohort studies. FundingUS Department of Defense, National Institute of Food and Agriculture.

Particle number size distribution and new particle formation in Xiamen, the coastal city of Southeast China in wintertime

New particle formation (NPF) has a great impact on regional and global climate, air quality and human health. This study uses a Scanning Mobility Particle Sizer (SMPS) for simultaneous measurement of particle number size distribution (PNSD) in wintertime to investigate NPF in the coastal city of Xiamen. The mean particle number concentration, surface area concentration and volume concentration were 7.25 × 103 cm−3, 152.54 μm2 cm−3, and 4.03 μm3 cm−3, respectively. Particle number concentration was mainly influenced by the nucleation mode and the Aitken mode, whereas the main contributor to particle surface area concentration and volume concentration was accumulation mode particles. The frequency of NPF events occurred was around 41.4% in December 2019. The typical growth rates of new formed particles were 1.41–2.54 nm h−1, and the observed formation rates were 0.49–1.43 cm−3 s−1. A comparative analysis of conditions between event and non-event days was performed. The results emphasized that air temperature, UV radiation and relative humidity were the most decisive meteorological factors, and NPF events usually occurred under clean atmospheric conditions with low PM concentrations. Although condensation sink was high when NPF event occurred, the level of SO2 and O3 concentration was also high.

Machine Learning to Assess for Acute Myocardial Infarction Within 30 Minutes.

Variations in high-sensitivity cardiac troponin I by age and sex along with various sampling times can make the evaluation for acute myocardial infarction (AMI) challenging. Machine learning integrates these variables to allow a more accurate evaluation for possible AMI. The goal was to test the diagnostic and prognostic utility of a machine learning algorithm in the evaluation of possible AMI. We applied a machine learning algorithm (myocardial-ischemic-injury-index [MI3]) that incorporates age, sex, and high-sensitivity cardiac troponin I levels at time 0 and 30 minutes in 529 patients evaluated for possible AMI in a single urban emergency department. MI3 generates an index value from 0 to 100 reflecting the likelihood of AMI. Patients were followed at 30-45 days for major adverse cardiac events (MACEs). There were 42 (7.9%) patients that had an AMI. Patients were divided into 3 groups by the MI3 score: low-risk (≤ 3.13), intermediate-risk (> 3.13-51.0), and high-risk (> 51.0). The sensitivity for AMI was 100% with a MI3 value ≤ 3.13 and 353 (67%) ruled-out for AMI at 30 minutes. At 30-45 days, there were 2 (0.6%) MACEs (2 noncardiac deaths) in the low-risk group, in the intermediate-risk group 4 (3.0%) MACEs (3 AMIs, 1 cardiac death), and in the high-risk group 4 (9.1%) MACEs (4 AMIs, 2 cardiac deaths). The MI3 algorithm had 100% sensitivity for AMI at 30 minutes and identified a low-risk cohort who may be considered for early discharge.

Rapid Dynamical Evolution of ITCZ Events over the East Pacific

Abstract The latitudinal location of the east Pacific Ocean intertropical convergence zone (ITCZ) changes on time scales of days to weeks during boreal spring. This study focuses on tropical near-surface dynamics in the days leading up to the two most frequent types of ITCZ events, nITCZ (Northern Hemisphere) and dITCZ (double). There is a rapid daily evolution of dynamical features on top of a slower, weekly evolution that occurs leading up to and after nITCZ and dITCZ events. Zonally elongated bands of anomalous cross-equatorial flow and off-equatorial convergence rapidly intensify and peak 1 day before or the day of these ITCZ events, followed 1 or 2 days later by a peak in near-equatorial zonal wind anomalies. In addition, there is a wide region north of the southeast Pacific subtropical high where anomalous northwesterlies strengthen prior to nITCZ events and southeasterlies strengthen before dITCZ events. Anomalous zonal and meridional near-surface momentum budgets reveal that the terms associated with Ekman balance are of first-order importance preceding nITCZ events, but that the meridional momentum advective terms are just as important before dITCZ events. Variations in cross-equatorial flow are promoted by the meridional pressure gradient force (PGF) prior to nITCZ events and the meridional advection of meridional momentum in addition to the meridional PGF before dITCZ events. Meanwhile, variations in near-equatorial easterlies are driven by the zonal PGF and the Coriolis force preceding nITCZ events and the zonal PGF, the Coriolis force, and the meridional advection of zonal momentum before dITCZ events.

