The objectives of the research proposed for SHARP are based on the hypotheses that a) climate change caused by the increase of GHG concentrations induces stratospheric changes, and that b) these stratospheric changes interact with the troposphere to influence future tropospheric climate and weather. The main subject of SHARP will therefore remain the synergistic investigation of the vertical interaction in the atmosphere related to climate change, i.e. to introduce the aspect of vertical coupling into the discussion of climate change. This is in line with the current efforts to include an increasing number of stratosphere resolving coupled climate models in the coming IPCC Assessment. Based on our own research in Phase I as well as on recent advances derived from published literature, we have identified the following innovative objectives for SHARP Phase II:

• SHARP-BDC

• SHARP-OCF

• SHARP-WV

• SHARP-STC

Open Research Questions to be addressed in SHARP-II

The following list gives an overview on the specific science questions that will be studied in SHARP-II:

1. How will stationary and transient planetary wave activity change in future climate? What are the reasons for the changes? How do these changes affect the forcing of the BDC?
2. How do gravity wave effects influence planetary wave activity and the BDC? Can we expect an accelerated strengthening of the BDC in the second half of this century?
3. How important is the interactive feedback between ocean and atmosphere for the tropical upwelling and the BDC? Will these feedback processes become more important in a future climate with increasing sea-surface temperatures?
4. Can we diagnose changes in residual circulation and in mixing separately from observations? Which tools (e.g. tracers) can provide information on changes in mixing? Can we diagnose past changes in transport in the lower and lowermost stratosphere from observations?
5. How will increasing greenhouse (GHG) gas concentrations and the subsequent changes in climate influence stratospheric transport and mixing separately? What are the drivers for changes in age of stratospheric air?
6. How well do we understand observed trends and variability in stratospheric ozone, NO₂, and BrO from the lowermost stratosphere to the stratopause given that we have more years of consolidated trace gas profile data available? Can state-of-the art CTMs and CCMs reproduce the observed trends and variability?
7. Which dynamical and chemical processes affecting stratospheric ozone have changed in the past and in particular, recent years? How closely are chemical and dynamical changes in ozone correlated? Are there variations in the relative contribution of chemistry and dynamics affecting polar ozone in spring?
8. How accurately can we determine the total bromine budget and, in particular, the contribution of the very-short-lived substances (VSLS)? What is the relative contribution of bromine and iodine to the halogen related ozone loss? How well can CCMs reproduce the transport and pathways to the stratosphere by implementing oceanic VSLS emission scenarios?
9. Can we predict the behaviour of the stratospheric ozone in the future polar winters and springs, both in terms of positive and negative anomalies? How will ozone evolve in a changing climate i.e. what is the relative contribution arising from a cooling stratosphere and changing dynamics (increase in the BDC) to trends and variability in lower stratospheric ozone? How will future changes in GHG and N₂O emission modify ozone recovery?
10. How will various possible GHG emission scenarios vary the impact on future stratospheric temperatures, atmospheric composition (in particular ozone), and aerosol composition, and related photochemistry? What is the exact role of the ocean-atmosphere coupling in a future climate?
11. Is there a decadal-scale trend in stratospheric H₂O, or do we observe low-frequency natural variability? If so, what are the drivers of natural variability, e.g. of the water vapour drop in 2000/2001?
12. How is the variation in stratospheric H₂O coupled to changes in the tropical tropopause temperature and underlying changes in the BDC, sea surface temperature, or other parameters? What are the implications for future stratospheric H₂O?
13. Which role do regional processes play for the import of water vapour into the stratosphere, like the tropical West Pacific or the monsoon systems?
14. Which role does convection play for the water vapour transport through the tropopause, on the regional and on the global scale, and how can this information be inferred from water vapour isotopologues?
15. Can we identify a correlation between H₂O and methane in the upper stratosphere in the light of recent changes of methane growth? What does this mean for future methane oxidation efficiency?
16. What mechanisms determine the specific features, like the seasonal evolution and persistence of the dynamical stratosphere-troposphere-coupling? What is the connection between tropo-spheric wave forcing and the stratospheric and tropospheric NAM or SAM response?
17. How will the radiative forcing (RF) of the troposphere-surface system and the radiative heating of the troposphere evolve due to future stratospheric composition changes, i.e. with ozone recovery from CFCs and under the influence of climate change?
18. How will the stratosphere-to-troposphere mass exchange (STE) be changed by the removal of CFCs from the atmosphere and the recovery of stratospheric O₃, and by increasing GHG concentrations in the future?
19. What is the role of additional climate feedback factors associated with atmosphere-ocean-cryosphere coupling for stratosphere-troposphere exchange?

How well is the STC represented in the different model configurations, and is the representation of the full stratosphere needed to represent the observed tropospheric variability and past changes? Does the inclusion of stratospheric chemistry improve STC and the simulated tropospheric signal?