On the mechanism of the seasonal variability of SST in the tropical Indian Ocean

A general form of an equation that "explicitly" diagnoses SST change is derived. All other equations in wide use are its special case. Combining with the data from an ocean general circulation model (MOM2) with an integration of 10 years (1987-1996), the relative importances of various processes that determine seasonal variations of SST in the tropical Indian Ocean are compared mainly for January, April, July and October. The main results are as follows. (1) The net surface heat flux is the most important factor affecting SST over the Arabian Sea, the Bay of Bengal and the region south of the equator in January; in April, its influence covers almost the whole region studied; whereas in July and October, this term shows significance only in the regions south of 10°S and north of the equator, respectively. (2) The horizontal advection dominates in the East African-Arabian coast and the region around the equator in January and July; in October, the region is located south of 10°S. (3) The entrainment is s     

Thermodynamics and Microphysical Characteristics of an Extreme Rainfall Event Under the Influence of a Low-level Jet over the South China Coast

In this paper, the data of Automatic Weather Stations (AWSs), ERA5 reanalysis, sounding, wind profile radar, and dual-polarization radar are used to study an extreme rainfall event in the south China Coast on 11 to 12 May 2022 from the aspects of thermodynamics and microphysical characteristics under the influence of low-level jets (LLJs). Results show that: (1) The extreme rainfall event can be divided into two stages: the first stage (S1) from 0000 to 0600 LST on May 12 and the second stage (S2) from 0700 to 1700 LST on the same day. During S1, the rainfall is mainly caused by the upper-level shortwave trough and the boundary layer jet (BLJ), characterized by strong upward motion on the windward side of mountains. In S2, the combined influence of the BLJ and synoptic-system-related low-level jet (SLLJ) increases the vertical wind shear and vertical vorticity, strengthening the rainstorm. In combination with the effect of topography, a warm and humid southwest flow continuously transports water vapor to farther north, resulting in a significant increase in rainfall over the study area (on the terrain’s windward slope). From S1 to S2, the altitude of a divergence center in the upper air decreases obviously. (2) The rainfalls in the two stages are both associated with the mesoscale convergence line (MCL) on the surface, and the wind field from the mesoscale outflow boundary (MOB) in S1 is in the same direction as the environmental winds. Due to a small area of convergence that is left behind the MOB, convection moves eastward quickly and causes a short duration of heavy rainfall. In S2, the convergence along the MOB is enhanced, which strengthens the rainfall and leads to strong outflows, further enhancing the surface convergence near the MOB and forming a positive feedback mechanism. It results in a slow motion of convection and a long duration of heavy rainfall. (3) In terms of microphysics, the center of a strong echo in S1 is higher than in S2. The warm-rain process of the oceanic type characterizes both stages, but the convective intensity in S2 is significantly stronger than that in S1, featuring bigger drop sizes and lower concentrations. It is mainly due to the strengthening of LLJs, which makes small cloud droplets lift to melting levels, enhancing the ice phase process (riming process), producing large amounts of graupel particles and enhancing the melting and collision processes as they fall, resulting in the increase of liquid water content (LWC) and the formation of large raindrops near the surface.     

Development of the Convective Boundary Layer Capping with a Thick Neutral Layer in Badanjilin: Observations and Simulations

In this study,the development of a convective boundary layer (CBL) in the Badanjilin region was investigated by comparing the observation data of two cases.A deep neutral layer capped a CBL that occurred on 30 August 2009.This case was divided into five sublayers from the surface to higher atmospheric elevations:surface layer,mixed layer,inversion layer,neutral layer,and sub-inversion layer.The development process of the CBL was divided into three stages:S1,S2,and S3.This case was quite different from the development of the three-layer CBL observed on 31 August 2009 because the mixed layer of the five-layer CBL (CBL5) eroded the neutral layer during S2.The specific initial structure of the CBL5 was correlated to the synoptic background of atmosphere during nighttime.The three-stage development process of the CBL5 was confirmed by six simulations using National Center for Atmospheric Research (USA) large-eddy simulation (NCAR-LES),and some of its characteristics are presented in detail.     

