The Modern-Era Retrospective Analysis for Research and Applications (MERRA) was undertaken by NASA’s Global Modeling and Assimilation Office with two primary objectives: to place observations from NASA’s Earth Observing System satellites into a climate context and to improve upon the hydrologic cycle represented in earlier generations of reanalyses. Focusing on the satellite era, from 1979 to the present, MERRA has achieved its goals with significant improvements in precipitation and water vapor climatology. Here, a brief overview of the system and some aspects of its performance, including quality assessment diagnostics from innovation and residual statistics, is given.By comparing MERRA with other updated reanalyses [the interim version of the next ECMWF Re-Analysis (ERA-Interim) and the Climate Forecast System Reanalysis (CFSR)], advances made in this new generation of reanalyses, as well as remaining deficiencies, are identified. Although there is little difference between the new reanalyses i...

MERRA: NASA’s Modern-Era Retrospective Analysis for Research and Applications

Abstract A two-dimensional version of the Pennsylvania State University mesoscale model has been applied to Winter Monsoon Experiment data in order to simulate the diurnally occurring convection observed over the South China Sea. The domain includes a representation of part of Borneo as well as the sea so that the model can simulate the initiation of convection. Also included in the model are parameterizations of mesoscale ice phase and moisture processes and longwave and shortwave radiation with a diurnal cycle. This allows use of the model to test the relative importance of various heating mechanisms to the stratiform cloud deck, which typically occupies several hundred kilometers of the domain. Frank and Cohen's cumulus parameterization scheme is employed to represent vital unresolved vertical transports in the convective area. The major conclusions are: Ice phase processes are important in determining the level of maximum large-scale heating and vertical motion because there is a strong anvil componen...

Numerical study of convection observed during the Winter Monsoon Experiment using a mesoscale two-dimensional model [presentation]

The Intergovernmental Panel on Climate Change (IPCC) Technical Paper Climate Change and Water draws together and evaluates the information in IPCC Assessment and Special Reports concerning the impacts of climate change on hydrological processes and regimes, and on freshwater resources – their availability, quality, use and management. It takes into account current and projected regional key vulnerabilities, prospects for adaptation, and the relationships between climate change mitigation and water. Its objectives are:

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Climate change and water.

Glacial melting in the Tibetan Plateau affects the water resources of millions of people. This study finds that—partly owing to changes in atmospheric circulations and precipitation patterns—the most intensive glacier shrinkage is in the Himalayan region, whereas glacial retreat in the Pamir Plateau region is less apparent.

Different glacier status with atmospheric circulations in Tibetan Plateau and surroundings

Increased forest fire activity across the western continental United States (US) in recent decades has likely been enabled by a number of factors, including the legacy of fire suppression and human settlement, natural climate variability, and human-caused climate change. We use modeled climate projections to estimate the contribution of anthropogenic climate change to observed increases in eight fuel aridity metrics and forest fire area across the western United States. Anthropogenic increases in temperature and vapor pressure deficit significantly enhanced fuel aridity across western US forests over the past several decades and, during 2000–2015, contributed to 75% more forested area experiencing high (>1 σ) fire-season fuel aridity and an average of nine additional days per year of high fire potential. Anthropogenic climate change accounted for ∼55% of observed increases in fuel aridity from 1979 to 2015 across western US forests, highlighting both anthropogenic climate change and natural climate variability as important contributors to increased wildfire potential in recent decades. We estimate that human-caused climate change contributed to an additional 4.2 million ha of forest fire area during 1984–2015, nearly doubling the forest fire area expected in its absence. Natural climate variability will continue to alternate between modulating and compounding anthropogenic increases in fuel aridity, but anthropogenic climate change has emerged as a driver of increased forest fire activity and should continue to do so while fuels are not limiting.

https://www.pnas.org/content/pnas/113/42/11770.full.pdf

Impact of anthropogenic climate change on wildfire across western US forests

The surface radiation is a crucial variable for understanding global climate and eco-environment change, which exhibits significant variations over time and space. In this study, we used in situ ground observations to estimate variations of the surface radiation budget over grassland and urban areas in a subtropical humid region. Our results revealed a positive radiation budget that varied over different land covers. Specifically, grassland exhibited a higher shortwave radiation, while urban area was characterized by the higher longwave radiation. Notably, the surface radiation budget (Rn) was much greater in grassland (77.60 W2/m) than that in urban area (61.93 W2/m), which was mainly attributed to the difference in longwave radiation. Additionally, the atmospheric pressure showed a strong correlation with the radiations, while precipitation and relative humidity presented relatively weak correlations. Furthermore, the correlations with climate were stronger in grassland than that in urban areas, suggesting complex interactions with anthropogenic factors during the process of urbanization. Results of this study would help reveal the characteristics and corresponding mechanisms of surface radiation budgets, which would support climatic adaptation and ecology management.

