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importantly, the near-cloud-free atmosphere and the Saharan dust (see Chaboureau et al. 2010 ) that was embedded in the air mass facilitated lidar observations with a high aerosol backscatter throughout the whole troposphere on this particular day. An overview of the methods used to observe wind and water vapor by the DWL and the DIAL is given in section 2 . Additionally, special ECMWF forecasts are introduced for a later comparison with the observations. The method to determine the water vapor
importantly, the near-cloud-free atmosphere and the Saharan dust (see Chaboureau et al. 2010 ) that was embedded in the air mass facilitated lidar observations with a high aerosol backscatter throughout the whole troposphere on this particular day. An overview of the methods used to observe wind and water vapor by the DWL and the DIAL is given in section 2 . Additionally, special ECMWF forecasts are introduced for a later comparison with the observations. The method to determine the water vapor
1. Introduction During a stratospheric sudden warming (SSW) event, the polar stratospheric temperature increases accompanied by a weakening of the polar night jet. Major SSW events (MSSW) are defined as SSW events with a reversal of the zonal mean zonal wind from westerlies to easterlies at 60°N and a 10-hPa layer. Those events represent the greatest part of intraseasonal variability in the winter middle atmosphere and are associated with low predictive skill at lead times more than 10 days
1. Introduction During a stratospheric sudden warming (SSW) event, the polar stratospheric temperature increases accompanied by a weakening of the polar night jet. Major SSW events (MSSW) are defined as SSW events with a reversal of the zonal mean zonal wind from westerlies to easterlies at 60°N and a 10-hPa layer. Those events represent the greatest part of intraseasonal variability in the winter middle atmosphere and are associated with low predictive skill at lead times more than 10 days
forecast. The forecasts are initialized at (top) 1200 UTC 14 Jun, (middle) 1200 UTC 26 Jul, and (bottom) 1200 UTC 10 Aug 2010. Onset occurs in the top panel, and decay occurs in the bottom panel. These forecasts were selected based on maxima in the ensemble spread in the 500-hPa geopotential field, associated with the block, as revealed in Hovmöller diagrams averaged between 40° and 80°N. Selecting the forecasts based on the ensemble spread only works for ensemble forecasts in which some members
forecast. The forecasts are initialized at (top) 1200 UTC 14 Jun, (middle) 1200 UTC 26 Jul, and (bottom) 1200 UTC 10 Aug 2010. Onset occurs in the top panel, and decay occurs in the bottom panel. These forecasts were selected based on maxima in the ensemble spread in the 500-hPa geopotential field, associated with the block, as revealed in Hovmöller diagrams averaged between 40° and 80°N. Selecting the forecasts based on the ensemble spread only works for ensemble forecasts in which some members
: Interaction of North Atlantic baroclinic wave packets and the Mediterranean storm track . Quart. J. Roy. Meteor. Soc. , 140 , 754 – 765 , https://doi.org/10.1002/qj.2171 . 10.1002/qj.2171 Aiyyer , A. , 2015 : Recurving western North Pacific tropical cyclones and midlatitude predictability . Geophys. Res. Lett. , 42 , 7799 – 7807 , https://doi.org/10.1002/2015GL065082 . 10.1002/2015GL065082 Andrews , D. G. , J. R. Holton , and C. B. Leovy , 1987 : Middle Atmosphere Dynamics. Academic
: Interaction of North Atlantic baroclinic wave packets and the Mediterranean storm track . Quart. J. Roy. Meteor. Soc. , 140 , 754 – 765 , https://doi.org/10.1002/qj.2171 . 10.1002/qj.2171 Aiyyer , A. , 2015 : Recurving western North Pacific tropical cyclones and midlatitude predictability . Geophys. Res. Lett. , 42 , 7799 – 7807 , https://doi.org/10.1002/2015GL065082 . 10.1002/2015GL065082 Andrews , D. G. , J. R. Holton , and C. B. Leovy , 1987 : Middle Atmosphere Dynamics. Academic
) and http://www.cosmo-model.org for more details on the computational methods]. The model is set up with a horizontal resolution of 0.025° (about 2.5 km at 35°N) and 57 vertical levels up to 30-km height, with an enhanced vertical resolution in the planetary boundary layer. Shallow convection is parameterized using the mass-flux scheme of Tiedtke (1989) , while middle and high convection are explicitly computed. For all parameterized processes, the default setup of COSMO is used ( Doms et al
) and http://www.cosmo-model.org for more details on the computational methods]. The model is set up with a horizontal resolution of 0.025° (about 2.5 km at 35°N) and 57 vertical levels up to 30-km height, with an enhanced vertical resolution in the planetary boundary layer. Shallow convection is parameterized using the mass-flux scheme of Tiedtke (1989) , while middle and high convection are explicitly computed. For all parameterized processes, the default setup of COSMO is used ( Doms et al
