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

One may infer from the poleward propagation of angular momentum that energy change in tropical regions may be manifested in polar regions through a poleward propagation. This idea does not seem to be extensively addressed in the literature. It has been found that the poleward propagation of total atmospheric energy appears to connect the tropics and the polar regions on the interannual timescale. The present study explores how this poleward propagation may be linked to prominent climate oscillations such as ENSO, PNA, NAO, AO, AAO, and PSA. Analysis suggests that the poleward propagation of energy is likely a result of the atmospheric circulation change modulated by the climate patterns of ENSO, PNA, NAO, AO from tropical to Arctic regions and by the climate patterns of ENSO, PSA, AAO from tropical to Antarctic regions. The existence of the poleward energy propagation may shed light on studies exploring the link- age between topical climate and polar climate.

Co-variability of poleward propagating atmospheric energy with tropical and higher-latitude climate oscillations

Atmospheric Rivers Impacting Northern California Exhibit a Quasi-Decadal Frequency

The future of the Colorado River water supply (WS) affects millions of people and the US economy. A recent study suggested a cross-basin correlation between the Colorado River and its neighboring Great Salt Lake (GSL). Following that study, the feasibility of using the previously developed multi-year prediction of the GSL water level to forecast the Colorado River WS was tested. Time-series models were developed to predict the changes in WS out to 10 years. Regressive methods and the GSL water level data were used for the depiction of decadal variability of the Colorado River WS. Various time-series models suggest a decline in the 10-year averaged WS since 2013 before starting to increase around 2020. Comparison between this WS prediction and the WS projection published in a 2012 government report (derived from climate models) reveals a widened imbalance between supply and demand by 2020, a tendency that is confirmed by updated WS observation. Such information could aid in management decision-making in the face of near-future water shortages.

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Feasibility of Multi-Year Forecast for the Colorado River Water Supply: Time Series Modeling

The semiarid climate and rugged terrain in the interior west of the United States do not favour the development of bow echoes, a type of convective storm associated with intense, damaging winds. However, on 21 April 2011, a bow echo associated with a fast-moving midtropospheric perturbation formed across the Great Salt Lake (GSL) in Utah, producing damaging winds along its path. Intrigued by the rarity of this bow echo and the inability of the North American Mesoscale model (NAM) to forecast it, this event was studied by using available observations and conducted simulations with the Advanced Research Weather Research and Forecasting (WRF) model. Sensitivity to the microphysics schemes (MPSs), horizontal grid spacing, intensity of moisture content, and a physical lake model in the WRF model were examined. It was found that: (a) reduction in grid spacing from 12 and 4 km to 1 km along with improved depiction of low-level moisture substantially improved the bow echo simulation, (b) the presence of GSL did not impact bow echo development, and (c) the WRF model appeared to inherit a phase error in the passage of the midtropospheric perturbation from the NAM initial and lateral boundary conditions. The phase error resulted in a 1–2 h delay in the bow echo passage. These results highlight the difficulties in simulating such a bow echo event, and suggest similar challenges future faced by subsequent regional climate downscaling studies on future extreme weather in the western United States.

Weather Research and Forecasting model simulations of a rare springtime bow echo near the Great Salt Lake, USA

Winter crop losses from extreme weather in Taiwan have increased in the recent decade, with those losses associated with pronounced wet-and-cold events (temperature 5 mm day−1). The regional and global patterns of atmospheric circulation and the sea surface temperature (SST) related to the extreme cold that damages fruits, vegetables, and paddy rice in northwest Taiwan were investigated. Cool SST anomalies in the western North Pacific (WNP) and warm SST in the central-eastern Pacific associated with the Pacific meridional mode (PMM) shared a significant role in the occurrence of wet-and-cold events in northwest Taiwan. The interactions of the WNP/PMM with the North Pacific Oscillation (NPO) and the Central Pacific type of El Nino led to a pronounced lead–lag relationship with the occurrence of wet-and-cold events. An empirical model was subsequently developed to predict the wet-and-cold event frequency using observed values of WNP, Nino-3.4, and Arctic Oscillation from year-1 and predicted indices of WNP and PMM derived from the Climate Forecast System Version 2 (CFSv2) outputs. The predictive skill of this hybrid empirical–dynamical model was statistically significant throughout the 6 months leading up to the occurrence of wet-and-cold events.

Shih-Yu Wang

Papers

Co-variability of poleward propagating atmospheric energy with tropical and higher-latitude climate oscillations

Atmospheric Rivers Impacting Northern California Exhibit a Quasi-Decadal Frequency

Feasibility of Multi-Year Forecast for the Colorado River Water Supply: Time Series Modeling

Weather Research and Forecasting model simulations of a rare springtime bow echo near the Great Salt Lake, USA

A seasonal prediction for the wet–cold spells leading to winter crop damage in northwestern Taiwan with a combined empirical–dynamical approach