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The two dominant patterns of the winter (December–February) intraseasonal surface air temperature (SAT) over central Asia is derived by empirical orthogonal function analysis, with the first (mode 1) featuring a regional monopole and the second (mode 2) featuring a northwest–southeast‐orientated dipole. Mode 1 is characterized with warmer (colder) Arctic and colder (warmer) Eurasia along with an anomalous high (low) over the Ural Mountains, while mode 2 is characterized with northwest–southeast dipole over Eurasia along with wave train‐like atmospheric circulation anomalies from the western Atlantic to Asia. Whether the two intraseasonal modes are modulated by lower‐boundary forcing is then investigated, and the results suggest that mode 1 is significantly modulated by sea ice concentration over the Greenland Sea, but by central‐Pacific ENSO for mode 2. Finally, the underlying mechanisms are diagnosed, and the results suggest that the diabatic heating related with decreased sea ice in Greenland Sea induce a positive height anomaly over Urals which favours the formation of Ural blocking and therefore tends to intensify the occurrence of mode 1. Also, central‐Pacific El Niño excites the Pacific–North American teleconnection, which alters North Atlantic subtropical jet extension, favours intensified energy conversion to intraseasonal wave train and subsequently intensifies the occurrence of mode 2. This study highlights the joint role of Arctic sea ice and the SST in the tropical central Pacific. [ABSTRACT FROM AUTHOR]

Large‐scale cold and warm spells successively attacked North Asia (NA) and resulted in a subseasonal alternation of extreme surface air temperature (SAT) before and after 15 January 2021. Our results show the synergistic effect of annual cycle and intraseasonal oscillation component (AC and ISO) of SAT and circulation anomalies caused temperature extremes. Before 15 January 2021, an eastward‐propagating Rossby wave train strengthened the cold circulation regime with an enhanced Ural blocking high (UBH) and surface Siberian high (SH). Circulation anomalies of the negative ISO were superimposed on the counterpart of AC, which easily resulted in cold extremes via nonlinear interaction of meridional temperature gradient. After mid‐January 2021, however, weakened UBH and SH caused warm advection and spells over NA. This synergistic effect of AC and ISO anomalies in SAT accounted for most historical temperature extremes, implying that AC anomalies have important indications for subseasonal alternation of temperature extremes. Plain Language Summary: Large‐scale cold and warm spells successively occurred in North Asia (NA) and resulted in the intraseasonal oscillation (ISO) of surface air temperature (SAT) extremes during 2020/21 winter. Here, we find the annual cycle (AC) of SAT and circulation anomalies provided a favorable background in regulating the subseasonal alternation of cold and warm extremes. The negative (positive) anomalies of AC (denoted PACN (PACP)) are characterized by enhanced (weakened) Ural blocking high (UBH) and Siberian high (SH), corresponding to cold (warm) NA circulation regimes before (after) 15 January 2021. During PACN (negative anomalies of ISO, PISON), a quasi‐barotropic Rossby wave train in the midlatitudes of Eurasia enhanced AC (ISO) of the UBH and SH, causing cold extremes in NA. While during the PACP and positive anomalies of ISO (PISOP), circulation anomalies like negative Arctic oscillation (AO) weakened UBH and SH, jointly resulting in warm extremes in NA. The subseasonal temperature change process in NA was mainly attributed to the conveyance of AC anomalies of meridional temperature gradient by subseasonal winds. Historical temperature extremes were almost attributed to the synergistic effect of AC and ISO of SAT anomalies, implying that the AC anomalies have important indications for subseasonal alternation of cold and warm extremes. Key Points: The successive cold and warm spells caused a subseasonal alternation of extreme surface air temperature (SAT) in North Asia during the 2020/21 winterThe annual cycle (AC) of meridional temperature gradient dominated by the nonlinear interaction of subseasonal advection in this winterCold and warm extremes in historical winters were verified by the synergistic effect of AC and intraseasonal oscillation in SAT anomalies [ABSTRACT FROM AUTHOR]

