Reconciling different methods of high‐latitude blocking detection

Tyrlis, Evangelos; Bader, Jürgen; Manzini, Elisa; Matei, Daniela

doi:10.1002/qj.3960

Cited by 13 publications

(16 citation statements)

References 105 publications

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“…The SH index is the regional average of the SLP in Siberia (40-60 °N, 70-120 °E). The blocking high index uses the improved detection method of Tyrlis et al (2021), which is more suitable for high-latitude blocking. The HLB index used here refers to blocking highs entering the Arctic (65-75 °N), because previous studies have shown that HLB is closely related to the phase transition of the AO (Dong et al, 2020) and the "warm Arctic-cold Eurasia" mode (Luo et al, 2016).…”

Section: Methodsmentioning

confidence: 99%

Inconsistent trends between early and late winters in extreme cold events in China from 1980 to 2021

Dong

Zhao

Cheng

et al. 2022

Front. Environ. Sci.

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Understanding intra-seasonal variation in extreme cold events (ECEs) has important implications for climate prediction and climate adaptation. However, the ECEs difference between early (from December 1 to January 15) and late (from January 16 to February 28) winters is a lack of sufficient understanding. Herein, we investigated the trends of ECEs over eastern China in early and late winters. Results showed that the number of days with ECEs had a faster and uniformly decreasing trend in late winter over eastern China, whereas the decreasing trend in early winter was not significant because of the dipole pattern with an increase of ECEs in northeast China and a decrease of ECEs in southeast China during the time period 1980–2021. This denoted that China was presenting a pattern of “cold early winter–warm late winter”. The feature of cold early winter was related to a significant increase in high-latitude blocking highs extending poleward and reaching the Arctic Circle in early winter during the last 20 years. In particular, there was a large-scale tilted high ridge from the Ural Mountains to northern Asia, which favored the negative phase of the Arctic oscillation. This, in turn, led to a strong Siberian high and East Asian winter monsoon. Strong cold advection related to the circulation anomalies caused an ECEs increase in northeast China and dominated the change in temperature over eastern China in early winter. By contrast, the decrease in ECEs in late winter in the last 20 years was more related to the interdecadal enhancement of the anticyclonic anomaly over the north Pacific (NPAC). The strong NPAC extended to East Asia in a zonal direction, causing strong warm anomalies in eastern China through warm advection and diabatic heating, which weakened the northerly and prevented the East Asian trough from moving south, resulting in a warmer East Asia and a uniform decrease in late winter.

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Section: Methodsmentioning

confidence: 99%

Inconsistent trends between early and late winters in extreme cold events in China from 1980 to 2021

Dong

Zhao

Cheng

et al. 2022

Front. Environ. Sci.

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“…A block is identified at a given grid cell if GHGN < 0 m/degree latitude and GHGS >0 m/degree latitude. Typically, a threshold of GHGN < − 10 is used, but due to recommendations from Tyrlis et al (2021), this has been relaxed. We have tested the sensitivity of results to this choice and find it has little influence on the overall results (not shown).…”

Section: Local Detection Of Ridges and Blockingmentioning

confidence: 99%

Large spread in the representation of compound long-duration dry and hot spells over Europe in CMIP5

Manning

Maraun

Loon

et al. 2023

Weather Clim. Dynam.

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Abstract. Long-duration, sub-seasonal dry spells in combination with high temperature extremes during summer have led to extreme impacts on society and ecosystems in the past. Such events are expected to become more frequent due to increasing temperatures as a result of anthropogenic climate change. However, there is little information on how long-duration dry and hot spells are represented in global climate models (GCMs). In this study, we evaluate 33 CMIP5 (coupled model intercomparison project 5) GCMs in their representation of long-duration dry spells and temperatures during dry spells. We define a dry spell as a consecutive number of days with a daily precipitation of less than 1 mm. CMIP5 models tend to underestimate the persistence of dry spells in northern Europe, while a large variability exists between model estimates in central and southern Europe, where models have contrasting biases. Throughout Europe, we also find a large spread between models in their representation of temperature extremes during dry spells. In central and southern Europe this spread in temperature extremes between models is related to the representation of dry spells, where models that produce longer dry spells also produce higher temperatures, and vice versa. Our results indicate that this variability in model estimates is due to model differences and not internal variability. At latitudes between 50–60∘ N, the differences in the representation of persistent dry spells are strongly related to the representation of persistent anticyclonic systems, such as atmospheric blocking and subtropical ridges. Furthermore, models simulating a higher frequency of anticyclonic systems than ERA5 also simulate temperatures in dry spells that are between 1.4, and 2.8 K warmer than models with a lower frequency in these areas. Overall, there is a large spread between CMIP5 models in their representation of long-duration dry and hot events that is due to errors in the representation of large-scale anticyclonic systems in certain parts of Europe. This information is important to consider when interpreting the plausibility of future projections from climate models and highlights the potential value that improvements in the representation of anticyclonic systems may have for the simulation of impactful hazards.

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“…2c and Fig. S1 of the Supporting Material), suggesting that not only the choice of blocking index (e.g., Kim and Kim 2019) but also the criterion of the index (e.g., Tyrlis et al 2021) need to be considered.…”

Section: Climatology Of Ural and Okhotsk Blockingsmentioning

confidence: 99%

Impact of winter blocking on surface air temperature in East Asia: Ural versus Okhotsk blocking

et al. 2022

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Atmospheric blockings and their impacts on wintertime surface air temperature in East Asia are investigated by using three blocking indices. Blockings in two specific regions that indirectly or directly modulate East Asian climate variability are analyzed: Ural (UR) blocking over East Asia's northwest and Okhotsk (OK) blocking over East Asia's northeast. Both lead to cold anomalies in East Asia but through slightly different mechanisms. In the typical case of UR blocking, cold air associated with a mid-level trough develops to the east of the quasi-stationary blocking and slowly moves southeastward as the Siberian high intensifies. Four days after the blocking onset, East Asia experiences significant cooling due to the temperature advection associated with anomalous temperature gradient and adiabatic cooling. During the typical OK blocking event, a preexisting cold anomaly over northern Eurasia is pushed southeastward by the westward expansion of the blocking.The anomalous meridional flow due to blocking-induced dipolar circulation over the North Pacific further reinforces the cold advection over East Asia, with a minor contribution of vertical processes.In both types of blocking, the cold anomaly persists even in the decaying phase, due to an offset between the temperature advection and the diabatic heating.

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Reconciling different methods of high‐latitude blocking detection

Cited by 13 publications

References 105 publications

Inconsistent trends between early and late winters in extreme cold events in China from 1980 to 2021

Inconsistent trends between early and late winters in extreme cold events in China from 1980 to 2021

Large spread in the representation of compound long-duration dry and hot spells over Europe in CMIP5

Impact of winter blocking on surface air temperature in East Asia: Ural versus Okhotsk blocking

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