Yves Rochon - Academia.edu (original) (raw)

Papers by Yves Rochon

The Arctic is recognized as one of the key areas of the globe, both in terms of its sensitivity t... more The Arctic is recognized as one of the key areas of the globe, both in terms of its sensitivity to climate change, and by the increasing economic activity that is expected with the opening up of Arctic areas in a warming climate. In addition, Arctic weather can have important influences in winter cold outbreaks of air which can affect Northern Hemisphere countries as far south as the subtropics with serious economic implications. Therefore, a revised assessment of Arctic satellite and surface observation capabilities and requirements is warranted, especially given the Arctic surface and upper air network is sparse. Observing System Simulation Experiments (OSSEs) are a powerful tool to assess added value of planned or hypothetical observing systems for weather analysis and prediction. This white paper reviews the current state of OSSE science with respect to the Arctic, and provides lines of investigation for the future, with a focus on weather and air quality observations in the Arc...

The supplemental material contains three complementary tables on comparisons of OMI and groundbas... more The supplemental material contains three complementary tables on comparisons of OMI and groundbased total column ozone measurements, followed by 20 complementary figures covering different topics, and the data graphically represented in the figures of the paper. Region Station name WMO ID + Latitude (deg) Longitude (deg) Elevation (m) Mean differences (%) [# of points]

An ensemble-variational inversion system is developed for the estimation of ammonia emissions usi... more An ensemble-variational inversion system is developed for the estimation of ammonia emissions using ammonia retrievals from the Cross-track Infrared Sounder (CrIS) for use in the Global Environmental Multiscale-Modelling Air quality and Chemistry (GEM-MACH) chemical weather model. A novel hybrid method to compare logarithmic retrieval parameters to model profiles is presented. Inversions for the monthly mean ammonia emissions over North America were performed for May to August 2016. Inversions using the hybrid comparison method increased ammonia emissions at most locations within the model domain, with total monthly mean emissions increasing by 11 %-41 %. The use of these revised emissions in GEM-MACH reduced biases with surface ammonia observations by as much as 25 %. The revised ammonia emissions also improved the forecasts of total (fine + coarse) ammonium and nitrate, as well as ammonium wet deposition, with biases decreasing by as much as 13 %, but they did not improve the forecasts of just the fine components of ammonium and nitrate. A comparison of biases resulting from inversions using different comparison methods shows favourable results for the hybrid comparison method.

We examine data assimilation coupling between meteorology and chemistry in the stratosphere from ... more We examine data assimilation coupling between meteorology and chemistry in the stratosphere from both weak and strong coupling strategies. The study was performed with the Canadian operational weather prediction Global Environmental Multiscale (GEM) model coupled online with the photochemical stratospheric chemistry developed at the Belgian Institute for Space Aeronomy, described in Part I. Here, the Canadian Meteorological Centre’s operational variational assimilation system was extended to include errors of chemical variables and cross-covariances between meteorological and chemical variables in a 3D-Var configuration, and we added the adjoint of tracer advection in the 4D-Var configuration. Our results show that the assimilation of limb sounding observations from the MIPAS instrument on board Envisat can be used to anchor the AMSU-A radiance bias correction scheme. Also, the added value of limb sounding temperature observations on meteorology and transport is shown to be signific...

