In Press

Articles in press have been peer-reviewed and accepted, which are not yet assigned to volumes/issues, but are citable by Digital Object Identifier (DOI).
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Original Paper
Can Taal Volcano eruption trigger an El Niño and lead to Eurasian warming?
Fei Liu, Chen Xing, jinbao li, Bin Wang, Jing Chai, Chaochao GAO, Gang Huang, jian liu, Deliang Chen
, Available online   , Manuscript accepted  01 April 2020, doi: 10.1007/s00376-020-2041-z
Abstract:
no abstract
A New Temperature Channel Selection Method Based on Singular Spectrum Analysis for Retrieving Atmosphere Temperature Profiles from FY-4A/GIIRS
Peipei YU, Chunxiang Shi, Ling YANG, Shuai SHAN
, Available online   , Manuscript accepted  31 March 2020, doi: 10.1007/s00376-020-9249-9
Abstract:
Hyperspectral data has important research and application value in the fields of meteorology and remote sensing. With the goal of improving retrievals of atmospheric temperature profiles, this paper outlines a novel temperature channel selection method based on Singular Spectrum Analysis (SSA) for the Geostationary Interferometric Infrared Sounder (GIIRS), which is the first infrared sounder operating in geostationary orbit. The method possesses not only the simplicity and rapidity of the principal component analysis method, but also the interpretability of the conventional channel selection method. The novel SSA method is used to decompose GIIRS sequence data and the reconstructed grouped components can be obtained to reflect the energy variations in the temperature-sensitive waveband of the respective sequence. At 700–780 cm−1, the channels selected using our method perform better than Infrared Atmospheric Sounding Interferometer (IASI) and Cross-track Infrared Sounder (CrIS) temperature channels when used as inputs to the neural network retrieval model.
Overview of the CMIP6 historical experiment datasets with the climate system model CAS FGOALS-f3-L
Yuyang Guo, Yongqiang Yu, Pengfei LIN, Hailong LIU, Bian He, Qing Bao, Shuwen Zhao, Xiaowei Wang
, Available online   , Manuscript accepted  20 March 2020, doi: 10.1007/s00376-020-2004-4
Abstract:
The 3-member historical simulations by the Chinese Academy of Sciences Flexible Global Ocean–Atmosphere–Land System model, version f3-L (CAS FGOALS-f3-L), which contribute to the Coupled Model Intercomparison Project phase 6 (CMIP6), are described in this study. The details of the CAS FGOALS-f3-L model, experiments settings and output datasets are briefly introduced. The datasets include monthly and daily outputs from the atmospheric, oceanic, land and sea ice component models of CAS FGOALS-f3-L, and all these data have been published online in the Earth System Grid Federation (ESGF, https://esgf-nodes.llnl.gov/projects/cmip6/). The three ensembles, which are initialized from the 600th, 650th, and 700th model year of the preindustrial experiment (piControl) and forced by the same historical forcing provided by CMIP6 from 1850 to 2014. The performance of the coupled model is validated in comparison with some latest observed atmospheric and oceanic datasets. It is shown that the CAS FGOALS-f3-L is able to reproduce the main features of the modern climate, including the climatology of air surface temperature and precipitation, the long-term changes in global mean surface air temperature, ocean heat content and sea surface steric height, and the horizontal and vertical distribution of temperature in the ocean and atmosphere. Meanwhile, there are still some obvious biases in the historical simulations like other state-of-the-art coupled general circulation models (GCMs), which are also illustrated. This paper can help the users to better understand the advantages and biases of the model and the datasets.
Atmospheric River Signatures in Radiosonde Profiles and Reanalyses at the Dronning Maud Land Coast, East Antarctica
Irina Gorodetskaya, Tiago Silva, Holger Schmithüsen, Naohiko Hirasawa
, Available online   , Manuscript accepted  04 March 2020, doi: 10.1007/s00376-020-9221-8
Abstract:
Atmospheric rivers (ARs) are an important component of the hydrological cycle linking moisture sources in lower latitudes to the Antarctic surface mass balance. We investigate AR signatures in the atmospheric vertical profiles at the Dronning Maud Land coast, East Antarctica, using regular and extra radiosonde measurements conducted during the Year of Polar Prediction Special Observing Period November 2018 - February 2019. Prominent AR events affecting Neumayer and Syowa locations cause a strong increase in specific humidity extending through mid-troposphere and a strong low-level jet (LLJ). At Neumayer, the peak in the moisture inversion (up to 4 g kg-1) is observed between 800-900 hPa, while the low-level jet (up to 32 m s-1) is concentrated below 900 hPa. At Syowa increase in humidity is less pronounced and peaks near the surface, while there is a substantial increase in wind speed (up to 40 m s-1) between 825-925 hPa. Moisture transport (MT) within the vertical profile during the ARs attains a maximum of 100 g kg-1 m s-1 at both locations, and is captured by both ERA-Interim and ERA5 re-analyses at Neumayer, while is strongly underestimated at Syowa. Composites of the enhanced MT events during 2009-2019 show that these events represent an extreme state of the lower tropospheric profile compared to its median values with respect to temperature, humidity, wind speed and consequently MT. High temporal and vertical resolution radiosonde observations are important for understanding contribution of these rare events to the total MT towards Antarctica and improving their representation in models.
