International Journal of Climatology最新文献

The unprecedented early spring (March–April) 2022 heat waves over Northwestern South Asia (NWSA) were marked by record-breaking temperatures and prolonged heat wave extremes. The area-averaged maximum temperature anomalies over NWSA reached 4.2°C above the 1976–2021 climatological mean, and the area-averaged heat wave frequency (HWF) peaked at 26 days. This study examines the northward shift of the subtropical westerly jet and atmospheric subsidence feedback related to these extreme events. Zonal wind at 200 hPa shows a northward displacement of the subtropical westerly jet axis from its climatological position (around 28°N) to approximately 1110 km northward (maximum shift) over the latitudes of NWSA in 2022. Statistically significant strong positive (negative) anomalies between 35°N and 60°N (10°N and 35°N) at upper levels (200–300 hPa) indicate enhanced (reduced) westerly winds in the subtropical jet stream region and stagnant atmospheric conditions over NWSA. Persistent geopotential height anomalies at 200 (500) hPa established a vertically coherent high-pressure ridge that drove subsidence over NWSA. Suppressed cloud cover (10%–20% decline) and increased surface net shortwave radiation (20–30 W m⁻²) enhance the near-surface temperatures. Thus, the northward displacement of the jet, high-pressure dominance, and radiative feedback collectively prolonged the heat wave conditions over NWSA. Improved monitoring of jet stream dynamics and geopotential height patterns can enhance heat wave predictability over NWSA in a warming climate.

Thunderstorms and lightning are the deadliest natural disasters in the Indian subcontinent. A better understanding of the regional and seasonal features of thunderstorm occurrences can provide valuable information on mitigating hazards in the region. The study demonstrated an improved method of understanding thunderstorm occurrences and thunder day (TD), an essential climate variable over the Indian region, using the total lightning data sets from the last 5 years. Total lightning data sets are used to find the Lightning flash rate density (FRD) in 0.05° grid resolution. Total lightning data are used to calculate TD, with the condition that a grid is considered to have a TD if it records at least two lightning flashes ensuring that TD corresponds to grids covering an area of approximately 15 km radius. A simultaneous comparison of lightning FRD and TD distribution is done in annual, interannual, seasonal, and monthly time scales spatially and statistically. The results reveal that the maximum TD observes 130–150 days in a year over a few places, including North-west Himalayan Jammu (Rajori), Southern peninsular Kerala (Kottayam), and north Odisha (Mayurbhanj). The north-western Himalayan foothills show the maximum TD but not the maximum FRD. The maximum number of TD in the study surpassed all the previous studies made by the station data sets where maximum TD remains in the range of 120–130 days per year. The minimum occurrences of the TD (< 15 days) show over Ladakh, a few parts of Arunachal, and the Kutch Gujarat region. Eastern part of the Indian region observes the most intense and frequent thunderstorms in terms of the number of lightning flash discharges per thunder day.

This study explores the climate zones' shift in Türkiye over time as a result of climate change, focusing on the period from 1954 to 2023. The analysis is based on high-resolution ERA5-Land reanalysis data and includes the record-breaking temperature extremes of the past decade. Climate zones were identified using the Ward linkage method, a hierarchical clustering algorithm approach, applied across 10-year moving windows within 30-year periods. This approach revealed eight distinct homogeneous climate regions and allowed for tracking their changes in location and extent over time. To examine these clusters, the De Martonne aridity index was used to assess temporal and spatial variability. The results indicate a notable contraction of very humid and extremely humid regions, alongside the emergence of a new arid zone in Southeastern Anatolia. The proportion of semi-arid areas increased significantly, from 9.03% in 1954–1983 to 14.62% in 1994–2023, highlighting a clear trend toward aridification. The changes in the zones were not uniform across the country. The Southeastern Anatolia, Mediterranean, Aegean, Marmara, and Central Anatolia geographical regions exhibit the most pronounced shifts, indicating region-specific impacts of climate change. The findings demonstrate the growing influence of climate change on Türkiye's hydroclimatic regime, indicating a clear tendency toward aridification and supporting broader global projections of a northward expansion of the subtropical climate zone.

