The Effect of Boreal Summer Intraseasonal Oscillation on Mixed Layer and Upper Ocean Temperature over the South China Sea

Intraseasonal oscillation of the mixed layer and upper ocean temperature has been found to occur over the South China Sea(SCS)in the summer monsoon season based on the multiple reanalysis and observational data in this study.The method of composite analysis and an upper ocean temperature equation assisted the analysis of physical mechanisms.The results show that the mixed layer depth(MLD)in the SCS has a significant oscillation with a 30-60 d period over the SCS region,which is closely related to boreal summer intraseasonal oscillation(BSISO)activities.The MLD can increase(decrease)during the positive(negative)phase of the BSISO and usually lags behind by approximately one-eighth of the lifecycle(5 days)of the BSISO-related convection.The BSISO may cause periodic anomalies at the air-sea boundary,such as wind stress and heat flux,so it can play a dominant role in modulating the variation in MLD.There also are significant intraseasonal seawater temperature anomalies in both the surface and subsurface layers of the SCS.In addition,during the initial phase of the BSISO,the temperature anomaly signals of the thermocline are obviously opposite to the sea surface temperature(SST),especially in the southern SCS.According to the results from the analysis of the temperature equation,the vertical entrainment term caused by BSISO-related wind stress is stronger than the thermal forcing during the initial stage of convection,and it is more significant in the southern SCS.

The 30–60-day Intraseasonal Oscillations over the Subtropical Western North Pacific during the Summer of 1998

The features of 30-60-day convection oscillations over the subtropical western North Pacific （WNP） were investigated, along with the degree of tropical-subtropical linkage between the oscillations over the WNP during summer 1998. It was found that 30-60-day oscillations were extremely strong in that summer over both the subtropical and tro]~ical WNP, providing a unique opportunity to study the behavior of subtropical oscillations and their relationship to tropical oscillations. Further analyses indicated that 30-60-day oscillations propagate westwards over the subtropical WNP and reach eastern China. In addition, 30-60-day oscillations in the subtropics are affected by those over the South China Sea （SCS） and tropical WNP through two mechanisms： （1） direct propagation from the tropics into the subtropics; and （2） a seesaw pattern between the tropics and subtropics, with the latter being predominant.

The Boreal Summer Intraseasonal Oscillation Simulated by Four Chinese AGCMs Participating in the CMIP5 Project

The performances of four Chinese AGCMs participating in the Coupled Model Intercomparison Project Phase 5 （CMIP5） in the simulation of the boreal summer intraseasonal oscillation （BSISO） are assessed. The authors focus on the major characteristics of BSISO： the intensity, significant period, and propagation. The results show that the four AGCMs can reproduce boreal summer intraseasonal signals of precipitation; however their limitations are also evident. Compared with the Climate Prediction Center Merged Analysis of Precipitation （CMAP） data, the models underestimate the strength of the intraseasonal oscillation （ISO） over the eastern equatorial Indian Ocean （IO） during the boreal summer （May to October）, but overestimate the intraseasonal variability over the western Pacific （WP）. In the model results, the westward propagation dominates, whereas the eastward propagation dominates in the CMAP data. The northward propagation in these models is tilted southwest-northeast, which is also different from the CMAP result. Thus, there is not a northeast-southwest tilted rain belt revolution off the equator during the BSISO＇s eastward journey in the models. The biases of the BSISO are consistent with the summer mean state, especially the vertical shear. Analysis also shows that there is a positive feedback between the intraseasonal precipitation and the summer mean precipitation. The positive feedback processes may amplify the models＇ biases in the BSISO simulation.

The Tropical Intraseasonal Oscillation in SAMIL Coupled and Uncoupled General Circulation Models