1. Introduction Synoptic-scale Rossby waves are manifest in the tropopause-level flow as a succession of troughs and ridges ( Rossby 1945 ). They play a vital role in the formation of midlatitude weather. In addition, high-impact weather events can be preceded by synoptic-scale Rossby waves ( Chang 2005 ; Blackburn et al. 2008 ; Martius et al. 2008 ; Wirth and Eichhorn 2014 ). Since they are present in the atmosphere for several days, they indicate the potential for improved predictability
1. Introduction Synoptic-scale Rossby waves are manifest in the tropopause-level flow as a succession of troughs and ridges ( Rossby 1945 ). They play a vital role in the formation of midlatitude weather. In addition, high-impact weather events can be preceded by synoptic-scale Rossby waves ( Chang 2005 ; Blackburn et al. 2008 ; Martius et al. 2008 ; Wirth and Eichhorn 2014 ). Since they are present in the atmosphere for several days, they indicate the potential for improved predictability
-tropospheric layer has been specified from 1000 to 750 hPa. Differing from their studies the upper layer is specified here from 500 to 100 hPa to exclude potential effects from low-level vortices extending into the middle troposphere. Vertical motion induced by these layers will be depicted at 700 hPa, which is typically close to the level of maximum vertical motion in extratropical cyclones. A few remarks should be made about the validity of using a QG diagnostic tool when investigating the dynamics of an
-tropospheric layer has been specified from 1000 to 750 hPa. Differing from their studies the upper layer is specified here from 500 to 100 hPa to exclude potential effects from low-level vortices extending into the middle troposphere. Vertical motion induced by these layers will be depicted at 700 hPa, which is typically close to the level of maximum vertical motion in extratropical cyclones. A few remarks should be made about the validity of using a QG diagnostic tool when investigating the dynamics of an
breeding vector technique ( Toth and Kalnay 1993 ). The breeding perturbations use previous ensemble forecasts to obtain the growing components of the analysis error. As numerical weather prediction models cannot resolve many small-scale features in the atmosphere, these have to be parameterized. In 1998 a stochastic physics scheme was implemented at the ECMWF to represent errors due to parameterizations ( Buizza et al. 1998 ). So far, comparisons between ensembles from different centers are rare
breeding vector technique ( Toth and Kalnay 1993 ). The breeding perturbations use previous ensemble forecasts to obtain the growing components of the analysis error. As numerical weather prediction models cannot resolve many small-scale features in the atmosphere, these have to be parameterized. In 1998 a stochastic physics scheme was implemented at the ECMWF to represent errors due to parameterizations ( Buizza et al. 1998 ). So far, comparisons between ensembles from different centers are rare
dynamical tropopause were calculated on the 325-K isentropic surface following the method of Martius et al. (2006a) . To identify atmospheric blocking events, a two-dimensional blocking index was derived from the ERA-40 and ERA-Interim datasets. The blocking identification is based on negative PV anomalies in the middle to upper troposphere and takes into account the three-dimensional structure of the phenomenon ( Schwierz et al. 2004 ). This index requires a minimum blocking lifetime of five days
dynamical tropopause were calculated on the 325-K isentropic surface following the method of Martius et al. (2006a) . To identify atmospheric blocking events, a two-dimensional blocking index was derived from the ERA-40 and ERA-Interim datasets. The blocking identification is based on negative PV anomalies in the middle to upper troposphere and takes into account the three-dimensional structure of the phenomenon ( Schwierz et al. 2004 ). This index requires a minimum blocking lifetime of five days
from the calculation initialized at 1200 UTC 17 September ( Fig. 6 ). In the PV of the trajectory (gray surface) the PV tower of Helene in the middle of the plot extends to the tropopause (indicated by the high PV values at upper levels). It is apparent that the tropopause in the vicinity of Helene is richly structured. The upper-level positive PV anomaly, which Helene encounters during its recurvature, is located northwest of Helene. Fig . 6. Total energy (colored surfaces) of the leading TL255 SV
from the calculation initialized at 1200 UTC 17 September ( Fig. 6 ). In the PV of the trajectory (gray surface) the PV tower of Helene in the middle of the plot extends to the tropopause (indicated by the high PV values at upper levels). It is apparent that the tropopause in the vicinity of Helene is richly structured. The upper-level positive PV anomaly, which Helene encounters during its recurvature, is located northwest of Helene. Fig . 6. Total energy (colored surfaces) of the leading TL255 SV
