Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | erent ff Sciences Discussions Earth System Hydrology and 1980 1979 ¨ olders, 2000). Obviously, this surface heterogeneity can result ect and a stronger turbulence over the oasis interior, both of which ff This discussion paper is/has been under review for the journal Hydrology and Earth System Sciences (HESS). Please refer to the corresponding final paper in HESS if available. presents a fantastic view ofsizes patchy (Friedrich fields and with M various surface properties and di tive lower soil moisture if landscapes in the oasis interior are comparatively1 uniform. Introduction The interaction between theof atmosphere great and interest the underlyingin for surface, climate the a theory heat, phenomenon water and moisture, (Kukharets weather and and forecasting, momentum Nalbandyan, is exchanges 2006). primarily between manifested Flying air over masses a and landscape soil in or mid-latitudes a relative homogeneity. Results show“cold-wet that island” the e inhomogeneity leadswill to reduce a the weaker oasis-desert oasis the secondary oasis, circulation resulting in andsimulation a increase of negative the homogeneity impact evaporation indicates on over that the the oasis oasis self-protecting may mechanism. be more The stable even with rela- vestigated. In this study,of two inhomogeneity. simulations In are thevegetation first designed cover case, fraction, for and land investigating surface surface the layer soilsensing parameters influence moisture data including are from land-use derived EOS/MODIS, by types, and satelliteMM5 then remote be model, used to specify the describeland respective a options use real in types the inhomogeneity are for setative the to uniform, MM5 oasis and default, interior. then in surfaceaverages In of which layer the the landscapes soil first in other moisture case the for and run, the oasis vegetation respective interior fraction oasis is is and desert rel- set surface to lying, be to represent Mesoscale meteorological modeling is anbudget important of tool the to oasis. help While understandmaintaining basic the in dynamic energy and the thermodynamic desert processes environmentlandscapes for is oasis of well self- oasis investigated, influence interior of on heterogeneous the processes are still important and remain to be in- Abstract Hydrol. Earth Syst. Sci. Discuss.,www.hydrol-earth-syst-sci-discuss.net/9/1979/2012/ 9, 1979–2004, 2012 doi:10.5194/hessd-9-1979-2012 © Author(s) 2012. CC Attribution 3.0 License. Impacts of inhomogeneous landscapes in oasis interior on the oasis self-maintaining mechanism by integrating numerical model with satellite data X. Meng, S. Lu, T. Zhang, Y. Ao,Key S. laboratory Li, of Y. Land Bao, Surfaceand L. Process Arid and Wen, Regions and Climate Environmental Change S. andScience, in Luo Engineering 320 Cold Research Donggang and Institute, West Arid Chinese Road, Regions, Academy 730000 Cold of Lanzhou, Gansu,Received: China 31 January 2012 – Accepted:Correspondence 3 to: February 2012 X. – Meng Published: ([email protected]) 14 FebruaryPublished by 2012 Copernicus Publications on behalf of the European Geosciences Union. 5 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | ects of ff ¨ olders and Raabe, ected by the ability ff ¨ olders and Raabe, 1996; Chen and ect the microscale to mesoscale cir- ff 1982 1981 cient technique to study the mesoscale weather ffi ¨ olders, 2000; M ect”, ““glacier wind” et al.” similar to sea-land breeze ff ecting moist convection, producing or impacting the atmospheric circulations locally Numeric simulation is quite an e As unique intrazonal landscapes, oases surrounded by deserts and Gobi play im- Studies have been done to investigate the land-atmosphere interaction over the In many situations, these locally induced circulations are important in determining ff heterogeneity losses in the model lead to substantial, nonlinear changes in temporal 1996). Ye andover Jia mid-latitude (1995) arid investigated areas themodeling, on impact indicating mesoscale of that boundary wellperturbations a layer in watered structures temperature horizontal mesoscale and and pressure humidity wheat more is climate gradient water created by transpired during associated from the the with day, whichsoil. vegetation results mesoscale canopy from and Zhang evaporated from et underlyingchanges al. wet in heterogeneity (2010) patterns design