Preliminary Results from Numerical Experiments of a Heavy Rain Process with PENN STATE / NCAR MM5

PENN STATE/NCAR MM5 is used to simulate precipitation of the heavy rain process during 12-13 July 1994.The effects of different PBL parameterizations,resolvable scale moisture schemes and cumulus parameterization on the process rainfall simulation are investigated.By comparing the results of hydrostatic and nor.hydrostatic experiments,the nonhydrostatic impact upon precipitation is also examined.It is found in this study thai PENN STATE/NCAR MM5 has advantage not only in theory but also in simulating results with real data.In MM5.however,the selection of physical processes,especially water-cycle process,is very important and crucial to precipitation forecast of the case.It is concluded that the model with Grell (1993) scheme for convection and condensation method for resolvable scale precipitation captured the rainstorm during 12-13 July 1994 in Beijing area more successfully

Some numerical experiments of the dynamics of the wintertime circulation in the Northern Huanghai Sea and the Bohai Sea

-Some numerical experiments have been developed to explain dynamically the mechanism of the formation of the wintertime circulation in the Northern Huanghai Sea and the Bohai Sea. From the results of the numerical experiments with Coriolis parameter having positive and negative values respectively, it is found that the current pattern characterized by flowing into the Bohai Sea in the northern part of the Bohai Straits and flowing out of the Bohai Sea in the southern part of the Bohai Straits is controlled basically by the bottom topography with 'the deepness on the northern side and shallowness on the southern side'in the Bohai Straits, and is not related to Coriolis parameter having positive and negative values. It also shows that the Huanghai Warm Current regarded as the inllow condition passing through the in-ports at the water boundary of the numerical experiments only influences the region near the water boundary and the eastern region of the Northern Huanghai Sea. In addition, the mechanism of the formation of several mesoscale eddies and the influence of the bottom topography on the wintertime circulation in the basin have been discussed.

Numerical experiments on the evolution in coronal magnetic configurations including a filament in response to the change in the photosphere

We investigate equilibrium height of a flux rope, and its internal equilib- rium in a realistic plasma environment by carrying out numerical simulations of the evolution of systems including a current-carrying flux rope. We find that the equilib- rium height of a flux rope is approximately described by a power-law function of the relative strength of the background field. Our simulations indicate that the flux rope can escape more easily from a weaker background field. This further confirms that a catastrophe in the magnetic configuration of interest can be triggered by a decrease in strength of the background field. Our results show that it takes some time to reach internal equilibrium depending on the initial state of the flux rope. The plasma flow inside the flux rope due to the adjustment for the internal equilibrium of the flux rope remains small and does not last very long when the initial state of the flux rope com- mences from the stable branch of the theoretical equilibrium curve. This work also confirms the influence of the initial radius of the flux rope in its evolution; the results indicate that a flux rope with a larger initial radius erupts more easily. In addition, by using a realistic plasma environment and a much higher resolution in our simulations, we notice some different characteristics compared to previous studies in Forbes.

On the correlation of nonlinear variables containing secular trend variations： numerical experiments

Due to global warming, the general circulation, underlying surfaces characteristics, and geophysical and meteorological elements all show evident secular trends. This paper points out that when calculating the correlation of two variables containing their own obvious secular trends, the interannual correlation characteristics between the two variables may be distorted （overestimated or underestimated）. Numerical experiments in this paper show that if two variables have opposite secular trends, the correlation coefficient between the two variables is reduced （the positive correlation is underestimated, or the negative correlation is overestimated）; and if the two variables have the same sign of secular trends, the correlation coefficient between the two variables is increased （the positive correlation is overestimated, or the negative correlation is underestimated）. Numerical experiments also suggest that the effect of secular trends on the interannual correlation of the two variables is interchangeable, that is to say, as long as the values of the two trends are not changed, the two variables interchange their positions, and the effect of the secular trends on the interannual correlation coefficient of the two variables remains the same. If the two variables have the same-（opposite-） sign trends, the effect of secular trends on the interannal correlation coefficient is more （less） distinctive. A meteorological example is given.

