A process-oriented evaluation of CAMS reanalysis ozone during tropopause folds over Europe for the period 2003–2018

Abstract. Tropopause folds are the key process underlying stratosphere-to-troposphere transport (STT) of ozone, thus, affecting tropospheric ozone levels and variability. In the present study we perform a process-oriented evaluation of Copernicus Atmosphere Monitoring Service (CAMS) reanalysis (CAMSRA) O3 during folding events, over Europe and for the time period from 2003 to 2018. A 3-D labeling algorithm is applied to detect tropopause folds in CAMSRA, while ozonesonde data from WOUDC (World Ozone and Ultraviolet Radiation Data Centre) and aircraft measurements from IAGOS (In-service Aircraft for a Global Observing System) are used for CAMSRA O3 evaluation. The profiles of observed and CAMSRA O3 concentrations indicate that CAMSRA reproduces the observed O3 increases in the troposphere during the examined folding events. Nevertheless, at some of the examined sites, CAMSRA overestimates the observed O3 concentrations, mostly at the upper portion of the observed increases, with a median fractional gross error (FGE) among the examined sites > 0.2 above 400 hPa. The use of a control run without data assimilation, reveals that the aforementioned overestimation of CAMSRA O3 arises from the data assimilation implementation. Overall, although data assimilation assists CAMSRA O3 to follow the observed O3 enhancements in the troposphere during the STT events, it introduces biases in the upper troposphere resulting in no clear quantitative improvement compared to the control run without data assimilation. Less biased assimilated O3 products, with finer vertical resolution in the troposphere, in addition to higher IFS (Integrated Forecasting System) vertical resolution, are expected to provide a better representation of O3 variability during tropopause folds.

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Aircraft measurements of gravity waves in the upper troposphere and lower stratosphere during the START08 field experiment

Atmospheric Chemistry and Physics ◽

10.5194/acp-15-7667-2015 ◽

2015 ◽

Vol 15 (13) ◽

pp. 7667-7684 ◽

Cited By ~ 13

Author(s):

Fuqing Zhang ◽

Junhong Wei ◽

Meng Zhang ◽

K. P. Bowman ◽

L. L. Pan ◽

...

Keyword(s):

Power Law ◽

Gravity Waves ◽

Lower Stratosphere ◽

Potential Temperature ◽

Shear Instability ◽

Aircraft Measurements ◽

Upper Troposphere ◽

Airborne Measurements ◽

Wide Range

Abstract. This study analyzes in situ airborne measurements from the 2008 Stratosphere–Troposphere Analyses of Regional Transport (START08) experiment to characterize gravity waves in the extratropical upper troposphere and lower stratosphere (ExUTLS). The focus is on the second research flight (RF02), which took place on 21–22 April 2008. This was the first airborne mission dedicated to probing gravity waves associated with strong upper-tropospheric jet–front systems. Based on spectral and wavelet analyses of the in situ observations, along with a diagnosis of the polarization relationships, clear signals of mesoscale variations with wavelengths ~ 50–500 km are found in almost every segment of the 8 h flight, which took place mostly in the lower stratosphere. The aircraft sampled a wide range of background conditions including the region near the jet core, the jet exit and over the Rocky Mountains with clear evidence of vertically propagating gravity waves of along-track wavelength between 100 and 120 km. The power spectra of the horizontal velocity components and potential temperature for the scale approximately between ~ 8 and ~ 256 km display an approximate −5/3 power law in agreement with past studies on aircraft measurements, while the fluctuations roll over to a −3 power law for the scale approximately between ~ 0.5 and ~ 8 km (except when this part of the spectrum is activated, as recorded clearly by one of the flight segments). However, at least part of the high-frequency signals with sampled periods of ~ 20–~ 60 s and wavelengths of ~ 5–~ 15 km might be due to intrinsic observational errors in the aircraft measurements, even though the possibilities that these fluctuations may be due to other physical phenomena (e.g., nonlinear dynamics, shear instability and/or turbulence) cannot be completely ruled out.

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Implementation of altimeter data assimilation on a regional wave forecasting system and its impact on wave and swell surge forecast in the Indian Ocean

Ocean Engineering ◽

10.1016/j.oceaneng.2021.109585 ◽

2021 ◽

Vol 237 ◽

pp. 109585

Author(s):

M. Seemanth ◽

P.G. Remya ◽

Suchandra Aich Bhowmick ◽

Rashmi Sharma ◽

T.M. Balakrishnan Nair ◽

...

