TY  - JOUR
A1  - Coumou, Dim
A1  - Lehmann, Jascha
A1  - Beckmann, Johanna
T1  - The weakening summer circulation in the Northern Hemisphere mid-latitudes
JF  - Science
N2  - Rapid warming in the Arctic could influence mid-latitude circulation by reducing the poleward temperature gradient. The largest changes are generally expected in autumn or winter, but whether significant changes have occurred is debated. Here we report significant weakening of summer circulation detected in three key dynamical quantities: (i) the zonal-mean zonal wind, (ii) the eddy kinetic energy (EKE), and (iii) the amplitude of fast-moving Rossby waves. Weakening of the zonal wind is explained by a reduction in the poleward temperature gradient. Changes in Rossby waves and EKE are consistent with regression analyses of climate model projections and changes over the seasonal cycle. Monthly heat extremes are associated with low EKE, and thus the observed weakening might have contributed to more persistent heat waves in recent summers.
Y1  - 2015
U6  - https://doi.org/10.1126/science.1261768
SN  - 0036-8075
SN  - 1095-9203
VL  - 348
IS  - 6232
SP  - 324
EP  - 327
PB  - American Assoc. for the Advancement of Science
CY  - Washington
ER  - 
TY  - THES
A1  - Beckmann, Johanna
T1  - Impacts of arctic climate change on sea level and and atmospheric circulation in the Northern mid-laltitudes
Y1  - 2018
ER  - 
TY  - JOUR
A1  - Zeitz, Maria
A1  - Reese, Ronja
A1  - Beckmann, Johanna
A1  - Krebs-Kanzow, Uta
A1  - Winkelmann, Ricarda
T1  - Impact of the melt-albedo feedback on the future evolution of the Greenland Ice Sheet with PISM-dEBM-simple
JF  - The Cryosphere : TC ; an interactive open access journal of the European Geosciences Union
N2  - Surface melting of the Greenland Ice Sheet contributes a large amount to current and future sea level rise. Increased surface melt may lower the reflectivity of the ice sheet surface and thereby increase melt rates: the so-called melt-albedo feedback describes this self-sustaining increase in surface melting. In order to test the effect of the melt-albedo feedback in a prognostic ice sheet model, we implement dEBM-simple, a simplified version of the diurnal Energy Balance Model dEBM, in the Parallel Ice Sheet Model (PISM). The implementation includes a simple representation of the melt-albedo feedback and can thereby replace the positive-degree-day melt scheme. Using PISM-dEBM-simple, we find that this feedback increases ice loss through surface warming by 60 % until 2300 for the high-emission scenario RCP8.5 when compared to a scenario in which the albedo remains constant at its present-day values. With an increase of 90 % compared to a fixed-albedo scenario, the effect is more pronounced for lower surface warming under RCP2.6. Furthermore, assuming an immediate darkening of the ice surface over all summer months, we estimate an upper bound for this effect to be 70 % in the RCP8.5 scenario and a more than 4-fold increase under RCP2.6. With dEBM-simple implemented in PISM, we find that the melt-albedo feedback is an essential contributor to mass loss in dynamic simulations of the Greenland Ice Sheet under future warming.
Y1  - 2021
U6  - https://doi.org/10.5194/tc-15-5739-2021
SN  - 1994-0416
SN  - 1994-0424
VL  - 15
IS  - 12
SP  - 5739
EP  - 5764
PB  - Copernicus
CY  - Katlenburg-Lindau
ER  -