Simulations of tropical intraseasonal oscillation （TISO） in SAMIL, the Spectral Atmospheric Model from the Institute of Atmospheric Physics （IAP） State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics （LASG） coupled and uncoupled general circulation models were comprehensively evaluated in this study. Compared to the uncoupled model, the atmosphere-ocean coupled model improved the TISO simulation in the following aspects： （1） the spectral intensity for the 30-80-day peak eastward periods was more realistic; （2） the eastward propagation signals over western Pacific were stronger; and （3） the variance distribution and stronger signals of Kelvin waves and mixed Rossby gravity waves were more realistic. Better performance in the coupled run was assumed to be associated with a better mean state and a more realistic relationship between precipitation and SST. In both the coupled and uncoupled runs, the unrealistic simulation of the eastward propagation over the equatorial Indian Ocean might have been associated with the biases of the precipitation mean state over the Indian Ocean, and the unrealistic split of maximum TISO precipitation variance over the Pacific might have corresponded to the exaggeration of the double Intertropical Convergence Zone （ITCZ） structure in precipitation mean state. However, whether a better mean state leads to better TISO activity remains questionable. Notably, the northward propagation over the Indian Ocean during summer was not improved in the mean lead-lag correlation analysis, but case studies have shown some strong cases to yield remarkably realistic northward propagation in coupled runs.

Effects of Intraseasonal Oscillation on the Anomalous East Asian Summer Monsoon During 1999

The 1999 East Asian summer monsoon was very unusual for its weak northward advance and remarkably anomalous climate conditions. The monsoonal southwesterly airflow and related rain belt in East Asia were blocked south of the Yangtze River Valley. The monsoonal airflow and major moisture transport conduct shifted eastward and turned northward to Japan from the tropical western Pacific rather than to East China from the South China Sea （SCS） as in normal years. Severe and prolonged drought occurred over extensive areas of North China and heavy precipitation in South China and Japan. The investigation on the possible intrinsic mechanisms related to such an anomalous monsoon year has shown that the unique behavior of intraseasonal oscillation may play an essential role during this process. During this year, the northward propagation of 30-60-day anomalous low-level cyclone/anticyclone collapsed in the region around 20°N and did not extend beyond the latitudes of the Yangtze River basin due to the barrier of strong cold air intrusion from the mid-latitudes. The southwesterly moisture flux on the northwestern flank of the anticyclonic moisture transport system in the western North Pacific, which was regulated by the northward shift of 30-60-day cyclonic/anticyclonic moisture transport, also did not reach the region north of 30°N as well. Under this circumstance, the weak northward advance of the monsoon westerlies and associated northward moisture transport could not arrive in North China and led to the severe droughts there in 1999. The SCS and South China were mostly affected by the airflow in the southern and northern flanks of the same 30-60-day cyclones or anticyclones, respectively, and thus controlled by the nearly reverse zonal wind and moisture convergent/divergent conditions. The rainfall in the SCS and South China showed out-of-phase oscillation through the transient local Hadley circulation, with the rainfall maximum occurring in the SCS （South China） when the 30-60-day anticyclone （cyclone） reached its peak phase.

Intraseasonal Oscillation in Global Ocean Temperature Inferred from Argo

The intraseasonal oscillation （ISO; 14 97-day ocean was studied based on Argo observations periods） of temperature in the upper 2000 m of the global from 20052008. It is shown that near the surface the ISO existed mainly in a band east of 60°E, between 10°S and 10°N, and the region around the Antarctic Circumpolar Current （ACC）. At other levels analyzed, the ISOs also existed in the regions of the Kuroshio, the Gulf Stream, the Indonesian throughflow, the Somalia current, and the subtropical eountercurrent （STCC） of the North Pacific. The intraseasonal signals can be seen even at depths of about 2000 m in some regions of the global ocean. The largest amplitude of ISO appeared at the thermocline of the equatorial Pacific, Atlantic and Indian Ocean, with maximum standard deviation （STD） exceeding 1.2°C. The ACC, the Kuroshio, and the Gulf Stream regions all exhibited large STD for all levels analyzed. Especially at 1000 m, the largest STD appeared in the south and southeast of South Africa a part of the ACC, with a maximum value that reached 0.5°C. The ratios of the intraseasonal temperature variance to the total variance at 1000 m and at the equator indicated that, in a considerable part of the global deep ocean, the ISO was dominant in the variations of temperature, since such a ratio exceeded even 50% there. A case study also confirmed the existence of the ISO in the deep ocean. These results provide useful information for the design of field observations in the global ocean. Analysis and discussion are also given for the mechanism of the ISO.

