Earth and Space Science
Latest articles in this journal
Earth and Space Science; doi:10.1029/2019ea000602
Earth and Space Science; doi:10.1029/2019ea000677
Abstract:The accurate identification of cloud over land is one of the key issues of the satellite data processing and the product retrievals. This paper describes a new cloud detection algorithm based on Level 1 data of Polarization and Directionality of Earth's Reflectance (POLDER). The simulation of multi‐angular normalized polarized reflectance is done for cloudless targets over land before the cloud identification processing. Firstly, the Normalized Difference Vegetation Index (NDVI) over land and reflectance of 670nm are used as two initial criterions for the cloud mask. Then, the difference between the simulation and POLDER observation of polarized reflectance is used as the third criterion to distinguish cloudless pixels from cloud ones. And this algorithm is proved to be more convenient and effective. This algorithm is also applied to cloud mask processing of the Multi‐Angular Polarization Imager (MAPI, onboard the Tiangong‐2) observation. The results show that this algorithm can effectively detect cloud targets over land, and its consistency with POLDER official cloud mask products is about 90%. This algorithm can provide reliable cloud mask products for the retrieval of optical and physical properties of land aerosol using MAPI data.
Earth and Space Science; doi:10.1029/2019ea000650
Abstract:Precipitable water vapor (PWV) and ionospheric vertical total electron content (VTEC) are two essential components of space‐atmosphere parameters. The zenith troposphere delay (ZTD) can be converted into PWV, which plays a crucial role in meteorological studies. In the meantime, the importance of the VTEC lies in providing ionospheric corrections for single‐frequency (SF) positioning, navigation and timing users. Currently, the global navigation satellite system (GNSS) has become one of the most commonly used tools for retrieving PWV and VTEC and normally relies on dual‐frequency (DF), geodetic‐grade receivers and antennas. However, this reliance also implies high hardware costs. In this paper, we propose a single‐frequency ionosphere and troposphere retrieval approach (SFITR) that enables the simultaneous retrieval of PWV and VTEC from multi‐GNSS data collected by low‐cost SF receivers. The use of SF receivers can greatly reduce the cost of hardware. Furthermore, the simultaneous provision of PWV and VTEC also has a positive effect on studying the coupling mechanisms of the ionosphere and troposphere. The accuracy of the estimated ZTD can be better than 10 mm compared with the troposphere products published by the International GNSS Service (IGS), and the PWV is no more than 3 mm compared with radiosonde‐derived results. Referring to the final IGS global ionosphere map (GIM) products and the Jason altimeter data, the VTEC retrieved from the SFITR method can perform at roughly equal levels compared to the customary DF method.
Earth and Space Science; doi:10.1029/2019ea000635
Abstract:The Ångström‐Prescott model (referred to as the A‐P model) is one of the most accurate and widely used models for estimating global solar radiation (Rs). In the absence of Rs measurements, and given the regional discrepancy of model parameters, it is crucial to increase the availability of these parameters and the applicability of parameter‐predicted models in different regions. In this study, we evaluated and compared the applicability and performance of the calibrated model and 8 predictive models in terms of A‐P model parameters, using daily Rs and meteorological data from 105 radiation stations in 7 natural geographic zones in China. These models were evaluated based on their coefficient of determination (R2), root mean square error (RMSE), Nash‐Sutcliffe efficiency coefficients (NSE), percent bias (PBIAS), and global performance indexes (GPI). Results indicated that altitude was the main factor determining the Ångström‐Prescott parameters in most regions. All models performed well, with acceptable accuracy across the whole country, however, their performances varied among regions. The best performing predictive models for the northeast region (zone 1), north China (zone 2), central China (zone 3), south China (zone 4), Inner Mongolia (zone 5), northwest region (zone 6), and Qinghai‐Tibet region (zone 7) were obtained: these were models 6, 1, 7, 3, 6, 1, and 7, respectively. The present results support the application of these predictive models for the estimation of daily global Rs in the corresponding regions of China, where measured Rs data are not available, and possibly in other regions with a similar climate.
Earth and Space Science; doi:10.1029/2019ea000750
Abstract:Unmodelled periodicities of GNSS coordinate time series lead to colored noise and therefore, unreal estimations of uncertainties and misinterpretation of geophysical phenomena. This paper firstly conducted Least Square Harmonics Estimation (LSHE) and Lomb‐Scargle periodogram method respectively on 25 CMONOC GNSS time series in Yunnan Province, China to establish the corresponding function models for each station. However, several prominent problems emerge: (1) design matrix singularity occurs when too close alternative frequencies are introduced; (2) low frequencies would be missed due to the cutoff of alternative frequencies. Consequently, periodical variations of a station would be depicted in an incorrect way. In order to solve these problems, this paper proposes a method that takes advantages of both LSHE and Lomb‐Scargle periodogram, that is, (1) to conduct an examination on the reciprocal of condition number of design matrix to avoid singularity problem, (2) to introduce the frequency results from the periodogram as a priori candidate frequencies to include low frequencies and improve accuracy of alternative frequencies. Compared with LSHE method and Lomb‐Scargle periodogram, the modified LSHE method reduces Root Mean Square (RMS) value of residuals by 0.83 mm and 0.43 mm, and reduces absolute spectrum indices of residuals by 0.11 and 0.04. Spectrum analysis and auto‐correlation function of residuals indicates corresponding residuals are closer to white noise, indicating modified LSHE method of this paper is valid to reduce colored noise through establishing a full periodicity model.
