ALBERT

Description: [1]  We have measured interseismic deformation across the Ashkabad strike-slip fault using 13 Envisat interferograms covering a total effective timespan of ~30 years. Atmospheric contributions to phase delay are significant and variable due to the close proximity of the Caspian Sea. In order to retrieve the pattern of strain accumulation, we show it is necessary to use data from Envisat's Medium Resolution Imaging Spectrometer (MERIS) instrument, as well numerical weather model outputs from the European Centre for Medium-Range Weather Forecasting (ECMWF), to correct interferograms for differences in water vapour and atmospheric pressure respectively. This has enabled us to robustly estimate the slip rate and locking depth for the Ashkabad fault using a simple elastic dislocation model. Our data are consistent with a slip rate of 5–12 mm/yr below a locking depth of 5.5–17 km for the Ashkabad fault, and synthetic tests support the magnitude of the uncertainties on these estimates. Our estimate of slip rate is 1.25–6 times higher than some previous geodetic estimates, with implications for both seismic hazard and regional tectonics, in particular supporting fast relative motion between the South Caspian Block and Eurasia. This result reinforces the importance of correcting for atmospheric contributions to interferometric phase for small strain measurements. We also attempt to validate a recent method for atmospheric correction based on ECMWF ERA-Interim model outputs alone and find that this technique does not work satisfactorily for this region when compared to the independent MERIS estimates.

Description: This study uses a regional fully coupled chemistry-transport model to assess changes in surface ozone over the summertime U.S. between present and a 2050 future time period at high spatial resolution (12 km grid spacing) under the SRES A2 climate and RCP8.5 anthropogenic precursor emission scenario. The impact of predicted changes in regional climate and globally enhanced ozone is estimated to increase surface ozone over most of the U.S; the 5 th - 95 th percentile range for daily 8-hour maximum surface ozone increases from 31-79 ppb to 30-87 ppb between the present and future time periods. The analysis of a set of meteorological drivers suggests that these mostly will add to increasing ozone, but the set of simulations conducted is targeted on understanding the competing effect of global versus local emission changes and does not allow separating the meteorological feedbacks from that due to enhanced global ozone. Statistically significant increases were found for future temperature, biogenic emissions and solar radiation. Stringent emission controls can counteract these likely positive feedbacks and if implemented as in RCP8.5, we estimate large reductions in surface ozone with the 5 th -95 th percentile reduced to 27-55 ppb. A comparison of the high-resolution projections to global model projections shows that the global model has a high positive bias in surface ozone compared to the regional model and compared to observations. On average, both the global and the regional model predict similar changes in ozone between the present and future time periods. However, on small spatial scales, the regional model shows pronounced differences between projections in urban and rural regimes that cannot be resolved at the coarse (2°x2°) resolution of the considered global model. This study confirms the key role of emission control strategies in future air quality projections and demonstrates the need for considering degradation of air quality with future climate change in emission policy making. It also illustrates the need for high resolution modeling when the objective is to address regional and local air quality or establish links to human health and society.