The East Asia-Western North Pacific Boreal Summer Intraseasonal Oscillation Simulated in GAMIL 1.1.1

We evaluate the performance of GAMILI.1.1 in a 27-year forced simulation of the summer intraseasonal oscillation （ISO） over East Asia （EA）-western North Pacific （WNP）. The assessment is based on two mea- sures： climatological ISO （CISO） and transient ISO （TISO）. CISO is the ISO component that is phase-locked to the annual cycle and describes seasonal march. TISO is the ISO component that varies year by year. The model reasonably captures many observed features of the ISO, including the stepwise northward advance of the rain belt of CISO, the dominant periodicities of TISO in both the South China Sea-Philippine Sea （SCS-PS） and the Yangtze River Basin （YRB）, the northward propagation of 30-50-day TISO and the westward propagation of the 12-25-day TISO mode over the SCS-PS, and the zonal propagating features of three major TISO modes over the YRB. However, the model has notable deficiencies. These include the early onset of the South China Sea monsoon associated with CISO, too fast northward propagation of CISO from 20°N to 40°N and the absence of the CISO signal south of 10°N, the deficient eastward propagation of the 30-50-day TISO mode and the absence of a southward propagation in the YRB TISO modes. The authors found that the deficiencies in the ISO simulation are closely related to the model＇s biases in the mean states, suggesting that the improvement of the model mean state is crucial for realistic simulation of the intraseasonal variation.

Intraseasonal Oscillation in the Tropical Indian Ocean

The features of the intraseasonal oscillation （ISO） of the tropical Indian Ocean are studied using several sources of observational data. It is shown that there are intraseasonal oscillations in the tropical Indian Ocean, but their periods vary with latitude： the major period is about 20-30 days in the equatorial region, about 30-50 days at 10°N/10°S latitude and 60-90 days at 20°N/20°S latitude. The intensity of the ISO increases with latitude but the speed of the westward propagation of the ISO decreases with latitude. The intensity and propagation speed of the ISO have clear interannual variation features. The atmospheric intraseasonal oscillation over the tropical Indian Ocean is also analyzed and compared with the oceanic intraseasonal oscillation. It is shown that the major period is in the range 30-60 days and the intensity and period of the atmospheric ISO decrease with latitude slightly. The zonal propagation of the atmospheric ISO also has some differences with the oceanic ISO. It is necessary to study the relationship between the atmospheric ISO and oceanic ISO in the tropical Indian Ocean deeply.

Modulation of Western North Pacific Tropical Cyclone Genesis by Intraseasonal Oscillation of the ITCZ:A Statistical Analysis

The present study investigates modulation of western North Pacific （WNP） tropical cyclone （TC） genesis in relation to different phases of the intraseasonal oscillation （ISO） of ITCZ convection during May to October in the period 1979 2008. The phases of the ITCZ ISO were determined based on 30-80-day filtered OLR anomalies averaged over the region （5°20′N, 120°150′E）. The number of TCs during the active phases was nearly three times more than during the inactive phases. The active （inactive） phases of ISO were characterized by low-level cyclonic （anticyclonic） circulation anomalies, higher （lower） midlevel relative humidity anomalies, and larger （smaller） vertical gradient anomalies of relative vorticity associated with enhanced （weakened） ITCZ convection anomalies. During the active phases, TCs tended to form in the center of the ITCZ region. Barotropic conversion from the low-level mean flow is suggested to be the major energy source for TC formation. The energy conversion mainly depended on the zonal and meridional gradients of the zonal flow during the active phases. However, barotropic conversion weakened greatly during the inactive phases. The relationship between the meridional gradient of absolute vorticity and low-level zonal flow indicates that the sign of the absolute vorticity gradient tends to be reversed during the two phases, whereas the same sign between zonal flow and the absolute vortieity gradient is more easily satisfied in the active phases. Thus, the barotropie instability of low-level zonal flow might be an important mechanism for TC formation over the WNP during the active phases of ISO.

Intensified Eastward and Northward Propagation of Tropical Intraseasonal Oscillation over the Equatorial Indian Ocean in a Global Warming Scenario

Northward propagation in summer and eastward propagation in winter are two distinguished features of tropical intraseasonal oscillation （TISO） over the equatorial Indian Ocean. According to numerical modeling results, under a global warming scenario, both propagations were intensified. The enhanced northward propagation in summer can be attributed to the enhanced atmosphere-ocean interaction and the strengthened mean southerly wind; and the intensified eastward propagation in winter is associated with the enhanced convection-wind coupling process and the strengthened equatorial Kevin wave. Future changes of TISO propagations need to be explored in more climate models.

