Data Assimilation Using Incremental Analysis Updates

Bloom, S. C.; Takacs, Lawrence L.; Silva, Arlindo da; Ledvina, David V.

doi:10.1175/1520-0493(1996)124<1256:dauiau>2.0.co;2

Cited by 714 publications

(613 citation statements)

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“…It is based on the GEOS (Goddard Earth Observing System) version 5.2.0 assimilation system, which uses 3D-Var assimilation with incremental analysis update (IAU; Bloom et al, 1996) to constrain the analyses. The model uses a 0.5 • × 0.667 • latitude-longitude grid with 72 hybrid sigmapressure levels, with about 0.8 km vertical spacing in the upper troposphere, increasing to ∼ 1.2 km in the UTLS.…”

Section: Merra and Merra-2mentioning

confidence: 99%

“…Because of the IAU procedure used (see, e.g., Bloom et al, 1996;Fujiwara et al, 2017), the differences between ASM and ANA are, to first order, half of the analysis increment, with ASM being closer to the model results and ANA (albeit less balanced) being closer to the observations. The ASM-ANA differences thus largely reflect small biases between the model and observations that develop over a short forecast period.…”

Section: Grid Output Product and Assimilated Field Choicesmentioning

confidence: 99%

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Reanalysis comparisons of upper tropospheric–lower stratospheric jets and multiple tropopauses

et al. 2017

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Abstract. The representation of upper tropospheric–lower stratospheric (UTLS) jet and tropopause characteristics is compared in five modern high-resolution reanalyses for 1980 through 2014. Climatologies of upper tropospheric jet, subvortex jet (the lowermost part of the stratospheric vortex), and multiple tropopause frequency distributions in MERRA (Modern-Era Retrospective analysis for Research and Applications), ERA-I (ERA-Interim; the European Centre for Medium-Range Weather Forecasts, ECMWF, interim reanalysis), JRA-55 (the Japanese 55-year Reanalysis), and CFSR (the Climate Forecast System Reanalysis) are compared with those in MERRA-2. Differences between alternate products from individual reanalysis systems are assessed; in particular, a comparison of CFSR data on model and pressure levels highlights the importance of vertical grid spacing. Most of the differences in distributions of UTLS jets and multiple tropopauses are consistent with the differences in assimilation model grids and resolution – for example, ERA-I (with coarsest native horizontal resolution) typically shows a significant low bias in upper tropospheric jets with respect to MERRA-2, and JRA-55 (the Japanese 55-year Reanalysis) a more modest one, while CFSR (with finest native horizontal resolution) shows a high bias with respect to MERRA-2 in both upper tropospheric jets and multiple tropopauses. Vertical temperature structure and grid spacing are especially important for multiple tropopause characterizations. Substantial differences between MERRA and MERRA-2 are seen in mid- to high-latitude Southern Hemisphere (SH) winter upper tropospheric jets and multiple tropopauses as well as in the upper tropospheric jets associated with tropical circulations during the solstice seasons; some of the largest differences from the other reanalyses are seen in the same times and places. Very good qualitative agreement among the reanalyses is seen between the large-scale climatological features in UTLS jet and multiple tropopause distributions. Quantitative differences may, however, have important consequences for transport and variability studies. Our results highlight the importance of considering reanalyses differences in UTLS studies, especially in relation to resolution and model grids; this is particularly critical when using high-resolution reanalyses as an observational reference for evaluating global chemistry–climate models.

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Section: Merra and Merra-2mentioning

confidence: 99%

Section: Grid Output Product and Assimilated Field Choicesmentioning

confidence: 99%

Reanalysis comparisons of upper tropospheric–lower stratospheric jets and multiple tropopauses

et al. 2017

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“…In order to adjust the model towards these observations we used the data assimilation technique of IAU (incremental analysis updating) processes (Bloom et al, 1996). Though more sophisticated methods like the "Practical Global State Estimation" (Wunsch and Heimbach, 2007) may have led to better results we decided to start the related model development with the implementation of a rather simple, straightforward and computationally less intensive algorithm.…”

Section: Data Assimilationmentioning

confidence: 99%

The circulation of Icelandic waters – a modelling study

et al. 2013

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Abstract. The three-dimensional flow, temperature and salinity fields of the North Atlantic, including the Arctic Ocean, covering the time period 1992 to 2006 are simulated with the numerical ocean model CODE. The simulation reveals several new insights and previously unknown structures which help us to clarify open questions on the regional oceanography of Icelandic waters. These relate to the structure and geographical distribution of the coastal current, the primary forcing of the North Icelandic Irminger Current (NIIC) and the path of the Atlantic Water south-east of Iceland. The model's adaptively refined computational mesh has a maximum resolution of 1 km horizontal and 2.5 m vertical in Icelandic waters. CTD profiles from this region and the river discharge of 46 Icelandic watersheds, computed by the hydrological model WaSiM, are assimilated into the simulation. The model realistically reproduces the established elements of the circulation around Iceland. However, analysis of the simulated mean flow field also provides further insights. It suggests a distinct freshwater-induced coastal current that only exists along the south-west and west coasts, which is accompanied by a counter-directed undercurrent. The simulated transport of Atlantic Water over the Icelandic shelf takes place in a symmetrical system of two currents, with the established NIIC over the north-western and northern shelf, and a hitherto unnamed current over the southern and southeastern shelf, which is simulated to be an upstream precursor of the Faroe Current (FC). Both currents are driven by barotropic pressure gradients induced by a sea level slope across the Greenland-Scotland Ridge. The recently discovered North Icelandic Jet (NIJ) also features in the model predictions and is found to be forced by the baroclinic pressure field of the Arctic Front, to originate east of the Kolbeinsey Ridge and to have a volume transport of around 1.5 Sv within northern Denmark Strait. The simulated multi-annual mean Atlantic Water transport of the NIIC increased by 85 % during 1992 to 2006, whereas the corresponding NIJ transport decreased by 27 %. Based on our model results we propose a new and further differentiated circulation scheme of Icelandic waters whose details may inspire future observational oceanography studies.

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“…A nonlinear observation operator, calculating sea surface dynamic height from the density profile, is adopted to assimilate the altimeterderived SSH anomalies [Fujii and Kamachi, 2003b]. The 3DVAR results are inserted into the model temperature and salinity fields above 1500 m by using the incremental analysis updates [Bloom et al, 1996]. More detailed descriptions of MOVE are given by Usui et al [2006aUsui et al [ , 2006b.…”

Section: A2 Assimilation Schemementioning

confidence: 99%