Keyword(s):

Indian Ocean ◽

Data Assimilation ◽

Altimeter Data ◽

Forecasting System ◽

The Indian Ocean ◽

Wave Forecasting

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Implementation and validation of a new operational wave forecasting system of the Mediterranean Monitoring and Forecasting Centre in the framework of the Copernicus Marine Environment Monitoring Service

Natural Hazards and Earth System Science ◽

10.5194/nhess-18-2675-2018 ◽

2018 ◽

Vol 18 (10) ◽

pp. 2675-2695 ◽

Cited By ~ 7

Author(s):

Michalis Ravdas ◽

Anna Zacharioudaki ◽

Gerasimos Korres

Keyword(s):

Mediterranean Sea ◽

Marine Environment ◽

Model Performance ◽

Environment Monitoring ◽

Marine Research ◽

Forecasting System ◽

The Mediterranean ◽

Marine Environment Monitoring ◽

Monitoring Service ◽

Wave Forecasting

Abstract. Within the framework of the Copernicus Marine Environment Monitoring Service (CMEMS), an operational wave forecasting system for the Mediterranean Sea has been implemented by the Hellenic Centre for Marine Research (HCMR) and evaluated through a series of preoperational tests and subsequently for 1 full year of simulations (2014). The system is based on the WAM model and it has been developed as a nested sequence of two computational grids to ensure that occasional remote swell propagating from the North Atlantic correctly enters the Mediterranean Sea through the Strait of Gibraltar. The Mediterranean model has a grid spacing of 1∕24∘. It is driven with 6-hourly analysis and 5-day forecast 10 m ECMWF winds. It accounts for shoaling and refraction due to bathymetry and surface currents, which are provided in offline mode by CMEMS. Extensive statistics on the system performance have been calculated by comparing model results with in situ and satellite observations. Overall, the significant wave height is accurately simulated by the model while less accurate but reasonably good results are obtained for the mean wave period. In both cases, the model performs optimally at offshore wave buoy locations and well-exposed Mediterranean subregions. Within enclosed basins and near the coast, unresolved topography by the wind and wave models and fetch limitations cause the wave model performance to deteriorate. Model performance is better in winter when the wave conditions are well defined. On the whole, the new forecast system provides reliable forecasts. Future improvements include data assimilation and higher-resolution wind forcing.

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Development of the Forecasting System of the Current from Sacrificial Anodes of Marine Structures using Data Assimilation

Zairyo-to-Kankyo ◽

10.3323/jcorr.63.43 ◽

2014 ◽

Vol 63 (2) ◽

pp. 43-49

Author(s):

Naoki Yoneya ◽

Yoshikazu Akira ◽

Kenkichi Tashiro ◽

Tomohiro Iida ◽

Toru Yamaji ◽

...

Keyword(s):

Data Assimilation ◽

Marine Structures ◽

Sacrificial Anodes ◽

Forecasting System ◽

Using Data

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A GSI-Based Coupled EnSRF–En3DVar Hybrid Data Assimilation System for the Operational Rapid Refresh Model: Tests at a Reduced Resolution

Monthly Weather Review ◽

10.1175/mwr-d-13-00242.1 ◽

2014 ◽

Vol 142 (10) ◽

pp. 3756-3780 ◽

Cited By ~ 40

Author(s):

Yujie Pan ◽

Kefeng Zhu ◽

Ming Xue ◽

Xuguang Wang ◽

Ming Hu ◽

...

Keyword(s):

