USING A NETWORK OF SCINTILLOMETERS AND CEILOMETERS FOR VALIDATION OF THE WRF-MESOSCALE MODEL

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1 P.1.2 USING A NETWORK OF SCINTILLOMETERS AND CEILOMETERS FOR VALIDATION OF THE WRF-MESOSCALE MODEL G.J. Steeneveld*, O.K. Hrtogensis*, A.F. Moene*, H. Klein Bltink +, nd A.A.M. Holtslg* *Wgeningen University, Wgeningen, The Netherlnds. + Royl Netherlnds Meteorologil Institute, De Bilt, The Netherlnds 1. INTRODUCTION 1 & BACKGROUND Foresting of ner surfe wether, speies trnsport nd dispersion, nd the inversion of greenhouse gs trnsport on the mesosle relies on the performne of the tmospheri oundry lyer (ABL) nd lnd surfe sheme in limited re models (e.g. Denning et l., 2008: Gerig et l., 2008). However, the PBL desription in NWP models still hs diffiulties (Steeneveld et l., 2008), espeilly in the stle ABL (SBL). Nighttime mixing is often overestimted nd the low level jet misrepresented. During dytime the representtion of ABL entrinment ould e improved. All together this results in errors in the diurnl yle of wind speed, diretion nd the thermodynmi vriles (Olivié, et l., 2004; Svensson nd Holtslg, 2007; Teixeir et l., 2008). Hene there is need to ompre mesosle model results with oservtions to understnd the model limittions s well s their strengths. In the study desried in this pper, the PBL shemes implemented in mesosle model WRF re evluted ginst network of in situ oservtions in The Netherlnds. Previous studies lso evluted WRF, ut these were mostly foused on omplex terrin, the synopti sle (Cheng nd Steenurgh, 2005) or ir qulity (Tie, 2007). Usully tmospheri mesosle models re evluted ginst point mesurements. However, then representtion errors our. Surfe fluxes re lulted on grid sle, so they lso should e evluted ginst oserved re verged fluxes. The innovtive spet of this study is the use of network of sintillometers nd eilometers for model evlution. We will ompre oserved surfe fluxes of momentum (u * ), sensile het (H) nd evpotrnspirtion (L v E), nd next lso the profiles of wind speed (U), potentil temperture (θ), nd speifi humidity (q). The seond im is to ompre modelled diurnl yle etween the MRF sheme (Troen nd Mhrt, 1986) nd its improved equivlent YSU (Noh et l., 2003). 2. OBSERVATIONS A sintillometer is n instrument tht onsists of light trnsmitter nd reeiver. The instrument 1 Corresponding uthor ddress: G.J. Steeneveld, Wgeningen Univ., Meteorology nd Air Qulity Group, P.O. ox 47, 6700 AA Wgeningen, The Netherlnds. E-mil: Gert-Jn.Steeneveld@wur.nl reords the integrted effet of the turulent perturtions of the ir s refrtive index (n), nd its struture prmeters (C n 2 ). Monin-Oukhov theory is used to onvert C n 2 to re-verged surfe fluxes of het, using 10 m wind s input. We use 5 optil Lrge Aperture Sintillometers (LAS) whih operte on sle of ~ m in regions of the Netherlnds with different vegettion types (Fig. 1). See Meijninger et l. (2002) for more informtion on the LAS. A eilometer is n instrument tht mesures the ABL height (h) using lser or other light tehniques. Fig. 1 lso indites 6 lotions with opertionl eilometers. In ddition to this network of innovtive instruments, we lso evlute the model ginst Cuw tower oservtions (e.g. Beljrs nd Bosveld, 1997), wind profiler, nd routine mirometeorologil oservtions. sintillometer eilometer Cuw Wgeningen Fig 1: The Netherlnds with sptil overge of sintillometer nd eilometer network. 3. MODEL SETUP & CASE DESCRIPTION We hve seleted two loud free ontrsting dys: 22 April 2007 (DOY 112) with wek winds (~1.5 m/s t 10m), nd 2 My 2007 (DOY 122) with moderte winds (~4.5 ms -1 t 10m) During the first period, The Netherlnds re loted under high with winds from the southest. In the seond period the wind is est-north-estern. The re onsists of minly grsslnd nd is flt nd reltively homogeneous. Also, the re hs lrge wter supply nd thus high soil moisture vilility. For these simultions, the initil nd oundry onditions (every 6 h) were provided y NCAR-FNL. WRF ws run in n re of 1600 x 1600 km with grid size of 54 km. In this domin, we nested 3 domins with grid sping of 18, 9 nd 2 km respetively to minimize model 1

