Anthropogenic Aerosols Significantly Reduce Mesoscale Convective System Occurrences and Precipitation Over Southern China in April

Abstract

Precipitation over Southern China in April, largely associated with mesoscale convective systems (MCSs), has declined significantly in recent decades. It is unclear how this decline in precipitation may be related to the concurrent increase of anthropogenic aerosols over this region. Here, using observation analyses and model simulations, we showed that increased levels of anthropogenic aerosols can significantly reduce MCS occurrences by 21% to 32% over Southern China in April, leading to less rainfall. Half of this MCS occurrence reduction was due to the direct radiative scattering of aerosols and the indirect enhancement of non‐MCS liquid cloud reflectance by aerosols, which stabilized the regional atmosphere. The other half of the MCS occurrence reduction was due to the microphysical and dynamical responses of the MCS to aerosols. Our results demonstrated the complex effects of aerosols on MCSs via impacts on both the convective systems and on the regional atmosphere.

Aerosol indirect effects in complex orography areas: a numerical study over the Great Alpine Region

“…The effect is to reduce the development of AIC (and of precipitation) and thus increase solar radiation at the ground: the negative temperature anomaly weakens in the high altitudes and it becomes positive in lowlands from late afternoon trough the night. This mechanism of suppression of convective clouds by aerosols due to the stabilization of the air column has been already studied over Southern China (Zhang et al, 2020), and it is also in agreement with the findings of Van Den Heever andCotton 2007 andDa Silva et al 2018. At high altitudes clouds are more frequent, as they form when the winds are diverted upwards along the slopes of the mountains.…”

“…The rate of warming observed over avere anche the last decades is elevation-dependent (Pepin et al, 2015), possibly also due to aerosols (Rangwala et al, 2010), which vary with altitude (in concentration and type) and affect the local sensitivity to large scale changes (Stjern et al, 2020). Aerosol effects could also extend to precipitation (Rosenfeld et al, 2008): the radiative effects of aerosols on clouds mostly act to suppress precipitation, because they decrease the amount of solar radiation that reaches the surface, increasing regional atmospheric stability (Zhang et al, 2020). Aerosols also have important microphysical effects on precipitation (Tao et al, 2012;Fiori et al, 2014): incresed Cloud Condensation Nuclei (CCN) slow the conversion of cloud droplets into raindrops (Thompson and Eidhammer, 2014).…”

Abrupt emissions reductions during COVID-19 contributed to record summer rainfall in China

“…The aerosol reduction-induced instability and vertical circulation change in eastern China were also reported in previous studies 26,27 . The reduced aerosol loadings can significantly enhance the occurrence of local convective systems 14 , causing the release of additional latent heat at higher altitudes through intensified ascending motions 20 . Therefore, profound positive heating anomalies can be observed at higher altitudes above 850 hPa, rather than near the surface (Fig.…”

“…In the last four decades, summer precipitation over eastern-central China has decreased significantly, which has been reported to be closely related to the increase in aerosols over the region 19 . By cooling and stabilizing the lower atmosphere directly through scattering of solar radiation and indirectly by serving as cloud condensation nuclei, anthropogenic aerosols can reduce the occurrence of mesoscale convective systems by one-fifth to one-third, resulting in less precipitation in April over southern China 20 . Menon et al argued that the increased summer flood in southern China and drought in northern China were mainly due to the absorbing black carbon aerosols, which heat the air, alter atmospheric stability, and disturb large-scale circulations and hydrologic cycle 21 .…”

High Resolution Chemistry Transport Modeling with the On-Line CHIMERE-WRF Model over the French Alps—Analysis of a Feedback of Surface Particulate Matter Concentrations on Mountain Meteorology

“…Regarding the effect of the on-line coupling, there is an increase of 5-10% of the LWC when the on-line coupling is activated (CPL01 vs. REF01) mainly due to a cooler temperature. This is the so-called Twomey effect for warm clouds [69,70]. Table 9.…”