The Asian and North American summer monsoons are the dominant climatological features of the Northern Hemispheric (NH) summertime circulation. The monsoons shape precipitation and regional circulation patterns worldwide, providing more than one-half of the global population with moisture (Wang & Ding, 2008;Wang et al., 2013). These monsoon circulations consist of cyclonic flow and convergence in the lower troposphere and intense anticyclonic circulations and divergence in the upper troposphere -lower stratosphere (UTLS). The cyclonic and anticyclonic circulations are coupled by persistent deep convection over South Asia (Tibetan Plateau) and North America (Colorado Plateau) during NH summer. Both UTLS anticyclones arise as response to diabatic heating within their respective hemispheres (Gill, 1980;Hoskins & Rodwell, 1995;Siu & Bowman, 2019) and are bounded by the subtropical westerly jet in the north and easterly jet in the south.The Asian summer monsoon (ASM) and North American summer monsoon (NASM) anticyclones have substantial intraseasonal variability in strength and location. The ASM anticyclone is centered aroundE and is evident in the UTLS by May. It shifts northward, peaks in strength, and extends over the large areas of eastern hemisphere by July, weakens in September, and disappears in October (Basha et al., 2020; Garny & Randel, 2013).The NASM anticyclone is not as strong or persistent as its Asian counterpart (Chen, 2003;Dunkerton, 1995). A nascent NASM forms in late May off the Pacific coast of Central America, near the eastern Pacific intertropical convergence zone, then it moves northward along the Pacific coast of Mexico until it is centered near northwestern Mexico extending into the southwestern United States (Douglas et al., 1993;Schoeberl et al., 2020). The NASM anticyclone becomes mature in July and August and gradually decays from late September (Vera et al., 2006).