Testing Stock Market Efficiency from Spillover Effect of Panama Leaks

On 3 April 2016, Mossack Fonseca provided the historically most significant leak of its shareholder’s data for owning offshore companies. Shareholders include many political and influential figures around the globe, which causes a moral hazard. The study analyses the effects of Panama leak events on five stock exchanges to ensure the market efficiency and investor perception related to the Panama leaks. Event study methodology is used on five occasions associated with Panama papers, i.e., the resignation of the Prime Minister of Iceland on 5 April 2016, Jurgen Mossack’s resignation on 7 April 2016, the resignation of the Spanish Minister of Industry on 15 April 2016, the 450 personalities of Pakistan that were nominated in Panama papers on 15 April 2016, and the formation of an inquiry commission to inquire into the matter. The market efficiency of five stock exchanges was checked, i.e., the KSE 100 of Pakistan, the OMXIPI exchange of Iceland, the IBEX 35 of Spain, the New York stock exchange (NYSE), and S&P 500. The market remains efficient for most events and investor behaviour changes for one or two days around the event day (this event has concise term significant abnormal returns in all stock exchanges or concise term significant abnormal macroeconomic effects are observed in all stock exchanges).

A qualitative investigation exploring why dance festivals are risky environments for drug use and potential adverse outcomes

BackgroundDance festivals have been shown to be high-risk events for use of drugs such as ecstasy/MDMA and possible adverse effects associated with use. However, few studies have examined what makes festivals such risky environments. We aimed to determine festival-specific risk factors for adverse outcomes related to drug use.MethodsIn-depth interviews were conducted with 35 key informants in North America who deemed themselves experts in new psychoactive substances, and identified as drug checkers, sellers, or experienced users. Interviews were coded in an inductive manner, and we conducted thematic analysis to identify relevant themes.ResultsWe identified four main themes focusing on festival attendance as a risk factor for risky drug use and related outcomes: attendees inexperienced with electronic dance music parties and party drugs, risky drug purchasing, risky drug use practices, and festival-specific environmental risk factors. Festivals attract a wide array of people not experienced with party drugs, yet drugs like ecstasy are commonly sought by such individuals inside festivals. Relying on strangers inside to purchase drugs is a risk factor for purchasing adulterated product. Fear of security/police at festivals leads to risky drug-taking such as ingesting one’s full batch of drugs at the entrance. These risks are compounded by environmental factors including crowding, hot temperature, and lack of water (which lead to dehydration), long/consecutive event days (which can lead to exhaustion), and inadequate medical emergency response.ConclusionsWe determined modifiable risk factors which can both inform future research and future prevention and harm reduction efforts in this scene.

Investor reactions to major events in the sub-prime mortgage crisis

We investigate how investor perceptions about the financial health of twenty-seven bank holding companies that controlled eighty percent of US banking assets at year-end 2006 changed during major events leading to the collapse of Lehman Brothers. We use the event study method to investigate whether and to what extent investors priced major events before the Lehman bankruptcy. Abnormal returns on the event days range from -9.25 to 4.80%. When the Federal Reserve Bank of New York is authorized to lend to Fannie Mae and Freddie Mac on 13 July 2008, sample bank holding companies average the lowest abnormal returns of -9.25. When the Federal Housing Agency places Fannie Mae and Freddie Mac under government conservatorship on 7 September 2008, abnormal returns average the highest at 4.80. The significant abnormal returns indicate that investors price the information released in the pre-crisis events.

What’s hidden behind bulk deals? A study on Indian stock market

Purpose Emerging market, like India, is characterised by poor institutional structure, weaker regulations and higher information asymmetry which may lead to stock price manipulation. This study shed some light on such manipulation by investigating front-running behaviour around the bulk deals of stocks traded at the National Stock Exchange (NSE) from 2010 to 2019.Design/methodology/approach The authors employ an event study methodology to identify front-running in pre-event period of bulk deals. The bulk deals are classified into Only Buy, Only Sell, Partial Buy and Partial Sell trades. They are further subsampled based on the category of investors. Through cross-sectional regression, the authors also identify factors explaining such front-running.Findings The results show that the front-runners can achieve 5%–7% returns within a week around the event day. Abnormal Returns (AR) before the deals are higher for “Buy” deals than “Sell” deals. The authors also examine the role of volume and delivery in explaining the AR and cumulative abnormal returns (CAR). Lagged CAR, change in volume and change in delivery explain the AR. The results are robust after controlling for Bullish and Bearish Periods.Originality/value To the best of authors’ knowledge, this is the first study that explores the front-running in “Partial Buy” and “Partial Sell” bulk deals. Further, it investigates whether the category of investors has any role in front running. It empirically tests the asymmetric market reaction between “Buy” and “Sell” trades. Finally, it examines the role of volume and delivery in front-running.