onnear-surface numerical a simulations meteorological number of fields, surface of flux atmosphericcesses, experiments exchanges, planetary to mesoscale boundary examine circulations, layer the and (PBL) e mesoscale pro- fluxes, indicating that the increased mechanism are still very important and remain to beand investigated. boundary layer structure overKukharets the inhomogeneous and landscape Nalbandyan, (Prabha 2006; etChen al., Ament 2007; and and Avissar, Simmer, 1994; 2006; Desai Avissar et and Liu, al., 1996; 2006; Lynn et al., 1995; M will develop an inversion layerinversion over layer the will oasis. help Both(Chu et the to al., mesoscale prevent 2005). circulation water These andanism. processes vapor the are However, over totally the called the oasis thecropland, oasis oasis urban, interior self-maintaining shelterbelt, flowing are mech- natural to vegetation, verycropland Gobi the inhomogeneous, and is constituting desert, desert irrigated particularly with during whenthe water, the the basic growing dynamic season and in thermodynamicinvestigated, Northwest processes the over of the impacts China oasis-desert (Fig. of system 1). is inhomogeneous well While oasis interior on oasis self-maintaining (Chu et al., 2005).the convective boundary Such layer thermally(Segal are driven and called Arritt, circulations as 1992), similar the and2005). as non-classical have been the In mesoscale observed sea addition, circulations inthe the breezes the evaporation oasis in field and is experiment thermal (Chen wetter et processes and al., in colder the than the afternoon surrounded on desert fair due weather to days, which heterogeneity between the oasis and desert is the key factor to maintain the oasis oasis-desert system, indicating that the local circulations driven by the thermal portant role in arid4–5 % and of semiarid the regionsof total of the area the social of world. wealth theGao in region, In et northwest but China, al., China over oases isand 90 2008). % take concentrated the up of within In overexploitation only the the of thesalinization, population oases water, last and (Han, and soil over 2001; desertification half and 95 and century, % sustainable biological agriculture, consequently however, resulting resources the have in have hindered rapid antion led urgency the growth and to to development processes of understand of (Liu drought, the population et oasis-desert al., interac- 2006, 2007; Li et al., 2011). systems (Mahfouf et al., 1987; Mahrtet et al., al., 2004; 1994; Sun Chuto et et al., energy, al., 2005; water 2007). Gao and et Such matterChu al., phenomena transport 2004; et are Lu (Bastin al., known 2005). and to Drobinski, contribute 2006; significantly Meng et al., 2009; mesoscale weather conditions (Wuboundary and layer (ABL), Raman, surface 1997). heterogeneitiesculations a through non-linear Indeed, processes in (PattonRoy et the and al., atmospheric 2005; Avissar, Mahrt 2002).of et the al., Turbulent 1994; surface surface Baidya fluxes tomosphere are redistribute into strongly the sensible radiative a and energySurface latent heterogeneities absorbed heat fluxes thus from (Mahrt induce thecreate et spatial sun “inland al., variability and breezes”, 1994; “oasis in the Chen e surface at- et heat al., fluxes 2003). that can a and even globally (Friedrich andAvissar, M 1994; Chen et al.,2005; 2003; Reen Courault et et al., al., 2006; 2007; Yates et Lynn al., et 2003; al., Zhang 1995; et Patton al., et 2010). al., in more complicated interactions between the atmosphere and the underlying surface, 5 5 25 15 20 10 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | N 0 56 ◦ E and 39 0 08 ◦ , mostly composed with 2 E and 99 0 39 ◦ erence is only 80 m. Its earthiness is very ff 1984 1983 E is used. The three systems extend 333 km, ◦ N, 98.9 ◦ N in the middle of the Heihe river basin (Fig. 1) in northwestern China, with 0 17 ◦ Satellite data such as land use types, vegetation fraction cover and soil moisture are The paper is structured as follows. Section 2 briefly presents a description of the same center located at120 km, 40.3 61 km and with grid spacing of 9 km, 3 km, and 1km respectively. Jinta oasis 3 Numerical simulations The nonhydrostatic MM5Model) (short is a for limited-area,signed nonhydrostatic, Fifth-Generation to terrain-following simulate Penn sigma-coordinate or model predict State/NCAR mesoscale de- coupled atmospheric Mesoscale