Deriving temporal and vertical distributions of methane in Xianghe using ground-based Fourier transform infrared and gas-analyzer measurements
Denghui Ji, Minqiang Zhou, Pucai Wang, Yang Yang, Ting Wang, Xiaoyu Sun, Christian Hermans, Bo Yao, Gengchen Wang
, Available online   , Manuscript accepted  03 March 2020, doi: 10.1007/s00376-020-9233-4
Abstract:
Methane (CH4) is one of the most important greenhouse gases in the atmosphere. It is worthwhile to study the temporal and vertical distribution of CH4 in source areas, e.g. Northern China. For this purpose, a ground-based high spectral resolution Fourier transform infrared spectrometer (FTIR), Bruker IFS 125HR, and in situ measurement instrument, Picarro G2301 were deployed in Xianghe (39.8°N,117.0°E), Hebei Province. So far, more than one year of measurement data of the FTIR and the Picarro have been recorded since June 2018. For FTIR measurements, we take two observations modes to retrieve the mole fraction of CH4, the Total Carbon Column Observing Network (TCCON) method (retrieval algorithm: GGG2014) and the Network for the Detection of Atmospheric Composition Change (NDACC) method (retrieval algorithm: SFIT4). Combined FTIR with in situ measurements, we show the temporal and vertical distribution of atmospheric CH4 in four vertical layers, near the ground, troposphere, stratosphere and the whole atmosphere. For the diurnal variation of CH4 near the ground, the concentration in nighttime is higher than that in daytime. For the seasonal variation of CH4, there is a maximum in August (about 1.95ppm) and a peak in December (about 1.92 ppm) from the FTIR total column measurements. In addition, we find that the CH4 in the troposphere is relatively well-mixed and the variation of the tropospheric column of CH4 is closer to that from the in situ measurements near the ground, and the variation of the stratospheric column of CH4 has a strong link with the tropopause height.
Direct observations of atmospheric transport and stratosphere-troposphere exchange from high-precision carbon dioxide and carbon monoxide profile measurements
You Yi, cai zhaonan, Yi Liu, Shuang-xi Fang, Yuli Zhang, Dongxu Yang, Yong Wang, miao Liang, maohua Wang
, Available online   , Manuscript accepted  03 March 2020, doi: 10.1007/s00376-020-9227-2
Abstract:
A new in situ measurement campaign of carbon dioxide (CO2) and carbon monoxide (CO) profiles was conducted in China on June 13 and 14, 2018. Interestingly, the derived CO and CO2 profiles were highly positively correlated on June 13 and highly negatively correlated on June 14 in the upper troposphere between 8 and 10 km. Backward trajectories, meteorological analyses, and CO2 horizontal distributions were combined to interpret this phenomenon. The results indicated that the source region experienced a local stratospheric intrusion and exhibited a large horizontal CO2 gradient. At the altitude where the CO concentration was lower, there was a higher CO2 concentration and vice versa. A laminar structure with multiple origins resulted in the highly negative correlation between CO2 and CO in the upper troposphere on June 14. The contribution of stratospheric airmass to the upper troposphere and that of tropospheric airmass to the lower stratosphere were 26.7% and 24.3%, respectively based on a mass balance approach. Another interesting phenomenon is that CO2 and CO levels increased substantially at approximately 8 km on June 13. Backward trajectory analyses showed that the airmass originated from a region with significant anthropogenic sources. The slope of CO2/CO representing the anthropogenic sources was 87.3 ppm/ppm. In addition, the CO2 profile showed that there was a large CO2 gradient of 4 ppm/km within the boundary layer on June 13, and this gradient disappeared on June 14.
Isentropic analysis of regional cold events over northern China
Qingyi LIU, Qian LIU, Guixing Chen
, Available online   , Manuscript accepted  28 February 2020, doi: 10.1007/s00376-020-9226-3
Abstract:
From the perspective of cold airmass (CAM) analysis, we examine the characteristics and mechanisms of regional cold events (RCEs) over northwestern and northeastern China in past 58 years (1958/1959–2015/2016). The RCEs in northwestern (northeastern) China are shown to have an average duration of 6.8 (4.7) days with a moderate (sharp) temperature drop. We quantitatively estimate the RCEs-related CAM, for the first time, using an isentropic analysis method. Before the RCEs in northwestern China, CAM is accumulated in western Siberia with convergent CAM flux under a blocking pattern in Ural region. During RCEs outbreak, CAM penetrates the valleys of Tianshan-Altay Mountains to Tarim Basin and Hexi Corridor. The CAM moves slowly because of the blocking pattern and orographic effect, which explains the relatively long duration of RCEs. As a comparison, during the RCEs in northeastern China, CAM depth anomaly originates more east and quickly passes the Mongolian Plateau guided by eastward-moving trough. Diagnostic analyses further show that adiabatic processes play a crucial role in regulating the local change of CAM depth during two kinds of RCEs. The advection term of adiabatic processes mainly increases CAM depth during RCEs outbreak, while the convergence term increases (reduces) CAM depth before (after) RCEs outbreak. Both terms are relatively strong during the RCEs in northeastern China, resulting in the change rate of CAM depth ~50% larger than those of northwestern China. Therefore, the variations of RCEs in duration and intensity can be well explained by the different evolution of CAM depth and flux.
