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<p>Winter fog is a major meteorological hazard for aviation operations over Delhi, India. This study provides a nearly three-decades (1996–97&#xa0;to&#xa0;2024–25) robust, multi-scale climatological assessment of winter fog season (November–February) using high-resolution METAR observations at Delhi IGI Airport, examining the fog frequency, intensity, and duration, extreme persistence of fog events, temporal variability, and links to meteorological drivers including planetary boundary layer height (PBLH) and environmental factors critical for aviation safety. Fog occurred on 70.5% of winter days with very dense fog (VDF:&#xa0;11.7%). January shows the highest frequency (87.5%), with general fog (GF) most frequent (~ 27&#xa0;days) and VDF occurring on ~ 9&#xa0;days, including several zero-visibility spell. Inter-decadal analyses reveal a decline in VDF from 29.7&#xa0;days in the late 1990s to 8.0&#xa0;days during the COVID-19 period with high variability, while shallow fog (SF) and GF days remained relatively stable. Climatologies indicate mid-winter peaks, a bimodal onset characterized by evening and early-morning peaks and maximum intensities between 06:00–09:00 A.M. Fog duration shows a bimodal pattern, with short-lived (1–2&#xa0;h) and prolonged (4–6&#xa0;h) events. Night-time fog persists longer and exhibits greater variability than daytime. Sen’s Slope trends show a decline in fog event frequency, but increasing overall fog persistence, particularly for GF and SF during day time, suggesting longer-lasting but less intense events. Elevated PM<sub>2.5</sub> (~ 246&#xa0;µg&#xa0;m<sup>–3</sup>) and PM<sub>10</sub> (~ 367&#xa0;µg&#xa0;m<sup>–3</sup>) under shallow PBLH (~ 45–60&#xa0;m), &#xa0;near saturated conditions (relative humidity &gt; 96%), low temperature (~9&#xa0;–11ºC) and weak wind (1.04 –2.59 m&#xa0;s<sup>-1</sup>)&#xa0;supports DF to VDF persistence, whereas higher temperatures , drier atmosphere , stronger winds , and deepened PBLH facilitate a stepwise dissipation pathway. Early-season intensification is evident in November (+ 0.37&#xa0;h/extreme event/season), highlighted by the record-breaking 70-h fog episode in 2016. Despite recent declines VDF, prolonged fog still disrupts aviation, emphasizing the need for integrated forecasting, air-quality monitoring, and urban climate adaptation to enhance aviation safety.</p>

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Three Decades of Winter Fog Variability at Delhi IGI Airport: Trends, Persistence, and Environmental Drivers Using Sen’s Slope and Transition Probability Analysis

  • 期刊论文

  • 发表日期：

    2026年6月23日

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  • Srabanti Ballav,
  • Anoop Kumar Mishra,
  • Gajendra Kumar,
  • Sourav Adhikary

摘要

Winter fog is a major meteorological hazard for aviation operations over Delhi, India. This study provides a nearly three-decades (1996–97 to 2024–25) robust, multi-scale climatological assessment of winter fog season (November–February) using high-resolution METAR observations at Delhi IGI Airport, examining the fog frequency, intensity, and duration, extreme persistence of fog events, temporal variability, and links to meteorological drivers including planetary boundary layer height (PBLH) and environmental factors critical for aviation safety. Fog occurred on 70.5% of winter days with very dense fog (VDF: 11.7%). January shows the highest frequency (87.5%), with general fog (GF) most frequent (~ 27 days) and VDF occurring on ~ 9 days, including several zero-visibility spell. Inter-decadal analyses reveal a decline in VDF from 29.7 days in the late 1990s to 8.0 days during the COVID-19 period with high variability, while shallow fog (SF) and GF days remained relatively stable. Climatologies indicate mid-winter peaks, a bimodal onset characterized by evening and early-morning peaks and maximum intensities between 06:00–09:00 A.M. Fog duration shows a bimodal pattern, with short-lived (1–2 h) and prolonged (4–6 h) events. Night-time fog persists longer and exhibits greater variability than daytime. Sen’s Slope trends show a decline in fog event frequency, but increasing overall fog persistence, particularly for GF and SF during day time, suggesting longer-lasting but less intense events. Elevated PM2.5 (~ 246 µg m–3) and PM10 (~ 367 µg m–3) under shallow PBLH (~ 45–60 m),  near saturated conditions (relative humidity > 96%), low temperature (~9 –11ºC) and weak wind (1.04 –2.59 m s-1) supports DF to VDF persistence, whereas higher temperatures , drier atmosphere , stronger winds , and deepened PBLH facilitate a stepwise dissipation pathway. Early-season intensification is evident in November (+ 0.37 h/extreme event/season), highlighted by the record-breaking 70-h fog episode in 2016. Despite recent declines VDF, prolonged fog still disrupts aviation, emphasizing the need for integrated forecasting, air-quality monitoring, and urban climate adaptation to enhance aviation safety.