Data Assimilation ◽

Hybrid System ◽

Control Variable ◽

Three Dimensional ◽

Horizontal Resolution ◽

Precipitation Forecast ◽

Background Error ◽

Hybrid Data Assimilation ◽

Noticeable Improvement ◽

Forecasting System

Abstract A coupled ensemble square root filter–three-dimensional ensemble-variational hybrid (EnSRF–En3DVar) data assimilation (DA) system is developed for the operational Rapid Refresh (RAP) forecasting system. The En3DVar hybrid system employs the extended control variable method, and is built on the NCEP operational gridpoint statistical interpolation (GSI) three-dimensional variational data assimilation (3DVar) framework. It is coupled with an EnSRF system for RAP, which provides ensemble perturbations. Recursive filters (RF) are used to localize ensemble covariance in both horizontal and vertical within the En3DVar. The coupled En3DVar hybrid system is evaluated with 3-h cycles over a 9-day period with active convection. All conventional observations used by operational RAP are included. The En3DVar hybrid system is run at ⅓ of the operational RAP horizontal resolution or about 40-km grid spacing, and its performance is compared to parallel GSI 3DVar and EnSRF runs using the same datasets and resolution. Short-term forecasts initialized from the 3-hourly analyses are verified against sounding and surface observations. When using equally weighted static and ensemble background error covariances and 40 ensemble members, the En3DVar hybrid system outperforms the corresponding GSI 3DVar and EnSRF. When the recursive filter coefficients are tuned to achieve a similar height-dependent localization as in the EnSRF, the En3DVar results using pure ensemble covariance are close to EnSRF. Two-way coupling between EnSRF and En3DVar did not produce noticeable improvement over one-way coupling. Downscaled precipitation forecast skill on the 13-km RAP grid from the En3DVar hybrid is better than those from GSI 3DVar analyses.

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Evaluation of near-tropopause ozone distributions in the Global Modeling Initiative combined stratosphere/troposphere model with ozonesonde data

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-8-1589-2008 ◽

2008 ◽

Vol 8 (1) ◽

pp. 1589-1634 ◽

Cited By ~ 2

Author(s):

D. B. Considine ◽

J. A. Logan ◽

M. A. Olsen

Keyword(s):

Annual Cycle ◽

Transport Model ◽

Model Simulation ◽

Atmospheric Composition ◽

Vertical Resolution ◽

Residual Circulation ◽

Vertical Diffusion ◽

Global Modeling ◽

Upper Troposphere ◽

The Tropics

Abstract. The NASA Global Modeling Initiative has developed a combined stratosphere/troposphere chemistry and transport model which fully represents the processes governing atmospheric composition near the tropopause. We evaluate model ozone distributions near the tropopause, using two high vertical resolution monthly mean ozone profile climatologies constructed with ozonesonde data, one by averaging on pressure levels and the other relative to the thermal tropopause. Model ozone is high-biased at the SH tropical and NH midlatitude tropopause by ~45% in a 4° latitude × 5° longitude model simulation. Increasing the resolution to 2°×2.5&deg increases the NH tropopause high bias to ~60%, but decreases the tropical tropopause bias to ~30%, an effect of a better-resolved residual circulation. The tropopause ozone biases appear not to be due to an overly vigorous residual circulation or excessive stratosphere/troposphere exchange, but are more likely due to insufficient vertical resolution or excessive vertical diffusion near the tropopause. In the upper troposphere and lower stratosphere, model/measurement intercomparisons are strongly affected by the averaging technique. NH and tropical mean model lower stratospheric biases are <20%. In the upper troposphere, the 2°×2.5&deg simulation exhibits mean high biases of ~20% and~35% during April in the tropics and NH midlatitudes, respectively, compared to the pressure-averaged climatology. However, relative-to-tropopause averaging produces upper troposphere high biases of ~30% and 70% in the tropics and NH midlatitudes. This is because relative-to-tropopause averaging better preserves large cross-tropopause O3 gradients, which are seen in the daily sonde data, but not in daily model profiles. The relative annual cycle of ozone near the tropopause is reproduced very well in the model Northern Hemisphere midlatitudes. In the tropics, the model amplitude of the near-tropopause annual cycle is weak. This is likely due to the annual amplitude of mean vertical upwelling near the tropopause, which analysis suggests is ~30% weaker than in the real atmosphere.

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Data assimilation of dust aerosol observations for CUACE/Dust forecasting system

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-7-8309-2007 ◽

2007 ◽

Vol 7 (3) ◽

pp. 8309-8332 ◽

Cited By ~ 16

Author(s):

T. Niu ◽

S. L. Gong ◽

G. F. Zhu ◽

H. L. Liu ◽

X. Q. Hu ◽

...

Keyword(s):

Data Assimilation ◽

Atmospheric Chemistry ◽

Three Dimensional ◽

System A ◽

Source Regions ◽

Operational Forecasts ◽

Forecasting System ◽

Dust Loading ◽

Data Assimilation System ◽

Assimilation System

Abstract. A data assimilation system (DAS) was developed for the Chinese Unified Atmospheric Chemistry Environment – Dust (CUACE/Dust) forecast system and applied in the operational forecasts of sand and dust storm (SDS) in spring 2006. The system is based on a three dimensional variational method (3D-Var) and uses extensively the measurements of surface visibility and dust loading retrieval from the Chinese geostationary satellite FY-2C. The results show that a major improvement to the capability of CUACE/Dust in forecasting the short-term variability in the spatial distribution and intensity of dust concentrations has been achieved, especially in those areas far from the source regions. The seasonal mean Threat Score (TS) over the East Asia in spring 2006 increased from 0.22 to 0.31 by using the data assimilation system, a 41% enhancement. The assimilation results usually agree with the dust loading retrieved from FY-2C and visibility distribution from surface meteorological stations, which indicates that the 3D-Var method is very powerful for the unification of observation and numerical modeling results.