Cold surges entering the Gulf of Mexico (GoM) generate northerly winds (Norte events), preceded by warm southerly winds (Surada events). These events were characterised in the Eastern Bay of Campeche (EBC) using ERA5 reanalysis data for 2002–2024. Both Norte and Surada events exhibited distinct intensity and predominant direction patterns in the EBC, compared with the broader GoM. Therefore, the separate identification of both events specific to the EBC was proposed. A minimum wind magnitude threshold (E) was determined for the EBC, above which events were considered sufficiently intense to be classified as Norte (2.4 ms⁻¹) or Surada (1.3 ms⁻¹) events in this region. It was shown that Norte events lasting < 24 h were associated with more intense Surada events; overall, 70.1% of Surada events exceeded the intensity of the corresponding Norte events, with a mean difference of 1.8 m s⁻¹. Empirical Orthogonal Functions analysis for the southern GoM revealed that, in ~30% of the cases (Modes 2 and 3), cold fronts moved with a significant zonal component in the southern GoM. This pattern was associated with intense Surada events and weak or even absent Norte events in the EBC. Mode 1 accounted for more than 63% of the variability and corresponded to Surada events followed by Norte events with similar behaviour in the entire region. This study demonstrates a distinct wind behaviour associated with cold surges on the eastern and western sides of the Bay of Campeche in the southern GoM. Norte and Surada events can negatively impact local marine and fisheries sectors, as wind intensity forecasts are often generalised for the entire GoM and can be unreliable in the EBC. These events are critical for coastal circulation and influence ecosystem dynamics, fisheries, and key oceanographic processes such as coastal-trapped waves, upwellings, and wave fields.

Jet streams are key components of mid- to high-latitude atmospheric circulation, strongly influencing global weather and climate through heat and momentum transport. Based on our previous work on jet stream shape variability and its climatic impacts, this study assesses the ability of CMIP6 models to simulate the relationship between jet stream shapes and surface air temperature (SAT), using both AMIP and historical runs. Based on weighted Taylor scores, interannual variability skill (IVS) scores and jet stream indices, AMIP simulations generally outperform historical runs in representing both jet streams and SAT. Most models capture SAT anomalies over East Asia and North America, underscoring a robust link between regional temperature extremes and distinct jet patterns. They also reproduce sea level pressure anomalies resembling the Arctic Oscillation (AO), suggesting that AO-like circulation is a key driver of temperature extremes across jet groups. In addition, horizontal temperature advection anomalies closely match SAT anomalies, highlighting their role as a primary term in the thermodynamic equation shaping temperature distributions in critical regions.

Ocean surface waves, which are gravity waves primarily driven by surface winds, significantly influence air-sea interactions, coastal ecology, and marine operations, among others. Tropical climate variability is shaped by ocean–atmosphere coupled modes such as the El Niño–Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD), which also influence ocean surface waves through changes in surface winds. This study examines the impact of the Atlantic Zonal Mode (AZM), a less-studied climate driver, on the interannual variability of ocean surface waves in the tropical Indo-West Pacific. A warm AZM induces surface wind anomalies that oppose the climatological winds. As a result, it reduces the wind sea by 0.2–0.3 m in the South China Sea (SCS) and by 0.1–0.2 m each in the Philippine Sea (PS) and the Bay of Bengal (BoB), and causes Southern Ocean swells to dominate by 0.1–0.2 m in the Arabian Sea. It is substantiated by consistent changes in the mean wave period and energy flux into waves. A warm AZM can favour marine operations in the SCS, PS, and BoB. On the contrary, a cold AZM is not observed to cause any statistically significant change in wave activity during the analysis period, highlighting an asymmetric impact of the AZM, the reasons for which require further investigation using wave model sensitivity experiments. Given the future projections of a weakening Atlantic cold tongue under global warming, the effects of warm AZM events may intensify, potentially leading to further reductions in tropical Indo-West Pacific wave activity. These findings highlight the importance of incorporating AZM impacts in wave climate assessments.