Stratospheric and Mesospheric Data Assimilation: The Role of Middle Atmospheric Dynamics

Polavarapu, Saroja; Pulido, Manuel

doi:10.1007/978-3-319-43415-5_19

Cited by 12 publications

(15 citation statements)

References 83 publications

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“…Primary tropopause altitude trends over Antarctica were found to vary considerably among the reanalyses, with increasing trends in ERA-Interim and MERRA-2 and decreasing trends in JRA-55 and CFSR. These conflicting trends over Antarctica may be a result of different ozone input sources and assimilation as well as the dynamical responses to ozone concentration changes (e.g., Martineau et al, 2016;Polavarapu and Pulido, 2017;Fujiwara et al, 2017). For example, ERA-Interim and MERRA-2 assimilate ozone retrievals (both profiles and total column ozone, TCO) from SBUV and SBUV/2, as well as TCO from OMI and profiles from Aura MLS, while JRA-55 only assimilates TCO and CFSR assimilates TCO and relatively coarsevertical-resolution profiles from SBUV and SBUV/2.…”

Section: Conclusion and Discussionmentioning

confidence: 99%

Global tropopause altitudes in radiosondes and reanalyses

Xian

Homeyer

2019

Atmos. Chem. Phys.

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Abstract. Accurate depictions of the tropopause and its changes are important for studies on stratosphere–troposphere exchange and climate change. Here, the fidelity of primary lapse-rate tropopause altitudes and double tropopause frequencies in four modern reanalyses (ERA-Interim, JRA-55, MERRA-2, and CFSR) is examined using global radiosonde observations. In addition, long-term trends (1981–2015) in these tropopause properties are diagnosed in both the reanalyses and radiosondes. It is found that reanalyses reproduce observed tropopause altitudes with little bias (typically less than ±150 m) and error comparable to the model vertical resolution. All reanalyses underestimate the double tropopause frequency (up to 30 % lower than observed), with the largest biases found in JRA-55 and the smallest in CFSR. The underestimates in double tropopause frequency are primarily attributable to the coarse vertical resolution of the reanalyses. Significant increasing trends in both tropopause altitude (40–120 m per decade) and double tropopause frequency (≥3 % per decade) were found in both the radiosonde observations and the reanalyses over the 35-year analysis period (1981–2015). ERA-Interim, JRA-55, and MERRA-2 broadly reproduce the patterns and signs of observed significant trends, while CFSR is inconsistent with the remaining datasets. Trends were diagnosed in both the native Eulerian coordinate system of the reanalyses (fixed longitude and latitude) and in a coordinate system where latitude is defined relative to the mean latitude of the tropopause break (the discontinuity in tropopause altitude between the tropics and extratropics) in each hemisphere. The coordinate relative to the tropopause break facilitates the evaluation of tropopause behavior within the tropical and extratropical reservoirs and revealed significant differences in trend estimates compared to the traditional Eulerian analysis. Notably, increasing tropopause altitude trends were found to be of greater magnitude in coordinates relative to the tropopause break, and increasing double tropopause frequency trends were found to occur primarily poleward of the tropopause break in each hemisphere.

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Section: Conclusion and Discussionmentioning

confidence: 99%

Global tropopause altitudes in radiosondes and reanalyses

Xian

Homeyer

2019

Atmos. Chem. Phys.

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“…The forecast error difference peaks at a later time in the SH (120 h in contrast to 102 h for the NH). This might be related to the time spent for the impact of stratospheric temperature gradient correction to reach the mid‐tropospheric geopotential; in turn a chain reaction is involved, composed of the stratospheric polar vortex, upper‐tropospheric jet stream, and tropospheric baroclinic eddies (Polavarapu and Pulido, ; Tripathi et al ., ). This hypothesis needs to be verified in the future.…”

Section: Resultsmentioning

confidence: 99%

Effects of the wind–mass balance constraint on ensemble forecasts in the hybrid‐4DEnVar

Song

Kang

2019

Quart J Royal Meteoro Soc

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Ensemble forecast covariance plays an important role in the hybridized background error covariance framework to improve the resultant analysis quality. However, a localization of ensemble samples is needed to fully take advantage of flow-dependent error modes. In this regard, it is an interesting and practical issue as to which variables, composing the ensemble perturbation, the localization should be applied to. This study examines this issue in a boreal-summer month by comparing two experimental sets: (a) a set of model variables, and (b) another set of model wind variables and unbalanced dry mass (temperature and surface pressure) used for the control variables. In the comparison, it is shown that imposing the wind-mass balance on the ensemble perturbation improves the Antarctic lower-stratospheric temperature and tropical mid-/lower-tropospheric humidity. The nonlinear wind-mass balance relationship smooths an evolution of humidity forecast forced by the resultant analysis increments.

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“…The internally generated planetary waves are expected to propagate up to the upper mesosphere and lower thermosphere [Garcia et al, 2005;Chandran et al, 2013;Sassi and Liu, 2014]; however, the MERRA reanalysis is available up to 0.1 hPa (while GEOS-5 model reaches 0.01 hPa). We also note that the highest levels of MERRA reanalysis are less constrained from observations (channel 14 of the Advanced Microwave Sounding Unit (AMSU) peaks at 1 hPa [Polavarapu and Pulido, 2017]). However, these heights are partially constrained by observational information propagating upward in the assimilation system.…”

Section: 1002/2017jd026597mentioning

confidence: 94%

A climatology of Rossby wave generation in the middle atmosphere of the Southern Hemisphere from MERRA reanalysis

Rodas

Pulido

2017

JGR Atmospheres

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A climatological characterization of Rossby wave generation events in the middle atmosphere of the Southern Hemisphere is conducted using 20 years of Modern‐Era Retrospective Analysis for Research and Applications (MERRA) reanalysis. An automatic detection technique of wave generation events is developed and applied to MERRA reanalysis. The Rossby wave generation events with wave period of 1.25 to 5.5 days and zonal wave number from one to three dominate the Eliassen‐Palm flux divergence around the stratopause at high latitudes in the examined 20 year period. These produce an eastward forcing of the general circulation between May and mid‐August in that region. Afterward from mid‐August to the final warming date, Rossby wave generation events are still present but the Eliassen‐Palm flux divergence in the polar stratopause is dominated by low‐frequency Rossby waves that propagate from the troposphere. The Rossby wave generation events are associated with potential vorticity gradient inversion, and so they are a manifestation of the dominant barotropic/baroclinic unstable modes that grow at the cost of smearing the negative meridional gradient of potential vorticity. The most likely region of wave generation is found between 60° and 80°S and at a height of 0.7 hPa, but events were detected from 40 hPa to 0.3 hPa (which is the top of the examined region). The mean number of events per year is 24, and its mean duration is 3.35 days. The event duration follows an exponential distribution.

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Stratospheric and Mesospheric Data Assimilation: The Role of Middle Atmospheric Dynamics

Cited by 12 publications

References 83 publications

Global tropopause altitudes in radiosondes and reanalyses

Global tropopause altitudes in radiosondes and reanalyses

Effects of the wind–mass balance constraint on ensemble forecasts in the hybrid‐4DEnVar

A climatology of Rossby wave generation in the middle atmosphere of the Southern Hemisphere from MERRA reanalysis

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