Dynamic Response of Phragmites australis and Suaeda salsa to Climate Change in the Liaohe Delta Wetland

Because of its unique geographical location and ecological function, the Liaohe Delta Wetland is important in maintaining regional ecological balance and security. Monitoring and evaluating changes in the wetland are therefore of great importance. We used medium-and high-resolution satellite data, meteorological station data, and site measurement data to analyze changes in the area and spatial distribution of Phragmites australis and Suaeda salsa in the Liaohe Delta Wetland from 1998 to 2017, as well as their growth response to the climate change. The results showed that during 1998–2017, the areas of both P. australis and S. salsa wetlands alternated through periods of decreasing,increasing, and then decreasing trends. The annual change in the area and spatial distribution range of S. salsa fluctuated more than that of P. australis. The annual variation of normalized difference vegetation index(NDVI) in P. australis wetland showed an upward trend from 1998 to 2017. The area of P. australis cover that was improved, unchanged, and decreased accounted for 81.8%, 12.3%, and 5.9%, respectively, of the total area;evaporation and wind speed were the main meteorological factors affecting the NDVI;and contribution rates of the climate change and human activities to the NDVI were 73.2% and 26.8%, respectively. The area with vegetation cover being mainly S.salsa that was improved, unchanged, and decreased accounted for 63.3%, 18.3%, and 18.4%, respectively, of the total area;and no meteorological factors significantly affected the NDVI of S. salsa in the region. The interaction between vegetation growth and meteorological factors may help to explain the increasing trend in vegetation cover.The improvement in wetland vegetation also led to carbon sequestration and an increase in sequestration capacity.     

Role of horizontal density advection in seasonal deepening of the mixed layer in the subtropical Southeast Pacific

The mechanisms behind the seasonal deepening of the mixed layer(ML) in the subtropical Southeast Pacific were investigated using the monthly Argo data from 2004 to 2012. The region with a deep ML(more than 175 m) was found in the region of(22?–30?S, 105?–90?W), reaching its maximum depth(～200 m) near(27?–28?S, 100?W) in September. The relative importance of horizontal density advection in determining the maximum ML location is discussed qualitatively. Downward Ekman pumping is key to determining the eastern boundary of the deep ML region. In addition, zonal density advection by the subtropical countercurrent(STCC) in the subtropical Southwest Pacific determines its western boundary, by carrying lighter water to strengthen the stratification and form a "shallow tongue" of ML depth to block the westward extension of the deep ML in the STCC region. The temperature advection by the STCC is the main source for large heat loss from the subtropical Southwest Pacific. Finally, the combined effect of net surface heat flux and meridional density advection by the subtropical gyre determines the northern and southern boundaries of the deep ML region: the ocean heat loss at the surface gradually increases from 22?S to 35?S, while the meridional density advection by the subtropical gyre strengthens the stratification south of the maximum ML depth and weakens the stratification to the north. The freshwater flux contribution to deepening the ML during austral winter is limited. The results are useful for understanding the role of ocean dynamics in the ML formation in the subtropical Southeast Pacific.     

Progress of MJO Prediction at CMA from Phase I to Phase II of the Sub-Seasonal to Seasonal Prediction Project

As one of the participants in the Subseasonal to Seasonal(S2S) Prediction Project, the China Meteorological Administration(CMA) has adopted several model versions to participate in the S2S Project. This study evaluates the models’ capability to simulate and predict the Madden-Julian Oscillation(MJO). Three versions of the Beijing Climate Center Climate System Model(BCC-CSM) are used to conduct historical simulations and re-forecast experiments(referred to as EXP1, EXP1-M, and EXP2, respectively)...     

Numerical Simulation on the Rainout-Removal of Sulfur Dioxide and Acidification of Precipitation from Stratiform Clouds

The rainout-removal of SO2 and the acidification of precipitation from stratiform clouds are simulated using a one-dimensional, time-dependent model, parameterized microphysically in which dissolution and dissociation of gaseous SO2 and H2O2, and oxidation reaction in aqueous phase are taken into account. The effects of dynamic fac-tors, including updraft flow and turbulent transport, and the concentration of gaseous SO2 and H2O2 being transported into the clouds on pH value of the precipitation, the conversion rate S(IV)－S (VI) and the wet deposition rate of SO2 are discussed.     