NUMERICAL EXPERIMENTS ON MULTI-LEVEL STATISTICAL ESTIMATION OF DYNAMIC BALANCE CONSTRAINTS IN GRAPES-3DVAR

This paper further explores the estimating and expressing of dynamic balance constraints using statistical methods in GRAPES-3DVAR(Version GM). Unlike the single-level scheme which only considers the coupling between mass and wind at one level, the multi-level scheme considers the coupling between their vertical profiles and calculates the balanced mass field at each layer using the rotational wind at all model levels. A reformed ridge regression method is used in the new scheme to avoid the multicollinearity problem and reduce the noises caused by unbalanced mesoscale disturbances. The results of numerical experiments show that the new scheme can get more reasonable vertical mass field, reduce the magnitude of the adjustment by the initialization, and improve the potential temperature analysis performance. Furthermore, the results of forecast verification in January(winter) and July(summer) both confirm that the new scheme can significantly improve the temperature forecast accuracy and bring slight positive effects to the pressure and wind forecast.

NUMERICAL EXPERIMENTS FOR THE EFFECTS OF TWO MODEL INITIALIZATION SCHEMES ON RAINFALL FORECAST IN THE 2008 FLOODING SEASON

In this paper, based on heavy rain numerical forecast model AREM(Advanced Regional Eta Model), two different initialization schemes, LAPS and GRAPES-3DVAR, are used to run assimilation experiments of AREM-LAPS and AREM-3DVAR with the same data source(NCEP forecast field, surface data and radio-soundings) during the period from 21 May to 30 July 2008 to investigate the effect of the two initialization schemes on the rainfall simulation. The result suggests that:(1) the forecast TS score by the AREM-LAPS is higher than that by the AREM-3DVAR for rainfall in different areas, at different valid time and with different intensity, especially for the heavy rain, rainstorm and extremely heavy rain;(2) the AREM-3DVAR can generally simulate the average rainfall distribution, but the forecast area is smaller and rainfall intensity is weaker than the observation, while the AREM-LAPS significantly improves the forecast;(3) the AREM-LAPS gives a better forecast for the south-north shift of rainfall bands and the rainfall intensity variation than the AREM-3DVAR;(4) the AREM-LAPS can give a better reproduction for the daily change in the mean-rainfall-rate of the main rain band, and rainfall intensity changes in the eastern part of Southwest China, the coastal area in South China, the middle-lower valleys of Yangtze river, the Valleys of Huaihe river, and Shandong peninsula, with the rainfall intensity roughly close to the observation, while the rainfall intensity simulated by the AREM-3DVAR is clearly weaker than the observation, especially in the eastern part of Southwest China; and(5) the comparison verification between the AREM-LAPS and AREM-3DVAR for more than 10 typical rainfall processes in the summer of 2008 indicates that the AREM-LAPS gives a much better forecast than AREM-3DVAR in rain-band area, rainfall location and intensity, and in particular, the rainfall intensity forecast is improved obviously.

FIXED-POINT CONTINUATION APPLIED TO COMPRESSED SENSING:IMPLEMENTATION AND NUMERICAL EXPERIMENTS

Fixed-point continuation （FPC） is an approach, based on operator-splitting and continuation, for solving minimization problems with l1-regularization：min ｜｜x｜｜1＋uf（x）.We investigate the application of this algorithm to compressed sensing signal recovery, in which f（x） = 1/2｜｜Ax-b｜｜2M,A∈m×n and m≤n. In particular, we extend the original algorithm to obtain better practical results, derive appropriate choices for M and u under a given measurement model, and present numerical results for a variety of compressed sensing problems. The numerical results show that the performance of our algorithm compares favorably with that of several recently proposed algorithms.

