Michele M. Rienecker

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

AbstractThe 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...

The North American Multimodel Ensemble: Phase-1 Seasonal-to-Interannual Prediction; Phase-2 toward Developing Intraseasonal Prediction

The recent U.S. National Academies report, Assessment of Intraseasonal to Interannual Climate Prediction and Predictability, was unequivocal in recommending the need for the development of a North American Multimodel Ensemble (NMME) operational predictive capability. Indeed, this effort is required to meet the specific tailored regional prediction and decision support needs of a large community of climate information users. The multimodel ensemble approach has proven extremely effective at quantifying prediction uncertainty due to uncertainty in model formulation and has proven to produce better prediction quality (on average) than any single model ensemble. This multimodel approach is the basis for several international collaborative prediction research efforts and an operational European system, and there are numerous examples of how this multimodel ensemble approach yields superior forecasts compared to any single model. Based on two NOAA Climate Test bed (CTB) NMME workshops (18 February and 8 April 2...

Decadal climate prediction: An update from the trenches

This paper provides an update on research in the relatively new and fast-moving field of decadal climate prediction, and addresses the use of decadal climate predictions not only for potential users of such information but also for improving our understanding of processes in the climate system. External forcing influences the predictions throughout, but their contributions to predictive skill become dominant after most of the improved skill from initialization with observations vanishes after about 6–9 years. Recent multimodel results suggest that there is relatively more decadal predictive skill in the North Atlantic, western Pacific, and Indian Oceans than in other regions of the world oceans. Aspects of decadal variability of SSTs, like the mid-1970s shift in the Pacific, the mid-1990s shift in the northern North Atlantic and western Pacific, and the early-2000s hiatus, are better represented in initialized hindcasts compared to uninitialized simulations. There is evidence of higher skill in initialize...

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).

Mechanisms for the Indian Ocean warming during the 1997-98 El Niño

This study examines primary mechanisms that gave rise to the basin-wide variations of the sea surface temperature (SST) in the Indian Ocean during the 1997–98 El Nino by using multi-source data sets. The evolution of some key atmosphere-ocean variables indicated that the SST variability in the Indian Ocean was largely attributable to the ENSO impact on the large-scale atmospheric circulation. During June-December 1997, when the El Nino in the Pacific was maturing, the Indian Ocean experienced the reversal of the Walker Circulation and the prolonged equatorward displacement of the southeast trades. The resultant changes in surface wind influenced the SST through the following means. In the equatorial region, the easterly winds associated with the reversed Walker Circulation forced equatorial Kelvin/Rossby waves, which then affected the equatorial ocean heat balance (mainly through upwelling/downwelling) and led to the reversal of the zonal SST gradient in the fall of 1997. The negative SST anomalies in the east and positive anomalies in the west in turn helped maintain and prolong the equatorial easterlies, a clear indication of coupled atmosphere-ocean interactions in operation. Outside of the equatorial waveguide, changes of latent heat flux induced by wind speed variations played a major role in the broad-scale warming. The effect was most significant during the summer/fall of 1997 when the southeasterly trade winds weakened considerably, leading to a dramatic reduction of latent heat release and subsequently a rapid surface warming in the southern ocean.

Initial Testing of a Massively Parallel Ensemble Kalman Filter with the Poseidon Isopycnal Ocean General Circulation Model

A multivariate ensemble Kalman filter (MvEnKF) implemented on a massively parallel computer architecture has been developed for the Poseidon ocean circulation model and tested with a Pacific basin model configuration. There are about 2 million prognostic state-vector variables. Parallelism for the data assimilation step is achieved by regionalization of the background-error covariances that are calculated from the phase‐space distribution of the ensemble. Each processing element (PE) collects elements of a matrix measurement functional from nearby PEs. To avoid the introduction of spurious long-range covariances associated with finite ensemble sizes, the background-error covariances are given compact support by means of a Hadamard (element by element) product with a three-dimensional canonical correlation function. The methodology and the MvEnKF implementation are discussed. To verify the proper functioning of the algorithms, results from an initial experiment with in situ temperature data are presented. Furthermore, it is shown that the regionalization of the background covariances has a negligible impact on the quality of the analyses. Even though the parallel algorithm is very efficient for large numbers of observations, individual PE memory, rather than speed, dictates how large an ensemble can be used in practice on a platform with distributed memory.

Evidence of an extratropical atmospheric influence during the onset of the 1997–98 El Niño

The major 1997–98 El Nino episode was initiated by a series of very energetic westerly wind bursts in late 1996 and early 1997. Downwelling oceanic Kelvin waves were subsequently generated and propagated rapidly eastward across the equatorial Pacific Ocean and induced significant warming in the eastern basin. By analyzing newly available wind products derived from SSM/I satellite observations, we found indications that these westerly wind bursts were embedded within the active phase of the tropical intraseasonal oscillation (the Madden-Julian Oscillation) but their amplitudes were greatly enhanced in the western Pacific sector. The local enhancement involved the development of equatorial twin cyclones which themselves were induced by northerly cold surges from East Asia/Western North Pacific into the tropical Pacific, demonstrating an extratropical atmospheric influence on tropical processes.

