Daily variations of airborne pollen in Beijing Olympic Park during August of three consecutive years and their relationships with meteorological factors

A three-year aeropalynological study was carried out in the month of August for each of the three years 2005, 2006 and 2007 in the Beijing Olympic Park. A total of 19550 pollen grains were counted （15057 grains in 2005, 2717 in 2006 and 1776 in 2007） for the following taxa： Gramineae, Chenopodiaceae, Humulus L., Artemisia L., Ambrosia L. and Pinus L. The analysis indicated that in the three consecutive years of 2005-007, airborne pollen types and daily number of pollen in August in the Beijing Olympic Park were closely related to environmental change and vegetation composition. The daily variations of airborne pollen displayed similar patterns in August in each of the three years, which were affected positively by periods of daily sunshine, negatively by daily relative humidity and daily precipitation. Continuously high daily temperatures and stable daily wind speeds seemed to have little effect on the fluctuation of airborne pollen.

Variations in Wave Energy and Amplitudes along the Energy Dispersion Paths of Nonstationary Barotropic Rossby Waves

The variations in the wave energy and the amplitude along the energy dispersion paths of the barotropic Rossby waves in zonally symmetric basic flow are studied by solving the wave energy equation,which expresses that the wave energy variability is determined by the divergence of the group velocity and the energy budget from the basic flow.The results suggest that both the wave energy and the amplitude of a leading wave increase significantly in the propagating region that is located south of the jet axis and enclosed by a southern critical line and a northern turning latitude.The leading wave gains the barotropic energy from the basic flow by eddy activities.The amplitude continuously climbs up a peak at the turning latitude due to increasing wave energy and enlarging horizontal scale(shrinking total wavenumber).Both the wave energy and the amplitude eventually decrease when the trailing wave continuously approaches southward to the critical line.The trailing wave decays and its energy is continuously absorbed by the basic flow.Furthermore,both the wave energy and the amplitude oscillate with a limited range in the propagating region that is located near the jet axis and enclosed by two turning latitudes.Both the leading and trailing waves neither develop nor decay significantly.The jet works as a waveguide to allow the waves to propagate a long distance.

Assimilation of GMS-5 satellite winds using nudging method with MM5

With the aid of Meteorological Information Composite and Processing System (MICAPS), satellite wind vectors derived from the Geostationary Meteorological Statellite-5 (GMS-5) and retrieved by National Satellite Meteorology Center of China (NSMC) can be obtained. Based on the nudging method built in the fifth-generation Mesoscale Model (MM5) of Pennsylvania State University and Na- tional Center for Atmospheric Research, a data preprocessor is developed to convert these satellite wind vectors to those with specified format required in MM5. To examine the data preprocessor and evaluate the impact of satellite winds from GMS-5 on MM5 simulations, a series of numerical experimental fore- casts consisting of four typhoon cases in 2002 are designed and implemented. The results show that the preprocessor can process satellite winds smoothly and MM5 model runs successfully with a little extra computational load during ingesting these winds, and that assimilation of satellite winds by MM5 nudging method can obviously improve typhoon track forecast but contributes a little to typhoon intensity forecast. The impact of the satellite winds depends heavily upon whether the typhoon bogussing scheme in MM5 was turned on or not. The data preprocessor developed in this paper not only can treat GMS-5 satellite winds but also has capability with little modification to process derived winds from other geostationary satellites.

Response of Northern Hemispheric Air Temperature to Arctic Sea Ice Decline

Two numerical experiments were performed by using the Community Atmosphere Model version 3 （CAM3） with different sea ice datasets to assess the con- tribution of the decline of Arctic sea ice to warming in the Northern Hemisphere. One observed sea ice cover data; experiment was driven by for the other one, the authors used the sea ice data of the 4xCO2 scenario simulated by the fourth-generation European Centre Hamburg atmos- pheric general circulation Model of Istituto Nazionale di Geofisica e Vulcanologia, Italy （1NGV ECHAM4）. The comparison of the two experiments indicates that the de- cline of the Arctic sea ice leads to a dramatic wanning over the high latitudes of the Northern Hemisphere, char- acterized by a maximum warming of more than 26~C over the Arctic region. The significant warming is closely re- lated to the enhanced atmospheric heat source. A 40-60 W m-2 increase in the apparent heat source was simulated in winter due to the decline of Arctic sea ice. In contrast, no significant change was found in the atmospheric ap- parent heat source in summer. As a result, the summer temperature change induced by the decline of Arctic sea ice appears to be weak. This study suggests that accurate sea ice cover data is crucial for future climate projection of air temperature in high latitudes.