Numerical Simulation and Analysis of Storm Surges Under Different Extreme Weather Event and Typhoon Experiments in the South Yellow Sea

In this study,a coupled tide-surge-wave model was developed and applied to the South Yellow Sea.The coupled model simulated the evolution of storm surges and waves caused by extreme weather events,such as tropical cyclones,cold waves,extratropical cyclones coupled with a cold wave,and tropical cyclones coupled with a cold wave.The modeled surge level and significant wave height matched the measured data well.Simulation results of the typhoon with different intensities revealed that the radius to the maximum wind speed of a typhoon with 1.5 times wind speed decreased,and its influence range was farther away from the Jiangsu coastal region;moreover,the impact on surge levels was weakened.Thereafter,eight hypothetical typhoons based on Typhoon Chan-hom were designed to investigate the effects of varying typhoon tracks on the extreme value and spatial distribution of storm surges in the offshore area of Jiangsu Province.The typhoon along path 2 mainly affected the Rudong coast,and the topography of the Rudong coast was conducive to the increase in surge level.Therefore,the typhoon along path 2 induced the largest surge level,which reached up to 2.91 m in the radial sand ridge area.The maximum surge levels in the Haizhou Bay area and the middle straight coastline area reached up to 2.37 and 2.08 m,respectively.In terms of typhoons active in offshore areas,the radial sand ridge area was most likely to be threatened by typhoon-induced storm surges.

NUMERICAL EXPERIMENTS FOR THE INFLUENCES OF SST ANOMALIES OVER THE SOUTH CHINA SEA-EASTERN TROPICAL INDIAN OCEAN ON THE SOUTH CHINA SEA SUMMER MONSOON ONSET

Numerical experiments with a low resolution atmospheric general circulation model (AGCM) were conducted to investigate the influences of SST anomalies (SSTA) over the South China Sea- tropical eastern indian Ocean (SCS-TEIO) on the onset of the South China Sea summer Monsoon (SCSM).With positive SSTA over the SCS-TEIO,the anomalous cyclones appear over both sides of the equator at low layer,which weakens the Somali and Australian cross-equatorial SW flow. The anomalous anticyclone in the east of Phillips strengthens the subtropical high with its ridge southwestward shifted.The anomalous anticyclones over both sides of equator at high layer strengthen the South Asia high,thus weaken the SCSM and delay its onset.With negative SSTA over the SCS-ETIO,the anomalous anticyclones appear over both sides of the equator at low layer,which strengthen the Australian but weaken the Somali cross-equatorial SW flow.The anomalous cyclone in northeast of Phillips will weaken the subtropical high.The stronger monsoon meridional circulation over the tropical western Pacific will strengthen the cross-equatorial southerly flow,and the anomalous cyclones over both sides of equator at high layer will weaken the South Asia high,hence strengthen the SCSM and advance its onset.

THE IMPACT OF RADIATIVE PROCESSES ON THE ONSET OF SUMMER MONSOON——NUMERICAL EXPERIMENTS

Two numerical experiments were performed by using ECMWF limited area model in order to assess the impact of radiative processes on the onset of summer monsoon.The control experiment includes all model physics and the other experiment is exclusive of radiative processes.The simulated results show that the radiative processes enhanced the monsoon circulation and the associated vertical circulation over South Asia.Especially over the Qinghai-Xizang Plateau,the build-up of the plateau monsoon depression and the beginning of the plat- eau rainy season are highly dependent upon the radiative processes. Through the radiation-cloud interaction,the “moist processes” were enhanced over land.More latent heat was released.The feedback of the physical processes caused the strengthening of the monsoon circulation over southern Asia.

A GLOBAL COUPLED OCEAN-ATMOSPHERE MODEL OF SHALLOW WATER WAVE AND ITS NUMERICAL EXPERIMENTS

A global coupled air-sea model of shallow water wave is developed based on coupled ocean-atmosphere dynamics.The coupling is realized through the air-sea interaction process that the atmosphere acts on the ocean by wind stress and the ocean acts on the atmosphere with heating proportional to sea surface temperature (SST)anomaly.The equation is harotropic primitive one.Response experiments of coupling system are also carried out SSTA in two categories of intensities.Compared with the results of AGCM simulation ex- periment in which only the dynamic change of air system is considered,it demonstrates that the air-sea interaction between the tropical ocean and the global atmosphere plays a very important role in the evolution of climate system.The results of numerical simulation show that it is encouraging.