Geoscientific Model Development, 2018

A study was undertaken to improve upon the prognosticative capability of Environment and Climate ... more A study was undertaken to improve upon the prognosticative capability of Environment and Climate Change Canada's (ECCC) UV Index forecast model. An aspect of that work, and the topic of this communication, was to investigate the use of the four UV broadband surface irradiance fields generated by ECCC's Global Environmental Multiscale (GEM) numerical prediction model to determine the UV Index. The basis of the investigation involves the creation of a suite of routines which employ high-spectral-resolution radiative transfer code developed to calculate UV Index fields from GEM forecasts. These routines employ a modified version of the Cloud-J v7.4 radiative transfer model, which integrates GEM output to produce high-spectral-resolution surface irradiance fields. The output generated using the highresolution radiative transfer code served to verify and calibrate GEM broadband surface irradiances under clear-sky conditions and their use in providing the UV Index. A subsequent comparison of irradiances and UV Index under cloudy conditions was also performed. Linear correlation agreement of surface irradiances from the two models for each of the two higher UV bands covering 310.70-330.0 and 330.03-400.00 nm is typically greater than 95 % for clear-sky conditions with associated rootmean-square relative errors of 6.4 and 4.0 %. However, underestimations of clear-sky GEM irradiances were found on the order of ∼ 30-50 % for the 294.12-310.70 nm band and by a factor of ∼ 30 for the 280.11-294.12 nm band. This underestimation can be significant for UV Index determination but would not impact weather forecasting. Corresponding empirical adjustments were applied to the broadband irradiances now giving a correlation coefficient of unity. From these, a least-squares fitting was derived for the calculation of the UV Index. The resultant differences in UV indices from the high-spectral-resolution irradiances and the resultant GEM broadband irradiances are typically within 0.2-0.3 with a root-mean-square relative error in the scatter of ∼ 6.6 % for clear-sky conditions. Similar results are reproduced under cloudy conditions with light to moderate clouds, with a relative error comparable to the clear-sky counterpart; under strong attenuation due to clouds, a substantial increase in the root-mean-square relative error of up to 35 % is observed due to differing cloud radiative transfer models.

Atmospheric Chemistry and Physics Discussions, 2018

The impact of assimilating total column ozone datasets from single and multiple satellite data so... more The impact of assimilating total column ozone datasets from single and multiple satellite data sources with and without bias correction has been examined with a version of the Environment and Climate Change Canada variational assimilation and forecasting system. The assimilated and evaluated data sources include the Global Ozone Monitoring Experiment-2 instruments on the MetOp-A and MetOp-B satellites (GOME-2A and GOME-2B), the total column ozone mapping instrument of the Ozone Mapping Profiler Suite (OMPS-NM) on the Suomi National Polar-orbiting Partnership (S-NPP) satellite, and the Ozone Monitoring Instrument (OMI) instrument on the Aura research satellite. Ground-based Brewer and Dobson spectrophotometers, and filter ozonometers, as well as the Solar Backscatter Ultraviolet satellite instrument (SBUV/2), served as independent validation sources for total column ozone. Regional and global mean differences of the OMI-TOMS data with measurements from the three ground-based instrument types for the three evaluated two month periods were found to be within 1 %, except for the polar regions with the largest differences from the comparatively small dataset in Antarctica exceeding 3 %. Values from SBUV/2 summed partial columns were typically larger than OMI-TOMS on average by 0.6 to 1.2±0.7 %, with smaller differences than with ground-based over Antarctica. The OMI-TOMS dataset was chosen as the reference used in the bias correction instead of the ground-based observations due to OMI's significantly better spatial and temporal coverage and interest in near-real time assimilation. Bias corrections as a function of latitude and solar zenith angle were performed with a two-week moving window using colocation with OMI-TOMS and three variants of differences with short-term forecasts. These approaches are shown to yield residual biases of less than 1 %, with the rare exceptions associated with bins with less data. These results were compared to a time-independent bias correction estimation that used colocations as a function of ozone effective temperature and solar zenith angle which, for the time period examined, resulted in larger changes in residual biases as a function of time for some cases. Assimilation experiments for the July-August 2014 period show a reduction of global and temporal mean biases for short-term forecasts relative to groundbased Brewer and Dobson data from a maximum of about 2.3 % in the absence of bias correction to less than 0.3 % in size when bias correction is included. Both temporally averaged and time varying mean differences of forecasts with OMI-TOMS are reduced to within 1 % for nearly all cases when bias corrected observations are assimilated for the latitudes where satellite data are present. The impact of bias correction on the standard deviations and anomaly correlation coefficients of