circulation. by In Noah this land-surface study,1994). version model 3 Since Meng (LSM) et was al.mechanism, used (2009) this have in successfully work simulated the is the a simulation oasis continuity self-maintaining (Grell of et that al., work. A triple-nested grid system with the derived from the Moderatedata Resolution in Imaging 36 Spectro-radiometer spectralprocessing (MODIS) and bands gathers application on for theal. the (2009). board satellite the data can Terra (EOS be found AM) in sensor. the work Details of of Meng the et experiment, which was performed2005. through In late the springweather field to stations campaign, (AWSs), early surface meteorological turbulent autumn elementstomated heat from fluxes Meso-net measured obtained 2003 (PAM) with stations from to (CSAT3/KH20, two foursoundings Campbell. Portable automatic were Sci. Au- collected Ins., for Utah) the and studysystem. of radar The energy observations and used water indata cycle this over can study the be were oasis-desert found obtained in in the July work 2004. of Details Meng of et the al. (2009) and Ao (2006). inhomogeneous oasis in northwest China well. 2.2 Datasets Observational meteorological data were collected at Jinta oasis during the Jinta field Jinta oasis is also a typical irrigation and agriculture oasis, which can represent the the oasis is continuousthe and national easy land resource to developing reclaim, and representative this areas region in China thus (Chen, is 2000). considered as one of The study area isand 40 Jinta oasis, situateda between yearly 98 average precipitationspiration of of about 2538.6 mm. 59.5farmland, mm The natural and total grassland an area and annualJinta is desert-oasis oasis potential about is transaction evapotran- 165 very 212 which km flat,good, are and mainly the shown including elevation in di mudgray Fig. brown soil, 1. soil tide which soil is distributed (meadow in soil), the wind edge sand regions soil (Ma et and al., typical 2002). The soil in 2 Study area and datasets 2.1 Study area an attempt to understandself-maintaining the mechanism. influence of heterogeneous oasis interiorstudy on area the and oasis theand datasets the experimental used design. in Sectionthe this 4 impact work. of evaluates the the inhomogeneous Section simulation landscapeThe results 3 on final and describes the section assesses oasis the summarizes self-maintaining the MM5 mechanism. gation. findings model and identifies areas requiring future investi- et al. (2009) improved meteorological simulationsespecially in the for Jinta description oasis in ofvolving Northwest the China, satellite inhomogeneous data. characteristics Thiswhich over they paper the presented is oasis that a the bya numerical continuity in- better simulation of including description the satellite for work data inhomogeneous can in underlying provide Meng surface, et while al. this (2009), work in will make evaluations and spatial patterns of PBL dynamic and thermodynamic processes. Meng 5 5 25 20 15 10 20 25 15 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 1986 1985 ects and their driven mesoscale circulations and emphasizes the ff C in the north of the oasis, while the maximum in the EXP is slightly erent inhomogeneity. ◦ ff ect and its self-protecting mechanism is the most evident in the af- ff ect ff ect that has been observed in the field experiment (Chen et al., 2005). ff As is discussed in the introduction, studies have considered the mechanisms of oa- Two simulations were performed in this work. In the first run, 1-km-resolution land ture is around 35 higher than MOD and in the west edge of the oasis. Comparing with land use types in and discussed in this part. 4.1 Oasis e As the oasis e ternoon (Chu et al.,(13:00 2005; Beijing Time) Chen will et be analyzed2 al., m and 2005), discussed air in processes temperature this and on work.display that specific 5 Figures 3 the humidity July and oasis from 2004, 4 is show the 05:00 a UTC two “cold simulations. island”. In Both the simulations MOD, the maximum of 2 m air tempera- level over the oasis and thea surrounded moisture-inversion desert level by over the thewhich secondary oasis circulation, can center producing help and the reduceover desert evaporation the neighboring over desert the the oasis, and2004). oasis So, creating and comparisons a is of these protecting good factors between belt for the the around two simulations plant the will