Impacts of High-Frequency Atmospheric Forcing on Southern Ocean Circulation and Antarctic Sea Ice
Yang WU, Zhaomin WANG, Chengyan LIU, Xia LIN
, Available online   , Manuscript accepted  27 February 2020, doi: 10.1007/s00376-020-9203-x
Abstract:
The relative contributions of atmospheric fluctuations on 6 h−2 d, 2−8 d, and 8 d−1 month time scales to the changes in the air−sea fluxes, the SO circulation, and Antarctic sea ice are investigated. It was found that the imposed forcing variability on the three time scales creates a significant increase in wind power input, and hence an increase of about 50%, 97%, and 5% of eddy kinetic energy relative to the simulation driven by monthly forcing, respectively. Also, SO circulation and the strength of the upper cell of meridional overturning circulation become strengthened. These results indicate more dominant effects of atmospheric variability on the 2−8 d time scale on the SO circulation. Meanwhile, the 6 h−2 d (2−8 d) atmospheric variability causes an increase in the total sea-ice extent, area, and volume, by about 33%, 30%, and 19% (17%, 20%, and 25%), respectively, relative to those in the experiment forced by monthly atmospheric variables. Such significant sea-ice increases are caused by a cooler ocean surface and stronger sea-ice transports owing to the enhanced heat losses and air-ice stresses induced by the atmospheric variability at 6 h−2 d and 2−8 d, while the effects of the variability at 8 d−1 month are rather weak. The influences of atmospheric variability found here mainly result from wind fluctuations. Our findings in this study indicate the importance of properly resolving high-frequency atmospheric variability in modeling studies.
Estimate of hydrofluorocarbon emissions for 2012-2016 in the Yangtze River Delta, China
Jingjiao Pu, Honghui Xu, Bo Yao, Yan Yu, Yujun Jiang, Qianli Ma, Liqu Chen
, Available online   , Manuscript accepted  26 February 2020, doi: 10.1007/s00376-020-9242-3
Abstract:
Hydrofluorocarbons (HFCs) have been widely used in China as substitutes for ozone-depleting substances (ODSs), the production and use of which are being phased out under the Montreal Protocol. China is a major consumer of HFCs around the world, with its HFC emissions in CO2-equivalent contributing to about 18% of the global emissions for the period of 2012-2016. Three methods are widely used to estimate the emissions of HFCs, namely bottom-up method, top-down method and tracer ratio method. In this study, tracer ratio method was adopted to estimate HFC emissions in the Yangtze River Delta (YRD), using CO as a tracer. The YRD region might have significant contribution to Chinese totals for its rapid economic growth. Weekly flask measurements for ten HFCs (HFC-23, HFC-32, HFC-125, HFC-134a, HFC-143a, HFC-152a, HFC-227ea, HFC-236fa, HFC-245fa and HFC-365mfc) were conducted at Lin’an Regional Background Station in YRD over the period of 2012-2016, and the HFC emissions were 2.4±1.4 kt yr-1 for HFC-23, 2.8±1.2 kt yr-1 for HFC-32, 2.2±1.2 kt yr-1 for HFC-125, 4.8±4.8 kt yr-1 for HFC-134a, 0.9±0.6 kt yr-1 for HFC-152a, 0.3±0.3 kt yr-1 for HFC-227ea and 0.3±0.2 kt yr-1 for HFC-245fa, respectively. The YRD total HFC emissions reached 53 MtCO2-e yr-1, contributing 34% of the national total. Per capita HFC CO2-equivalent emission was 240 kg yr-1, while the values of per unit area emission and per million GDP emission reached 150 Mg km-2 yr-1 and 3500 kg yr-1 (million CNY GDP)-1, which were much higher than national or global levels.
