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We study the spatial and temporal variability of summer marine fog in the Chukchi–Beaufort region (175°E−150°W, 70°–86°N) using the in‐situ visibility measurements aboard the Chinese research fleet Xuelong (I and II) and a fog product we derive using the Vertical Feature Mask product of the spaceborne Cloud‐Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) observations. The Xuelong in‐situ observations show that the fog frequency in the Chukchi–Beaufort region has a maximum of ∼18% in the early morning and is less than 10% in the rest of the day. The latitudinal distribution of the Xuelong‐based in‐situ fog frequency further shows high fog occurrences at 74°N and 79°N, which are related to the local high fog occurrences near 72°–74°N and 76°–80°N in the central Chukchi–Beaufort region, as revealed by the longitude‐latitude pattern of the CALIPSO‐based spaceborne fog frequency distribution. The CALIPSO‐based fog frequency is also shown to be lower along the continental coastlines than in the Chukchi–Beaufort region. This longitude‐latitude distribution may be explained by a reduced fog formation due to the Pacific warm current flowing into the Arctic region through the Bering Strait in the summer as well as an enhanced fog formation in the Chukchi–Beaufort region when the southward flow of the Beaufort Gyre interacts with the Pacific warm current. Key Points: Pacific Arctic marine fog occurrence frequency are derived using ship‐based and satellite‐based measurementsShip‐based marine fog occurrence in the early morning is two times more frequent than that in the eveningLongitude‐latitude fog frequency distribution is linked to Pacific warm flow and its interaction with Arctic cold front [ABSTRACT FROM AUTHOR]

The Congo basin, with an area of about 3.7 million km2 in the tropical region, contains the second largest rainforest and is considered as a carbon sink for the atmosphere. Here, using Orbiting Carbon Observatory‐2 satellite observations, we show that the atmospheric CO2 over the Congo basin is ∼2 ppm higher than the regional background during June–August, which is primarily due to biomass burning and significantly reduced photosynthetic activities during the dry season. The contribution from the biomass burning is larger than that from the biosphere during June–August. Current budget estimations suggest emissions from biomass burning during the dry season alone account for ∼72% of the Congo basin annual biomass burning emissions and are ∼40% more than the largest terrestrial uptake in the same region during January–March (wet season). Therefore, better seasonal fire management in this region is an important strategy for achieving timely reductions in global carbon emissions as set by international agreements. Key Points: During the dry season, more atmospheric CO2 (∼2 ppm) is over the Congo basin than the surrounding areaEnhanced biomass burning and reduced photosynthetic activity contribute to high CO2Strong sinking air helps to trap atmospheric CO2 over the Congo basin during June–August [ABSTRACT FROM AUTHOR]

Previous studies suggested that the Amazon, the largest rainforest on Earth, changes from a CO2 sink to a CO2 source during the dry/fire season. However, the biospheric contributions to atmospheric CO2 are not well understood during the two main seasons, the dry/fire season and the wet season. In this article, we utilize Orbiting Carbon Observatory 2 (OCO‐2) Solar‐Induced Fluorescence (SIF) to explore photosynthetic activity during the different seasons. The spatiotemporal variability of OCO‐2 SIF, OCO‐2 CO2, precipitation, and burned area are investigated over the Amazon from September 2014 to December 2019. Averaging over the entire Amazon region, we found a positive temporal correlation (0.94) between OCO‐2 SIF and Global Precipitation Climatology Project precipitation and a negative temporal correlation (−0.64) between OCO‐2 SIF and OCO‐2 CO2, consistent with the fact that precipitation enhances photosynthesis, which results in higher values for SIF and rate of removal of CO2 from the atmosphere above the Amazon region. We also observed seasonality in the spatial variability of these variables within the Amazon region. During the dry/fire (August–October) season, low SIF values, low precipitation, high vapor pressure deficit (VPD), large burned areas, and high atmospheric CO2 are mainly found over the southern Amazon region. In contrast, during the wet season (January–March), high SIF values, high precipitation, low VPD, smaller burned areas, and low CO2 are found over both the central and southern Amazon regions. The seasonal difference in SIF suggests that photosynthetic activity is reduced during the dry/fire season relative to the wet season as a result of low precipitation and high VPD, especially over the southern Amazon region, which will contribute to more CO2 in the atmosphere during the dry/fire season. Key Points: The anomalously high SIF region moves with the precipitation from the north to the south of the Amazon from the dry/fire season to the wet seasonPhotosynthetic activity is reduced over the southern Amazon region during the dry/fire season as a result of low precipitation and high vapor pressure deficitSeasonal differences in SIF suggest that less CO2 will be removed from the atmosphere through photosynthesis during the dry/fire season [ABSTRACT FROM AUTHOR]

Space‐based remote sensing of the column‐averaged methane dry air mole fraction (XCH4) has greatly increased our understanding of the spatiotemporal patterns in the global methane cycle. The potential to retrieve multiple pieces of vertical profile information would further improve the quantification of CH4 across space‐time scales. We conduct information analysis for channel selection and evaluate the prospects of retrieving multiple pieces of information as well as total column CH4 from both ground‐based and space‐based near‐infrared remote sensing spectra. We analyze the degrees of freedom of signal (DOF) in the CH4 absorption bands near 2.3 μm and 1.6 μm and select ∼1% of the channels that contain >95% of the information about the CH4 profile. The DOF is around 4 for fine ground‐based spectra (resolution = 0.01 cm−1) and 3 for coarse space‐based spectra (resolution = 0.20 cm−1) based on channel selection and a signal‐to‐noise ratio (SNR) of 300. The DOF varies from 2.2 to 3.2 when SNR is between 100 and 300, and spectral resolution is 0.20 cm−1. Simulated retrieval tests in clear‐sky conditions using the selected channels reveal that the retrieved partial column‐averaged CH4 values are not sensitive to the a priori profiles and can reflect local enhancements of CH4 in different partial air columns. Both the total and partial column‐averaged retrieval errors in all tests are within 1% of the true state. These simulated tests highlight the possibility to retrieve up to three to four pieces of information about the vertical distribution of CH4 in reality. [ABSTRACT FROM AUTHOR]