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A nudging-based data assimilation method: the Back and Forth Nudging (BFN) algorithm

Nonlinear Processes in Geophysics ◽

10.5194/npg-15-305-2008 ◽

2008 ◽

Vol 15 (2) ◽

pp. 305-319 ◽

Cited By ~ 56

Author(s):

D. Auroux ◽

J. Blum

Keyword(s):

Data Assimilation ◽

Variational Method ◽

Burgers Equation ◽

Reconstruction Error ◽

Sea Surface ◽

Reference Trajectory ◽

Discrete Observations ◽

Lorenz Model ◽

Time Period ◽

The Difference

Abstract. This paper deals with a new data assimilation algorithm, called Back and Forth Nudging. The standard nudging technique consists in adding to the equations of the model a relaxation term that is supposed to force the observations to the model. The BFN algorithm consists in repeatedly performing forward and backward integrations of the model with relaxation (or nudging) terms, using opposite signs in the direct and inverse integrations, so as to make the backward evolution numerically stable. This algorithm has first been tested on the standard Lorenz model with discrete observations (perfect or noisy) and compared with the variational assimilation method. The same type of study has then been performed on the viscous Burgers equation, comparing again with the variational method and focusing on the time evolution of the reconstruction error, i.e. the difference between the reference trajectory and the identified one over a time period composed of an assimilation period followed by a prediction period. The possible use of the BFN algorithm as an initialization for the variational method has also been investigated. Finally the algorithm has been tested on a layered quasi-geostrophic model with sea-surface height observations. The behaviours of the two algorithms have been compared in the presence of perfect or noisy observations, and also for imperfect models. This has allowed us to reach a conclusion concerning the relative performances of the two algorithms.

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A Global Survey of Static Stability in the Stratosphere and Upper Troposphere

Journal of Climate ◽

10.1175/2009jcli3369.1 ◽

2010 ◽

Vol 23 (9) ◽

pp. 2275-2292 ◽

Cited By ~ 66

Author(s):

Kevin M. Grise ◽

David W. J. Thompson ◽

Thomas Birner

Keyword(s):

Inversion Layer ◽

Broad Band ◽

Static Stability ◽

Stability Field ◽

Vertical Resolution ◽

Quasi Biennial Oscillation ◽

Upper Troposphere ◽

Global Survey ◽

High Vertical Resolution

Abstract Static stability is a fundamental dynamical quantity that measures the vertical temperature stratification of the atmosphere. However, the magnitude and structure of finescale features in this field are difficult to discern in temperature data with low vertical resolution. In this study, the authors apply more than six years of high vertical resolution global positioning system radio occultation temperature profiles to document the long-term mean structure and variability of the global static stability field in the stratosphere and upper troposphere. The most pronounced feature in the long-term mean static stability field is the well-known transition from low values in the troposphere to high values in the stratosphere. Superposed on this general structure are a series of finer-scale features: a minimum in static stability in the tropical upper troposphere, a broad band of high static stability in the tropical stratosphere, increases in static stability within the core of the stratospheric polar vortices, and a shallow but pronounced maximum in static stability just above the tropopause at all latitudes [i.e., the “tropopause inversion layer” (TIL)]. The results shown here provide the first global survey of static stability using high vertical resolution data and also uncover two novel aspects of the static stability field. In the tropical lower stratosphere, the results reveal a unique vertically and horizontally varying static stability structure, with maxima located at ∼17 and ∼19 km. The upper feature peaks during the NH cold season and has its largest magnitude between 10° and 15° latitude in both hemispheres; the lower feature exhibits a weaker seasonal cycle and is centered at the equator. The results also demonstrate that the strength of the TIL is closely tied to stratospheric dynamic variability. The magnitude of the TIL is enhanced following sudden stratospheric warmings in the polar regions and the easterly phase of the quasi-biennial oscillation in the tropics.

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