Michael G. Bosilovich

The Global Land Data Assimilation System

A Global Land Data Assimilation System (GLDAS) has been developed. Its purpose is to ingest satellite- and ground-based observational data products, using advanced land surface modeling and data assimilation techniques, in order to generate optimal fields of land surface states and fluxes. GLDAS is unique in that it is an uncoupled land surface modeling system that drives multiple models, integrates a huge quantity of observation-based data, runs globally at high resolution (0.25°), and produces results in near–real time (typically within 48 h of the present). GLDAS is also a test bed for innovative modeling and assimilation capabilities. A vegetation-based “tiling” approach is used to simulate subgrid-scale variability, with a 1-km global vegetation dataset as its basis. Soil and elevation parameters are based on high-resolution global datasets. Observation-based precipitation and downward radiation and output fields from the best available global coupled atmospheric data assimilation systems are employe...

The common land model

The Common Land Model (CLM) was developed for community use by a grassroots collaboration of scientists who have an interest in making a general land model available for public use and further development. The major model characteristics include enough unevenly spaced layers to adequately represent soil temperature and soil moisture, and a multilayer parameterization of snow processes; an explicit treatment of the mass of liquid water and ice water and their phase change within the snow and soil system; a runoff parameterization following the TOPMODEL concept; a canopy photo synthesis-conductance model that describes the simultaneous transfer of CO2 and water vapor into and out of vegetation; and a tiled treatment of the subgrid fraction of energy and water balance. CLM has been extensively evaluated in offline mode and coupling runs with the NCAR Community Climate Model (CCM3). The results of two offline runs, presented as examples, are compared with observations and with the simulation of three other la...

The Modern-Era Retrospective Analysis for Research and Applications, Version 2 (MERRA-2)

The Modern-Era Retrospective Analysis for Research and Applications, Version 2 (MERRA-2) is the latest atmospheric reanalysis of the modern satellite era produced by NASAs Global Modeling and Assimilation Office (GMAO). MERRA-2 assimilates observation types not available to its predecessor, MERRA, and includes updates to the Goddard Earth Observing System (GEOS) model and analysis scheme so as to provide a viable ongoing climate analysis beyond MERRAs terminus. While addressing known limitations of MERRA, MERRA-2 is also intended to be a development milestone for a future integrated Earth system analysis (IESA) currently under development at GMAO. This paper provides an overview of the MERRA-2 system and various performance metrics. Among the advances in MERRA-2 relevant to IESA are the assimilation of aerosol observations, several improvements to the representation of the stratosphere including ozone, and improved representations of cryospheric processes. Other improvements in the quality of MERRA-2 compared with MERRA include the reduction of some spurious trends and jumps related to changes in the observing system, and reduced biases and imbalances in aspects of the water cycle. Remaining deficiencies are also identified. Production of MERRA-2 began in June 2014 in four processing streams, and converged to a single near-real time stream in mid 2015. MERRA-2 products are accessible online through the NASA Goddard Earth Sciences Data Information Services Center (GES DISC).

Evaluation of the Reanalysis Products from GSFC, NCEP, and ECMWF Using Flux Tower Observations

AbstractReanalysis products produced at the various centers around the globe are utilized for many different scientific endeavors, including forcing land surface models and creating surface flux estimates. Here, flux tower observations of temperature, wind speed, precipitation, downward shortwave radiation, net surface radiation, and latent and sensible heat fluxes are used to evaluate the performance of various reanalysis products [NCEP–NCAR reanalysis and Climate Forecast System Reanalysis (CFSR) from NCEP; 40-yr European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA-40) and ECMWF Interim Re-Analysis (ERA-Interim) from ECMWF; and Modern-Era Retrospective Analysis for Research and Applications (MERRA) and Global Land Data Assimilation System (GLDAS) from the Goddard Space Flight Center (GSFC)]. To combine the biases and standard deviation of errors from the separate stations, a ranking system is utilized. It is found that ERA-Interim has the lowest overall bias in 6-hourly air temper...

Numerical Simulation of the 1993 Midwestern Flood: Land–Atmosphere Interactions

Abstract During the summer of 1993, persistent and heavy precipitation caused a long-lived, catastrophic flood in the midwestern United States. In this paper, Midwest hydrology, atmospheric circulation of the 1993 summer, and feedback between the surface and precipitating systems were investigated using the Purdue Regional Model (PRM). The 30-day PRM control simulations reproduced the large-scale atmospheric features that characterized the summer of 1993. Specifically, the upper-level jet stream and trough over the northwestern United States are present in control cases, as well as the Great Plains low-level jet, general pattern of moisture transport, and heavy precipitation in the Midwest. The daily precipitation record (area averaged over the heaviest rainfall) indicates that the model also reproduces the evolution and periodicity of precipitation events comparable with the observations and correctly depicts the differences between June and July. The sensitivity of the low-level jet, planetary boundary ...

North American extreme temperature events and related large scale meteorological patterns: A review of statistical methods, dynamics, modeling, and trends

Abstract The objective of this paper is to review statistical methods, dynamics, modeling efforts, and trends related to temperature extremes, with a focus upon extreme events of short duration that affect parts of North America. These events are associated with large scale meteorological patterns (LSMPs). The statistics, dynamics, and modeling sections of this paper are written to be autonomous and so can be read separately. Methods to define extreme events statistics and to identify and connect LSMPs to extreme temperature events are presented. Recent advances in statistical techniques connect LSMPs to extreme temperatures through appropriately defined covariates that supplement more straightforward analyses. Various LSMPs, ranging from synoptic to planetary scale structures, are associated with extreme temperature events. Current knowledge about the synoptics and the dynamical mechanisms leading to the associated LSMPs is incomplete. Systematic studies of: the physics of LSMP life cycles, comprehensive model assessment of LSMP-extreme temperature event linkages, and LSMP properties are needed. Generally, climate models capture observed properties of heat waves and cold air outbreaks with some fidelity. However they overestimate warm wave frequency and underestimate cold air outbreak frequency, and underestimate the collective influence of low-frequency modes on temperature extremes. Modeling studies have identified the impact of large-scale circulation anomalies and land–atmosphere interactions on changes in extreme temperatures. However, few studies have examined changes in LSMPs to more specifically understand the role of LSMPs on past and future extreme temperature changes. Even though LSMPs are resolvable by global and regional climate models, they are not necessarily well simulated. The paper concludes with unresolved issues and research questions.