Background Characteristics of Atmospheric CO2 and the Potential Source Regions in the Pearl River Delta Region of China
Boru Mai, Xuejiao Deng, Fang Zhang, Hao He, Tian Luan, Fei Li, Xia Liu
, Available online   , Manuscript accepted  24 February 2020, doi: 10.1007/s00376-020-9238-z
Abstract:
Mole fractions of atmospheric CO2 (XCO2) have been continuously measured from October 2014 to March 2016 at the Guangzhou Panyu Atmospheric Composition Site (23.00°N, 113.21°E; 140 m MSL) in the Pearl River Delta (PRD) region using a cavity ring-down spectrometer. Approximately 66.63%, 19.28%, and 14.09% of the observed values were filtered as background, pollutant source, and sink due to biospheric uptake, respectively, by applying a robust local regression procedure. Their corresponding mean values were 424.12 ± 10.12 ppm (×10−6 mol mol−1), 447.83 ± 13.63 ppm, and 408.83 ± 7.75 ppm. The background XCO2 levels were highest in spring and winter, moderate in autumn, and lowest in summer. The diurnal XCO2 was at a minimum from 1400–1600 LST (Local Standard Time) and a maximum at 0500 LST the next day. The increase of XCO2 in spring and summer was mainly associated with polluted air masses from south coastal Vietnam, the South China Sea, and the southeast Pearl River Estuary. With the exception of summer, airflow primarily from marine regions southeast of Taiwan that passed over the Pearl River Estuary had a greater impact on XCO2, suggesting an important potential source region.
Impacts of Urbanization on the Precipitation Characteristics in Guangdong Province, China
Meng YAN, Johnny C. L. CHAN, Kun ZHAO
, Available online   , Manuscript accepted  21 February 2020, doi: 10.1007/s00376-020-9218-3
Abstract:
With the development of urbanization, whether precipitation characteristics in Guangdong Province, China, from 1981 to 2015 have changed are investigated using rain gauge data from 76 stations. These characteristics include annual precipitation, rainfall frequency, intense rainfall (defined as hourly precipitation ≥ 20 mm), light precipitation (defined as hourly precipitation ≤ 2.5 mm), and extreme rainfall (defined as hourly rainfall exceeding the 99.9th percentile of the hourly rainfall distribution). During these 35 years, the annual precipitation shows an increasing trend in the urban areas. While rainfall frequency and light precipitation have a decreasing trend, intense rainfall frequency shows an increasing trend. The heavy and extreme rainfall frequency both exhibit an increasing trend in the Pearl River Delta region, where urbanization is the most significant. These trends in both the warm seasons (May−October) and during the pre-flood season (April−June) appear to be more significant. On the contrary, the annual precipitation amount in rural areas has a decreasing trend. Although the heavy and extreme precipitation also show an increasing trend, it is not as strong and significant as that in the urban areas. During periods in which a tropical cyclone makes landfall along the South China Coast, the rainfall in urban areas has been consistently more than that in surrounding areas. The precipitation in the urban areas and to their west is higher after 1995, when the urbanization accelerated. These results suggest that urbanization has a significant impact on the precipitation characteristics of Guangdong Province.
Modeling the Impacts of Nitrogen Dynamics on Regional Terrestrial Carbon and Water Cycles over China with Noah-MP-CN
Jingjing LIANG, Zong-Liang YANG, Xitian CAI, Peirong LIN, Hui ZHENG, Qingyun BIAN
, Available online   , Manuscript accepted  16 February 2020, doi: 10.1007/s00376-020-9231-6
Abstract:
As an important part of biogeochemical cycling, the nitrogen cycle modulates terrestrial ecosystem carbon storage, water consumption, and environmental quality. Modeling the complex interactions between nitrogen, carbon and water at a regional scale remains challenging. Using China as a testbed, this study presents the first application of the nitrogen-augmented community Noah land surface model with multi-parameterization options (Noah-MP-CN) at the regional scale. Noah-MP-CN parameterizes the constraints of nitrogen availability on photosynthesis based on the Fixation and Uptake of Nitrogen plant nitrogen model and the Soil and Water Assessment Tool soil nitrogen model. The impacts of nitrogen dynamics on the terrestrial carbon and water cycles are investigated by comparing the simulations with those from the original Noah-MP. The results show that incorporating nitrogen dynamics improves the carbon cycle simulations. Noah-MP-CN outperforms Noah-MP in reproducing leaf area index (LAI) and gross primary productivity (GPP) for most of China, especially in the southern warm and humid regions, while the hydrological simulations only exhibit slight improvements in soil moisture and evapotranspiration. The impacts of fertilizer application over cropland on carbon fixation, water consumption and nitrogen leaching are investigated through a trade-off analysis. Compared to halved fertilizer use, the actual quantity of application increases GPP and water consumption by only 1.97% and 0.43%, respectively; however, the nitrogen leaching is increased by 5.35%. This indicates that the current level of fertilizer use is a potential concern for degrading the environment.