A STUDY ON TYPHOON MOVEMENT PART Ⅰ:THE EFFECT OF DIABATIC HEATING AND HORIZONTAL TEMPERATURE DISTRIBUTION

A basic equation governing the movement of a typhoon has been derived based on the system of primitive equations of motion in the atmosphere. The role of several forcing factors which cause the deviation of the typhoon from the steering current have been discussed based on the governing equation. What is presented in Part Ⅰ is a theoretical analysis on the effects of diabatic heating and the horizontal temperature distribution. It is shown that the accelerations of a typhoon caused by diabatic heating and temperature advection coincide with the direction of the volume-averaged "diabatic steering velocity" QV and the "steering velocity of temperature advection" A_TV (V is the air velocity,Q the diabatic heating rate and A_T the temperature advection ), respectively. The precipitation (or condensation heating) on the right (left) side of a typhoon will accelerate (decelerate) the typhoon. The precipitation in the front (rear ) of the typhoon will turn it to the left (right) of its ordainal path. A typhoon will speed up (slow down) when it moves towards a region of cold (warm) air.     

Study on Microwave Remote Sensing of Atmosphere,Cloud and Rain

In this paper, recent research of microwave remote sensing of atmosphere, cloud and rain in China is presented. It includes the following aspects:(1) Progress in the development of multifrequency radiometer and its characteristics and parameters;(2) Application of microwave remote sensing in prediction of atmospheric boundary layer. The atmospheric temperature profiles are derived with 5 mm (54.5 GHz) radiometer angle-scanning observations. Due to the fact that microwave radiometer could monitor the atmospheric temperature profile continuously and make the initialization of numerical model any time, it is helpful for improving the accuracy in prediction of the evolution of atmospheric boundary layer;(3) Theory and application of microwave radiometers in monitoring atmospheric temperature, humidity and water content in cloud. The field experiment of International Satellite Cloud Climatology Project (ISCCP) at Shionomisaki and Amami Oshima of Japan for studies of cloud and weather has been described;(4) S     

Sources of Subseasonal Prediction Skill for Heatwaves over the Yangtze River Basin Revealed from Three S2S Models

Based on the reforecast data(1999–2010) of three operational models [the China Meteorological Administration(CMA), the National Centers for Environmental Prediction of the U.S.(NCEP) and the European Centre for MediumRange Weather Forecasts(ECMWF)] that participated in the Subseasonal to Seasonal Prediction(S2S) project, we identified the major sources of subseasonal prediction skill for heatwaves over the Yangtze River basin(YRB). The three models show limited prediction skills in terms of the ...     

CHARACTERISTICS OF HEAT FLUX OVER THE TROPICAL WESTERN PACIFIC DURING THE IOP OF TOGA-COARE

Based on the surface meteorological and radiosonde data during the IOP of TOGA-COARE (Tropical Ocean Global Atmospheric-Coupled Ocean Atmospheric Response Experiment) at the observation site (2°15′S, 158°E)of "R/V Shiyan 3", characteristics of the heat flux, especially that pertaining two WWBs (westerly wind bursts)over the tropical western Pacific for the IOP, are exhaustively analyzed. Meanwhile, the relationships among large-scale circulation and mid-and-high latitude circulation are discussed. The results show that the latent and sensible heat fluxes from sea surface to air over the tropical western Pacific are very strong in both the WWBs,and that their causes of formation have important relations with cross-equatorial flow from the winter hemisphere,and the heat exchange over sea surface varies with different weather condition.     

Impacts of snow cover on vegetation phenology in the arctic from satellite data

The dynamics of snow cover is considered an essential factor in phenological changes in Arctic tundra and other northern biomes. The Moderate Resolution Imaging Spectroradiometer (MODIS)/Terra satellite data were selected to monitor the spatial and temporal heterogeneity of vegetation phenology and the timing of snow cover in western Arctic Russia (the Yamal Peninsula) during the period 2000-10. The magnitude of changes in vegetation phenology and the timing of snow cover were highly heterogeneous across latitudinal gradients and vegetation types in western Arctic Russia. There were identical latitudinal gradients for "start of season" (SOS) (r2 = 0.982, p<0.0001), "end of season" (EOS) (r2 = 0.938, p<0.0001), and "last day of snow cover" (LSC) (r2 = 0.984, p<0.0001), while slightly weaker relationships between latitudinal gradients and "first day of snow cover" (FSC) were observed (r2 = 0.48, p<0.0042). Delayed SOS and FSC, and advanced EOS and LSC were found in the south of the region, while there were completely different shifts in the north. SOS for the various land cover features responded to snow cover differently, while EOS among different vegetation types responded to snowfall almost the same. The timing of snow cover is likely a key driving factor behind the dynamics of vegetation phenology over the Arctic tundra. The present study suggests that snow cover urgently needs more attention to advance understanding of vegetation phenology in the future.     