Interaction Between Typhoon and Western Pacific Subtropical Anticyclone:Data Analyses and Numerical Experiments

Three kinds of typhoons with distinct tracks are sorted based on a set of typhoon data from 1958 to 1998. The results of composite analyses confirm that different typhoon tracks correspond to different patterns of the subtropical anticyclone over the western Pacific （SAWP）. When the tracks are westward, the SAWP is strong, with a zonal form, and stretches westward; when the tracks are recurving, the main body of the SAWP shifts eastward and breaks near 160~E; and when the tracks are northward, the SAWP is located far east of its normal position. Based on the above result, two different initial fields are configured, one has a zonal and strong SAWP, and the other has a meridional and weak SAWP. By using the GOALS R42L9 climate model, a temperature disturbance is added into these two different initial fields to force the formation of a typhoon. Westward and northward tracked typhoons are well simulated, thus verifying that different patterns of the SAWP have different effects on typhoon tracks. Results also show that typhoons can induce barotropic Rossby waves propagating to the mid and high latitudes. Under different background zonal flows, the wave trains triggered by the typhoons of westward and northward tracks are also different, and their effects on the mid and high latitude circulations and the SAWP are different. Compared to a n.orthward tracked typhoon, a westward tracked typhoon is able to induce positive geopotential height anomaly to its north and northwest, resulting in the SAWP strengthening and developing westward.

Numerical Experiments on the Spin-up Time for Seasonal-Scale Regional Climate Modeling

In this paper, the numerical experiments on the issue of spin-up time for seasonal-scale regional climate modeling were conducted with the newly Regional Climate Model （RegCM3）, in the case of the abnormal climate event during the summer of 1998 in China. To test the effect of spin-up time on the regional climate simulation results for such abnormal climate event, a total of 11 experiments were performed with different spin-up time from 10 days to 6 months, respectively. The simulation results show that, for the meteorological variables in the atmosphere, the model would be running in “climate mode” after 4-8-day spin-up time, then, it is independent of the spin-up time basically, and the simulation errors are mainly caused by the model＇ s failure in describing the atmospheric processes over the model domain. This verifies again that the regional climate modeling is indeed a lateral boundary condition problem as demonstrated by earlier research work. The simulated mean precipitation rate over each subregion is not sensitive to the spin-up time, but the precipitation scenario is somewhat different for the experiment with different spin-up time, which shows that there exists the uncertainty in the simulation to precipitation scenario, and such a uncertainty exhibits more over the areas where heavy rainfall happened. Generally, for monthly-scale precipitation simulation, a soin-uo time of 1 month is enough, whereas a spin-up time of 2 months is better for seasonal-scale one. Furthermore, the relationship between the precipitation simulation error and the advancement/withdrawal of East Asian summer monsoon was analyzed. It is found that the variability of correlation coefficient for precipitation is more significant over the areas where the summer monsoon is predominant. Therefore, the model＇s capability in reproducing precipitation features is related to the heavy rainfall processes associated with the advancement/withdrawal of East Asian summer monsoon, which suggests that it is necessary to develop a more reliable parameterization scheme to capture the convective precipitation of heavy rainfall pro- cesses associated with the activities of East Asian summer monsoon, so as to improve the climate modeling over China.