Different Impacts of Intraseasonal Oscillations on Precipitation in Southeast China between Early and Late Summers

This study investigates the influences of boreal summer intraseasonal oscillation(BSISO), which originates from the equatorial Indian Ocean and prevails over the Indo-Pacific region, on precipitation over Southeast China, including South China and Yangtze River Valley. The results indicate that the BSISO-related precipitation anomalies are remarkably different between early summer(May–June) and late summer(July–August). The BSISO-related precipitation anomalies tend to appear more northward in late summer in comparison with early summer. Accordingly, the BSISO is significantly related to precipitation anomalies over South China during many phases in early summer but related to very weak anomalies during all the phases in late summer. Such northward shifts of precipitation anomalies from early summer to late summer are clearest during phases 4 and 7, when the lower-tropospheric anticyclonic and cyclonic circulation anomalies dominate over the subtropical western North Pacific, respectively. Finally, we explain the differences between early and late summers through the seasonal northward migration of climatological equivalent potential temperature gradient, which is located in the South China during early summer but migrates northward to the YRV during late summer.

CLIMATOLOGICAL CHARACTERISTICS OF SPRING PRECIPITATION OVER SOUTHERN CHINA AND ITS INTRASEASONAL OSCILLATION

Based on observations and reanalysis data,the characteristics of the evolution of climatological spring precipitation over Southern China(SPSC) and the associated climatological intraseasonal oscillation(CISO) and atmospheric circulation are studied.Results show that SPSC increases in an oscillatory way.Although the evolution of SPSC is similar in different regions,there are also differences.In different regions of Southern China,the onset dates of the rain season are from the 12 th to 24 th pentad and the peak dates are after the 20 th pentad.CISO is an important component of SPSC,which is not only statistically significant,but also accompanies a dynamically coherent structure.The peak wet/dry phase of each CISO cycle corresponds to a significant rainfall increasing/decreasing period and modulates the evolution of SPSC.The rainfall growth in the second half of March and mid-April is the result of the modulation.The wet/dry phase of CISO is accompanied by low-level convergent(upper-level divergent) and cyclonic(anti-cyclonic) circulation,which favors ascending motion to develop over Southern China.

Performance of FGOALS-s2 in Simulating Intraseasonal Oscillation over the South Asian Monsoon Region

The capability of the current version of the air-sea coupled climate model, the Flexible Global Ocean- Atmosphere-Land System model, Spectral Version 2 （FGOALS-s2）, in simulating the boreal summer in- traseasonal oscillation （ISO） over the south Asian monsoon （SAM） region is diagnosed, in terms of dominant period, propagation direction, and vertical structure. Results show that the coupled model can reasonably simulate the main features of observed ISO propagation compared to the chosen AGCM. These features in- clude the eastward movement of intraseasonal 850-hPa zonal wind over the Arabian Sea and Bay of Bengal, the vertical structure in active phases, and the realistic phase relationship between ISO and underlying SST. However, the eastward propagation cannot be reproduced in the uncoupled model. This suggests that air- sea interaction is important in generating intraseasonal variability over the SAM region. Nevertheless, some deficiencies remain in the coupled model, which may relate to physical processes depicted by the cumulus parameterization and PBL schemes within its atmospheric component.

Comparison of coupled and uncoupled models in simulating Monsoon Intraseasonal Oscillation from CMIP6

The monsoon intraseasonal oscillation(MISO)is the dominant variability over the Indian Ocean during the Indian summer monsoon(ISM)season and is characterized by pronounced northward propagation.Previous studies have shown that general circulation models(GCMs)still have difficulty in simulating the northwardpropagating MISO,and that the role of air-sea interaction in MISO is unclear.In this study,14 atmosphere-ocean coupled GCMs(CGCMs)and the corresponding atmosphere-only GCMs(AGCMs)are selected from Phase 6 of the Coupled Model Intercomparison Project(CMIP6)to assess their performance in reproducing MISO and the associated vortex tilting mechanism.The results show that both CGCMs and AGCMs are able to well simulate the significant relationship between MISO and vortex tilting.However,80%of CGCMs show better simulation skills for MISO than AGCMs in CMIP6.In AGCMs,the poor model fidelity in MISO is due to the failure simulation of vortex tilting.Moreover,it is found that failure to simulate the downward motion to the north of convection is responsible for the poor simulation of vortex tilting in AGCMs.In addition,it is observed that there is a significant relationship between the simulated sea surface temperature gradient and simulated vertical velocity shear in the meridional direction.These findings indicate that air-sea interaction may play a vital role in simulating vertical motions in tilting and MISO processes.This work offers us a specific target to improve the MISO simulation and further studies are needed to elucidate the physical processes of this air-sea interaction coupling with vortex tilting.