An Assessment of the Uncertainties in Ocean Surface Turbulent Fluxes in 11 Reanalysis, Satellite-Derived, and Combined Global Datasets

AbstractOcean surface turbulent fluxes play an important role in the energy and water cycles of the atmosphere–ocean coupled system, and several flux products have become available in recent years. Here, turbulent fluxes from 6 widely used reanalyses, 4 satellite-derived flux products, and 2 combined product are evaluated by comparison with direct covariance latent heat (LH) and sensible heat (SH) fluxes and inertial-dissipation wind stresses measured from 12 cruises over the tropics and mid- and high latitudes. The biases range from −3.0 to 20.2 W m−2 for LH flux, from −1.4 to 6.0 W m−2 for SH flux, and from −7.6 to 7.9 × 10−3 N m−2 for wind stress. These biases are small for moderate wind speeds but diverge for strong wind speeds (>10 m s−1). The total flux biases are then further evaluated by dividing them into uncertainties due to errors in the bulk variables and the residual uncertainty. The bulk-variable-caused uncertainty dominates many products’ SH flux and wind stress biases. The biases in the bu...

Intercomparison of water and energy budgets for five Mississippi subbasins between ECMWF reanalysis (ERA‐40) and NASA Data Assimilation Office fvGCM for 1990–1999

[1] Using monthly means for 1990-1999, we assess the systematic biases in temperature and humidity and the surface energy and water budgets of both European Centre for Medium-Range Weather Forecasts (ECMWF) 40-year reanalysis (ERA-40) and the of the NASA Data Assimilation Office atmospheric finite-volume general circulation model (fvGCM) for five Mississippi subbasins. We compare ERA-40 and the fvGCM with basin averages of surface observations of temperature, humidity and precipitation, the river basin estimates for the hydrological balance from Maurer et al. [2002], and the International Satellite Cloud Climatology Project (ISCCP) retrieved skin temperature and surface radiation fluxes. We show the role of the soil water analysis in ERA-40, which generally supplies water in summer and removes it in winter and spring. The ERA-40 snow analysis increments are a significant contribution to the (smaller) frozen water budget. Compared with National Climate Data Center (NCDC) observations of screen temperature, ERA-40 generally has a relatively small (< 1 K) positive temperature bias in all seasons for the Mississippi basins, while the fvGCM has a large cold bias in temperature in winter. The ISCCP skin temperature estimate is generally high in winter and a little low in summer, compared to ERA-40 and the NCDC screen level temperature. For the western basins, summer precipitation is high in the fvGCM, while for the eastern basins it is high in ERA-40 (in 12-24 hour forecasts after spin-up). Summer evaporation is higher in the fvGCM than in ERA-40, while winter evaporation has a high bias in ERA-40, leading to a corresponding high bias in specific humidity. Net shortwave radiation probably has a high bias in the fvGCM in summer. The seasonal cycle of incoming shortwave is much flatter in ERA-40 than the ISCCP data, suggesting that the reanalysis may have too much reflective cloud in summer and too little in the cooler seasons. The temperature biases at the surface in both the fvGCM and the ISCCP data clearly have a negative impact on the surface long-wave radiation fluxes, although the bias in the net long-wave flux is rather less.

The Spatiotemporal Structure of Twentieth-Century Climate Variations in Observations and Reanalyses. Part II: Pacific Pan-Decadal Variability

Abstract The spatiotemporal structure of Pacific pan-decadal variability (PDV) is isolated in global long-term surface temperature (ST) datasets and reanalysis atmospheric parameter fields from which El Nino–Southern Oscillation (ENSO) effects have been removed. Empirical orthogonal function (EOF) and combined EOF analysis of the resulting time series identify PDV as one of two primary modes of long-term variability, the other being a global warming (GW) trend, which is addressed in a companion paper (Part I). In this study, it is shown that one of several PDV interdecadal regime shifts occurred during the 1990s. This significant change in the Pacific basin is comparable but antiphase to the well-known 1976 climate regime shift and is consistent with the observed changes in biosystems and ocean circulation. A comprehensive picture of PDV as manifested in the troposphere and at the surface is described. In general, the PDV spatial patterns in different parameter fields share some similarities with the patt...

Precipitation Recycling over the Central United States Diagnosed from the GEOS-1 Data Assimilation System

Abstract Precipitation recycling has been computed for 15 yr of reanalysis data from the National Aeronautics and Space Administration Goddard Earth Observing System (GEOS-1) Data Assimilation System using monthly mean hydrological data and a bulk diagnostic recycling model. This study focuses on the central United States and the extreme summers of 1988 (drought) and 1993 (flood). It is found that the 1988 summer recycling ratio is larger than that of 1993, and that the 1988 recycling ratio is much larger than average. The 1993 recycling ratio was less than average during the summer, but it was larger than average during the springtime, when the soil was being primed for flooding. In addition, the magnitude of summertime recycled precipitation was smaller than average in both 1988 and 1993. During the summer of 1993, the extremely large moisture transport dominates evaporation as the source of water for the extreme summer precipitation. The diagnosed recycling data show that the recycled precipitation is ...