Earth and Space Science; doi:10.1029/2019ea000717
Abstract:Using hourly observation data of precipitation and PM2.5 at 12 sites in Beijing from 2015 to 2017, this study investigates the impacts of different types of precipitation on PM2.5 mass concentration, along with the characteristics of precipitation and PM2.5. There were totally 91~123 precipitation events annually, 69.7% ~ 79.4% of which has precipitation amount less than 5 mm. By investigating the differences of PM2.5 mass concentration between 1 hour after and before the precipitation events, this study finds distinct impacts of different types of precipitation on PM2.5 mass concentration. For precipitation events with amount of 0.1~0.5 mm, PM2.5 mass concentration increased with precipitation amount with a rate of 0.85 μg/m3 per 0.1 mm. For precipitation events with amount of 0.5~10 mm, there was no clear relationship between precipitation amount and PM2.5 mass concentration. For precipitation events with amount larger than 10 mm, PM2.5 mass concentration decreased with precipitation amount with a rate of 0.17 μg/m3 per 1 mm. Further analysis shows that weak precipitation less than 10 mm increased PM10 and heavy precipitation larger than 10 mm decreased PM10. The aerosol amount also affects the response of PM2.5 to precipitation, with weak pollution prone to increase with precipitation and heavy pollution prone to decrease with precipitation. Likely mechanisms are discussed, which include the aerosol hygroscopic growth and gas‐particle conversion that increase aerosol amount, and precipitation scavenging that decreases aerosol amount. Shortly, the mechanisms that increase (decrease) aerosol amount more probably dominants when precipitation is light (heavy).
Earth and Space Science; doi:10.1029/2019ea000799
Abstract:Atmospheric NH3 plays a vital role not only in the environmental ecosystem but also in atmosphere chemistry. To further understand the effects of NH3 on the formation of haze pollution in Beijing, ambient NH3 and related species were measured and simulated at high resolutions during the wintertime Air Pollution and Human Health‐Beijing (APHH‐Beijing) campaign in 2016. We found that the total NHx (gaseous NH3+particle NH4+) was mostly in excess of the SO42‐‐NO3‐‐NH4+‐water equilibrium system during our campaign. This NHx excess made medium aerosol acidity, with the median pH value being 3.6 and 4.5 for polluted and non‐polluted conditions, respectively, and enhanced the formation of particle phase nitrate. Our analysis suggests that NH4NO3 is the most important factor driving the increasing of aerosol water content (AWC) with NO3‐ controlling the prior pollution stage and NH4+ the most polluted stage. Increased formation of NH4NO3 under excess NHx, especially during the nighttime, may trigger the decreasing of aerosol deliquescence relative humidity (DRH) even down to less than 50% and hence lead to hygroscopic growth even under RH conditions lower than 50% and the wet aerosol particles become better medium for rapid heterogeneous reactions. A further increase of RH promotes the positive feedback "AWC‐heterogeneous reactions" and ultimately leads to the formation of severe haze. Modelling results by NAQPMS show the control of 20% NH3 emission may affect 5~11% of PM2.5 formation under current emissions conditions in the North China Plain (NCP).
Earth and Space Science; doi:10.1029/2019ea000688
Abstract:A number of previous studies show that the long‐term Arctic winter warming causes severe cold over East Asia and North America. We use the atmospheric data from NCEP/NCAR Reanalysis to define the Arctic rapid tropospheric daily warming (RTDW) events that in one day, Arctic average 1000hPa air temperature is over 3
Earth and Space Science; doi:10.1029/2019ea000711
Earth and Space Science; doi:10.1029/2019ea000583
Abstract:The heat transfer scaling theories for Rayleigh‐Bénard convection (RBC) are reviewed and discussed for configurations with and without rotation and magnetic fields. Scaling laws are a useful tool in studying and characterizing geophysical flows as they provide a basis for extrapolation to extreme parameter regimes that remain unobtainable by current computational and experimental efforts. Specifically, power law scalings that relate the efficiency of the heat transport, as measured by the non‐dimensional Nusselt number Nu, to the thermal driving are pursued. Relations of the functional form Nu ∝ (Ra/Rac)α are considered. Given the strongly stabilizing influences of rotation and magnetic fields, thermal driving is considered in the context of the supercriticality of the system given by the ratio of the Rayleigh number Ra, measuring the thermal forcing, to the critical Rac, above which convection occurs. Analytical predictions for the exponent α are presented for the regimes of convection, rotating convection, and magnetoconvection, and the scalings are benchmarked against available numerical and experimental results in the accessible regimes. The exponents indicate that the thermal bottleneck to heat transport occurs within the thermal boundary layers for non‐rotating RBC and the turbulent interior for rotating RBC. For magnetoconvection, a single exponent of α = 1 is obtained for all theories and no bottleneck is identified.