ALBERT

Description: ENSO (El Niño-Southern Oscillation) has profound effects on the global water cycle, which can be examined at the process level by investigating the associated water isotopologues. Many isotope-based studies are aimed at understanding ENSO variability in the tropics, however focusing principally on near-surface processes and isotopologue signals. The goal of the present study is to investigate the atmospheric processes governing the changes in the isotopic composition of water vapor both near the surface and at mid troposphere in the Pacific region during ENSO events, using a combination of remote sensing data and model simulations. For the lower atmosphere (i.e., 1000 hPa), our results show that rainout processes, less rain re-evaporation offalling droplets, and increase of convective updrafts and diffusive exchange within the convective systems, contribute to “the isotope amount effect” and isotopically deplete the water vapor during wet conditions, in agreement with previous studies. However, we find that the ENSO associated isotopic signal in the mid troposphere (i.e., 500 hPa) diverges from the near-surface response. Analysis suggests that transport of enriched water vapor from lower atmospheric layers through convective updrafts controls the enrichment of mid tropospheric water vapor over the Pacific Ocean. In the observations, a strong positive correlation between the increase of convective precipitation and the isotopic composition of water vapor clearly points to such a mechanism (R of 0.7-0.8 in the Central Pacific and 0.5-0.6 in the West Pacific). Model results confirm this mechanisms though producing slightly lower correlation values, with R values of 0.6 in the Central Pacific and 0.5 in the West Pacific. However, the distinction between convective and stratiform precipitation remains a result of model dependent parameterization. Our analysis suggests that two issues should be investigated in more detail in further studies: 1) the equilibrium and dis-equilibrium between rain droplets and surrounding vapor for convective and stratiform precipitation and 2) different convection schemes in the different isotopic GCMs describing the triggering of convection and uplift of lower layer air to higher layers. Ideally such a comparison of different isotopic GCMs can provide us with an interesting benchmark test for the performance of the different convection schemes during ENSO, and can help to disentangle the importance of the different processes contributing to the amount effect.

Description: [1]  Over the past decade the development of SCIAMACHY retrievals has increased the interest in the use of satellite measurements for studying the global sources and sinks of methane. Meanwhile measurements are becoming available from the more advanced GOSAT. The aim of this study is to investigate the application of GOSAT retrievals to inverse modelling, for which we make use of the TM5-4DVAR inverse modelling framework. Inverse modelling calculations are performed using data from two different retrieval approaches: a full physics [ Butz et al ., 2011; Schepers et al ., 2012] and a lightpath proxy ratio method [ Frankenberg et al ., 2005a; Butz et al ., 2011; Schepers et al ., 2012]. The performance of these inversions is analyzed in comparison with inversions using SCIAMACHY retrievals and measurements from the NOAA-ESRL flask-sampling network. In addition, we compare the inversion results against independent surface, aircraft and total-column measurements. Inversions with GOSAT data show good agreement with surface measurements, whereas for SCIAMACHY a similar performance can only be achieved after significant bias corrections. Some inconsistencies between surface and total column methane remain in the Southern Hemisphere. However, comparisons with measurements from the TCCON in-situ FTS network indicate that those may be caused by systematic model errors rather than by shortcomings in the GOSAT retrievals. The global patterns of methane emissions derived from SCIAMACHY (with bias correction) and GOSAT retrievals are in remarkable agreement and allow an increased resolution of tropical emissions. The satellite inversions increase tropical methane emission by 30 to 60 TgCH 4 /yr compared to initial a priori estimates, partly counterbalanced by reductions in emissions at mid to high latitudes.

Description: Observations show that heavy oxygen isotope composition in precipitation (δ18Op) increases from coastal southeastern (SE) China to interior northwestern (NW) China during the wet season, contradicting expectations from simple Rayleigh distillation theory. Here we employ stable isotopes of precipitation and vapor from satellite measurements and climate model simulations to characterize the moisture processes that control Asian monsoon precipitation and relate these processes to speleothem paleoclimate records. We find that δ18Op is low over SE China as a result of local and upstream condensation and that δ18Op is high over NW China because of evaporative enrichment of 18O as raindrops fall through dry air. We show that δ18Op at cave sites over southern China is weakly correlated with upstream precipitation in the core of the Indian monsoon region rather than local precipitation, but it is well-correlated with the δ18Op over large areas of southern and central China, consistent with coherent speleothem δ18Op variations over different parts of China. Previous studies have documented high correlations between speleothem δ18Op and millennial timescale climate forcings, and we suggest that the high correlation between insolation and speleothem δ18Op in southern China reflects the variations of hydrologic processes over the Indian monsoon region on millennial and orbital timescales. The δ18Op in the drier part (north of ∼30°N) of China, on the other hand, has consistently negative correlations with local precipitation and may capture local hydrologic processes related to changes in the extent of the Hadley circulation.

Description: [1]  The causes of renewed growth in the atmospheric CH 4 burden since 2007 are still poorly understood and the subject of intensive scientific discussion. Here, we present a reanalysis of global CH 4 emissions during the 2000s, based on the TM5-4DVAR inverse modeling system. We use high-accuracy surface observations from the NOAA Earth System Research Laboratory global cooperative air sampling network for 2000–2010, together with retrievals of column-averaged CH 4 mole fractions from the Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY) instrument onboard ENVISAT from 2003 onwards. [2]  Using climatological OH fields, derived global total emissions for 2007–2010 are 16–20 Tg CH 4 /yr higher than for 2003–2005. Most of the inferred increase was located in the tropics (9–14 Tg CH 4 /yr) and mid-latitudes of the northern hemisphere (6–8 Tg CH 4 /yr), while no significant trend was derived for Arctic latitudes. The atmospheric increase can be attributed mainly to an increase of anthropogenic emissions. However, the derived trend in anthropogenic emissions is significantly smaller than the one estimated in the EDGARv4.2 emission inventory. Superimposed on the increasing trend in anthropogenic CH 4 emissions are significant inter-annual variations (IAV) of CH 4 emissions from wetlands (up to ±10 Tg CH 4 /yr), and biomass burning (up to ±7 Tg CH 4 /yr). [3]  Various sensitivity experiments have been performed to investigate the impact of the SCIAMACHY observations (compared to inversions using only surface observations), of the OH fields used, and of a priori emission inventories on the derived CH 4 emission trends and their inter-annual variability. Despite significant differences among these sensitivity experiments in their latitudinal attribution of IAV of CH 4 emissions, they show a reasonably consistent picture regarding the IAV aggregated on larger latitude bands. Furthermore, all sensitivity experiments show very similar performance against a comprehensive independent dataset of observations used for validation, including NOAA ship and aircraft profile samples, HIPPO aircraft transects, and CARIBIC aircraft data. Comparison of model simulations with BARCA aircraft measurements, however, show significantly better agreement in the free troposphere over the Amazon for the inversions using the SCIAMACHY and NOAA surface observations compared to inversions using only the surface observations, demonstrating the usefulness of the satellite measurements to better constrain tropical CH 4 emissions.