New particle formation event detection with Mask R-CNN

Abstract. Atmospheric new particle formation (NPF) is an important source of climate-relevant aerosol particles which has been observed at many locations globally. To study this phenomenon, the first step is to identify whether an NPF event occurs or not on a given day. In practice, NPF event identification is performed visually by classifying the NPF event or non-event days from the particle number size distribution surface plots. Unfortunately, this day-by-day visual classification is time-consuming and labor-intensive, and the identification process renders subjective results. To detect NPF events automatically, we regard the visual signature (banana shape) which has been observed all over the world in NPF surface plots as a special kind of object, and a deep learning model called Mask R-CNN is applied to localize the spatial layouts of NPF events in their surface plots. Utilizing only 358 human-annotated masks on data from the Station for Measuring Ecosystem–Atmosphere Relations (SMEAR) II station (Hyytiälä, Finland), the Mask R-CNN model was successfully generalized for three SMEAR stations in Finland and the San Pietro Capofiume (SPC) station in Italy. In addition to the detection of NPF events (especially the strongest events), the presented method can determine the growth rates, start times, and end times for NPF events automatically. The automatically determined growth rates agree with the manually determined growth rates. The statistical results validate the potential of applying the proposed method to different sites, which will improve the automatic level for NPF event detection and analysis. Furthermore, the proposed automatic NPF event analysis method can minimize subjectivity compared with human-made analysis, especially when long-term data series are analyzed and statistical comparisons between different sites are needed for event characteristics such as the start and end times, thereby saving time and effort for scientists studying NPF events.

Asian dust storms result in a higher risk of the silicosis hospital admissions.

Previous studies found that silicosis was majorly associated with occupation-related risks. However, little evidence was available to clarify the relation between Asian dust storm (ADS) and silicosis hospital admissions. This present paper aims to investigate the association between ADS events and hospital admissions for silicosis. We applied a Poisson time-series regression on the 2000-2012 National Health Insurance Research Database in Taiwan, linking air quality data and ambient temperature data to estimate the impact of ADS on silicosis hospital admissions in the age-specific groups. A total of 2154 hospital admissions were recorded for silicosis in Taiwan, for a daily average number of 0.45. The number rises from 0.43 on a day without ADS to 0.70 on the outbreak day and continues increasing to 0.83 one day after outbreak. Among patients under 45, the effect of ADS appears on the event day as well as several post-event days (lag2-6) at the significant level of p < 0.1. There is also a significant lag effect on post-event day 2 (p < 0.05) for those aged above 74. Asian dust storms do result in a rise of silicosis hospital admissions, particularly for those above 74, those under 45, and for females.

DAMPAK COVID-19 TERHADAP ABNORMAL RETURN DAN VOLUME PERDAGANGAN SAHAM

The COVID-19 pandemic is a non-natural disaster that has a huge impact around the world. This research is a quantitative research with event study method. The purpose of this research is to test the capital market reaction by looking at abnormal returns and trading volume activity before and after the COVID-19 non-natural disaster. The event day in this study was April 13rd, 2020 when the Presidential Decree was issued regarding the designation of COVID-19 as a national disaster. Using purposive sampling method, the sample of this study were 27 companies engaged in the hotel, restaurant, and tourism sub-sectors listed on the Indonesia Stock Exchange. The event period is 11 days, namely 5 days before the event, 1 day at the time of the event and 5 days after the event. Data analysis using t-test and wilxocon signed ranks test. The results of this study are: 1) there is no abnormal return during the event period, 2) there is no difference in the average abnormal return before and after the COVID-19 non-natural disaster event, 3) there is no difference in the average trading volume activity before and after the COVID-19 non-natural disaster event and after the COVID-19 non-natural disaster event.&#x0D; Keywords: Event Study, Abnormal Return, Trading Volume Activity, COVID-19.