A Comparative Analysis of Upper-Ocean Heat Content Variability from an Ensemble of Operational Ocean Reanalyses

AbstractOcean heat content (HC) is one of the key indicators of climate variability and also provides ocean memory critical for seasonal and decadal predictions. The availability of multiple operational ocean analyses (ORAs) now routinely produced around the world is an opportunity for estimation of uncertainties in HC analysis and development of ensemble-based operational HC climate indices. In this context, the spread across the ORAs is used to quantify uncertainties in HC analysis and the ensemble mean of ORAs to identify, and to monitor, climate signals. Toward this goal, this study analyzed 10 ORAs, two objective analyses based on in situ data only, and eight model analyses based on ocean data assimilation systems. The mean, annual cycle, interannual variability, and long-term trend of HC in the upper 300 m (HC300) from 1980 to 2009 are compared.The spread across HC300 analyses generally decreased with time and reached a minimum in the early 2000s when the Argo data became available. There was a good...

Indian Ocean warming of 1997–1998

The Indian Ocean underwent substantial changes in 1997–1998. The observations show not only the appearance of a dipole mode in the tropical region but also a persistent basin-scale warming. We present in this study an analysis of the basin-scale sea surface temperature (SST) variations during 1997–1998 using satellite observations, in situ temperature measurements, and National Centers for Environmental Prediction reanalyses. We find that the Indian SST anomaly peaks occurred at two periods, i.e., November–December–January coinciding with the Nino3 peak and the following April–May–June, and were phase locked to the Indian Ocean seasonal cycle. The changes of SST in the equatorial ocean were related to a coupled interaction between the atmosphere and the ocean. Oceanic upwelling in the east and downwelling in the west played a major role in giving rise to the SST anomalies associated with the dipole mode structure. The upwelling off the coast of Sumatra elevated the regional thermocline by more than 80 m in December 1997. On the other hand, the changes of SST in the southern Indian Ocean were largely induced by the changes of local latent flux. During boreal fall-winter of 1997 the southeasterly trades were displaced and abnormally prolonged in their northernmost equatorial position. This shifted the center of the trades toward the equator, weakened the winds in the central Southern Ocean, reduced the latent heat flux in the region, and subsequently induced a surface warming. The total change of the SST anomalies integrated over the two periods, July–December 1997 and January–May 1998, were explained well by the same period latent flux integral in both intensity and pattern. The cross-basin upper ocean temperature sections show that the extratropical warming was rather uniformly distributed in the upper 60 m, further supporting the role of mixed-layer processes in the warming.

Variability and frontogenesis in the large‐scale oceanic frontal zones

Sea surface temperature (SST) from weekly global advanced very high resolution radiometer data for the period of 1982–1992 and estimates of the surface forcing due to wind stress and net heat flux are used to investigate a global monthly climatology of large-scale oceanic frontal zones (OFZs), the variability of SST gradient in several frontal zones, and the meridional frontogenesis in the North Pacific. Subpolar frontal zones are identifiable in the SST gradient field throughout the whole year while subtropical frontal zones appear as seasonal phenomena in the northern hemisphere. The magnitude and position of subtropical fronts were found to vary synchronously in both hemispheres, with maximum intensity in November to March. During this period, subtropical fronts in the northern hemisphere become clearly identifiable, separate features, while in the southern hemisphere their southern boundaries tend to merge with the subpolar front. In the northern hemisphere, the northward shift of the subtropical frontal zones during late boreal spring results in a merger of the subpolar and subtropical zones by August. In the southern hemisphere, subtropical fronts separate from the subpolar front during this period and become clearly distinguishable, though less intense. Singular spectrum analysis of the 11-year time series of SST gradient in several OFZs revealed a seasonal signal as well as interannual variations that, in the equatorial zone, are related to El Nino events. The amplitude of the annual cycle is comparable in the subtropical and subpolar North Pacific, but the subtropics leads the subpolar zone by about 4 months. Combined forcing due to wind stress and net surface heat flux was found to be sufficient to describe most of the observed frontogenesis variability in North Pacific midlatitudes on seasonal timescales, but not on shorter timescales. In the subtropical zone, the Ekman convergence alone was not sufficient to provide the observed frontogenesis/frontolysis on seasonal time scales. In fact, when the maximum frontogenesis associated with Ekman convergence occurs in late spring/early summer, this is counteracted by the frontolytic effect of Ekman pumping and the dominating frontolytic effect of surface heat forcing. In summer, Ekman convergence is more important in the subpolar area where it is enhanced by the smaller frontogenetic effect of both Ekman pumping and surface heat forcing. Surface forcing due to wind stress and heat flux considered in this study does not explain the high-amplitude intraseasonal frontogenesis variations, especially in the subpolar region.