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This study investigates the influence of climate change on widespread fog conditions over the Indo-Gangetic Plains (IGP) of north India using observations, reanalysis data of atmospheric parameters, coupled model inter-comparison project 6 (CMIP6) projections following four future scenarios based on the shared socio-economic pathways (SSP126, SSP245, SSP370, SSP585), and advanced analysis techniques including machine learning. Two parameters fog fraction and widespread fog days (WFDs) are estimated in this study by functional mapping of fog observations with 8 atmospheric parameters for the period 1981–2018 using three empirical/machine learning approaches. Of these, we note that the deep learning convolutional neural network (CNN) exhibits superiority in performance by showing the mapping closer to the observed, and also offers promising potential for operational purposes to provide fog outlooks for the IGP region. Temporal evolution of fog fractions and WFDs is analyzed from the CMIP6 projections following the aforementioned four future scenarios using CNN for the future periods of the twenty-first century. It is noted that there is a substantial enhancement in the CMIP6 projected fog fractions as high as 57% during the period (2015–2045) relative to the historical (1981–2014) period, while the largest increase of 154% is seen in projected WFDs. It is also seen that the near-future period (2015–2045) witnesses a larger prevalence of WFDs, for all scenarios except SSP126, due to the combined effects of air pollution and greenhouse warming. The post-2046 periods, however, generally indicate signatures of decline in foggy days with widespread conditions relative to historical period in most of the scenarios except SSP370. The severity in fog conditions following the high-emission scenarios SSP370 and SSP585 during this period comes from the relative impact of mitigation strategies of pollutants. The findings provide insights into the possible future changes in widespread fog conditions suitable for the IGP region. [ABSTRACT FROM AUTHOR]

Boreal wintertime planetary-scale atmospheric circulations and their possible consequences to widespread fog occurrences over the Indo-Gangetic Plains (IGP) region of the Himalayan valley are investigated in this study. Among the different fog types, radiation fog type seen at night or early morning hours favored by large-scale subsidence aloft and strong near-surface inversion is focused in this study. A composite analysis reveals that upper air circulation associated with 105 fog days over the IGP region show a trail linked to circulation anomalies over the Eurasian continents and the Arctic Circle. The findings suggest that there is a footprint of the Arctic Oscillation (AO) and conventional Eurasian (EU) circulation patterns linked to anticyclonic circulation aloft over the IGP region. Although widespread IGP fog occurrences under the large-scale subsidence environment are seen to occur during both phases of AO, the negative AO phase (high pressure environment over the Arctic Circle) portends a greater likelihood for fog occurrences in the IGP region. A coupling of positive mid-tropospheric height anomalies over western Eurasia and the anticyclonic circulation anomalies over the IGP region is evident during the IGP fog periods concomitant with EU positive (height excess over Siberia) phase. Further, anomalous circulation over the IGP region during the fog periods appears to rely more on the strength of the AO negative phase than the circulation strengths over Eurasia. On the contrary, the Eurasian circulation largely appears to influence the subsidence aloft over the IGP region irrespective of the strength of the AO positive phase. It is also noted that upper-air circulation during non-foggy periods over the IGP region has conformity with positive AO phase and rapidly progressing EU pattern. These planetary-scale teleconnection pathways offer new dynamical insights into comprehending widespread IGP fog scenario, which have been hitherto perceived mostly from a regional context. [ABSTRACT FROM AUTHOR]