Effects of Dust Event Days on Influenza: Evidence from Arid Environments in Lanzhou

Airborne aerosol is believed to be an important pathway for infectious disease transmissions like COVID-19 and influenza. However, the effects of dust event days on influenza have been rarely explored, particularly in arid environments. This study explores the effects of ambient particulate matter (PM) and dust events on laboratory-confirmed influenza in a semi-arid city. A descriptive analysis of daily laboratory-confirmed influenza (influenza) cases, PM (PM10 and PM2.5), meteorological parameters, and dust events were conducted from 2014 to 2019 in Lanzhou, China. The case-crossover design combined with conditional Poisson regression models was used to estimate the lagging effects of PM and dust events on influenza. In addition, a hierarchical model was used to quantitatively evaluate the interactive effect of PM with ambient temperature and absolute humidity on influenza. We found that PM and dust events had a significant effect on influenza. The effects of PM10 and PM2.5 on influenza became stronger as the cumulative lag days increased. The greatest estimated relative risks (RRs) were 1.018 (1.011,1.024) and 1.06 1(1.034,1.087), respectively. Compared with the non-dust days, the effects of dust events with duration ≥ 1 day and with duration ≥ 2 days on influenza were the strongest at lag0 day, with the estimated RRs of 1.245 (95% CI: 1.061-1.463) and 1.483 (95% CI: 1.232-1.784), respectively. Subgroup analysis showed that pre-school children and school-aged children were more sensitive to PM and dust events exposure. Besides, we also found that low humidity and temperature had an interaction with PM to aggravate the risk of influenza. In summary, ambient PM and dust events exposure may increase the risk of influenza, and the risk of influenza increases with the dust events duration. Therefore, more efforts from the government as well as individuals should be strengthened to reduce the effect of PM on influenza, particularly in cold and dry weather.

Impacts of bank mergers on shareholder's wealth

We examine the effect of the news about merger of six banks into four major banks, employing the standard event study method with the market model on a sample of four bidders and six target banks. We find significant impact of merger announcement on the bidder and target banks. While the bidder banks are negatively impacted, the target banks experience positive impacts on the event day and day after, followed by negative results later on. No previous study is found to have addressed this question on how the merger announcements impact the bidder and target bank's stock returns in India.

Hosting IOI 2019 Azerbaijan: Back to the Future

Who would guess that the 31st International Olympiad in Informatics (IOI) in Baku, Azerbaijan will be referred to as “the last normal” one for so long? While the IOI community looks forward to the upcoming onsite events, the readers may be interested in a retrospective report on the IOI 2019 from the host organizing, scientific and technical committees. This report covers the whole process throughout bidding, preparations, event days and closeout, shares some pain points and provides a number of practical recommendations. The authors hope that by looking back at the IOI 2019 Azerbaijan they will also help potential hosts of future IOIs.

Impact of cross-border mergers and acquisitions on short-term gain to shareholders of target firms in India – effect of the mode of payment and industry relatedness

We examine the effect of announcements of cross-border mergers and acquisitions on short-term gain to shareholders of target firms in India. Using event study, we analyse 137 listed target firms taken from Bloomberg in post-financial crisis era from 2009 to 2019. Our analysis does shows short-term gains on acquisition of Indian firms, with the gains being high in and around the event day. Moreover, the return is positive both for pre- and post-event day windows, though the pre-event day window return is higher as compared to post-event day window. Notably, the return for the shareholders on an acquisition announcement is higher for cash payment, as compared to other payment modes. Further, the wealth effect for acquisitions in the related industry is higher compared to the acquisitions in unrelated industries. We have done multivariate analysis with the cumulative average abnormal return as the dependent variable, and mode of payment and industry relatedness as independent variables. The analysis shows a higher return for acquisitions in the related industry with cash payment. The findings of this research by and large concur with earlier studies, and are useful for foreign investors to appreciate the market behaviour in acquisitions of Indian firms post 2009.

Characterization of Particulate Matter (PM1 and PM2.5) from Incense Burning Activities in Temples in Vietnam and Taiwan

