TY  - JOUR
A1  - Jaiser, Ralf
A1  - Akperov, Mirseid
A1  - Timazhev, A.
A1  - Romanowsky, Erik
A1  - Handorf, Dörthe
A1  - Mokhov, I. I.
T1  - Linkages between arctic and mid-latitude weather and climate
BT  - unraveling the impact of changing sea ice and sea surface temperatures during Winter
JF  - Meteorologische Zeitschrift
N2  - The study addresses the question, if observed changes in terms of Arctic-midlatitude linkages during winter are driven by Arctic Sea ice decline alone or if the increase of global sea surface temperatures plays an additional role. We compare atmosphere-only model experiments with ECHAM6 to ERA-Interim Reanalysis data. The model sensitivity experiment is implemented as a set of four combinations of sea ice and sea surface temperature boundary conditions. Atmospheric circulation regimes are determined and evaluated in terms of their cyclone and blocking characteristics and changes in frequency during winter. As a prerequisite, ECHAM6 reproduces general features of circulation regimes very well. Tropospheric changes induced by the change of boundary conditions are revealed and further impacts on the large-scale circulation up into the stratosphere are investigated. In early winter, the observed increase of atmospheric blocking in the region between Scandinavia and the Urals are primarily related to the changes in sea surface temperatures. During late winter, we f nd a weakened polar stratospheric vortex in the reanalysis that further impacts the troposphere. In the model sensitivity study a climatologically weakened polar vortex occurs only if sea ice is reduced and sea surface temperatures are increased together. This response is delayed compared to the reanalysis. The tropospheric response during late winter is inconclusive in the model, which is potentially related to the weak and delayed response in the stratosphere. The model experiments do not reproduce the connection between early and late winter as interpreted from the reanalysis. Potentially explaining this mismatch, we identify a discrepancy of ECHAM6 to reproduce the weakening of the stratospheric polar vortex through blocking induced upward propagation of planetary waves.
KW  - Weather regimes
KW  - Blocking
KW  - Cyclones
KW  - Wave Propagation
KW  - Stratosphere
Y1  - 2023
U6  - https://doi.org/10.1127/metz/2023/1154
SN  - 0941-2948
SN  - 1610-1227
VL  - 32
IS  - 3
SP  - 173
EP  - 194
PB  - Schweizerbart
CY  - Stuttgart
ER  - 
TY  - JOUR
A1  - He, Yongli
A1  - Huang, Jianping
A1  - Li, Dongdong
A1  - Xie, Yongkun
A1  - Zhang, Guolong
A1  - Qi, Yulei
A1  - Wang, Shanshan
A1  - Totz, Sonja Juliana
T1  - Comparison of the effect of land-sea thermal contrast on interdecadal variations in winter and summer blockings
JF  - Climate dynamics : observational, theoretical and computational research on the climate system
N2  - The influence of winter and summer land-sea surface thermal contrast on blocking for 1948-2013 is investigated using observations and the coupled model intercomparison project outputs. The land-sea index (LSI) is defined to measure the changes of zonal asymmetric thermal forcing under global warming. The summer LSI shows a slower increasing trend than winter during this period. For the positive of summer LSI, the EP flux convergence induced by the land-sea thermal forcing in the high latitude becomes weaker than normal, which induces positive anomaly of zonal-mean westerly and double-jet structure. Based on the quasiresonance amplification mechanism, the narrow and reduced westerly tunnel between two jet centers provides a favor environment for more frequent blocking. Composite analysis demonstrates that summer blocking shows an increasing trend of event numbers and a decreasing trend of durations. The numbers of the short-lived blocking persisting for 5-9 days significantly increases and the numbers of the long-lived blocking persisting for longer than 10 days has a weak increase than that in negative phase of summer LSI. The increasing transient wave activities induced by summer LSI is responsible for the decreasing duration of blockings. The increasing blocking due to summer LSI can further strengthen the continent warming and increase the summer LSI, which forms a positive feedback. The opposite dynamical effect of LSI on summer and winter blocking are discussed and found that the LSI-blocking negative feedback partially reduces the influence of the above positive feedback and induce the weak summer warming rate.
KW  - Land-sea thermal contrast
KW  - Blocking
KW  - Asymmetric warming
KW  - Double-jet
Y1  - 2017
U6  - https://doi.org/10.1007/s00382-017-3954-9
SN  - 0930-7575
SN  - 1432-0894
VL  - 51
IS  - 4
SP  - 1275
EP  - 1294
PB  - Springer
CY  - New York
ER  -