An Observing System Simulation Experiment (OSSE) is performed to evaluate the impact of atmospher... more An Observing System Simulation Experiment (OSSE) is performed to evaluate the impact of atmospheric motion vectors (AMVs) made available from the future polar Communications and weather (PCW) mission. PCW is a 2-satellite constellation on a highly elliptical orbit (HEO) which will fill the AMV observation gap in the Arctic. All currently assimilated data types at Environment Canada are simulated. A nature run (NR) is used as truth. The HEO AMVs are extracted from NR cloud tops every 6 hours. Simulated observations are perturbed appropriately. Assimilation cycles are run in 3D-var. The control experiments include geostationary AMV, and it can exclude or include currently available polar AMVs from MODIS or AVHRR. The test experiment includes HEO AMVs in area 50-90 o N. When comparing cycles with no AMV versus one with PCW AMVs, results indicate a clear positive impact, not only in region 50-90 o N, but also in region 20-50 o N. The gain in predictability at days 3-5 is of the order of...

The Stratospheric Wind Interferometer For Transport studies (SWIFT) is a Canadian satellite instr... more The Stratospheric Wind Interferometer For Transport studies (SWIFT) is a Canadian satellite instrument designed to measure stratospheric winds and ozone densities. The measurement technique is known as Doppler Michelson Imaging Interferometry. This paper describes a mission simulation for SWIFT which includes the instrument simulation, simulation of the measurement along the orbit and performing the data processing accordingly. The mission simulation is carried out to assess instrument performance and test the SWIFT data reduction algorithms. The mission simulation also includes error analysis. One of the aspects of the error analysis is to evaluate the impact of the instrument characteristics on wind error. The error analysis can be used to assess different instrument configurations and measurement scenarios and can serve to suggest optimum ways for processing the data. The simulations and error analysis are repeated for various design options in order to quantify the expected SWIF...

Tellus A, 2009

Numerical experiments are used to assess the potential benefit of the assimilation of tropospheri... more Numerical experiments are used to assess the potential benefit of the assimilation of tropospheric and stratospheric observations on mesospheric prediction. A simulated atmosphere taken as truth is created using the Canadian Middle Atmosphere Model (CMAM). The truth is sampled at the locations of the measurements from the actual observing system to produce observations which are then assimilated with the CMAM-DAS (Data Assimilation System). Obtained forecasts are compared with the truth and error statistics are calculated. An assessment based on predictability shows that upward propagation of information resulting from the assimilation of tropospheric and stratospheric observations improves the mesosphere in the largest scales (with horizontal wavenumbers less than approximately 10). At the same time, the principle inability of the system to predict mesospheric small scales is demonstrated.

Reviews of Geophysics, 2012

The Wind Imaging Interferometer (WINDII) was launched on the NASA's Upper Atmosphere Research Sat... more The Wind Imaging Interferometer (WINDII) was launched on the NASA's Upper Atmosphere Research Satellite on 12 September 1991 and operated until 2003. Its role in the mission was to measure vector winds in the Earth's atmosphere from 80 to 110 km, but its measurements extended to nearly 300 km. The approach employed was to measure Doppler shifts from a suite of visible region airglow lines emitted over this altitude range. These included atomic oxygen O(1 S) and O(1 D) lines, as well as lines in the OH Meinel (8,3) and O 2 Atmospheric (0,0) bands. The instrument employed was a Doppler Michelson Interferometer that measured the Doppler shift as a phase shift of the cosinusoidal interferogram generated by single airglow lines. An extensive validation program was conducted after launch to confirm the accuracy of the measurements. The dominant wind field, the first one observed by WINDII, was that of the migrating diurnal tide at the equator. The overall most notable WINDII contribution followed from this: determining the influence of dynamics on the transport of atmospheric species. Currently, nonmigrating tides are being studied in the thermosphere at both equatorial and high latitudes. Other aspects investigated included solar and geomagnetic influences, temperatures from atmospheric-scale heights, nitric oxide concentrations, and the occurrence of polar mesospheric clouds. The results of these observations are reviewed from a perspective of 20 years. A future perspective is then projected, involving more recently developed concepts. It is intended that this description will be helpful for those planning future missions.