Particulate matter (PM) emitted from incense burning is a serious problem because of its effects on human health and the environment, especially on the air quality of Southeast Asia. This study investigated the PM1 and PM2.5 concentrations in two temples in Vietnam and Taiwan, focusing on events (i.e., new moon and full moon day) and non-event days using PM sensors. Moreover, PM2.5 samples were collected to determine organic carbon (OC) and elemental carbon (EC) concentrations. The PM1 and PM2.5 concentrations in Vietnam (22.7 ± 18.7 and 36.5 ± 33.9 µg m-3, respectively) were lower than those at the Taiwan temple (74.5 ± 53.4 and 97.0 ± 65.4 µg m-3, respectively). The incense burning activity in the Taiwan temple occurred inside the temple while the incense burner at Vietnam’s temple was located outdoors. During the event days, PM1 and PM2.5 concentrations were about two times greater than on non-event days, highlighting the impact of incense burning on the PM concentrations. By breaking the study area into control and exposure sites, we found that the people inside the temple experienced 2–5 times higher PM concentrations as compared to those in the ambient air. The PM1/PM2.5 ratio was 0.6 ± 0.1 for the Vietnam temple, which was lower than the Taiwan value (0.7 ± 0.1). The OC and EC concentrations in the Taiwan temple were 129.40 ± 97.68 and 1.16 ± 2.31 µg m-3, respectively, significantly greater than those found in the Vietnam temple (OC = 27.70 ± 7.66 µg m-3, EC = 1.63 ± 0.93 µg m-3). Furthermore, the OC/EC ratio in the Vietnam temple (20.24) was similar to those reported from incense and biomass in previous research. The increase in religious activities was the major factor leading to the enhancement of the air pollutant levels surrounding the study areas. This study provides valuable information on PM and carbonaceous aerosols emitted from incense burning in Southeast Asia megacities.

The reaction of energy markets to regional conflict: evidence from event study approach

This article explores the impact of the Russia-Ukraine conflict on energy markets by using the event study approach. The analysis of the average abnormal returns (AARs) and cumulative average abnormal returns (CAARs) before and after the launch of the ‘special military operation’ by Russian military forces on 24 February 2022 reveals a strong positive impact of this military action on clean energy and conventional energy markets, especially on the clean energy market. All clean energy indices are significant on the event day, while only half of the conventional energy indices respond significantly. Moreover, some conventional energy indices, such as DJ Oil & Gas, have no significant response to the event.

Problems in the management of Tokyo 2020 Paralympic Games cycling events at Fuji International Speedway during the COVID-19 pandemic.

I write to report my department’s experience of the Tokyo 2020 Paralympic Games cycling events.1 The Tokyo 2020 Paralympic Games cycling events at Fuji International Speedway (FIS) at Gotemba City in eastern Shizuoka Prefecture, Japan, were held without spectators from August 31, 2021 to September 3, 2021. Time trial races were held on the first day of the cycling events, while road races were held on the second to fourth days. Fuji International Speedway is licensed as a grade 1 circuit by the Federation Internationale de l'Automobile. Hospital A at Gotemba City was engaged as a designated hospital by the Tokyo 2020 Organizing Committee (TOC) for the Olympic and Paralympic Games. However, Hospital A did not have an acute critical care center and could not treat patients with multiple severe injuries. In addition, Hospital A could not receive emergency patients due to an outbreak of COVID-19 that occurred in the hospital just before the Paralympic Games cycling events; thus, Hospital A lost its function as the designated hospital for the Paralympic Games cycling events at FIS. In that time, Shizuoka Prefecture experienced its fifth and largest wave of the COVID-19 pandemic, which had started after the Tokyo 2020 Olympic Games, even though Tokyo was under a state of emergency (Fig. 1). During peacetime, patients involved in car accidents at the FIS are managed by a physician-staffed helicopter (helicopter emergency medical service [HEMS]) operated by Juntendo Shizuoka Hospital (JSH), which has a level 1 acute critical care center because such patients have a high risk of having multiple severe injuries.2, 3 The hospital is located in eastern Shizuoka Prefecture and is the leader of the medical control council system, which oversees the activities of the Gotemba Fire Department, as a member of the Japanese Medical Association.2-4 No official plan was established by the TOC in preparation for the unlikely situation where the designated hospital could not fulfill its function, thus requiring JSH to provide backup assistance in the event that Hospital A was unable to handle any patients with severe injuries. However, JSH regularly provides such backup assistance. During the Tokyo 2020 Paralympic Games cycling events at FIS, three Paralympians with fall-related severe injuries were directly transported to JSH by ground ambulance, which took approximately 60 min. Gotemba Fire Department requested the dispatch of the Eastern Shizuoka HEMS, however, the HEMS was not available due to other missions. The patients (male, n = 2; female, n = 1) were aged in their 40s to 60s. The diagnoses were cerebral concussion (n = 1), traumatic subarachnoid hemorrhage with elbow avulsion (n = 1), and pneumothorax with lung contusion (n = 1). All three Paralympians required admission to JSH, and fortunately obtained favorable outcomes and safely returned to their own nation. Fall-related accidents that extraordinary athletes experience during cycling events could result in fatal or multiple severe injuries.1 Accordingly, hospitals that are designated for the management of such athletes should be able to treat such patients to obtain a favorable outcome.5 In addition, a backup designated hospital is necessary in the event of infectious disease outbreaks, such as the COVID-19 pandemic. Unfortunately, no official post-event verification was carried out by the TOC after the Olympic and Paralympic Games. This work was supported in part by a Grant-in-Aid for Special Research in Subsidies for ordinary expenses of private schools from The Promotion and Mutual Aid Corporation for Private Schools of Japan. Conflict of interest: None.