Relationship between Solar Wind−Magnetosphere Energy and Eurasian Winter Cold Events
Xinping XU, Shengping HE, Huijun WANG
, Available online   , Manuscript accepted  12 February 2020, doi: 10.1007/s00376-020-9153-3
Abstract:
The profound impact of solar irradiance variations on the decadal variability of Earth’s climate has been investigated by previous studies. However, it remains a challenge to quantify the energetic particle precipitation (EPP) influence on the surface climate, which is an emerging research topic. The solar wind is a source of magnetospheric EPP, and the total energy input from the solar wind into Earth’s magnetosphere (Ein) shows remarkable interdecadal and interannual variability. Based on the new Ein index, this study reveals a significant interannual relationship between the annual mean Ein and Eurasian cold extremes in the subsequent winter. Less frequent cold events are observed over Eurasia (primarily north of 50°N) following the higher-than-normal Ein activity in the previous year, accompanied by more frequent cold events over northern Africa, and vice versa. This response pattern shows great resemblance to the first empirical orthogonal function of the variability of cold extremes over Eurasia, with a spatial correlation coefficient of 0.79. The pronounced intensification of the positive North Atlantic Oscillation events and poleward shift of the North Atlantic storm track associated with the anomalously higher Ein favor the anomalous extreme atmospheric circulation events and thus less frequent extreme cold temperatures over northern Eurasia on the interannual time scale. It is further hypothesized that the wave−mean flow interaction in the stratosphere and troposphere is favorable for the connection of Ein signals to tropospheric circulation and climate in the following winter.
On the Epochal Variability in the Frequency of Cyclones during the Pre-Onset and Onset Phases of the Monsoon over the North Indian Ocean
P. P. BABURAJ, S. ABHILASH, K. MOHANKUMAR, A. K. SAHAI
, Available online   , Manuscript accepted  08 February 2020, doi: 10.1007/s00376-020-9070-5
Abstract:
In this paper we examine the epochal changes in the frequency of cyclones over the North Indian Ocean during the pre-onset and onset phases of the monsoon. We consider three epochs; namely, the early (1955−74), middle (1975−94) and recent (1995−2014) epochs. It is found that the number of cyclones in the Bay of Bengal (BOB) decreases throughout the three epochs. Over the Arabian Sea (ARB), however, there is a decrease in the early epoch, before then reaching a minimum in the middle epoch followed by an increase in the recent epoch, thus exhibiting epochal variability. Dynamic and thermodynamic parameters along with Genesis Potential Index (GPI) are examined to understand the frequency variation in cyclogenesis over the ARB and BOB. Over the ARB, thermodynamic factors such as mid-level moisture, surface latent heat flux and sensible heat flux, and dynamic parameters such as lower-level convergence and upper-level divergence, are favorable during the early and recent epochs but unfavorable during the middle epoch, and these results are found to be consistent with the observed epochal variability in the frequency of cyclogenesis. However, all these influential parameters are found to have decreased over the BOB during the entire 60-year period.
An Observing System Simulation Experiment to Assess the Potential Impact of a Virtual Mobile Communication Tower–based Observation Network on Weather Forecasting Accuracy in China. Part 1: Weather Stations with a Typical Mobile Tower Height of 40 m
Xuanming ZHAO, Jiang ZHU, Lijing CHENG, Yubao LIU, Yuewei LIU
, Available online   , Manuscript accepted  08 February 2020, doi: 10.1007/s00376-020-9058-1
Abstract:
The importance of a national or regional network of meteorological stations for improving weather predictions has been recognized for many years. Ground-based automatic weather stations typically observe weather at a height of 2−10 m above ground level (AGL); however, these observations may have two major shortcomings. Large portions of data cannot be used if the station height is significantly lower than the model surface level; and such observations may contain large representativity errors as near-surface observations are often affected by the local environment, such as nearby buildings and tall trees. With the recent introduction of a significant number of mobile communication towers that are typically over 40 m AGL in China, a campaign has been proposed to use such towers to build a future observing system with an observing height of 40 m. A series of observing system simulation experiments has been conducted to assess the potential utility of such a future observing system as part of a feasibility study. The experiments were conducted using the Weather Research and Forecasting model and its Rapid Update Cycle data assimilation system. The results revealed the possibility of improving weather forecasting by raising present weather stations to a height of 40 m; this would not only enable more observations to pass the terrain check, but should also reduce interpolation errors. Additionally, improvements for temperature, humidity and wind forecasting could be achieved as the accuracy of the initial conditions increases.
An Observing System Simulation Experiment to Assess the Potential Impact of a Virtual Mobile Communication Tower–based Observation Network on Weather Forecasting Accuracy in China. Part 1: Weather Stations with a Typical Mobile Tower Height of 40 m
Xuanming ZHAO, Jiang ZHU, Lijing CHENG, Yubao LIU, Yuewei LIU
, Available online   , Manuscript accepted  08 February 2020, doi: 10.1007/s00376-020-9058-1
Abstract:
The importance of a national or regional network of meteorological stations for improving weather predictions has been recognized for many years. Ground-based automatic weather stations typically observe weather at a height of 2−10 m above ground level (AGL); however, these observations may have two major shortcomings. Large portions of data cannot be used if the station height is significantly lower than the model surface level; and such observations may contain large representativity errors as near-surface observations are often affected by the local environment, such as nearby buildings and tall trees. With the recent introduction of a significant number of mobile communication towers that are typically over 40 m AGL in China, a campaign has been proposed to use such towers to build a future observing system with an observing height of 40 m. A series of observing system simulation experiments has been conducted to assess the potential utility of such a future observing system as part of a feasibility study. The experiments were conducted using the Weather Research and Forecasting model and its Rapid Update Cycle data assimilation system. The results revealed the possibility of improving weather forecasting by raising present weather stations to a height of 40 m; this would not only enable more observations to pass the terrain check, but should also reduce interpolation errors. Additionally, improvements for temperature, humidity and wind forecasting could be achieved as the accuracy of the initial conditions increases.