growing oasis be presented (Zhang and Huang, over the desert andlow-level hot, downward dry over air the flowing fromthe oasis. the atmospheric desert static The into stability the updraftprevent oasis that over and water reduces the the loss the downdraft desert increases oasis and2005; reduces evaporation, soil Zhang both and desertification of Huang, whichvegetation over 2004; can and the protective Lu oasis forest et andto can al., decrease protect eliminate 2004). the it the evaporation Secondly, over windThirdly, (Chu the the the from et moist oasis oasis the al., air and with desert, in resist cropland, which the sandstorm lower helps (Meng level et over al., the 2009). oasis can be transferred to the higher sis self-maintaining in aoasis surrounded “cold-wet” desert e environment.processes Most from of the them followingwith focus ways. the on surrounded Firstly, desert the the becausetion of oasis and the is soil oasis-desert processes a heterogeneity and cold-wet caused their vegeta- island changes, comparing producing a secondary circulation upward form of the oasis interior. 4 Results and discussion In the previous worksurface of temperature Meng and et atmospheric al. profileshumidity (2009), including potential were wind temperature, fields, evaluated specific land bythat surface MOD using heat simulation the fluxes, is land observationalmechanism illustrated and data, to inhomogeneity. and be So, this theon the work oasis best validation only self-protecting simulation mechanism focuses shows for produced on by oasis the heterogeneity analysis self-maintaining versus of the impacts relative uni- the EXP, vegetation fraction anddesert surface are layer replaced soil with the moisture valuesto initials of the present over averages the of that oasis the bothconditions oasis and and but simulations desert di respectively have similar vegetation coverage and soil moisture use types, vegetation fraction andthe soil coupled moisture MM5-LSM system. data derived Thisshown from simulation to be is MODIS a referred are better to run input asheterogeneity for in simulating MOD, the (Meng which meteorogical has conditions et been andcorridor, the al., oasis-desert water, 2009). urban, farmlandfor As and the land grass heterogeneity use of (Fig.uniform, types the 2), in in oasis it which this interiors. is landthe run taken The oasis use include as interior other types the is a run come mostly “real” oasis is composed from simulation to by the present vegetation. MM5 the This default relatively run (Fig. is referred 2), to showing as that EXP. In sigma levels are defined.of Meng The et parameterization al. schemesBeijing (2009). Time) are The and the model ended sameoasis on was as e 5 initialized the on July work 2004 4 at July 12:00 2004 UTC, at during 12:00 which UTC there (20:00 is a strong was located at the center of the third domain. In the vertical, 23 unevenly spaced full 5 5 25 15 20 10 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | ect, ect, ff ff ected due ff C, which is in the MOD ◦ 1 erences in the − ff in the EXP run, ect in the EXP is 1 ff − erence between oasis and desert ff ect for both “cold” and “wet” condition, ff 1988 1987 erence in the two simulations: over the oasis, diver- ff ect. According to the land use types in Fig. 2, the area ff in the MOD simulation, and it is about 2.8 g kg 1 − erence between oasis and desert in the MOD is about 5 in the EXP run. The contour lines are more density over the oasis from ff 1 − C less than it is in the EXP, indicating that “cold island” e ◦ To co-operate the wind field, Figs. 7 and 8 display the divergence and vertical velocity The EXP simulation presents a stronger e From 2 m specific humidity shown in Fig. 4, both simulations can simulate the oasis To furthermore investigate the influence of inhomogeneity on the “wet island” e the oasis and the desert will be enhanced and water vapor over the oases will flow cases, it shows that in thecenter oasis, in over the the bare MOD soilcenters, run or but the the corridor, a MOD there divergence simulation is onemight a has be convergent in stronger resulted EXP. by From turbulence the the comparing relativein lower values with soil of the moisture the the for EXP EXP, using divergent which thedivergence case. oasis-averaged and values convergence over However, the oasis itthe in should oasis MOD interior case be can and result noted strengthenthe in the that