NUMERICAL EXPERIMENTS FOR THE INFLUENCE OF ANOMALOUS SEA SURFACE TEMPERATURE ON THE SOUTH CHINA SEA SUMMER MONSOON

Several sensitivity experiments are done by using the T42L9 global spectral model developed by IAP for investigating the influence of sea surface temperature anomaly (SSTA) in different regions on the South China Sea Summer Monsoon (SCSM).It shows that when SSTA presents a La Nina pattern,the onset date of SCSM will be earlier and the convection in the South China Sea region will be consistently stronger,and vice versa.Specially,SSTA in the central and eastern Pacific plays a main role in the variation of the onset and the strength of SCSM.When SSTA of this area is lower,the onset of SCSM comes earlier,the strength of SCSM becomes stronger, otherwise,the conclusion is contrary.The influence of SSTA in the tropical West Pacific on the onset date of SCSM is not clear,but it strongly affects the strength of the monsoon.The warmer SST in this region will bring about a stronger SCSM,and vice versa.The relationship between SSTA in the tropical western Indian Ocean and SCSM has been investigated.It is found that the SSTA in this region can influence the onset of SCSM,and plays a role similar to the one in the eastern Pacific.The above results also reflect that the activity of SCSM has a close relationship with the El Nino or La Nina events.The onset and the strength change of the SCSM are obviously influenced by the heating status anomaly on the tropic Pacific through the Walker circulation.

Experiments in numerical modelling of the Pacific sea surface temperature anomalies

By using the atmosphere-ocean coupled model (CGCM) which is composed of a 2-level global atmospheric general circulation model and a 4-layer Pacific oceanic general circulation model developed in the Institute of Atmospheric Physics of Chinese Academy of Sciences, and two model climatological fields got from the two independent models' numerical integrations respectively, the Pacific sea surface temperature anomalies (SSTA) from 1988 to 1989 are simulated in this paper with observed atmospheric general circulation data and sea surface temperature fields as initial conditions and monthly coupling scheme. In order to remove systematic biases of the model climatological fields, interaction variables between atmosphere and ocean are also corrected simultaneously. The experiments show that the simulation results can be improved effectively if these interaction variables are corrected in spite of the fact that there always exist systematic biases in independent numerical simulations of atmospheric part and oceanic part within CGCM. The basic characteristics of the observed Pacific SSTA in September and October 1988 have been simulated by using the correction scheme, such as the negative SSTA domain in the whole E-quatorial Pacific east to 150°E and the positive SSTA domain in the Western Pacific, the northern subtropical Pacific and nearly the whole Southern Pacific. Further numerical simulations show that the model can simulate not only the SSTA in the Pacific and its seasonal variations but also its interannual changes (for example, La Nino event in the Equatorial Pacific terminated after May 1989) to a certain degree. Furthermore, some problems existing in experiment processes and what we shoud do in the following stage are also discussed and analysed in this paper.

EXPERIMENTS ON ASSIMILATION OF INITIAL VALUES IN NUMERICAL PREDICTION OF A WARM-SECTOR PRECIPITATION IN SOUTH CHINA

In order to understand the impact of initial conditions upon prediction accuracy of short-term forecast and nowcast of precipitation in South China, four experiments i.e. a control, an assimilation of conventional sounding and surface data, testing with nudging rainwater data and the assimilation of radar-derived radial wind, are respectively conducted to simulate a case of warm-sector heavy rainfall that occurred over South China, by using the GRAPES_MESO model. The results show that (1) assimilating conventional surface and sounding observations helps improve the 24-h rainfall forecast in both the area and order of magnitude; (2) nudging rainwater contributes to a significant improvement of nowcast, and (3) the assimilation of radar-derived radial winds distinctly improves the 24-h rainfall forecast in both the area and order of magnitude. These results serve as significant technical reference for the study on short-term forecast and nowcast of precipitation over South China in the future.

NUMERICAL EXPERIMENTS IN SYMMETRIC AND ASYMMETRIC MOTIONS IN THE BAROTROPIC PRIMITIVE EQUATION MODEL ATMOSPHERE

Three numerical experiments have been carried out by using a spectral barotropic primitive equation mo- del.It is found that the results obtained are quite similar to those with the barotropic filtered model.The main results read as follows: (1)In the case with symmetric orography or without orography,if the motion is symmetric(with re- spect to the equator,the same is true hereafter)at the initial instant,then it would be symmetric afterwards. (2)The antisymmetric orography distribution could cause antisymmetric motion,and the original sym- metric motion might become asymmetric. In order to explain the above results,it has been proved that they are theoretically valid.And it is found that if the motion is antisymmetric at the initial instant,then it would become asymmetric.Therefore,no pure antisymmetric motion could be maintained.

