A STUDY ON FIELD WATER CIRCULATION PATTERN IN THE DRYLAND OF NORTHERN CHINA

Based on the observed data of soil moisture from locating experiments from 1986 to 1990, the pattern of field water circulation in dryland of northern China, where the mean annual precipitation is 300 600 mm, is studied in this paper using the method of water balance. The results show that water satisfying ratio of spring seeding crops is 83.7 90.8 percent and that of winter wheat is about 70 percent in these areas; about 80 90 percent of water consumption of spring seeding crops and about 60 70 percent of water consumption of winter wheat comes from precipitation during the growing period, the rest comes from the soil water storage before the seeding period. But the available soil water is not used thoroughly, about 30 70 percent of available soil water remains unused when the crops are harvested. At the fallow period, the amount of soil water lost by evaporation is very important, which takes up 57 68 percent of precipitation in winter wheat field and 73 244 percent in field of spring seeding crops. Thus restraining soil evaporation, raising the storage ratio of natural precipitation and the soil water utilization efficiency of crops, strengthening the circulation ability of soil water by adopting efficient measures of agricultural techniques, are the main ways for exploiting and developing the potential productivity of natural precipitation in these areas.

Progress in satellite gravity recovery from implemented CHAMP,GRACE and GOCE and future GRACE Follow-On missions

Firstly, the Earth＇s gravitational field from the past Challenging Minisatellite Payload （CHAMP） mission is determined using the energy conservation principle, the combined error model of the cumulative geoid height influenced by three instrument errors from the current Gravity Recovery and Climate Experiment （GRACE） and future GRACE Follow-On missions is established based on the semi-analytical method, and the Earth＇s gravitational field from the executed Gravity Field and Steady-State Ocean Circulation Explorer （GOCE） mission is recovered by the space-time-wise approach. Secondly, the cumulative geoid height errors are 1.727 × 10^-1 m, 1.839 × 10^-1 m and 9.025 × 10^ -2 m at degrees 70,120 and 250 from the implemented three-stage satellite gravity missions consisting of CHAMP, GRACE and GOCE, which preferably accord with those from the existing earth gravity field models involving EIGEN-CHAMP03S, EICEN-GRACE02S and GO_CONS GCF 2 DIR R1. The cumulative geoid height error is 6.847 × 10 ^-2 m at degree 250 from the future GRACE Follow-On mission. Finally, the complementarity among the four-stage satellite gravity missions including CHAMP, GRACE, GOCE and GRACE Follow-On is demonstrated contrastively.

Rupture area analysis of the Ecuador (Musine) Mw = 7.8 thrust earthquake on April 16, 2016, using GOCE derived gradients

The Ecuador Mw - 7.8 earthquake on April 16, 2016, ruptured a nearly 200 km long zone along the plate interface between Nazca and South American plates which is coincident with a seismic gap since 1942, when a Mw - 7.8 earthquake happened. This earthquake occurred at a margin characterized by moderately big to giant earthquakes such as the 1906 （Mw 8.8）. A heavily sedimented trench explains the abnormal lengths of the rupture zones in this system as inhibits the role of natural barriers on the propagation of rupture zones. High amount of sediment thickness is associated with tropical climates, high erosion rates and eastward Pacific dominant winds that provoke orographic rainfalls over the Pacific slope of the Ecuatorian Andes. Offshore sediment dispersion off the oceanic trench is controlled by a close arrangement of two aseismic ridges that hit the Costa Rico and South Ecuador margin respectively and a mid ocean ridge that separates the Cocos and Nazca plate trapping sediments. Gravity field and Ocean Circulation Explorer （GOCE） satellite data are used in this work to test the possible relationship between gravity signal and earthquake rupture structure as well as registered aftershock seismic activity. Reduced vertical gravity gradient shows a good correlation with rupture structure for certain degrees of the harmonic expansion and related depth of the causative mass; indicating, such as in other analyzed cases along the subduction margin, that fore-arc structure derived from density heterogeneities explains at a certain extent propagation of the rupture zones. In this analysis the rupture zone of the April 2016 Ecuador earthquake developed through a relatively low density zone of the fore-arc sliver. Finally, aftershock sequence nucleated around the area of maximum slips in the rupture zone, suggesting that heterogeneous density structure of the fore-arc determined from gravity data could be used in forecasting potential damaged zones associated with big ruptures along the subduction border.

