Why have changes in the North Atlantic Oscillation increased during the 20th century? Can climate change be predicted in the future?

The North Atlantic Oscillation explains a large part of the climate variability across the North Atlantic Ocean From the east coast of North America across Europe, many studies of the North Atlantic Oscillation in extreme weather conditions in this region, especially in Winter is relevant. It has motivated a significant study of this pattern. However, an overlooked feature is how the North Atlantic Oscillation has changed over time. There is a significant increase in the variance of the pattern. The North Atlantic Oscillation (NAO) increased during the 20th century from 32% in 1930 to 53% at the end of the 20th century. Whether this change is due to natural variation, a forced response to climate change, or a combination thereof is not yet clear. However, we found no evidence for a forced response from the Model Comparison Project Phase 6 (CMIP6) set of 50 pairwise models. All of these models showed significant internal variability in the strength of the North Atlantic Oscillation, but were biased toward it. In the region, this has direct implications for both long-term and short-term forecasting where regional climate changes are extreme. The North Atlantic Oscillation (NAO) is a pattern of variability associated with sea surface pressure over the North Atlantic Ocean with a subpolar low and subtropical high. The NAO is associated with large-scale changes in the position and intensity of both the storm track and the jet stream over the North Atlantic, and therefore plays a direct role in shaping the atmospheric transport of heat and moisture across the basin (Fasullo et al., 2020). ). It has also been shown that the NAO has a large effect on the Atlantic meridional overturning circulation and therefore the oceanic heat transfer, and this is the largest time scale of 20-30 years, which leads to changes in northern hemisphere temperatures of a few tenths. a degree (Delworth and Zeng, 2016). NAO has positive and negative. It shows significant interannual phase and changes. The positive phase of NAO shows between the two phases of pressure below the normal limit in the subpolar region and high pressure above the normal limit in the subtropics. It is often associated with a decrease in temperature and precipitation, an anomaly in southern Europe and an increase in precipitation, an anomaly in northern Europe, the effects of the NAO across the basin and the positive phase are also associated with it. Positive temperature anomaly in the eastern United States. The opposite pattern and its effects are observed during the period when the NAO is in its negative phase (Weisheimer et al., (2017). It has long been established that the NAO dominates climate variability over a large part of the Northern Hemisphere. The eastern coast of North America across Europe to the center of Russia and from the Arctic in the north to the subtropical Atlantic Ocean (Horrell et al., 2003) is one of the important components of winter variability and is related to the frequency and intensity of weather extremes. in Europe (Hilock and Goodes, 2004; Scaife et al., 2008; Fan et al., 2016). Therefore, it is necessary to understand the scale of natural variability in the NAO, how the NAO responds to changes in external forcing, and whether these If current climate models fail to account for natural variability or NAO forcing, this could lead to radical predictions of extreme climate change in Europe on time scales of decades to centuries.An index for the NAO is often identified in one of two ways. The first approach is to calculate the normalized difference in surface pressure between the subtropical high (Azores High) and subpolar low (Icelandic Low) over the North Atlantic sector. The second approach is to perform an Empirical orthogonal function (EOF) analysis on sea level pressure over the North Atlantic region. An EOF analysis separates the variability in the sea level pressure into orthogonal modes, with the first mode containing the largest proportion of the variability and each subsequent mode containing progressively less. When an EOF analysis is used to calculate the NAO, the first mode indicates the NAO index, while the second and third modes usually provide the North Atlantic ridge and Scandinavian blocking patterns (Cassou et al., 2004).

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