Due to the much longer persistence and larger meridional span of blocking highs than synoptic ridges, development and collapse of blocking highs always lead to significant anomalous weather events including cold air outbreaks in winter.  The development and decay of blocking high systems have been understood from various dynamical perspectives, but not from the perspective of air mass transport yet, which, however, can provides a physical understanding of the formation and decaying of blocking highs where large mass of air get accumulated and diverged.

How is the air mass accumulated to build up the blocking highs? Recently Dr. LI Yafei (now working in Tianjin Meteorological Administration) and his PhD supervisor Prof. REN Rongcai from the State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics (LASG) at the Institute of Atmospheric Physics (IAP), Chinese Academy of Sciences (CAS) addressed this question.

They examined the lifetime of the four main blocking highs (the Greenland, Atlantic–Europe, Uraland North Pacific blocking highs) observed in the northern winter, and calculated the isentropic mass and its transport using the daily European Centre for Medium-Range Weather Forecasts Re-Analysis Interim data set in 1979–2016.

They revealed the climatological spatio-temporal features of the air mass and its transport during the life cycle of the four blocking highs, and found that positive mass anomalies corresponding to formation of a blocking high only appear in the mid-troposphere, rather than in the lower layer where air mass is much denser. Budget analysis indicates that adiabatic mass transport along isentropic surfaces always converges in the mid-troposphere, being the main contributor to the build-up of blocking highs. By contrast, diabatic mass transport across isentropic surfaces moves the air mass from the mid- to lower troposphere and only contributes to destroy the blocking high.

The study was recently published in International Journal of Climatology.

Reference：
Li,Yafei, Rongcai Ren*, M. Cai and Yueyue Yu, 2020: Climatological features of blocking highs from the perspective of air mass and mass transport, Int. Journal of Climatology, 40: 782-794, DOI: 10.1002/joc.6238

Link: https://doi.org/10.1002/joc.6238

Figure Composite evolutions of (a) air mass (shd) and its tendency (cn), and (b) the adiabatic and (c) diabatic mass transport convergence (shd) for Ural blocking as an example. The contours in (c) indicate the diabatic mass fluxes. (Image by LI Yafei)

Contact: REN Rongcai, rrc@lasg.iap.ac.cn