Interdecadal changes in synoptic transient eddy activity over the Northeast Pacific and their role in tropospheric Arctic amplification

Abstract

Arctic amplification refers to the greater surface warming of the Arctic than of other regions during recent decades. A similar phenomenon occurs in the troposphere and is termed “tropospheric Arctic amplification” (TAA). The poleward eddy heat flux and eddy moisture flux are critical to Arctic warming. In this study, we investigate the synoptic transient eddy activity over the North Pacific associated with TAA and its relationship with the subtropical jet stream, and propose the following mechanism. A poleward shift of the subtropical jet axis results in anomalies of the meridional gradient of zonal wind over the North Pacific, which drive a meridional dipole pattern of synoptic transient wave intensity over the North Pacific, referred to as the North Pacific Synoptic Transient wave intensity Dipole (NPSTD). The NPSTD index underwent an interdecadal shift in the late 1990s accompanying that of the subtropical jet stream. During the positive phase of the NPSTD index, synoptic eddy heat flux transports more heat to the Arctic Circle, and the eddy heat flux diverges, increasing Arctic temperature. This mechanism highlights the need to consider synoptic transient eddy activity over the North Pacific as the link between the mean state of the North Pacific subtropical upper jet and TAA.

Regime shift of the leading mode of winter surface wind speed in northwest China in 2003/04 and its possible link with Barents–Kara sea ice

“…A regime shift is generally defined as a rapid transition from one mean state to another one in a time series (Rodionov, 2004; Xiao et al, 2012; Xiao & Li, 2007, 2011). A moving t ‐test technique is wildly used to detect the regime shift in a time series of ocean or atmosphere variable (Xiao et al, 2012, 2021; Xiao & Li, 2007, 2011; Xiao & Ren, 2021, 2023). Xiao and Li (2007) developed a moving t ‐test method by fulfilling the effective freedom degree correction, normal distribution skewness and kurtosis test and multiple testing corrections to better detect the regime shift in the ocean and atmosphere systems.…”

Atmospheric energy change in the Arctic troposphere under Arctic warming

“…To understand the latest change of tropospheric energy over the Arctic, we calculated linear trends in the last 20 years (1999–2018), and obtained the total, internal, potential and latent energy trends of 16.74 ± 17.42 × 10 19 , 10.56 ± 11.33 × 10 19 , 4.70 ± 5.72 × 10 19 and 1.46 ± 0.76 × 10 19 J·decade −1 , respectively. The total, internal and potential energy increased from 1999 to 2018 much faster than in period from 1979 to 2018, even though they have confidence lower than 95%, which could reflect accelerated warming in the last two decades (Ballinger et al ., 2021; Xiao and Ren, 2021). The significant increase of latent energy in the last 20 years is also larger than the 40‐year increase, and could coincide the enhanced wetting in the Arctic (Serreze et al ., 2012; Vihma et al ., 2016; Rinke et al ., 2019).…”

“…Obviously, the significant increase of total energy is supported by the significant trend of internal energy. The unconfident increase of internal energy in winter, which seems at odds with confident warming occurring in the Arctic troposphere (Screen and Simmonds, 2010b; Cohen et al ., 2020; Xiao and Ren, 2021), could be possibly related to tropospheric mass change. To understand winter internal energy trend, we integrated tropospheric mass over the Arctic, and derived its trend in winter, as −8.41 ± 53.17 × 10 13 kg·decade −1 .…”