Quarterly Journal of the Royal Meteorological Society, 2009

... Yulia Nezlin,1* Saroja Polavarapu2 and Yves J. Rochon2 1Department of Physics, University of ... more ... Yulia Nezlin,1* Saroja Polavarapu2 and Yves J. Rochon2 1Department of Physics, University of Toronto, Canada 2Atmospheric Science and ... It was applied to the Canadian Middle Atmosphere Model Data Assimilation System (CMAM-DAS) to choose among various filtering ...

Quarterly Journal of the Royal Meteorological Society, 2007

Monthly Weather Review, 2004

Incremental analysis updating (IAU) refers to a method of smoothly inserting instantaneous analys... more Incremental analysis updating (IAU) refers to a method of smoothly inserting instantaneous analysis increments into a numerical model by spreading the increments over a time period. In this work, this method is shown to be identical to applying a digital filter to the time evolution of analysis increments [a method known as incremental digital filtering (IDF)] for the case of linear models with time-invariant coefficients. The equivalence of the two methods can be used to show that the constant weights typically employed in IAU applications result in too much damping of long waves. For weakly nonlinear models, the two methods will not produce identical filtered states even if the filter coefficients are the same. The implications of the similarities and differences of the two methods are discussed.

Journal of Geophysical Research, 2007

Journal of Geophysical Research, 2011

Journal of Geophysical Research, 1993

Journal of Geophysical Research, 2004

Journal of Geophysical Research: Atmospheres, 1996

This paper describes the current state of the validation of wind measurements by the wind imaging... more This paper describes the current state of the validation of wind measurements by the wind imaging interferometer (WINDII) in the 0(1S) emission. Most data refer to the 90-to-l10-km region. Measurements from orbit are compared with winds derived from ground-based observations using optical interferometers, MF re[de[rs and the European Incoherent-Scatter radar (EISCAT) during overpasses of the WINDII fields of view. Although the data from individual passes do not always agree well, the averages indicate good agreement for the zero reference between the winds measured on the ground and those obtained from orbit. A comparison with winds measured by the high resolution Doppler imager (HRDI) instrument on UARS has also been made, with excellent results. With one exception the WINDII zero wind reference agrees with all external measurement methods to within 10 m s-• at the present time. The exception is the MF radar winds, which show large station-to-station differences. The subject of WINDII comparisons with MF radar winds requires further study. The thermospheric O(•S) emission region is less amenable to validation, but comparisons with EISCAT radar data give excellent agreement at 170 km. A zero wind calibration has been obtained for the O(•D) emission by comparing its averaged phase with that for 0(1S) on several days when alternating 1D/•S measurements were made. Several other aspects of the WINDII performance have been studied using data from on-orbit measurements. These concern the instrument 's phase stability, its pointing, its responsivity, the phase distribution in the fields of view, and the behavior of two of the interference filters. In some cases, small adjustments have been made to the characterization database used to analyze the atmospheric data. In general, the WINDII characteristics have remained very stable during the mission to date. A discussion of measurement errors is included in the paper. Further study of the instrument performance may bring improvement, but the utimate limitation for wind validation appears to be atmospheric variability and this needs to be better understood.

Advances in Space Research, 1996

ABSTRACT The WINDII imager on UARS provides measurements of the integral emission rate emitted fr... more ABSTRACT The WINDII imager on UARS provides measurements of the integral emission rate emitted from the atmosphere along the line-of-sight viewing the Earth's limb. The auroral OI 557.7 nm and the N2 1PG emissions are among various selected auroral emissions observed by WINDII. Simultaneous ground-based photometric measurements of the OI 557.7 nm and N2+ 1NG emissions from CANOPUS, when available, allow the derivation of volume emission rate profiles by the employment of a 2-D inversion method. Using the N2 1PG volume emission rate, which is proportional to the total energy flux, the OI 557.7 nm emission has been modelled and compared with the experimental OI 557.7 nm emission. The emission rate ratios were interpreted in terms of atomic oxygen density. It is shown that [O] inferred from the experiment varies significantly in magnitude and scale height from the MSIS neutral atmosphere predictions.