MODULATION OF TC GENESIS OVER THE NORTHWESTERN PACIFIC BY ATMOSPHERIC INTRASEASONAL OSCILLATION

The influence of intraseasonal oscillation (ISO) on TC genesis over the northwestern Pacific is studied through comparing analyses of the more and less TC years from 1979 to 2006. It is indicated that the ISO strongly affects the TC genesis. In the years for more TC genesis, the ISO is weak and propagates insignificantly in the area to the west of the Philippines, but the ISO is strong in the area to the east of the Philippines and propagates significantly northwestward. In this situation, the Walker cell shifts gradually westward from the tropical western Pacific to the tropical eastern Indian Ocean. Convergent winds appear in the lower atmosphere while divergent winds in the upper atmosphere, suggesting the presence of enhanced ascending flow over the 140-160°E region and a favorable condition for TC genesis. Moreover, in the years for less TC genesis, the ISO gradually becomes stronger in the area to the west of the Philippines and significant eastward propagation prevails from the eastern Indian Ocean to the area around 120°E; the ISO is weak in the area to the east of the Philippines. During these years, the Walker circulation gradually moved eastward, with convergent winds in the upper troposphere and divergent winds in the lower troposphere. Sinking motion was significant, unfavorable for the TC genesis over the Northwestern Pacific.

RELATIONSHIP BETWEEN SUMMER LOW-FREQUENCY RAINFALL OVER SOUTHERN CHINA AND PROPAGATION OF TROPICAL INTRASEASONAL OSCILLATION

This study investigates the relationship between summer low-frequency rainfall over southern China and tropical intraseasonal oscillation(ISO) in the atmosphere by examining systematically the propagation features of the tropical ISO in terms of focusing on five large-scale low-frequency rainfall regimes in summer over southern China. It is demonstrated that there is a close linkage between the five rainfall regimes over southern China and the northward propagation of the tropical ISO. The moist ISO signals, which influence the low-frequency rainfall events in different regions of southern China, mainly propagate northwestward from the tropical ocean to the southeast of China. The southeast China rainfall regime is intimately associated with the moist ISO signals propagating northwestward from the equatorial mid-western Pacific Ocean. For both the Yangtze River regime and South of Yangtze River regime, the moist ISO signals over the northern South China Sea show an evident northward propagation towards the Yangtze River region, and then propagate westward. It is further found that the interaction between the northward propagation of low-latitude ISO signals and the southward propagation of high-latitude ISO signals can also make a clear influence on the low-frequency rainfall in southern China. For the Southern China regime, the moist ISO signals show a significant northward propagation from the Philippines. Moreover, for the rainless regime, southern China is under dry ISO signals' control, and the latter shows no clear propagation to southern China. This study may provide insights for the extended-range forecasting of summer rainfall in southern China.

Structure and Propagation Characteristics of Climatological Mean Kinetic Energy of Disturbance of Intraseasonal Oscillation in Asian Summer Monsoon Zone

[Objective] The research aimed to study the structure and propagation characteristics of climatological mean kinetic energy of disturbance of intraseasonal oscillation in Asian summer monsoon zone. [Method] When South China Sea monsoon started to break out, the kinetic energy of intraseasonal oscillation disturbance in the monsoon zone was analyzed, especially the researches about the variation of South China Sea monsoon, the development of Indian monsoon and the advancement of East Asian monsoon. [Result] The developed process of Asian summer monsoon had the close relationship with the kinetic energy activity of 30-60 d low-frequency oscillation disturbance. The kinetic energy of disturbance explained the eruption, occurrence, development and termination of monsoon from the energy angle. It was found that the kinetic energy of disturbance in Arabian Sea zone, Bay of Bengal and South China Sea area was the strongest, especially in Arabian Sea zone. It illustrated that Arabian Sea zone (Somali jet) was the biggest energy source of Asian monsoon. The starting mark of monsoon eruption in the whole Asia was the abrupt eruption of South China Sea monsoon. The eruption of South China Sea monsoon in the middle dekad of May was the westward transmission result of kinetic energy of disturbance on the east sea surface of Philippines. The kinetic energy of disturbance in East Asian monsoon zone had the seasonal northward advancement in summer. The high kinetic energy center of disturbance in Indian monsoon zone changed from one to two. They were respectively in Arabian Sea and Bay of Bengal. [Conclusion] The research provided the theory basis for analyzing the atmospheric intraseasonal oscillation.

