Ryoichi Imasu

TransCom model simulations of hourly atmospheric CO2: Analysis of synoptic-scale variations for the period 2002-2003

The ability to reliably estimate CO2 fluxes from current in situ atmospheric CO2 measurements and future satellite CO2 measurements is dependent on transport model performance at synoptic and shorter timescales. The TransCom continuous experiment was designed to evaluate the performance of forward transport model simulations at hourly, daily, and synoptic timescales, and we focus on the latter two in this paper. Twenty-five transport models or model variants submitted hourly time series of nine predetermined tracers (seven for CO2) at 280 locations. We extracted synoptic-scale variability from daily averaged CO2 time series using a digital filter and analyzed the results by comparing them to atmospheric measurements at 35 locations. The correlations between modeled and observed synoptic CO2 variabilities were almost always largest with zero time lag and statistically significant for most models and most locations. Generally, the model results using diurnally varying land fluxes were closer to the observations compared to those obtained using monthly mean or daily average fluxes, and winter was often better simulated than summer. Model results at higher spatial resolution compared better with observations, mostly because these models were able to sample closer to the measurement site location. The amplitude and correlation of model-data variability is strongly model and season dependent. Overall similarity in modeled synoptic CO2 variability suggests that the first-order transport mechanisms are fairly well parameterized in the models, and no clear distinction was found between the meteorological analyses in capturing the synoptic-scale dynamics.

TransCom model simulations of hourly atmospheric CO2 : experimental overview and diurnal cycle results for 2002

[1] A forward atmospheric transport modeling experiment has been coordinated by the TransCom group to investigate synoptic and diurnal variations in CO2. Model simulations were run for biospheric, fossil, and air-sea exchange of CO2 and for SF6 and radon for 2000-2003. Twenty-five models or model variants participated in the comparison. Hourly concentration time series were submitted for 280 sites along with vertical profiles, fluxes, and meteorological variables at 100 sites. The submitted results have been analyzed for diurnal variations and are compared with observed CO2 in 2002. Mean summer diurnal cycles vary widely in amplitude across models. The choice of sampling location and model level account for part of the spread suggesting that representation errors in these types of models are potentially large. Despite the model spread, most models simulate the relative variation in diurnal amplitude between sites reasonably well. The modeled diurnal amplitude only shows a weak relationship with vertical resolution across models; differences in near-surface transport simulation appear to play a major role. Examples are also presented where there is evidence that the models show useful skill in simulating seasonal and synoptic changes in diurnal amplitude.

Imposing strong constraints on tropical terrestrial CO2 fluxes using passenger aircraft based measurements

[1] Because very few measurements of atmospheric carbon dioxide (CO2) are available in the tropics, estimates of surface CO2 fluxes in tropical regions are beset with considerable uncertainties. To improve estimates of tropical terrestrial fluxes, atmospheric CO2 inversion was performed using passenger aircraft based measurements of the Comprehensive Observation Network for Trace gases by Airliner (CONTRAIL) project in addition to the surface measurement data set of GLOBALVIEW–CO2. Regional monthly fluxes at the earth’s surface were estimated using the Bayesian synthesis approach focusing on the period 2006–2008 using the Nonhydrostatic Icosahedral Atmospheric Model-based Transport Model (NICAM-TM). By adding the aircraft to the surface data, the posterior flux errors were greatly reduced; specifically, error reductions of up to 64% were found for tropical Asia regions. This strong impact is closely related to efficient vertical transport in the tropics. The optimized surface fluxes using the CONTRAIL data were evaluated by comparing the simulated atmospheric CO2 distributions with independent aircraft measurements of the Civil Aircraft for the Regular Investigation of the atmosphere Based on an Instrument Container (CARIBIC) project. The inversion with the CONTRAIL data yields the global carbon sequestration rates of 2.22 � 0.28 Pg C yr � 1 for the terrestrial biosphere and 2.24 � 0.27 Pg C yr � 1 for the oceans (the both are adjusted by riverine input of CO2). For the first time the CONTRAIL CO2 measurements were used in an inversion system to identify the areas of greatest impact in terms of reducing flux uncertainties.

Sensing HDO/H2O in the Ural’s atmosphere using ground-based measurements of IR solar radiation with a high spectral resolution

The Ural Atmospheric Fourier Station (UAFS) based on a Bruker IFS-125M Fourier spectrometer conjugated with an A547N automated solar tracker is described. The UAFS is located in the forest area (57.038°N; 59.545°E) and is intended for trace gas monitoring in the background atmosphere. The examples of solar-radiation near-IR atmospheric transmittance spectra measured with a high spectral resolution are presented, as well as the first results of retrieval of the heavy water fraction in the Ural atmosphere.