2 errors due to lk of horizontl resolution. Moreover, the U.S. Geologil Survey provided the lnd surfe properties for WRF suh s soil moisture vilility, surfe roughness, nd lnd use. D1 D2 D3 Fig. 2: Model onfigurtion for WRF. WRF ws run with 3 different ABL shemes. First, we use the so-lled MRF sheme (Troen nd Mhrt, 1986; Hong nd Pn, 1996) whih utilizes presried ui eddy diffusivity profile with height, with the mgnitude depending on the hrteristi veloity sle t the surfe lyer. This sheme llows for non-lol het trnsport during the dy. This extension is needed to represent trnsport y lrge eddies on the sle of the ABL itself, insted of lol trnsport. A wellknown drwk of this widely used sheme is exessive dytime ABL top entrinment, nd overestimtion of the turulent trnsport t night (e.g. Vil et l., 2002; Steeneveld et l., 2008). The 2 nd sheme is n extension MRF, (so lled YSU). The extensions onsist of ) inlusion of presried entrinment rte t the ABL top, ) non-lol trnsport of momentum, nd ) Prndtl numer (K M /K H ) depending on height (see lso Noh et l., 2003). As suh, we will evlute whether these modifitions irumvent the defiienies in the MRF sheme. Finlly the 3 rd sheme is 1.5 order losure sheme (MYJ) nd uses prognosti eqution for the turulent kineti energy (see Stull, 1988; Steeneveld et l., 2008). Then the eddy diffusivity is determined y multiplition of the turulent kineti energy nd length sle. The NOAH lnd surfe sheme hs een used (e.g. Ek et l, 2002). For ompleteness, we utilize the Kin- Fritsh umulus onvetion sheme, the RRTM sheme for long wve rdition, the Dudhi sheme for shortwve rdition, nd the WSM 3- lss simple ie mirophysis sheme. In the surfe lyer we use Monin-Oukhov theory s in Jnji (2000). 4. RESULTS ) Clm onditions: DOY 112 The modeled nd oserved H, L v E nd u * for Wgeningen re shown in Fig. 3: ll shemes overestimte dytime H y ~60 Wm -2, while t night ll shemes overestimte the mgnitude of H. However, the sintilometer flux H s is lrger ompred to the eddy ovrine flux H e, nd loser to the model forest. Note tht H e for Cuw is lso shown for omprison. L v E is forested orretly for the full diurnl yle, nd is lso onsistent with eddy ovrine results. Unfortuntely, ll shemes predit u * ftor 2 lrger thn oserved during the dy. At night u * vnishes, while WRF keeps u * t lest 0.14 ms -1. This might our due to the model s reltively lrge roughness length (0.15 m), s dvised for Cuw (Beljrs nd Holtslg, 1991). The surfe skin temperture (T s ) is orretly forested during the dy, ut overestimted t night. This is due to the ft tht inoming longwve rdition in MRF nd YSU is overestimted y 5-10 Wm -2. Finlly, h is well represented y the eilometer (t lest for one lgorithm). Note tht the modeled h ws lulted from the modeled wind nd temperture profile, using Troen nd Mhrt (1986). 2

3 d e Fig.3: Modeled nd oserved time series of sensile (), ltent het flux (), frition veloity (), surfe skin temperture (d), nd ABL height (e).+ Cuw EC flux, = Wgeningen EC flux, Wgeningen sintillometer flux. Fig. 4 shows the modeled profiles of θ, q, nd U. For the dytime ll ABL shemes overestimte the ABL temperture, lthough the ner surfe temperture grees with the oservtions. Speifi humidity is overestimted ompred to the rdio sounding, espeilly for MYJ. Fig.4: Modeled profiles of potentil temperture, humidity, wind speed for DOY ,00 UTC. O = De Bilt sounding, X= Cuw tower. YSU seems to detrin moisture ompred to MRF. YSU seems to produe muh more well mixed U profile ompred to MRF, whih results in out 0.5 ms -1 wind speed differene. However, U is 1 ms -1 too high ompred with tower oservtions nd more ompred to the sounding whih we my onsider suspiious lose to the surfe. 3

4 At night (DOY 112, 00 UTC) the MYJ sheme reprodues the inversion orretly, while MRF nd YSU underestimte the surfe inversion strength, while lso the free tmospheri strtifition is underestimted. All shemes simulte q quite well lose to the surfe. For wind speed onsiderle differenes re seen. MYJ represent the low level jet in very lose greement with tower oservtions. YSU forests the LLJ muh etter thn MRF. This is due to YSU s lrger ner surfe wind speed t dytime, whih results in lrger mplitude of the intertil osilltion t night. ) Windy onditions: DOY 122 Next we evlute the model performne for DOY 122. The forested sensile het flux is pproximtely similr for ll shemes, nd grees well with H s. Note tht the dytime H s is muh lrger thn H e in this se. It is lso worth noting the ler pek of modeled nd simulted H fter the trnsition (Fig. 6). Fig.5: Modeled potentil temperture ), humidity (), wind speed () for DOY , 12UTC. 4

5 d e Fig.6: Modeled nd oserved time series of sensile (), ltent het flux (), frition veloity (), surfe skin temperture (d), nd ABL height (e).+ Cuw EC flux, = Wgeningen EC flux, Wgeningen sintillometer flux. The simulted L v E is overestimted, lthough it ompres well with the mesured flux t Cuw. WRF strongly overestimtes u *, espeilly for the dy. Also note tht u * from the sintillometer itertion is sustntilly lower thn from eddy ovrine. Predited T s shows ool is t night, ut is orret during the dy. The dytime h is overpredited ompred with the eilometer oservtions. MRF overestimtes h t night, ompred to YSU nd MYJ. The simulted θ is underestimted, espeilly y MYJ (Fig. 7). This is inonsistent with the lrge surfe H. Therefore, the modeled het dvetion or entrinment is misrepresented. At the sme time q is underestimted ner the surfe, nd the wind speed profile is orretly modeled. Fig.7: Modeled potentil temperture ), humidity (), wind speed () for DOY , 12UTC. 5. CONCLUSIONS We hve evluted the model performne of WRF in the oundry lyer ginst network of eilometers nd sintillometers in the Netherlnds. As suh, this is the first pper in whih grid sle model fluxes re ompred with re verged surfe flux oservtions. The MRF, YSU nd MYJ shemes re used. We find tht the WRF-YSU sheme shows improved skill for the dytime wind profiles, nd nighttime low-level jet ompred to MRF. A ommon defiieny of the shemes is n overestimtion of dytime fluxes, 5

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