Temperature Inversion in the Bay of Bengal Prior to the Summer Monsoon Onsets in 2010 and 2011

Freshwater input such as runoff and rainfall can enhance stratification in the Bay of Bengal(BOB) through the formation of a "barrier layer",which can lead to the formation of a temperature inversion.The authors focused on the temperature inversion in spring,especially before the onset of the summer monsoon,because previous research has mainly focused on the temperature inversion in winter.Using the hydrographic data from two cruises performed during 24-30 April 2010 and 1-4 May 2011,the authors found that inversions appeared at two out of nine Conductivity-Temperature-Depth Recorder(CTD) stations across the 10°N section and at seven out of 13 CTD stations across the 6°N section in the BOB.In 2010,the inversions(at stations N02 and N05) occurred at depths of approximately 50-60 meters,and their formation was caused by the advection of cold water over warm water.In 2010,the N02 inversion was mainly influenced by the warm saline water from the east sinking below the cold freshwater from the west,while the N05 inversion was affected by the warm saline water from its west sinking below the cold freshwater from its east.In 2011,the inversions appeared at depths of 20-40 meters(at stations S01,S02,S07,S08,and S09) and near 50 m(S12 and S13).The inversions in 2011 were mainly caused by the net heat loss of the ocean along the 6°N section.     

Temperature Inversion in the Bay of Bengal Prior to Summer Monsoon Onsets in 2010 and 2011

Freshwater input such as runoff and rainfall can enhance stratification in the Bay of Bengal(BOB) through the formation of a "barrier layer",which can lead to the formation of a temperature inversion.The authors focused on the temperature inversion in spring,especially before the onset of the summer monsoon,because previous research has mainly focused on the temperature inversion in winter.Using the hydrographic data from two cruises performed during 24-30 April 2010 and 1-4 May 2011,the authors found that inversions appeared at two out of nine Conductivity-Temperature-Depth Recorder(CTD) stations across the 10°N section and at seven out of 13 CTD stations across the 6°N section in the BOB.In 2010,the inversions(at stations N02 and N05) occurred at depths of approximately 50-60 meters,and their formation was caused by the advection of cold water over warm water.In 2010,the N02 inversion was mainly influenced by the warm saline water from the east sinking below the cold freshwater from the west,while the N05 inversion was affected by the warm saline water from its west sinking below the cold freshwater from its east.In 2011,the inversions appeared at depths of 20-40 meters(at stations S01,S02,S07,S08,and S09) and near 50 m(S12 and S13).The inversions in 2011 were mainly caused by the net heat loss of the ocean along the 6°N section.     

STUDY ON AIR-SEA HEAT EXCHANGE MECHANISM IN EL NINO AND LA NINA EVENTS

2°×2° mean monthly COADS grid data in 1974 and 1987 of E1 Nino and La Nina years are used to compute thesensible and latent heat fluxes,the net longwave radiation,the incident solar radiation and heat budget on the tropicalPacific surface(30°S—30°N).The difference of the heat budget between El Nino and La Nina mainly occurred on theequatorial ocean surface,especially the water area west of Ecuador and Peru.During El Nino,the sensible and latentheat exchange increased,the net longwave radiation and incident solar radiation decreased and the net gain(loss) of heatreduced(increased) on the ocean surface.During La Nina,the circumstances were opposite.Finally an ideal model ofair-sea heat exchange mechanism for the El Nino-La Nina cycle is summarized. Key words:El Nino,La Nina,air-sea heat exchange,COADS grid data     

Impacts of Drying on the Agricultural Structure of North China

It is one of subprojects of the National Basic Theoretical Research Project "The Living Environment Evolution and the Prediction Research on Drying Trend in North China." The project includes three parts:(1) the regionalization of ecological functional zones and discussions;(2) changes of water resources and their impacts on the agricultural production;(3) impacts of drying on the agricultural structure of arid or semiarid areas in North China and the corresponding countermeasures.     

THE ASIAN SUMMER MONSOON AND ITS RELATIONS TO THE RAINFALL IN CHINA

In this paper, four problems are discussed: (1) the monsoon circulation over southern Asia; (2) the seasonal variation of the general circulation of the atmosphere; (3) the influence of the monsoon on the rainfall in southwestern China; and (4) the source region of water vapor for the rainfall in the Changjiang valley.     

