Early summer surface air temperature variability over Pakistan and the role of El Nino-Southern Oscillation teleconnections

Early summer (May-June) is the season where the surface air temperature (SAT) variability is largest and may result in extreme temperature conditions over Pakistan. Therefore, we analysed the early summer interannual SAT variability over Pakistan for the period 1981-2018 using observational dataset and model simulations. We noted that upper-level anticyclonic circulation anomalies over Pakistan, which are associated with upper to the middle tropospheric descending motion, favour clear skies with an increase in net shortwave radiation that leads to extreme surface warming over the region. Moreover, the El Nino-Southern Oscillation (ENSO) based on Nino3.4 SST index is negatively associated with SAT anomalies over Pakistan. The cold ENSO phase favours the positive geopotential height anomalies due to the strengthening of the Walker circulation that enhance the sinking motion and result in less cloudiness leading to the extreme higher surface temperature conditions over Pakistan, while the opposite happens in the warm ENSO phase. Moreover, the Saudi-KAU Atmospheric Global Climate Model (AGCM) simulated large-scale patterns that are in good agreement with the observations. Sensitivity experiments with the AGCM confirm that cold SST anomalies in the ENSO region significantly favour above-normal SAT anomalies over Pakistan, while the opposite happens in the warm ENSO phase. These results are important to understand and potentially predict regional heatwaves over the South Asian region, particularly over Pakistan.

Automated summary

The study analyzed the interannual surface air temperature (SAT) variability over Pakistan during early summer. It found that upper-level anticyclonic circulation anomalies over Pakistan and the El Nino-Southern Oscillation (ENSO) were negatively associated with SAT anomalies. The Saudi-KAU Atmospheric Global Climate Model (AGCM) simulations were in good agreement with the observations, with sensitivity experiments confirming the influence of cold and warm ENSO phases on SAT anomalies. These results are important for understanding and potentially predicting regional heatwaves in the South Asian region, particularly in Pakistan.