Impact of Assimilation of Radiosonde and UAV Observations from the Southern Ocean in the Polar WRF Model
Qizhen SUN, Timo VIHMA, Marius O. JONASSEN, Zhanhai ZHANG
, Available online   , Manuscript accepted  08 February 2020, doi: 10.1007/s00376-020-9213-8
Abstract:
Weather forecasting in the Southern Ocean and Antarctica is a challenge above all due to the rarity of observations to be assimilated in numerical weather prediction (NWP) models. As observations are expensive and logistically challenging, it is important to evaluate the benefit that additional observations could bring to NWP. Atmospheric soundings applying unmanned aerial vehicles (UAVs) have a large potential to supplement conventional radiosonde sounding observations. Here, we applied UAV and radiosonde sounding observations from an RV Polarstern cruise in the ice-covered Weddell Sea in austral winter 2013 to evaluate the impact of their assimilation in the Polar version of the Weather Research and Forecasting (Polar WRF) model. Our experiments revealed small to moderate impacts of radiosonde and UAV data assimilation. In any case, the assimilation of sounding data from both radiosondes and UAVs improved the analyses of air temperature, wind speed, and humidity at the observation site for most of the time. Further, the impact on the results of 5-day-long Polar WRF experiments was often felt over distances of at least 300 km from the observation site. All experiments succeeded in capturing the main features of the evolution of near-surface variables, but the effects of data assimilation varied between different cases. Due to the limited vertical extent of the UAV observations, the impact of their assimilation was limited to the lowermost 1−2-km layer, and assimilation of radiosonde data was more beneficial for modeled sea level pressure and near-surface wind speed.
Recent Near-surface Temperature Trends in the Antarctic Peninsula from Observed, Reanalysis and Regional Climate Model Data
Deniz BOZKURT, David H. BROMWICH, Jorge CARRASCO, Keith M. HINES, Juan Carlos MAUREIRA, Roberto RONDANELLI
, Available online   , Manuscript accepted  22 January 2020, doi: 10.1007/s00376-020-9183-x
Abstract:
This study investigates the recent near-surface temperature trends over the Antarctic Peninsula. We make use of available surface observations, ECMWF’s ERA5 and its predecessor ERA-Interim, as well as numerical simulations, allowing us to contrast different data sources. We use hindcast simulations performed with Polar-WRF over the Antarctic Peninsula on a nested domain configuration at 45 km (PWRF-45) and 15 km (PWRF-15) spatial resolutions for the period 1991−2015. In addition, we include hindcast simulations of KNMI-RACMO21P obtained from the CORDEX-Antarctica domain (~50 km) for further comparisons. Results show that there is a marked windward warming trend except during summer. This windward warming trend is particularly notable in the autumn season and likely to be associated with the recent deepening of the Amundsen/Bellingshausen Sea low and warm advection towards the Antarctic Peninsula. On the other hand, an overall summer cooling is characterized by the strengthening of the Weddell Sea low as well as an anticyclonic trend over the Amundsen Sea accompanied by northward winds. The persistent cooling trend observed at the Larsen Ice Shelf station is not captured by ERA-Interim, whereas hindcast simulations indicate that there is a clear pattern of windward warming and leeward cooling. Furthermore, larger temporal correlations and lower differences exhibited by PWRF-15 illustrate the existence of the added value in the higher spatial resolution simulation.
Specific Relationship between the Surface Air Temperature and the Area of the Terra Nova Bay Polynya, Antarctica
Yifan DING, Xiao CHENG, Xichen LI, Mohammed SHOKR, Jiawei YUAN, Qinghua YANG, Fengming HUI
, Available online   , Manuscript accepted  19 January 2020, doi: 10.1007/s00376-020-9146-2
Abstract:
Antarctic polynyas play an important role in regional atmosphere−ice−ocean interactions and are considered to help generate the global deep ocean conveyer belt. Polynyas therefore have a potential impact on the Earth’s climate in terms of the production of sea ice and high-salinity shelf water. In this study, we investigated the relationship between the area of the Terra Nova Bay polynya and the air temperature as well as the eastward and northward wind based on the ERA5 and ERA-Interim reanalysis datasets and observations from automatic weather stations during the polar night. We examined the correlation between each factor and the polynya area under different temperature conditions. Previous studies have focused more on the effect of winds on the polynya, but the relationship between air temperature and the polynya area has not been fully investigated. Our study shows, eliminating the influence of winds, lower air temperature has a stronger positive correlation with the polynya area. The results show that the relationship between the polynya area and air temperature is more likely to be interactively influenced. As temperature drops, the relationship of the polynya area with air temperature becomes closer with increasing correlation coefficients. In the low temperature conditions, the correlation coefficients of the polynya area with air temperature are above 0.5, larger than that with the wind speed.
