Introducing new lightning schemes into the CHASER (MIROC) chemistry climate model

Abstract. The formation of nitrogen oxides (NOx) associated with lightning activities (hereinafter designated as LNOx) is a major source of NOx. In fact, it is regarded as the most dominant NOx source in the upper troposphere. Therefore, improve the prediction accuracy of lightning and LNOx in chemical climate models is crucially important. This study implemented two new lightning schemes with the CHASER (MIROC) global chemical transport/climate model. The first lightning scheme is based on upward cloud ice flux (ICEFLUX scheme), whereas the second, also adopted in the European Centre for Medium-Range Weather Forecasts (ECMWF) forecasting system (original ECMWF scheme). In the case of the original ECMWF scheme, by tuning the equations and adjustment factors for land and ocean, a modified ECMWF scheme was also tested in CHASER. In the original version of CHASER (MIROC), lightning is initially parameterized with the widely used cloud top height scheme (CTH scheme). Model evaluations with lightning observations conducted using an optical transient detector (OTD) indicate that both the ICEFLUX and ECMWF schemes simulate the spatial distribution of lightning more accurately on a global scale than the CTH scheme does. The modified ECMWF scheme showed the highest prediction accuracy for the global distribution of lightning. Validation by atmospheric tomography (ATom) aircraft observations and tropospheric monitoring instrument (TROPOMI) satellite observations shows that the ICEFLUX scheme reduced the model biases to a greater extent than the ECMWF schemes when compared using the CTH scheme. The effects of the newly introduced lightning schemes on the tropospheric chemical fields were evaluated by comparison with the CTH scheme. Although the newly implemented lightning schemes have a minor effect on the tropospheric mean oxidation capacity compared to the CTH scheme, they led to marked change of oxidation capacity in different regions of the troposphere. Long-term trend analyses of flash and surface temperatures predicted using CHASER (2001–2020) show that lightning schemes predicted an increasing trend of lightning, except for the ICEFLUX scheme, which predicted a decreasing trend of lightning. The global lightning rates of increase during 2001–2020 predicted by the CTH scheme were 17.86 %/°C and 2.60 %/°C, respectively, with and without nudging, which are slightly beyond the range of an earlier study (5 %/°C–16 %/°C). Furthermore, the ECMWF schemes predicted a larger increasing trend of lightning flash rates under global warming by a factor of 3 (modified ECMWF scheme) and 5 (original ECMWF scheme) compared to the CTH scheme without nudging. In conclusion, the two new lightning schemes improved global lightning prediction in the CHASER model. However, further research is needed to assess the reproductivity of long-term trends of lightning. </jats:p

Primary Evaluation of the GCOM-C Aerosol Products at 380 nm Using Ground-Based Sky Radiometer Observations

The Global Change Observation Mission-Climate (GCOM-C) is currently the only satellite sensor providing aerosol optical thickness (AOT) in the ultraviolet (UV) region during the morning overpass time. The observations in the UV region are important to detect the presence of absorbing aerosols in the atmosphere. The recently available GCOM-C dataset of AOT at 380 nm for January to September 2019 were evaluated using ground-based SKYNET sky radiometer measurements at Chiba, Japan (35.62° N, 140.10° E) and Phimai, central Thailand (15.18° N, 102.56° E), representing urban and rural sites, respectively. AOT retrieved from sky radiometer observations in Chiba and Phimai was compared with coincident AERONET and multi-axis differential optical absorption spectroscopy (MAX-DOAS) AOT values, respectively. Under clear sky conditions, the datasets showed good agreement. The sky radiometer and GCOM-C AOT values showed a positive correlation (R) of ~0.73 for both sites, and agreement between the datasets was mostly within ±0.2 (the number of coincident points at both sites was less than 50 for the coincidence criterion of ≤30 km). At Chiba, greater differences in the AOT values were primarily related to cloud screening in the datasets. The mean bias error (MBE) (GCOM-C – sky radiometer) for the Chiba site was −0.02 for a coincidence criterion of ≤10 km. For a similar coincidence criterion, the MBE values were higher for observations at the Phimai site. This difference was potentially related to the strong influence of biomass burning during the dry season (Jan–Apr). The diurnal variations in AOT, inferred from the combination of GCOM-C and ozone monitoring instrument (OMI) observations, showed good agreement with the sky radiometer data, despite the differences in the absolute AOT values. Over Phimai, the AOT diurnal variations from the satellite and sky radiometer observations were different, likely due to the large differences in the AOT values during the dry season.</jats:p