Preliminary Estimation of Moisture Exchange in Rongbuk Valley on the Northern Slope of Mt. Qomolangma

Using observed wind and water vapor data from June 2006,water vapor exchange between the Rongbuk Valley and its above atmosphere is estimated for the first time.The water vapor level shows a high value from 23-29 June and a low from 12-21 June,which co-incide with the South Asian summer monsoon (SASM) active and break stages,respectively.The water vapor can be strongly injected into the closed region of the Rongbuk Valley from the outside atmosphere,with an average strength of 0.4 g s-1 m-2 in June 2006,given that no evaporation occurred.The air moisture exchange proc-esses can be greatly affected by the SASM evolution through changes in local radiation forcing.

Variations in Amplitudes and Wave Energy along the Energy Dispersion Paths for Rossby Waves in the Quasigeostrophic Barotropic Model

Variations in wave energy and amplitude for Rossby waves are investigated by solving the wave energy equation for the quasigeostrophic barotropic potential vorticity model.The results suggest that compared with rays in the nondivergent barotropic model,rays in the divergent model can have enhanced meridional and zonal propagation,accompanied by a more dramatic variability in both wave energy and amplitude,which is caused by introducing the divergence effect of the free surface in the quasigeostrophic model.For rays propagating in a region enclosed by a turning latitude and a critical latitude,the wave energy approaches the maximum value inside the region,while the amplitude approaches the maximum at the turning latitude.Waves can develop when both the wave energy and amplitude increase.For rays propagating in a region enclosed by two turning latitudes,the wave energy approaches the minimum value at one turning latitude and the maximum value at the other latitude,while the total wavenumber approaches the maximum value inside the region.The resulting amplitude increases if the total wavenumber decreases or the wave energy increases more significantly and decreases if the total wavenumber increases or the wave energy decreases more significantly.The matched roles of the energy from the basic flow and the divergence of the group velocity contribute to the slightly oscillating wave energy,which causes a slightly oscillating amplitude as well as the slightly oscillating total wavenumber.

Air Pollution Prediction Via Graph Attention Network and Gated Recurrent Unit

PM2.5 concentration prediction is of great significance to environmental protection and human health.Achieving accurate prediction of PM2.5 concentration has become an important research task.However,PM2.5 pollutants can spread in the earth’s atmosphere,causing mutual influence between different cities.To effectively capture the air pollution relationship between cities,this paper proposes a novel spatiotemporal model combining graph attention neural network(GAT)and gated recurrent unit(GRU),named GAT-GRU for PM2.5 concentration prediction.Specifically,GAT is used to learn the spatial dependence of PM2.5 concentration data in different cities,and GRU is to extract the temporal dependence of the long-term data series.The proposed model integrates the learned spatio-temporal dependencies to capture long-term complex spatio-temporal features.Considering that air pollution is related to the meteorological conditions of the city,the knowledge acquired from meteorological data is used in the model to enhance PM2.5 prediction performance.The input of the GAT-GRU model consists of PM2.5 concentration data and meteorological data.In order to verify the effectiveness of the proposed GAT-GRU prediction model,this paper designs experiments on real-world datasets compared with other baselines.Experimental results prove that our model achieves excellent performance in PM2.5 concentration prediction.

MULTI-TIMESCALE VARIATIONS OF SOMALI JET AND ITS RELATION WITH PRECIPITATION IN CHINA

Based on the ERA reanalysis winds data, the multi-time scale variations of Somali jet are analyzed synthetically. The jet's influences on rainfall in China on interannual, interdecadal and sub-monthly scales are also studied using correlation and composite analyses. The results demonstrate that the interdecadal variations of the jet are significant.The Somali jet became weaker in the 1960 s and became the weakest in the early 1970 s before enhancing slowly in the late 1970 s. Moreover, the relation between the Somali jet and summer precipitation in China is close, but varies on different timescales. Preliminary analysis shows that the intensity variations in May and June during the early days of establishment are well correlated with summer precipitation in China. The Somali jet intensity on the interdecadal scale is closely related with interdecadal variations of the precipitation in China. Regardless of leading or contemporaneous correlation, the correlations between the Somali jet intensity and the rainfall in northern and southern China show obvious interdecadal variations. Moreover, the link between the anomalies of the jet intensity in May-August and precipitation evolution on synoptic scale in China is further studied. China has more rainfall with positive anomalies of the Somali jet but less rainfall with negative anomalies during the active period of the jet. The influence of positive Somali jet anomalies on China precipitation is more evident.