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Variation in the surface radiation budget over different land covers in a subtropical humid region: evidence from ground observations

Heavy metal pollution in testing ranges is one of the most widely concerning environmental problems. The ammunition static detonation test area, the bomb falling area, and the living area of a testing range in Jilin were selected as the study objects. The contents of heavy metals (As, Cd, Cr, Cu, Ni, Pb, and Zn) in 112 topsoil samples and two soil profiles were analyzed, and their distribution characteristics and sources were analyzed in detail. After that, the pollution degree and potential ecological risk of heavy metals were investigated using multiple pollution index assessment methods. The results showed that the average contents of As, Cd, Cu, Ni, and Zn in the soil of the ammunition static detonation test area were higher than the soil background values in Jilin province, and the contents of Cu, Zn, As, and Cd showed strong spatial heterogeneity. The average concentrations of As, Cd, and Ni in the soil of the bomb falling area exceeded their background values. The average contents of As and Cd in the soil of the living area were higher than the background values, and the variation coefficients of Pb, Cd, Zn, and Cr were relatively high, indicating that they may have been affected by human activities. In different test areas, the contents of As, Cr, Cu, Ni, and Zn in the soil samples were significantly different (P<0.05). The ammunition static detonation test area was more strongly affected by the test activities than the bomb falling area, and the heavy metal contents in the surface layer of the soil profile were significantly higher. There was no obvious vertical migration of heavy metals in the soil profiles. The results of multivariate statistics and source identification analysis using absolute principal component score-multiple linear regression (APCS-MLR) showed that Zn, Pb, and Cd were mainly affected by pollution sources related to test activities; Cr and Ni were mainly affected by natural sources of soil forming materials; and the sources of As and Cu were more complicated. The geo-accumulation index showed that Cd in the three areas and Ni in the bomb falling area belonged to pollution level 1 (uncontaminated to moderately contaminated). The Nemerow comprehensive pollution index showed that the pollution levels among the different functional areas were:living area>ammunition static detonation test area>bomb falling area, and the three functional areas were slightly polluted. The potential ecological risk index showed that the study area was at moderate ecological risk level, and Cd was considered to be the main soil pollution factor.

[Distribution Characteristics and Pollution Assessment of Heavy Metals in Soils of a Testing Range].

The lake elevation of the Great Salt Lake (GSL), a large closed basin in the arid western United States, is characterized by a pronounced quasi-decadal oscillation (QDO) (Lall and Mann 1995). Wang et al. (2009a) found that the variation of the GSL elevation is very coherent with the QDO of sea surface temperature anomalies in the tropical central Pacific, known as the Pacific QDO (White and Liu 2008a, b). The Pacific QDO can be depicted by the SST anomalies in the NINO4 region (Allan 2000), denoted as ΔSST (NINO4). Fig. 1 illustrates the coherence between the GSL elevation and ΔSST (NINO4). However, such a coherence denies any direct association between the precipitation over the GSL watershed and the Pacific QDO because, in a given frequency, the precipitation variations always lead the GSL elevation variations. In other words, a direct link between the Pacific QDO and the precipitation source of the GSL is absent. What causes the GSL elevation to vary so coherently with ΔSST (NINO4) is therefore an intriguing question.

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The Pacific QDO as a natural predictor for the Great Salt Lake elevation

We investigate the feasibility of developing decadal prediction models for autumn rainfall ( R A ) over Central Vietnam by utilizing a published tree-ring reconstruction of October–November (ON) rainfall derived from the earlywood width measurements from a type of Douglas-fir (Pseudotsuga sinensis). Autumn rainfall for this region accounts for a large percentage of the annual total, and is often the source of extreme flooding. Central Vietnam’s R A is characterized by a pronounced decadal oscillation signal. We use the decadal mode of R A along with its notable autocorrelation and significant cross-correlation with basin-wide Pacific sea surface temperature (SST) variability, to develop four discrete time-series models. The sparse autoregressive model, with Pacific SST as an external variable, accounts for most of the autoregressive R A , while taking advantage of the predictability from the basin-wide Pacific climate oscillation. Using this model, the decadal prediction of R A can be reasonably achieved with a 10-year-ahead forecasting skill score (SS) about 0.46. We therefore suggest, with this paper, that forecasting R A for Central Vietnam for multiple years ahead is possible using a time-series model.

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Shih-Yu Wang

Papers

Variation in the surface radiation budget over different land covers in a subtropical humid region: evidence from ground observations

[Distribution Characteristics and Pollution Assessment of Heavy Metals in Soils of a Testing Range].

The Pacific QDO as a natural predictor for the Great Salt Lake elevation

Feasibility of Predicting Vietnam’s Autumn Rainfall Regime Based on the Tree-Ring Record and Decadal Variability

Amplified drought trends in Nepal increase the potential for Himalayan wildfires