Decadal changes of the intraseasonal oscillation during 1979–2016

The Intraseasonal Oscillation (ISO) is the cornerstone for 2–8-week subseasonal prediction. Understanding the decadal variation of the ISO is important for improving subseasonal prediction;however, there is still a gap in our knowledge of ISO dynamics. Here, we presented a method, an Empirical Orthogonal Function (EOF) analysis of 11-year-sliding ISO evolution, to objectively detect decadal variation of the ISO originated from the equatorial Indian Ocean (EIO) during 1979–2016. The results show that the properties of ISO have a notable decadal change since 1998 for both boreal summer and boreal winter seasons, mainly in its evolution rather than in its intensity at origin. During the pre-1998 epoch, the boreal summer intraseasonal oscillation (BSISO), was confined to the Indian Ocean;since 1998, however, it propagated northeastward across the Maritime Continent (MC) and the intraseasonal variability over the western North Pacific was significant enhanced. On the other hand, the boreal-winter ISO, usually known as Madden-Julian Oscillation (MJO) shows minor changes in MC ‘barrier effect’ between the two epochs, and continuously propagates eastward across the MC. The MJO only shows suppressed activity over the central equatorial Pacific in the post-1998 epoch. These decadal changes are related to the eastern Pacific cooling during the ‘global warming hiatus’ period rather than to the four-decade global warming. Results here provide a set of potential precursors for foreseeing ISO propagation under different mean states.

Evolution of Intraseasonal Oscillation over the Tropica lWestern Pacific/South China Sea and Its Effect to the Summer Precipitation in Southern China

In this paper, the evolution of intraseasonal oscillation over the South China Sea and tropical western Pacific area and its effect to the summer rainfall in the southern China are studied based on the ECMWF data and TBB data) analyses. A very low-frequency waves exist in the tropics and play an important role in dominating intraseasonal oscillation and lead to special seasonal variation of intraseasonal oscillation over the South China Sea/tropical western Pacific area. The intraseasonal oscillation (convection) over the South China Sea and tropical western Pacific area is closely related to the summer rainfall (convection) in the southern China. Their relationship seems to be a seesaw feature, and this relationship resulting from the different pattern of convection in those two regions is caused by the differnt type of local meridional circulation.

Relationship Between an Abrupt Drought-Flood Transition over Mid-Low Reaches of the Yangtze River in 2011 and the Intraseasonal Oscillation over Mid-High Latitudes of East Asia

NCEP/NCAR daily reanalysis data and Chinese daily gridded precipitation data are used to study the relationship between an aprupt drought-flood transition over the mid-low reaches of the Yangtze River in 2011 and the intraseasonal oscillation （ISO; 30-60 days） in the mid-high latitude meridional circulation of the upper troposphere over East Asia. The abrupt transition from drought to flood occurs in early June. The first two recovered fields of the complex empirical orthogonal function show that northward-propagating westerlies from low latitudes converge with southward-propagating westerlies from high latitudes over the mid-low reaches of the Yangtze River （MLRYR） in mid late May. The timing of this convergence corresponds to the flood period in early-mid June. The ISO index is significantly and positively correlated with rainfall over the MLRYR. During the dry phase （before the transition）, the upper troposphere over the MLRYR is characterized by cyclonic flow, easterly winds, and convergence. The regional circulation is dominated by a wave train with a cyclone over east of Lake Baikal, an anticyclone over northern China, and a cyclone over the MLRYR. During the wet phase, the situation is reversed. The configuration of the wave train during the dry phase favors the southward propagation of westerly wind disturbances, while the configuration of the wave train during the wet phase favors the development and maintenance of a pumping effect and sustained ascending motions over the MLRYR.