- Low cloud errors over the southeastern Atlantic in the NCEP CFS and their association with lower-tropospheric stability and air-sea interactionJournal of Geophysical Research 113 (d12), D12114 (2008)"The low cloud errors in the tropical Atlantic and their connection with lower-tropospheric stability and air-sea interaction in a simulation of the Climate Forecast System (CFS) are investigated. The CFS is the coupled ocean-atmosphere circulation model for operational climate prediction at the National Centers for Environmental Prediction. Compared with observations, the CFS produces too few low clouds over the southeastern Atlantic and too many high clouds over the whole tropical Atlantic. The center of the low clouds is also shifted westward in the model away from the cold tongue region to the central ocean. The underestimation of low clouds in the southeastern Atlantic may be one of the potential sources of the warm biases of sea surface temperature (SST) in this region. The low clouds are linked to a stable or inversion layer between 850 hPa and 925 hPa in observations, but are associated with a stable layer between 700 hPa and 850 hPa in the CFS, which may suggest that low clouds are generated in a higher layer in the CFS than in the real world. On average, the lower troposphere is less stable in the CFS than in the observations over the tropical Atlantic region, which is more favorable for the development of deep convection. Moreover, the low cloud variability in the South Atlantic is mainly associated with SST and wind stress anomalies in the subtropical South Atlantic in the CFS and in the southeastern Atlantic and along the African coast in the observations. "Influence of sea surface temperature on soil moisture and precipitation interactions over the southwestJournal of Geophysical Research 113 (d12), D12116 (2008)"This paper presents a hypothesis that soil moisture (SM) and precipitation (P) interactions over the Southwest depend on sea surface temperature anomalies (SSTAs). On the basis of moisture transport and geography, the Southwest can be separated into two regions. The western region (32°–36°N, 107.5°–113°W) includes Arizona and western New Mexico and the eastern region (32°–36°N, 103°–107°W) includes eastern New Mexico. For both regions, years from 1900 to 2004 are classified based on the winter to summer P evolution. When winter and the following summer P anomalies have an inverse relationship, SSTAs do not persist. The summer SSTAs have strong influence on P. Soil moisture does not play a major role in modulating P anomalies. For cases that wetness (dryness) occurs in both winter and the following summer, the SSTA forcing associated with the P regime tends to persist. Positive SM-P feedbacks enhance P anomalies. For eastern New Mexico, there is a linear relationship between SM anomalies in spring and P anomalies in summer when SSTAs persist. "A study of anthropogenic impacts of the radiation budget and the cloud field in East Asia based on model simulations with GCMJournal of Geophysical Research 113 (d12), D12211 (2008)"We investigated the effects of man-made air pollutants on the climate of East Asia, focusing on eastern China where anthropogenic aerosol concentrations are rapidly increasing. The increasing emission of anthropogenic aerosols causes serious air pollution episodes and various effects on the climate in this region. It is therefore necessary to quantify the contribution of aerosols to the change in the radiation budget and the cloud field. Our purpose of this study is to evaluate the sensitivity of anthropogenic aerosols and other anthropogenic factors such as greenhouse gas (GHG) upon the radiative forcing. Then an aerosol transport model coupled to a general circulation model and an ocean mixed-layer model was used to investigate the relationships among the anthropogenic aerosol forcing, GHG forcing, surface radiation budget, and cloud field. Our simulation results showed that copious anthropogenic aerosol loading causes significant decrease in the surface downward shortwave radiation flux (SDSWRF), which indicates that a direct effect of aerosols has the greatest influence on the surface radiation. It is found from our model simulations that low-level clouds increase but convective clouds decrease due to reduced convective activity caused by surface cooling when anthropogenic aerosol increases, and GHG increase has an insignificant effect on SDSWRF but a significant effect on the cloud field. In other word model simulations suggested that the aerosol forcing mainly causes a reduction of SDSWRF, whereas the change in the cloud field is influenced both anthropogenic aerosol and GHG effects. Thus this work demonstrated with sensitivity experiments the importance of aerosols to cause significant climate effects in the East Asian region, though further study is needed because our study is based on results from one specific model and limited data analysis. "High Resolution Dynamics Limb Sounder: Experiment overview, recovery, and validation of initial temperature dataJournal of Geophysical Research 113 (d16), D16S43 (2008)"The High Resolution Dynamics Limb Sounder (HIRDLS) experiment was designed to provide global temperature and composition data on the region from the upper troposphere to the mesopause with vertical and horizontal resolution not previously available. The science objectives are the study of small-scale dynamics and transports, including stratosphere-troposphere exchange, upper troposphere/lower stratosphere chemistry, aerosol, cirrus and PSC distributions, and gravity waves. "..."While this optical blockage also impacted radiometric performance, extensive effort has gone into developing corrections for the several effects of the obstruction, so that radiances from some of the channels can be put into retrievals for temperature. Changes were also necessary for the retrieval algorithm. The validation of the resulting temperature retrievals is presented to demonstrate the effectiveness