Primary Evaluation of the GCOM-C Aerosol Products at 380 nm Using Ground-Based Sky Radiometer Observations

The Global Change Observation Mission-Climate (GCOM-C) is currently the only satellite sensor providing aerosol optical thickness (AOT) in the ultraviolet (UV) region during the morning overpass time. The observations in the UV region are important to detect the presence of absorbing aerosols in the atmosphere. The recently available GCOM-C dataset of AOT at 380 nm for January to September 2019 were evaluated using ground-based SKYNET sky radiometer measurements at Chiba, Japan (35.62&deg; N, 140.10&deg; E) and Phimai, central Thailand (15.18&deg; N, 102.56&deg; E), representing urban and rural sites, respectively. AOT retrieved from sky radiometer observations in Chiba and Phimai was compared with coincident AERONET and multi-axis differential optical absorption spectroscopy (MAX-DOAS) AOT values, respectively. Under clear sky conditions, the datasets showed good agreement. The sky radiometer and GCOM-C AOT values showed a positive correlation (R) of ~0.73 for both sites, and agreement between the datasets was mostly within &plusmn;0.2 (the number of coincident points at both sites was less than 50 for the coincidence criterion of &le;30 km). At Chiba, greater differences in the AOT values were primarily related to cloud screening in the datasets. The mean bias error (MBE) (GCOM-C &ndash; sky radiometer) for the Chiba site was &minus;0.02 for a coincidence criterion of &le;10 km. For a similar coincidence criterion, the MBE values were higher for observations at the Phimai site. This difference was potentially related to the strong influence of biomass burning during the dry season (Jan&ndash;Apr). The diurnal variations in AOT, inferred from the combination of GCOM-C and ozone monitoring instrument (OMI) observations, showed good agreement with the sky radiometer data, despite the differences in the absolute AOT values. Over Phimai, the AOT diurnal variations from the satellite and sky radiometer observations were different, likely due to the large differences in the AOT values during the dry season

Continuous multi-component MAX-DOAS observations for the planetary boundary layer ozone variation analysis at Chiba and Tsukuba, Japan, from 2013 to 2019

AbstractGround-based remote sensing using multi-axis differential optical absorption spectroscopy (MAX-DOAS) was used to conduct continuous simultaneous observations of ozone (O3), nitrogen dioxide (NO2), and formaldehyde (HCHO) concentrations at Chiba (35.63° N, 140.10° E, 21 m a.s.l.) and Tsukuba (36.06° N, 140.13° E, 35 m a.s.l.), Japan, for 7 years from 2013 to 2019. These are urban and suburban sites, respectively, in the greater Tokyo metropolitan area. NO2 and HCHO are considered to be proxies for nitrogen oxides (NOx) and volatile organic compounds (VOCs), respectively, both of which are major precursors of tropospheric O3. The mean concentrations below an altitude of 1 km were analyzed as planetary boundary layer (PBL) concentrations. For a more spatially representative analysis around the urban area of Chiba, four MAX-DOAS instruments directed at four different azimuth directions (north, east, west, and south) were operated simultaneously and their data were unified. During the 7-year period, the satellite observations indicated an abrupt decrease in the tropospheric NO2 concentration over East Asia, including China. This suggested that the transboundary transport of O3 originating from the Asian continent was likely suppressed or almost unchanged during the period. Over this time period, the MAX-DOAS observations revealed the presence of almost-constant annual variations in the PBL O3 concentration, whereas reductions in NO2 and HCHO concentrations occurred at rates of approximately 6–10%/year at Chiba. These changes provided clear observational evidence that a decreasing NOx concentration significantly reduced the amount of O3 quenched through NO titration under VOC-limited conditions in the urban area. Under the dominant VOC-limited conditions, the MAX-DOAS-derived concentration ratio of HCHO/NO2 was found to be below unity in all months. Thus, the multi-component observations from MAX-DOAS provided a unique data set of O3, NO2, and HCHO concentrations for analyzing PBL O3 variations.</jats:p