Limiting excess atmospheric ammonia (NH3) is one of the great challenges for humanity in the 21st century but can only be achieved with adequate monitoring means in place. Here, we report the first NH3 measurements from the Geostationary Interferometric Infrared Sounder (GIIRS) onboard the Chinese FY‐4A satellite. The instrument scans almost all of Asia 10 times per day. We show that GIIRS′ unprecedented temporal sampling can be exploited to measure diurnal and nocturnal variations of NH3 and demonstrate this on two case studies over Punjab and the North China Plain. Day–night variations are found to be almost absent in winter, but can reach a factor 2–3 in the warmer months. These case studies are very promising given the future landscape of geostationary sounders, but also show that improved knowledge on lower tropospheric air temperatures and the vertical profile of NH3 is key to better exploit their measurements. Plain Language Summary: To reduce the worldwide concentrations of ammonia (NH3) in the air is one of the great challenges for humanity in the 21st century, but this can only be achieved with stringent policies in place, and with the support of accurate and frequent measurements. In this paper, we report the first ammonia measurements from the Geostationary Interferometric Infrared Sounder (GIIRS) onboard the Chinese FY‐4A satellite. The satellite is positioned above Indonesia and measures almost all of Asia 10 times per day. We show that GIIRS' measurements can be used to measure ammonia both during day and night. We look into more detail at two locations, over Punjab (Pakistan) and the North China Plain. Day‐night variations are found to be almost absent in the colder months, but can reach a factor 2–3 in the warmer months. These case studies are very promising given the future landscape of geostationary sounders, but demonstrate also that improved knowledge on the air temperature at the surface and the behavior of ammonia at higher altitudes will result in more accurate ammonia measurements. Key Points: We report the first observations of atmospheric NH3 from the geostationary satellite FY‐4A GIIRS over AsiaThe potential of GIIRS to reveal the diurnal and nocturnal variations of NH3 total columns is demonstrated over two sitesTo better exploit geostationary data, improved temperature profiles and knowledge on the vertical NH3 distribution is needed [ABSTRACT FROM AUTHOR]

This study investigates changes in the East Asian winter monsoon (EAWM) under 1.5 and 2.0°C global warming (1.5 and 2.0GW) targets using multi‐model results from the Coupled Model Intercomparison Project phase 5 (CMIP5). It is found that the surface air temperature increases over the Asian continent and Pacific, and the precipitation increases over the northern Asian continent in winter during the 1.5 and 2.0GW periods. For the 1.5GW period, large uncertainties can be found in the projection of EAWM system members (i.e., Siberian high, Aleutian low, low‐level winds over eastern Asia, East Asian trough [EAT] and East Asian jet stream [EAJS]). For the 2.0GW period, more than two‐thirds of the models show that the Siberian high, the EAT and the meridional shear of the EAJS are weakened, but the Aleutian low is intensified. In addition, the intensified Aleutian low enhances low‐level northwesterly wind along the coast of northeastern Asia. Compared to those in the 1.5GW period, the EAWM system members show more robust changes during the 2.0GW period, except for the low‐level winds at mid‐latitude eastern Asia. These conclusions are suitable for both the RCP4.5 and RCP8.5 scenarios. [ABSTRACT FROM AUTHOR]

The impact of North American (NA) snow cover on the Northern Hemisphere climate has drawn increasing attention in recent years. This study reveals a negative relationship between NA snow cover in December and surface air temperature (SAT) over the midlatitude Asia in the following January. The results show that, in December, the extensive snow cover decreases SAT over NA via local diabatic cooling, which further intensifies the Atlantic jet stream by enlarging the meridional gradient of the 1,000‐ to 300‐hPa layer thickness, especially along 40°N. Meanwhile, we found negative sea surface temperature (SST) anomalies over the Western North Atlantic and enhanced transient eddy activity over the Eastern North Atlantic due to anomalous net energy conversion from the mean flow. In January, a zonally oriented dipole of transient eddy anomalies straddles the North Atlantic, with the negative–positive (west–east) anomaly centres attributing to local oceanic cooling and the persistence of the eddy–mean flow interaction, respectively. Such dipole of transient eddy activity in turn favours the downstream development of the Atlantic jet stream. Besides, the changes in surface turbulent heat flux over the North Atlantic trigger a Rossby wave train that propagates across Europe and towards the Far East. Coincident with the strengthened Siberian High and the accelerated East Asian jet stream in January, SAT decreases over the midlatitude Asia. Hence, our analysis indicates that December NA snow cover could potentially be exploited for subseasonal predictability over Asia. [ABSTRACT FROM AUTHOR]