Retrieval of minor constituents from thermal infrared spectra observed by GOSAT TANSO-FTS sensor

The thermal infrared band of the main sensor of the greenhouse gas observing satellite (GOSAT), the TANSO-FTS, must be calibrated with accuracy higher than 0.3 K in the brightness temperature Tbb for retrieving CO2 concentration with accuracy of 1% in the upper atmosphere. However, that accuracy has not been achieved because of some error sources. One is the systematic bias in the radiance spectrum resulting from effects of radiation emitted from internal optics and multiple scattering of target signals. Another is the polarization effect of the pointing mirror. Both effects can be merged into two parameters, gain and offset, in the two point calibration procedure. They can be tuned by comparing the spectrum with well-calibrated spectra such as those from the AIRS sensor. Based on the corrected radiance spectra, global CO2 concentrations were processed. However, they show peculiar latitudinal distribution implying the existence of temporally variant parameters that can affect the calibration. This bias can be reduced by referring to housekeeping data of the satellite in the calibration procedure. The stratospheric ozone distribution is also analyzed. The sensor demonstrated the difference in the ozone hole feature between spring 2009 and 2010 over the South Pole.

Seasonal methane content in atmosphere of the permafrost boundary zone in Western Siberia determined from IMG/ADEOS and AIRS/AQUA data

To quantify carbon exchange fluxes in subarctic peatlands, new techniques and software for monitoring of methane using high-resolution emission spectra of atmosphere observed from Space have been developed. Neural network technique is promissing for nstantaneous retrieval of methane content in atmosphere from huge amount of data provided by AIRS/AQUA sensor. IMG/ADEOS data, FIRE-ARMS forward simulations and retrieval of methane profiles from IMG spectra on the base of constrained optimization were used for the purposes of validation of the neural network techniques applied to AIRS/AQUA data. Preliminary maps of methane content in atmosphere of the permafrost boundary zone in Western Siberia are obtained from AIRS/AQUA data.

Chapter 2: Evaluation and Selection of CFC Alternatives

Abstract This chapter reports on the effect of fluorine compounds in the atmosphere. These compounds have been evaluated for their role in ozone layer depletion and global warming. The state of their application, the use of alternatives and the alternatives themselves were analyzed. There are also explanations of the science behind ozone depletion potential and global-warming potential, of associated evaluation methods, and new methods that can compensate for previous deficiencies. The results suggest that fluorine compounds with short atmospheric lifetimes are suitable as chlorofluorocarbon alternatives.

The amplitude of the CO2 seasonal cycle in the atmosphere of the Ural region retrieved from ground-based and satellite near-IR measurements

A series of ground-based high-resolution Fourier-transform measurements of atmospheric transmittance in the near infrared region (4000–10000 cm−1) recorded at the Ural Atmospheric Station in 2012–2013 was processed in order to retrieve relative concentrations of CO2 and CH4 in the atmospheric column. Retrieved values of methane concentration do not show a noticeable seasonal cycle, while retrieved CO2 concentrations show clear seasonal variations with high amplitude, which are also observed in GOSAT measurements over the Ural region. The estimated amplitude of CO2 seasonal variations is 14–15 ppm. The comparison between CO2 ground-based and GOSAT measurements shows a good agreement, while satellite values are overestimated by approximately 3 ppm. There is no noticeable correlation between CH4 values, which could be explained by the presence of local methane sources in the area of GOSAT observations.

Radiometric calibration accuracy of GOSAT-TANSO-FTS (TIR) relating to CO2 retrieval error

Radiometric calibration accuracy of 0.3 K in Tbb is necessary to retrieve CO2 concentration profile with accuracy of 1 % in the upper atmosphere. In case of the thermal infrared (TIR) band (band 4) of GOSAT-TANSO-FTS, interferometric phase correction procedure is very important because the total transmittance of the optics at the band is about 70 % because of opacity of dichroic mirrors of band 1-3 placed obstructing the field of view of band 4, and the mirrors reflect the radiation emitted from inside of the optics. Based on the results from the thermal vacuum tests (TVTs) of the sensor, it is found that interferometric signal is almost zero when the sensor view a target of which temperature is about 280- 300K because the radiation emitted from inside of the spectrometer controlled at about 296 K has completely opposite phase to that of the target. It is also found that the interferometric final phase of the calibrated signal varies when the total signal is almost zero because of weak signals that have phases differ from both of those of targets and calibrators. A candidate phase correction procedure is proposed based on that adopted for a previous space FTS sensor, IMG/ADEOS. Non-linearity correction for the detector and polarization efficiency correction are also desccussed.

Latitudinal distribution of methane as observed by IMG sensor aboard ADEOS satellite

Interferometric Monitor for Greenhouse gases aboard advanced earth observing satellite (ADEOS) is a Fourier transform type spectrometer which had been developed for measuring greenhouse gases in the atmosphere, particularly in the troposphere. It had been operated for about 7 months from November 1996 up to the end of the life time of the ADEOS on June 1997. During the operational period IMG had measured over 138000 terrestrial thermal emission spectra of which the signal to noise ratio is sufficient for retrieving atmospheric parameters such as temperature and gas concentrations. As most of the data had been obtained during the 4-days operational period which had been scheduled twice in each system request period, we have obtained about 15 global data sets of the IMG data during the whole IMG operational period. A cloud detection and correction method which was based on the analysis of the initially retrieved temperature profiles were presented. Using the cloud correction method, latitudinal distribution of methane was preliminary analyzed and an example of the result was shown.