Effects of Changing Precipitation and Warming on Functional Traits of Zonal Stipa Plants from Inner Mongolian Grassland

The mechanisms driving changes in dominant plant species are the key for understanding how grassland ecosystems respond to climate change.In this study,we examined plant functional traits(morphological characteristics:plant height,leaf area,and leaf number;biomasses:aboveground,belowground,and total;and growth indices:root-to-shoot ratio,specific leaf area,and leaf mass ratio) of four zonal Stipa species(S.baicalensis,S.bungeana,S.grandis,and S.breviflora) from Inner Mongolian grassland in response to warming(control,+1.5,+2.0,+4.0,and +6.0℃),changing precipitation(-30%,-15%,control,+15%,and+30%),and their combined effects via climate control chambers.The results showed that warming and changing precipitation had significant interactive effects,different from the accumulation of single-factor effects,on functional traits of Stipa species.The correlation and sensitivity of different plant functional traits to temperature and precipitation differed.Among the four species,the accumulation and variability of functional traits had greater partial correlation with precipitation than temperature,except for leaf number,leaf area,and specific leaf area,in S.breviflora,S.bungeana,and S.grandis.For S.baicalensis,the accumulation and variability of plant height,aboveground biomass,and root-to-shoot ratio only had significant partial correlation with precipitation.However,the variability of morphological characteristics,biomasses,and some growth indices,was more sensitive to temperature than precipitation in S.bungeana,S.grandis,and S.breviflora—except for aboveground biomass and plant height.These results reveal that precipitation is the key factor determining the growth and changes in plant functional traits in Stipa species,and that temperature mainly influences the quantitative fluctuations of the changes in functional traits.     

AN ANALYSIS OF THE CHARACTERISTICS OF EQUATORIAL WESTERLIES

The real-time data of the high level atmosphere obtained by the R/V Xiangyanghong No.5 involved in the international TOGA-COARE project at 2°S, 155°E and at fixed real time of 05, 11, 19 and 23 h GMT each day from Nov. 5, 1992 to Feb. 18, 1993 are used to analyze diagnostically the vertical structure of wind and humidity over the central area of the warm pool. The results show that (1) the lowfrequency oscillation of the equatorial westerlies (i. e. reconstruction-development-decline) is closely related to the vigour and interruption of the Asian-Australian monsoon (including air flow across the equator caused by East Asia cold wave), (2) the variabilities of the vertical structure of wind and humidity, and the processes of precipitation and gale weather in the troposphere of the warm pool area are closely related to the intensity of the equatorial westerlies, and (3) there are strong wind belts over the high and low level atmosphere in the western equatorial Pacific at the inception of the ENSO event, and jet flow at the high and low level atmosphere during the equatorial westerly burst.     

Factors Limiting the Forecast Skill of the Boreal Summer Intraseasonal Oscillation in a Subseasonal-to-Seasonal Model

In this study,we evaluate the forecast skill of the subseasonal-to-seasonal(S2S)prediction model of the Beijing Climate Center(BCC)for the boreal summer intraseasonal oscillation(BSISO).We also discuss the key factors that inhibit the BSISO forecast skill in this model.Based on the bivariate anomaly correlation coefficient(ACC)of the BSISO index,defined by the first two EOF modes of outgoing longwave radiation and 850-hPa zonal wind anomalies over the Asian monsoon region,we found that the hindcast skill degraded as the lead time increased.The ACC dropped to below 0.5for lead times of 11 days and longer when the predicted BSISO showed weakened strength and insignificant northward propagation.To identify what causes the weakened forecast skill of BSISO at the forecast lead time of 11 days,we diagnosed the main mechanisms responsible for the BSISO northward propagation.The same analysis was also carried out using the observations and the outputs of the four-day forecast lead that successfully predicted the observed northward-propagating BSISO.We found that the lack of northward propagation at the 11-day forecast lead was due to insufficient increases in low-level cyclonic vorticity,moistening and warm temperature anomalies to the north of the convection,which were induced by the interaction between background mean flows and BSISO-related anomalous fields.The BCC S2S model can predict the background monsoon circulations,such as the low-level southerly and the northerly and easterly vertical shears,but has limited capability in forecasting the distributions of circulation and moisture anomalies.