Occurrence rate and duration of space weather impacts on high-frequency radio communication used by aviation

High frequency (HF) radio wave propagation is sensitive to space weather-induced ionospheric disturbances that result from enhanced photoionization and energetic particle precipitation. Recognizing the potential risk to HF radio communication systems used by the aviation industry, as well as potential impacts on GNSS navigation and the risk of elevated radiation levels, the International Civil Aviation Organization (ICAO) initiated the development of a space weather advisory service. For HF systems, this service specifically identifies shortwave fadeout, auroral absorption, polar cap absorption, and post-storm maximum useable frequency depression (PSD) as phenomena impacting HF radio communication and specifies moderate and severe event thresholds to describe event severity. This paper examines the occurrence rate and duration of events crossing the moderate and severe thresholds. Shortwave fadeout was evaluated based on thresholds in the solar X-ray flux. Analysis of 40-years of solar X-ray flux data showed that moderate and severe level solar X-ray flares were observed, on average, 123 and 5 times per 11-year solar cycle, respectively. The mean event duration was 68 min for moderate level events and 132 min for severe level events. Auroral absorption events crossed the moderate threshold for 40 events per solar cycle, with a mean event duration of 5.1 h. The severe threshold was crossed for 3 events per solar cycle with a mean event duration of 12 h. Polar cap absorption had the longest mean duration at ~8 h for moderate events and 1.6 days for severe events; on average, 24 moderate and 13 severe events were observed per solar cycle. Moderate and severe thresholds for shortwave fadeout, auroral absorption, and polar cap absorption were used to determine the expected impacts on HF radio communication. Results for polar cap absorption and shortwave fadeout were consistent with each other, but the expected impact for auroral absorption was shown to be 2–3 times higher. Analysis of 22 years of ionosonde data showed moderate, and severe PSD events occurred, on average, 200 and 56 times per 11-year solar cycle, respectively. The mean event duration was 5.5 h for moderate-level events and 8.5 h for severe-level events. During solar cycles 22 and 23, HF radio communication was expected to experience moderate or severe impacts due to the ionospheric disturbances caused by space weather, a maximum of 163 and 78 days per year, respectively, due to the combined effect of absorption and PSD. The distribution of events is highly non-uniform with respect to the solar cycle: 70% of moderate or severe events were observed during solar maximum compared to solar minimum.

Mechanisms of the subseasonal influences of Scandinavian events on winter surface air temperature over Eastern China

Based on the daily Japanese 55-year Reanalysis dataset from 1958 to 2020, this study reveals that positive-phase Scandinavian (SCA) teleconnection events can cause significant negative surface air temperature (SAT) anomaly over the whole eastern China from 6 to 12 days after the peak day of SCA events. Clearly, the timing of this significant impact exceeds the e-folding timescale of approximately 6 days of SCA events by approximately one week. During the first stage (from peak day to 6 days after peak day), the vertical coupling between the upper and lower tropospheric circulation anomalies over Eurasian continent facilitates the accumulation of cold air masses from the higher latitude to the north of the Tibetan Plateau, which becomes a precursory signal of persistent negative SAT anomaly affecting eastern China. During the second stage (from 7 to 12 days after peak day), the diabatic heating anomaly caused by precipitation anomaly becomes an important factor in the persistence of the negative SAT anomaly over eastern China. Firstly, the persistent negative diabatic heating anomaly near Lake Baikal before day 12 is conducive to the maintenance of anomalously enhanced Siberian High over eastern China. Secondly, corresponding to the gradually southward movement of the positive precipitation anomaly over East Asia, significant negative diabatic heating anomaly gradually substitutes the positive diabatic heating anomaly over East Asia, which is also favorable for the maintenance of the local anticyclonic anomaly. Eventually, the sustained anticyclonic anomaly can induce the persistent negative SAT anomaly over eastern China.