EFFECTS OF THREE-DIMENSIONAL STRUCTURE OF HEATING FIELD ON THE SUMMER MONSOON CIRCULATION IN ASIA

In this paper,a primitive equation linear wave model is used to examine the effects of three-dimen- sional structure of heating field on the behavior of stationary planetary waves in summer and to compare the roles of different heating functions for the formation and maintenance of summer monsoon circulation in Asia.It is shown that the aloft heating connected with the latent heating,especially the deep condensation heating associated with the cumulus convection in low latitudes,plays a crucial part in the Asian summer mon- soon and the structures of planetary wave responses are quite sensitive to the vertical distribution of heating.

An iterative Wiener filtering method based on the gravity gradient invariants

How to deal with colored noises of GOCE （Gravity field and steady - state Ocean Circulation Explorer） satellite has been the key to data processing. This paper focused on colored noises of GOCE gradient data and the frequency spectrum analysis. According to the analysis results, gravity field model of the optima] degrees 90-240 is given, which is recovered by COCE gradient data. This paper presents an iterative Wiener filtering method based on the gravity gradient invariants. By this method a degree-220 model was calculated from GOCE SGG （Satellite Gravity Gradient） data. The degrees above 90 of ITG2010 were taken as the prior gravity field model, replacing the low degree gravity field model calculated by GOCE orbit data. GOCE gradient colored noises was processed by Wiener filtering. Finally by Wiener filtering iterative calculation, the gravity field model was restored by space-wise harmonic analysis method. The results show that the model＇s accuracy matched well with the ESA＇s （European Space Agency） results by using the same data,

A STUDY OF CIRCULATION CHARACTERISTICS AND INDEX OF SOUTH CHINA SEA SUMMER MONSOON

Based on height and wind data of NCEP/NCAR and OLR data,patterns of upper air circulation from April to October have been analyzed,and the South China Sea (SCS) Summer Monsoon Onset (SMO) and retreat have been defined.The empirical formula fitting to the onset index of the SCS SMO has been established,and the onset and ending time of monsoon,together with the intensity index sequence during 1953—1999 are given by the analysis of characteristics of thermodynamic and dynamic factors during the process of SMO.The emergence and development of symmetric vortex pair at both sides of the equator in tropical East Indian Ocean,which may excite the SCS SMO,can be taken as a short-term prediction indicator of SMO.

ZONAL MEAN STRUCTURES OF THE EXTRATROPICAL TROPOSPHERE

The study of mean circulation fields requires evaluation of eddy foreings in the atmosphere.Due to the difficulty in calculating the eddy forcings on theory,the mean state equations including the eddy forcings were used mostly for diagnostic studies only.Using the geostrophic perturbation solutions obtained by McHall (1991a),we may deal with theoretically the eddy fluxes and their convergence.This allows us to employ the mean state equations for the study of mean circulation fields.It will be found that the time averaged zonal mean structure and circulation of the troposphere at middle and high latitudes can be reproduced basically in terms of the mass and momentum balances in geostrophic wave circulations.

MM5 Simulations of the China Regional Climate During the Mid-Holocene

Using a regional climate model MM5 nested with an atmospheric global climate model CCM3, a series of simulations and sensitivity experiments have been performed to investigate responses of the mid-Holocene climate to different factors over China. Model simulations of the mid-Holocene climate change, especially the precipitation change, are in good agreement with the geologic records. Model results show that relative to the present day （PD） climate, the temperature over China increased in the mid-Holocene, and the increase in summer is more than that in winter. The summer monsoon strengthened over the eastern China north of 30°N, and the winter monsoon weakened over the whole eastern China; the precipitation increased over the west part of China, North China, and Northeast China, and decreased over the south part of China. The sensitive experiments indicate that changes in the global climate （large-scale circulation background）, vegetation, earth orbital parameter, and CO2 concentration led to the mid-Holocene climate change relative to the PD climate, and changes in precipitation, temperature and wind fields were mainly affected by change of the large-scale circulation background, especially with its effect on precipitation exceeding 50%. Changes in vegetation resulted in increasing of temperature in both winter and summer over China, especially over eastern China; furthermore, its effect on precipitation in North China accounts for 25% of the total change. Change in the orbital parameter produced the larger seasonal variation of solar radiation in the mid-Holocene than the PD, which resulted in declining of temperature in winter and increasing in summer; and also had an important effect on precipitation with an effect equivalent to vegetation in Northeast China and North China. During the mid-Holocene, CO2 content was only 280×10^-6, which reduced temperature in a very small magnitude. Therefore, factors affecting the mid-Holocene climate change over China from strong to weak are large-scale circulation pattern, vegetation, earth orbital parameter, and CO2 concentration.