A Numerical Study on the Effects of Orography During the Landfall Process of Typhoon Haitang

The landfall process of typhoon Haitang which affected East China seriously was simulated by using the MM5 model and the track, intensity, precipitation and structure of typhoon were successfully reproduced. Then through the sensitive test, the effects of terrain were analyzed Results show that the irregular track during the period of typhoon passing through Taiwan and later landfalling at Fujian was in relation to the occurring and developing of orthographic impressed depression. The amount of rainfall was enhanced more than one time and the strength of typhoon was weakened 4 to 5 hPa. It is found that the effect of terrain on the structure of typhoon is limited at low level and is backward in space compared with the one at high level. In addition, the phenomenon that the equivalent temperature in the typhoon＇s moving direction inclines to the west on the eye of landfall may be concerned with the terrain.

A Numerical Study of the Interaction between Two Simultaneous Storms:Goni and Morakot in September 2009

Significant anomalous tracks were observed when the severe tropical storm Goni （0907） and typhoon Morakot （0908） in September 2009 were evaluated in short distances. The relationship between the two is regarded as a case of binary interaction. Based on an MM5 model （fifth=generation mesoscale model of Pennsylvania State University-National Center for Atmospheric Research）, in this study a series of sensitivity experiments were designed to determine the binary interaction between them. The sensitivity of the storm characteristics to the binary interaction was demonstrated through modeling experiments with different TC intensities and sizes based on the bogus vortices initialization. Furthermore, the contributions of large-scale environmental flow and the effects of interaction between the motions of the cyclones were distinguished by numerical experiments using only one of the TC vortices. Results from these experiments show that Morakot （0908） had a greater impact on the motion of Goni （0907）, whereas Goni （0907） had a relatively limited impact on Morakot （0908）. At the upper level, the northeasterly jet flow in the third quadrant of Morakot （0908） enhanced the upper-level divergence of Goni （0907） and had an important role in maintaining and increasing Goni＇s （0907） intensity. And at the lower level, Morakot （0908）, with strong convergence and ascending airflow, made a stable transport channel of southwesterly warm and wet flow, thus supporting the lower-level water vapor convergence of Goni （0907）. Goni （0907）, which was located upriver of the southwesterly flow, intercepted part of the water vapor transportation in the southwesterly flow, causing the water vapor convergence to strengthen while the water vapor convergence of Morakot （0908） weakened.

NUMERICAL SIMULATION OF THE RELATIONSHIP BETWEEN THE MAINTENANCE AND INCREASE IN HEAVY RAINFALL OF THE LANDING TROPICAL STORM BILIS AND MOISTURE TRANSPORT FROM LOWER LATITUDES

The NCEP/NCAR reanalysis, Japan Meteorological Agency(JMA) tropical cyclone tracks and intensive surface observations are used to diagnose the features of moisture transport of tropical storm Bilis(No. 0604), which is simulated by the WRF(weather research and forecasting) mesoscale numerical model. It is shown that the Bilis was linked with the moisture channel in the lower latitudes after its landing. Meanwhile, the cross-equatorial flows over 80°-100°E and Somali were active and brought abundant water vapor into the tropical storm, facilitating the maintenance of the landing storm with intensified heavy rainfall along its path. The simulation suggested that the decreased water vapor from lower latitudes prevents the maintenance of Bilis and the development of rainfall. While the cross-equatorial flows over 80°-100°E and Somali were in favor of keeping the cyclonic circulation over land. If the moisture supply fro m the Somali jet stream was reduced, the strength and area of heavy rainfall in tropical cyclone would be remarkably weakened. Consequently, the decreased water vapor from lower latitudes can remarkably suppress the deep convection in tropical storm, then Bilis was damped without the persistent energy support and the rainfall was diminished accordingly.