of these corrections. The random errors range from ∼0.5 K at 20 km to ∼1.0 at 60 km, close to those predicted. Comparisons with high-resolution radiosondes, lidars, ACE-FTS, and ECMWF analyses give a consistent picture of HIRDLS temperatures being 1–2 K warm from 200 to 10 hPa and within ±2 K of standards from 200 to 2 hPa (but warmer in the region of the tropical tropopause), above which HIRDLS appears to be cold. Comparisons show that both COSMIC and HIRDLS can see small vertical features down to about 2 km wavelength. While further improvements in the data are expected, these data will allow HIRDLS to provide important support toward reaching the Aura objectives. "Diurnal and vertical variability of the sensible heat and carbon dioxide budgets in the atmospheric surface layerJournal of Geophysical Research 113 (d12), D12119 (2008)"The diurnal and vertical variability of heat and carbon dioxide (CO2) in the atmospheric surface layer are studied by analyzing measurements from a 213 m tower in Cabauw (Netherlands). Observations of thermodynamic variables and CO2 mixing ratio as well as vertical profiles of the turbulent fluxes are used to retrieve the contribution of the budget terms in the scalar conservation equation. On the basis of the daytime evolution of turbulent fluxes, we calculate the budget terms by assuming that turbulent fluxes follow a linear profile with height. This assumption is carefully tested and the deviation from linearity is quantified. The budget calculation allows us to assess the importance of advection of heat and CO2 during day hours for three selected days. It is found that, under nonadvective conditions, the diurnal variability of temperature and CO2 is well reproduced from the flux divergence measurements. Consequently, the vertical transport due to the turbulent flux plays a major role in the daytime evolution of both scalars and the advection is a relatively small contribution. During the analyzed days with a strong contribution of advection of either heat or carbon dioxide, the flux divergence is still an important contribution to the budget. For heat, the quantification of the advection contribution is in close agreement with results from a numerical model. For carbon dioxide, we qualitatively corroborate the results with a Lagrangian transport model. Our estimation of advection is compared with traditional estimations based on the Net Ecosystem-atmosphere Exchange (NEE). "Does the Madden-Julian Oscillation influence aerosol variability?Journal of Geophysical Research 113 (d12), D12215 (2008)..."These results indicate that the MJO and its associated cloudiness, rainfall, and circulation variability systematically influence the variability in remote sensing aerosol retrieval results. Several physical and retrieval algorithmic factors that may contribute to the observed aerosol-rainfall relationships are discussed. Preliminary analysis indicates that cloud contamination in the aerosol retrievals is likely to be a major contributor to the observed relationships, although we cannot exclude possible contributions from other physical mechanisms. Future research is needed to fully understand these complex aerosol-rainfall relationships. "A Bayesian calibration of a simple carbon cycle model: The role of observations in estimating and reducing uncertaintyGlobal Biogeochemical Cycles 22 (2), GB2030 (2008)"The strengths of future carbon dioxide (CO2) sinks are highly uncertain. A sound methodology to characterize current and predictive uncertainties in carbon cycle models is crucial for the design of efficient carbon management strategies. We demonstrate such a methodology, Markov Chain Monte Carlo (MCMC), by performing a Bayesian calibration of a simple global-scale carbon cycle model with historical carbon cycle observations to (1) estimate probability density functions (PDFs) of key carbon cycle parameters, (2) derive statistically sound probabilistic predictions of future CO2 sinks, and (3) assess the utility of hypothetical observation systems to reduce prediction uncertainties. We find that the PDFs of model parameter estimates are not normally distributed, and the residuals show statistically significant temporal autocorrelation. The assumption of normally distributed PDFs likely causes biased results, and the neglect of autocorrelation in the residual of the annual CO2 time series causes overconfidence in parameter estimates and predictions. "..."Although CO2 observations provide a strong constraint on the total carbon sink, adding independent observations of terrestrial and oceanic fluxes has the potential to reduce uncertainty in predictions of this total sink more rapidly. Assimilating hypothetical annual observations of terrestrial and oceanic CO2 fluxes with realistic uncertainties reduces predictive uncertainties about CO2 sinks in the year 2050 by as much as a factor of 2 compared to assimilating CO2 concentrations alone. "Amount of CO2 emissions irreversibly leading to the total melting of GreenlandAmount of COsub2sub emissions irreversibly leading to the total melting of GreenlandGeophysical Research Letters 35 (12), L12503 (2008)"The long-term response of Greenland to anthropogenic warming is of critical interest for the magnitude of the sea-level rise and for climate-related concerns. To explore its evolution over several millennia we use a climate-ice sheet model forced by a range of CO2 emission scenarios, accounting for the natural removal of anthropogenic CO2 from the atmosphere. Above 3000 GtC, the melting appears irreversible, while below 2500 GtC, Greenland only experiences a partial melting followed by a re-growth phase. Delaying emissions through sequestration slows significantly the melting, but has only a limited impact on the ultimate fate of Greenland. Its behavior is therefore mostly dependent on the cumulative CO2 emissions. This study demonstrates that the fossil fuel emissions of the next century will have dramatic consequences on sea-level rise for several millennia. "