the turbulence turbulence instability the is and for evaporation strong interactionalthermal over enough mechanism the heterogeneity oasis. to between of Once break oasis up and desert, the secondary water and circulation heat driven exchange by between the region as anthe entirety introduction, comparing the with airat the flow the surrounded divergent edge from desert. ofupdraft, the holding the water oasis over As oasis, the to oasis it and andfavorable desert, preventing mechanism is it then produces flowing for discussed into convergent downdraft protecting the around desert. in the the This oasis. is oasis-desert the However, transition comparing to between the two gences occur in most timerun, but and convergence divergence can be overto seen the the over oasis the relative in corridor uniform the in ofover EXP the the the case MOD oasis oasis is interior. interior shownwind Wind due to speed speed be to in was the less the reduced two a vegetationinhomogeneity to simulations, does in but be have over both very the influence small cases. patches on in wind No the fields. oasis, big indicating di thatat the 850 hPa in the two simulations. In both simulations, the oasis area is a divergence Figure 6 displays the modeledcases horizontal winds can at 850 simulate hPa inover the the the two oasis, pattern simulations. there of is Both however di low-level divergence and high-level convergence 4.2 Mesoscale circulation surface to 700 hpa inhpa layer EXP, and than in also MOD appearcirculation, run. with and The will a humidity be inversion deeper islarger further humidity related “wet discussed inversion with island” later. the in comparing oasis with 700- From mesoscale the the MOD contours, simulation. the EXPindicating run that the has concentration a ofthe vegetation production in the of oasis the interiorof oasis is oasis e more in favorable EXP for ismore larger stable than for the it oasis is “cold-wet” in island. the MOD, showing that a larger oasis can also be the vertical latitudinal sectionin of Fig. specific 5 humidity (grid inthe 18 the oasis to middle as of 50 aand the from “wet 5.2 oasis g west island”, kg is to with shown east a is maximum mainly contour oasis). value of Both 4.6 g simulations kg present the influence of the inhomogeneity. as a “wet island”. TheSimilar driest as region is 2 m over the airover desert, temperature, the and specific the oasis wettest humidity in isnortheast distributes over the the center along oasis. MOD in with the simulation, the EXPis but vegetation simulation. about concentrates Humidity 1.8 and di g kg maximumsshowing that occur the in “wet the island” of the EXP is much greater than the MOD. both simulations occurred in the lakestemperature in di the south. Focusing onabout the 1 “cold island” e greater than MOD. Furthermore, minimumssimulation, occur while in they the center happen of along the with oasis the in vegetation the in EXP the MOD simulation due to Fig. 2, maximums in both simulations are around where bare soils are. Minimums in 5 5 25 15 20 10 25 20 10 15 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | (2 m specific humidity). Vertical sections 1 ect, both simulations show that the oasis- − ff 1990 1989 to 1.8 g kg 1 − C (2 m air temperature) due to the oasis-interior inhomogeneity and the “wet ◦ C to 5 ect and then reduce the dynamic driver of the oasis-desert secondary circulation. This work only focuses on the analysis of inhomogeneity, and doesn’t consider the Water and energy cycle is the most important factors for the oasis self-protecting. For the oasis-desert secondary circulation, the moister and more heterogeneous Similar as the simulation for the oasis e Figures 9 and 10 show the vertical section of divergence and vertical velocity from ◦ ff influence of the oasis area.the oasis Land than use the types MM5self-maintaining from default. mechanism. MODIS And data the So, showof a area the smaller is inhomogeneity. results area also of of an Further thisinvestigate important the work study factor oasis for will may area the separately. enlarge need oasis the to influence better constrain the heterogeneity and break up, water and heat exchangeand between water the oasis vapor and over theoases desert the drier will oases be and will enhanced drier,desertification. flow even into going the into surrounding the deserts vicious and circle make the of water deficiency and soil landscapes make the