Peculiar COVID-19 effects in the Greater Tokyo Area revealed by spatiotemporal variabilities of tropospheric gases and light-absorbing aerosols

Abstract. This study investigated the spatiotemporal variabilities in nitrogen dioxide (NO2), formaldehyde (HCHO), ozone (O3), and light-absorbing aerosols within the Greater Tokyo Area, Japan, the most populous metropolitan area in the world. The analysis was based on total column, partial column, and in situ observations retrieved from multiple platforms and additional information obtained from reanalysis and box model simulations. This study mainly covers the 2013–2020 period, focusing on 2020, when air quality was influenced by the coronavirus disease 2019 (COVID-19) pandemic. In 2020 overall, NO2 concentrations were reduced by about 10 % annually, with reductions exceeding 40 % in some areas during the pandemic state of emergency. Light-absorbing aerosol levels were also reduced for most of 2020, while smaller fluctuations in HCHO and O3 were observed. Moreover, the degree of weekly cycling of NO2, HCHO, and light-absorbing aerosol levels was significantly enhanced in urban areas during 2020. The latter changes were unprecedented in recent years and potentially related to coincident reduced mobility in Japan, which, in contrast to other countries, was anomalously low on weekends in 2020. This finding suggests that, despite the lack of strict legal restrictions in Japan, widespread adherence to recommendations designed to limit the spread of the pandemic caused modification of common habits, resulting in unique air quality changes. </jats:p

MAX-DOAS observations of formaldehyde and nitrogen dioxide at three sites in Asia and comparison with the global chemistry transport model CHASER

Abstract. Formaldehyde (HCHO) and nitrogen dioxide (NO2) concentrations and profiles were retrieved from ground-based multi-axis differential optical absorption spectroscopy (MAX-DOAS) observations during January 2017 through December 2018 at three sites in Asia: (1) Phimai (15.18° N, 102.5° E), Thailand; (2) Pantnagar (29° N, 78.90° E) in the Indo Gangetic plain (IGP), India; and (3) Chiba (35.62° N, 140.10° E), Japan. The observations were used to evaluate the NO2 and HCHO partial columns and profiles (0–4 km) simulated using the global chemistry transport model (CTM) CHASER. The NO2 and HCHO concentrations at all three sites showed consistent seasonal variations throughout the investigated period. Biomass burning affected the HCHO and NO2 variation in Phimai during the dry season and in Pantnagar during spring (March–May) and post-monsoon (September–November). The results on the HCHO to NO2 ratio (RFN), an indicator of high ozone sensitivity, show that the transition region (i.e., 1&lt; RFN &lt; 2) changes regionally, echoing the recent finding on the effectiveness of RFN. Moreover, reasonable estimates of transition regions can be derived accounting for the NO2- HCHO chemical feedback. CHASER demonstrated good performances reproducing the HCHO and NO2 abundances at Phimai, mainly above 500 m from the surface. Model results agree with the measured variations, ranging within the one sigma standard deviation of the observations. Despite the complex terrain of Pantnagar (mountainous terrain), the modeled NO2 estimates between 1.8–2 km were reasonable. Simulations at higher resolution improved the modeled NO2 estimates in Chiba, reducing the mean bias error (MBE) in the 0–2 km height by 35 %. However, resolution-based improvements were limited to the surface layers. Sensitivity studies showed pyrogenic emissions in Phimai contribute to the HCHO and NO2 concentrations up to ~ 50 and ~35 %, respectively. </jats:p