Two-Year Observation of Fossil Fuel Carbon Dioxide Spatial Distribution in Xi’an City
Xiaohu XIONG, Weijian ZHOU, Shugang WU, Peng CHENG, Hua DU, Yaoyao HOU, Zhenchuan NIU, Peng WANG, Xuefeng LU, Yunchong FU
, Available online   , Manuscript accepted  09 January 2020, doi: 10.1007/s00376-020-9241-4
Abstract:
The need for atmospheric carbon dioxide (CO2) reduction in the context of global warming is widely acknowledged by the global scientific community. Fossil fuel CO2 (CO2ff) emissions occur mainly in cities, and can be monitored directly with radiocarbon (14C). In this research, annual plants [Setaria viridis (L.) Beauv.] were collected from 26 sites in 2013 and 2014 in the central urban district of Xi'an City. The Δ14C content of the samples were analyzed using a 3 MV Accelerator Mass Spectrometer, and CO2ff concentrations were calculated based on mass balance equations. The results showed that the CO2ff mixing ratio ranged from 15.9 to 25.0 ppm (part per million, equivalent to μmol mol−1), with an average of 20.5 ppm in 2013. The range of measured values became larger in 2014, from 13.9 ppm to 33.1 ppm, with an average of 23.5 ppm. The differences among the average CO2ff concentrations between the central area and outer urban areas were not statistically significant. Although the year-to-year variation of the CO2ff concentration was significant (P < 0.01), there was a distinctly low CO2ff value observed in the northeast corner of the city. CO2ff emissions from vehicle exhaust and residential sources appeared to be more significant than two thermal power plants, according to our observed CO2ff spatial distribution. The variation of pollution source transport recorded in our observations was likely controlled by southwesterly winds. These results could assist in the optimal placement of regional CO2 monitoring stations, and benefit the local government in the implementation of efficient carbon emission reduction measures.
Comparison of Ozone Fluxes over a Maize Field Measured with Gradient Methods and the Eddy Covariance Technique
Zhilin ZHU, Xinzhai TANG, Fenghua ZHAO
, Available online   , Manuscript accepted  06 January 2020, doi: 10.1007/s00376-020-9217-4
Abstract:
Ozone (O3) fluxes were measured over a maize field using the eddy covariance (EC) technique and gradient methods. The main objective was to evaluate the performance of the gradient methods for measuring the O3 flux by comparing them with the EC O3 flux. In this study, turbulent exchange coefficients (K) calculated with three methods were compared. These methods were the aerodynamic gradient (AG) method (in which K is calculated by using wind speed and temperature gradients), the aerodynamic gradient combined with EC (AGEC) method, in which the friction velocity and other variables are based on EC measurements, and the modified Bowen ratio using the EC sensible heat flux and temperature gradient (MBR) method. Meanwhile, the effects of the measurement and calculation methods of the O3 concentration gradient were analyzed. The results showed that: (1) on average, the transfer coefficient computed by the MBR method was 40% lower, and the coefficient determined with the AG method was 25% higher, than that determined with the AGEC method. (2) The gradient method’s O3 fluxes with the MBR, AGEC, and AG methods were 30.4% lower, 11.7% higher, and 45.6% higher than the EC O3 flux, respectively. (3) The effect of asynchronous O3 concentration measurements on the O3 gradient must be eliminated when using one analyzer to cyclically measure two-level O3 concentrations. The accuracy of gradient methods for O3 flux is related to the exchange coefficient calculation method, and its precision mainly depends on the quality of the O3 gradient.
Towards More Snow Days in Summer since 2001 at the Great Wall Station, Antarctic Peninsula: The Role of the Amundsen Sea Low
Minghu DING, Wei HAN, Tong ZHANG, Xiaoyuan YUE, Jeremy FYKE, Ge LIU, Cunde XIAO
, Available online   , Manuscript accepted  21 November 2019, doi: 10.1007/s00376-019-9196-5
Abstract:
The variation in the precipitation phase in polar regions represents an important indicator of climate change and variability. We studied the precipitation phase at the Great Wall Station and Antarctic Peninsula (AP) region, based on daily precipitation, synoptic records and ERA-Interim data during the austral summers of 1985−2014. Overall, there was no trend in the total precipitation amount or days, but the phase of summer precipitation (rainfall days versus snowfall days) showed opposite trends before and after 2001 at the AP. The total summer rain days/snow days increased/decreased during 1985−2001 and significantly decreased at a rate of −14.13 d (10 yr)−1/increased at a rate of 14.31 d (10 yr)−1 during 2001−2014, agreeing well with corresponding variations in the surface air temperature. Further, we found that the longitudinal location of the Amundsen Sea low (ASL) should account for the change in the precipitation phase since 2001, as it has shown a westward drift after 2001 [−41.1° (10 yr)−1], leading to stronger cold southerly winds, colder water vapor flux, and more snow over the AP region during summertime. This study points out a supplementary factor for the climate variation on the AP.