secondaryvergent circulation turbulences stronger over and also thethe the oasis oasis convergent maintain, interior. and while di- thecan The interactional result mechanism stronger in of circulation divergence theevaporation is and over instability convergence the favorable over oasis. for the Furthermore,e oasis the turbulence interior will and decrease the strengthenOnce “cold the the island” oasis-interior turbulence is inhomogeneous and enough, the secondary circulation is easy to Comparison between the two simulations show6 that the “cold island” isisland” decreased is from reduced from 2.8 gfurther kg indicate thathumidity the inversion over homogeneity the in oasis, preventing the water in oasis the interior oasis from help evaporating. to produce stronger can simulate the homogeneity well. The influence of inhomogeneitynism of the is oasis investigated interior byvations on using of oasis the land self-maintaining mesoscale surface mecha- modeldefault parameters land MM5 from use (MOD) MODIS types data. withing, of satellite To surface the do obser- soil oasis moisture a are and comparison,of taken vegetation the oasis as fraction MM5 and were a replaced desert relatively byhomogeneity. homogeneous respectively using The surface in the results ly- the averages indicate comparative thecharacters simulation MOD of (EXP) simulation the to is heterogeneous represent a land the good surface case lying to in describe the the oasis interior, and the EXP lower soil moisture and vegetationdisturbances fraction. and The water inhomogeneity loss. of the MOD will lead to 5 Conclusions with the turbulence, airflow has moregoes up up over and the down oasis turbulence interior inin in the lower-level the atmosphere MOD EXP over run, case, the but showing oasis only that interior the in turbulence is the stronger MODdesert run. interactions can produce athe secondary oasis circulation self-protecting. in The in MODfraction the simulation seems lower with atmosphere to larger for have soilEXP a moisture simulation and stronger vegetation seems circulation to than be it easier is for in oasis the self-maintaining EXP although simulation, it but has the relative vicious circle of water deficiency and soil desertification (Mengthe et two al., simulations. 2009). Inand Fig. convergence 9, can over be the seen oasisthe below edge (i.e. 800 and from hPa convergent in grid in the 18 the MOD to center run, 50), of but both the mainly divergence oasis divergent in at the EXP simulation. 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H., Rind, D., and Avissar, R.: The Importance of Mesoscale Circulations Generated Lu, S., An, X., and Chen, Y.: Simulation of oasis breeze circulation in the arid region of the Liu, S., Liu, H., Hu, Y., Zhang, C., Liang, F., and Wang, J.: Numerical simulations of land 5 5 15 30 10 25 20 15 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 1996 1995 Location of Jinta Oasis in Heihe River Basin (Geocover mosaics) and land use map of Land-use maps for the third domain of the two simulations. Fig. 2. Jinta Oasis. Fig. 1. Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 1998 1997 2 m air temperature on 5 July 2004, 05:00 UTC (13:00 Beijing Time) of the two simula- 2 m specific humidity of the two simulations (the same time as Fig. 3). Fig. 4. tions. Fig. 3. Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | , and interval is 0.2. 1 − 2000 1999 Vertical latitudinal section of specific humidity in the middle of the oasis for the two Horizontal winds at 850 hPa in Jinta oasis for the two simulations (the same time as Fig. 6. Fig. 3). Fig. 5. simulations (the same time as Fig. 3). Unit is g kg Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 2002 2001 , and interval is 10. 1 − , and interval is 50.00. 1 − s 5 − Horizontal vertical velocity at 850 hPa in Jinta oasis for the two simulations (the same Horizontal divergence at 850 hPa in Jinta oasis for the two simulations (the same time Fig. 8. time as Fig. 3). Unit is cm s Fig. 7. as Fig. 3). Unit is 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | , and interval is 10. 1 − 2004 2003 , and interval is 10.00. 1 − s 5 − Vertical latitudinal section of vertical velocity in the middle of the oasis for the two Vertical latitudinal section of divergence in the middle of the oasis for the two simulations Fig. 10. simulations (the same time as Fig. 3). Unit is cm s (the same time as Fig. 3). Unit is 10 Fig. 9.