Impacts of hydraulic redistribution on eco-hydrological cycles： A case study over the Amazon basin

Hydraulic redistribution(HR)refers to the process of soil water transport through the low-resistance pathway provided by plant roots.It has been observed in field studies and proposed to be one of the processes that enable plants to resist water limitations.However,most land-surface models(LSMs)currently do not include this underground root process.In this study,a HR scheme was incorporated into the Community Land Model version 4.5(CLM4.5)to investigate the effect of HR on the eco-hydrological cycle.Two paired numerical simulations(with and without the new HR scheme)were conducted for the Tapajos National Forest km83(BRSa3)site and the Amazon.Simulations for the BRSa3 site in the Amazon showed that HR during the wet season was small,<0.1 mm day^(–1),transferring water from shallow wet layers to deep dry layers at night;however,HR in the dry season was more obvious,up to 0.3 mm day^(–1),transferring water from deep wet layers to shallow dry layers at night.By incorporating HR into CLM4.5,the new model increased gross primary production(GPP)and evapotranspiration(ET)by 10%and 15%,respectively,at the BRSa3 site,partly overcoming the underestimation.For the Amazon,regional analysis also revealed that vegetation responses(including GPP and ET)to seasonal drought and the severe drought of 2005 were better captured with the HR scheme incorporated.

The GRAPES Variational Bias Correction Scheme and Associated Preliminary Experiments

The variational assimilation theory is generally based on unbiased observations. In practice, however, almost all observations suffer from biases arising from observational instruments, radiative transfer operator, precondition of data, and so on. Therefore, a bias correction scheme is indispensable. The current scheme for radiance bias correction in the GRAPES 3DVar system is an offline scheme. It is actually a static correction for the radiance bias before the process of cost function minimization. In consideration of its effects on forecast results, this kind of scheme has some shortcomings. Thus, this study provides a variational bias correction （VarBC） scheme for the GRAPES 3DVar system following Dee’s idea. In the VarBC scheme, the observation operator is modified and a new control variable is defined by taking the predictor coefficients as the control parameters. According to the feature of the GRAPES-3DVAR, an incremental formulation is applied and the original bias correction scheme is maintained in the actual process of observations. The VarBC is designed to co-exist with the original scheme, because it is a dynamic revision to the observational operator on the basis of the old method, i.e., it adjusts the model state vector along with the control parameters to an unbiased state in the process of minimization and the assimilation system remains consistent with available information automatically. Preliminary experimental results show that the mean departures of background-minus-observation and analysis-minus-observation are reduced as expected. In a case study of the heavy rainfall that happened in South China on 11–13 June 2008, the 500-hPa geopotential height is better simulated using the analyzed field from the VarBC as the initial condition.

Emission inventory evaluation using observations of regional atmospheric background stations of China

Any accurate simulation of regional air quality by numerical models entails accurate and up-to-date emissions data for that region.The INTEX-B2006 （I06）,one of the newest emission inventories recently popularly used in China and East Asia,has been assessed using the Community Multiscale Air Quality model and observations from regional atmospheric background stations of China.Comparisons of the model results with the observations for the species SO2,NO 2,O 3 and CO from the three regional atmospheric background stations of Shangdianzi,Longfengshan and Linan show that the model can basically capture the temporal characteristics of observations such as the monthly,seasonal and diurnal variance trends.Compared to the other three species,the simulated CO values were grossly underestimated by about two-third or one-half of the observed values,related to the uncertainty in CO emissions.Compared to the other two stations,Shangdianzi had poorer simulations,especially for SO2 and CO,which partly resulted from the site location close to local emission sources from the Beijing area;and the regional inventory used was not capable of capturing the influencing factors of strong regional sources on stations.Generally,the fact that summer gave poor simulation,especially for SO2 and O 3,might partly relate to poor simulations of meteorological fields such as temperature and wind.

Heavy Precipitation over the Jing–Jin–Ji Region in Early October: What Controls Its Interannual Variability?

Heavy regional precipitation(HRP)over Beijing,Tianjin,and Hebei Province(the Jing–Jin–Ji region or JJJ)in early October(1–10 October)is a high-impact climate event because of travel and outdoor activities by exceptionally large population during the Chinese National Day Holidays(CNDH).What causes the year-to-year variation of the HRP during early October is investigated through an observational analysis.It is found that the HRP arises from moisture transport by southerly anomalies to the west of an anomalous low-level anticyclone over the subtropical northwestern Pacific(SNWP).Sensitivity numerical experiments reveal that the low-level anticyclonic anomaly is caused by a dipole heating pattern over tropical western and central Pacific associated with a La Niña-like SST anomaly(SSTA)pattern in the Pacific and by a negative heating anomaly over North Europe.The latter connects the SNWP anticyclone through a Rossby wave train.Anomalous ascent associated with a positive heating anomaly over the tropical western Pacific may strengthen the local Hadley Cell,contributing to maintenance of the low-level anomalous anticyclone over SNWP and extending westwards of the western Pacific subtropical high(WPSH).Therefore,both the tropical Pacific and midlatitude heating signals over North Europe may be potential predictors for HRP forecast in the JJJ region in early October.