Refractory Black Carbon Results and a Method Comparison between Solid-state Cutting and Continuous Melting Sampling of a West Antarctic Snow and Firn Core
Luciano MARQUETTO, Susan KASPARI, Jefferson Cardia SIMÕES, Emil BABIK
, Available online   , Manuscript accepted  24 October 2019, doi: 10.1007/s00376-019-9124-8
Abstract:
This work presents the refractory black carbon (rBC) results of a snow and firn core drilled in West Antarctica (79°55'34.6"S, 94°21'13.3"W) during the 2014−15 austral summer, collected by Brazilian researchers as part of the First Brazilian West Antarctic Ice Sheet Traverse. The core was drilled to a depth of 20 m, and we present the results of the first 8 m by comparing two subsampling methods—solid-state cutting and continuous melting—both with discrete sampling. The core was analyzed at the Department of Geological Sciences, Central Washington University (CWU), WA, USA, using a single particle soot photometer (SP2) coupled to a CETAC Marin-5 nebulizer. The continuous melting system was recently assembled at CWU and these are its first results. We also present experimental results regarding SP2 reproducibility, indicating that sample concentration has a greater influence than the analysis time on the reproducibility for low rBC concentrations, like those found in the Antarctic core. Dating was carried out using mainly the rBC variation and sulfur, sodium and strontium as secondary parameters, giving the core 17 years (1998−2014). The data show a well-defined seasonality of rBC concentrations for these first meters, with geometric mean summer/fall concentrations of 0.016 μg L−1 and geometric mean winter/spring concentrations of 0.063 μg L−1. The annual rBC concentration geometric mean was 0.029 μg L−1 (the lowest of all rBC cores in Antarctica referenced in this work), while the annual rBC flux was 6.1 μg m−2 yr−1 (the lowest flux in West Antarctica records so far).
Antarctic Radiosonde Observations Reduce Uncertainties and Errors in Reanalyses and Forecasts over the Southern Ocean: An Extreme Cyclone Case
Kazutoshi SATO, Jun INOUE, Akira YAMAZAKI, Naohiko HIRASAWA, Konosuke SUGIURA, Kyohei YAMADA
, Available online   , Manuscript accepted  30 April 2019, doi: 10.1007/s00376-019-8231-x
Abstract:
Cyclones with strong winds can make the Southern Ocean and the Antarctic a dangerous environment. Accurate weather forecasts are essential for safe shipping in the Southern Ocean and observational and logistical operations at Antarctic research stations. This study investigated the impact of additional radiosonde observations from Research Vessel "Shirase" over the Southern Ocean and Dome Fuji Station in Antarctica on reanalysis data and forecast experiments using an ensemble data assimilation system comprising the Atmospheric General Circulation Model for the Earth Simulator and the Local Ensemble Transform Kalman Filter Experimental Ensemble Reanalysis, version 2. A 63-member ensemble forecast experiment was conducted focusing on an unusually strong Antarctic cyclonic event. Reanalysis data with (observing system experiment) and without (control) additional radiosonde data were used as initial values. The observing system experiment correctly captured the central pressure of the cyclone, which led to the reliable prediction of the strong winds and moisture transport near the coast. Conversely, the control experiment predicted lower wind speeds because it failed to forecast the central pressure of the cyclone adequately. Differences were found in cyclone predictions of operational forecast systems with and without assimilation of radiosonde observations from Dome Fuji Station.
Stratospheric Ozone-induced Cloud Radiative Effects On Antarctic Sea Ice
Yan XIA, Yongyun HU, Jiping LIU, Yi HUANG, Fei XIE, Jintai LIN
, Available online   , Manuscript accepted  19 April 2019, doi: 10.1007/s00376-019-8251-6
Abstract:
Recent studies demonstrate that the Antarctic Ozone Hole has important influences on Antarctic sea ice. While most of these works have focused on effects associated with atmospheric and oceanic dynamic processes caused by stratospheric ozone changes, here we show that stratospheric ozone-induced cloud radiative effects also play important roles in causing changes in Antarctic sea ice. Our simulations demonstrate that the recovery of the Antarctic Ozone Hole causes decreases in clouds over Southern Hemisphere (SH) high latitudes and increases in clouds over the SH extratropics. The decrease in clouds leads to a reduction in downward infrared radiation, especially in austral autumn. This results in cooling of the Southern Ocean surface and increasing Antarctic sea ice. Surface cooling also involves ice-albedo feedback. Increasing sea ice reflects solar radiation and causes further cooling and more increases in Antarctic sea ice.
News & Views
The 13th and 14th Workshops on Antarctic Meteorology and Climate
Matthew A. LAZZARA, Sophie A. ORENDORF, Taylor P. NORTON, Jordan G. POWERS, David H. BROMWICH, Scott CARPENTIER, John J. CASSANO, Steven R. COLWELL, Arthur M. CAYETTE, Kirstin WERNER
, Available online   , Manuscript accepted  27 November 2019, doi: 10.1007/s00376-019-9215-6
Abstract: