1. Tendencies of change for different characteristics of extratropical cyclones in the Northern Hemisphere Mirseid G. Akperov and Igor I. Mokhov A. M. Obukhov Institute of Atmospheric Physics, RAS, Moscow, Russia

2. Aim of work: Estimates of different characteristics of extratropical cyclones (including their number, size and intensity) and their changes in dependence on surface temperature.

3. Data Cyclone’s characteristics (number, size and intensity) were obtained from NCEP/NCAR reanalysis data and model simulations (including INM RAS, IPSL CM4) similar to (Bardin and Polonsky 2005, Akperov et al. 2007).

4. Interannual variations of the NH extratropical cyclones number (normalized) based on reanalysis data and model (GCM) simulations (SRES-A2) (with duration > 3 days) Mokhov, Chernokulsky, Akperov, Dufresne, Le Treut, 2009: Doklady Earth Sci., 424(3), 393-397.

5. Sensitivity of the cyclones number (N) to the surface air temperature (T s ) change can be estimated according to model* considerations: Sensitivity of the cyclone characteristic size (L) to the surface temperature (T s ) change can be estimated with the use an assessment of (L) by the Rossby radius (L R ) T e-p – equator to pole surface air temperature difference  – lapse rate (Mokhov and Akperov, 2006),  а - dry adiabatic lapse rate,  ma – moist adiabatic lapse rate,  - fraction of clouds * Mokhov I.I., Mokhov O.I, Petukhov V.K., Khairullin R.R., 1992: Izvestiya, Atmos. Oceanic Phys., 28(1), 11-26.

6. Coefficients of lapse rate  [К/km] regressions to Т s [К] obtained from reanalysis data in interannual variability Winter Summer Annual mean (Mokhov and Akperov, 2006)

7. Northern Hemisphere (as a whole) ( 1/N)*(dN/dT s )= - 0.027(±0.012) K -1, (1/L)*(dL/dT s )= - 0.001(±0.008) K -1 (by reanalysis data) (1/N)*(dN/dT s )= - 0.047 K -1, (1/L)*(dL/dT s )= - 0.002 K -1 (model: dry atmosphere) (1/N)*(dN/dT s )= - 0.040 K -1, (1/L)*(dL/dT s )= - 0.008 K -1 (model: moist atmosphere) Estimates of sensitivity of the NH extratropical cyclones number N and their size L to the surface temperature (T s ) change for different latitudes by NCEP/NCAR reanalysis data and model * considerations * Mokhov I.I., Mokhov O.I, Petukhov V.K., Khairullin R.R., 1992: Izvestiya, Atmos. Oceanic Phys., 28(1), 11-26. Mokhov I.I., Mokhov O.I, Petukhov V.K., Khairullin R.R., 1992: Rus. Meteorol. Hydrol., 1, 5-11.

8. Changes in distribution functions of the NH extratropical cyclones in dependence on their intensity (a) and size (b) between 2081-2100 and 1981-2000 from IPSL-CM4 simulations with SRES-A2 scenario

9. Conclusions An expected general tendency of decrease in the total number of the NH extratropical cyclones (statistically insignificant from observations) under global warming is accompanied by remarkable interannual and interdecadal variations. An expected general tendency of decrease in the total number of the NH extratropical cyclones (statistically insignificant from observations) under global warming is accompanied by remarkable interannual and interdecadal variations. General tendency of decrease in the total number of the NH extratropical cyclones under general warming is accompanied by decrease in the number of small cyclones and increase in the number of large and intensive cyclones. General tendency of decrease in the total number of the NH extratropical cyclones under general warming is accompanied by decrease in the number of small cyclones and increase in the number of large and intensive cyclones. Estimates with reanalysis data exhibit tendency of increase (statistically insignificant) in the number of extratropical cyclones in middle and high latitudes with the increase of surface air temperature. Opposite sign tendency for these latitudes from simple tropospheric model estimates is similar to general tendency for small cyclones from GCM simulations. Uncertainties can be related with nonlinear effects and stratospheric changes and with interdecadal variations like North Atlantic Oscillation. Estimates with reanalysis data exhibit tendency of increase (statistically insignificant) in the number of extratropical cyclones in middle and high latitudes with the increase of surface air temperature. Opposite sign tendency for these latitudes from simple tropospheric model estimates is similar to general tendency for small cyclones from GCM simulations. Uncertainties can be related with nonlinear effects and stratospheric changes and with interdecadal variations like North Atlantic Oscillation.