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An Idealized Numerical Simulation of Meso- -scale Low on the Baiu Front

An Idealized Numerical Simulation of Meso- -scale Low on the Baiu Front. Hirotaka Tagami 1 , Hiroshi Niino 2 1: Advance Soft corporation 2:Ocean Research Institute, Univ of Tokyo. 1:Introduction and Purpose 2:Setting 3:Result 4:Conclusion. An example of Meso- -Low (MAL).

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An Idealized Numerical Simulation of Meso- -scale Low on the Baiu Front

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  1. An Idealized Numerical Simulation of Meso--scale Low on the Baiu Front Hirotaka Tagami1, Hiroshi Niino2 1: Advance Soft corporation 2:Ocean Research Institute, Univ of Tokyo 1:Introduction and Purpose 2:Setting 3:Result 4:Conclusion

  2. An example of Meso--Low (MAL) 18UTC 4th July 2005 Weather map GMS IR image ●Only a few hPa lower than the environment. ●Active Cloud Cluster accompanies. MAL on the Baiu Front (BF) often causes torrential rain in the Baiu season.

  3. Past studies on the structure and dynamics of MAL Vertical structure with sonde data Yoshizumi (1977) Vertical structure 400 • Cold air to the east of trough • Trough tilts eastward with height • (Ninomiya and Akiyama,1971, Akiyama1990b) • Warm core above the low • Meridionally different 500 600 700 800 900 1000 0 500km Shade; potential temperature anomaly (θ’) (blue; negative, red; positive) Contour; geopotential anomaly Theoretical study for vertical structure Adiabatic coolingassociated with updraft enforced by diabatic heating (Yanase and Niino, 2004)

  4. Problems Analytical Study:  Mechanism of 3-dimensional structure  Developing process (Energy budget).  The environment of MALsis different from case to case. Theoretical Study:  Meridionally uniform environment  Crudely parameterized convective heating  Non-linear effects Purposes • Obtainment of realistic environment for the BF • Idealized numerical simulationwithout cumulus convective parameterization • General structure and developing process • (Sensitivity to the baroclinicity)

  5. Model and Setting • The anelastic equation system (for energy budget analysis) ofMeteorological Research Institute / Numerical Prediction Division Non-Hydrostatic Model (Saito et al. 2000; NHM) is modified. • Zonal BC：cyclic • Meridional and Vertical BC：free slip • 500x500x36（dx=dy=5km,dz=500m) • Cloud Physic：Cold rain scheme (Lin et al. 1983) • No cumulus convective parameterization • Newtonian cooling (e-folding time = 5hour) is applied to the deviation of zonal mean of u,v,w, θ. • f-plane at 32.5゜N  Anomaly : deviation from zonal mean.  Horizontal smoothing over 100km square is applied to the model result.

  6. km km • 726 casesdistinctBF are selected between 1958 and 2002 • 8-day low-pass filter • Superposed while keeping the south edge of BF • Geostrophic zonal wind • Distribution at 125°E is given uniformly in the x-direction • qv is modified with modification of RH (≦95%) • Thermal wind valanced weak vortex（diameter :1000km height : 6km, max velocity : 2m/s） Design of Environment Field Meridionally vertical section of Basic Field for control run (CNTL) Temperature (contour; every 5K), zonal wind(larger than 10m/s, shadowed every 5m/s) Relative Humidity[%] z y ↑:south edge of BF

  7. Result of CNTL vertical integration of condensational water [10-1g] & surface pressure [hPa] (2hPa) GMS IR image 00UTC 21 June 2001 & SLP of RANAL ·Round shaped Cloud Cluster appears in SE quadrant ·Cloud zone such as cold front (trailing portion, Ninomiya et al. 1988)

  8. Horizontal Structure u’ and v’ & updraft (shaded) at T=60hr z=1km [km] Center of LLJ [m/s] [km] y [m/h] x In the low-level ;  Horizontal trough is oriented in SW-NE at north side of the LLJ. Barotropic energy conversion can occur.

  9. Vertical Structure contour：P’(every 0.2hPa), shadow：positive ’[K] (meridionally averaged over 100km through the center) T=60hourの at the center T=60hourの 150km north from the center [km] [km] z [km] [km] x slightly or westward tilting of the trough  Pressure trough tilts eastward  Cold anomaly to the east Meridionally different vertical structure

  10. Distribution of each terms, averaged 25-30hr Interval is each 0.1K/hr in (a)～(d), 0.5K/hr in (e)、(f) x=0 : Center of Low Heat Budget Analysis around MAL (b)zonal advection (a)tendency  Negative tendency ( c ) meridional advection (d) (e) + (f)  Cold areais induced by sum of adiabatic cooling and latent heat. (e)vertical advection (f)condensational heating  Cold area depends on the adiabatic cooling. z x Condensational heating induces warm core at middle- or upper-level →updraft is enforced

  11. K→K’ is mainly barotropic conversion, and about 1/4 of the increase of K’, Energy Diagram between 50 and 60hr. Normalized with EKE. Dimension is [10-6s-1]. Developing Process -energy budget- Mean Available Potential Energy Mean Kinetic Energty Eddy Kinetic Energy (EKE) Eddy Available Potential Energy (EPE) Loading with precipitation Condensational heating Developing mainly depends on P’→K’ P’ mainly depends on Q, and P→P’ is much small.

  12. Conclusion • Several observational features is well reproduced under an idealized environment without cumulus parameterization. (warm core, shape of cloud cluster, trailing portion) • A vertical trough of MAL tilts eastward with heihgt, because adiabatic cooling induces cold area in low-level to the east of low. • The vertical structure is meridionally different. (Because of the difference of contribution of adiabatic cooling.) • The development mainly depends on EPE induced by condensational heating.

  13. Thank you for Listening!

  14. contour：P’(every 0.2hPa), shadow：positive ’[K] (meridionally averaged over 100km through the center) Vertical Structure T=60hourの at the center T=60hourの 150km north from the center [km] [km] z [km] [km] x slightly or westward tilting of the trough  Pressure trough tilts eastward  Cold anomaly to the east Meridionally different vertical structure contour：P’(every 0.05hPa), shadow：positive ’[K] When condensation is not concidered, [km] Vertical trough tilts westward with height. [km]

  15. K→K’ is mainly barotropic conversion, and about 1/4 of the increase of K’, Developing Process -energy budget- Energy Diagram between 50 and 60hr. Normalized with TKE. Dimension is [10-6s-1]. Tendency of EKE averagedover whole region [J m-3] Mean Available Potential Energy Mean Kinetic Energty Eddy Kinetic Energy (EKE) Eddy Available Potential Energy (EPE) [hour] Loading with precipitation Condensational heating Developing mainly depends on P’→K’ P’ mainly depends on Q, and P→P’ is much small.

  16. Sensitivity to the Baroclinicity Environmental U and T of CNTL and B15 CNTL Environment: ●Baroclinicity is as same as 1.5 times of one of CNTL ●qv becomes small amount in north side ●Wind velocity becomes large B15

  17. Overview Vertical integration of condensational water [10-1g] and SLP[hPa] at 70hr. B15 CNTL y x ●Cloud Cluster exists to the east of low.

  18. Horizontal Structure u’,v’ and w at z=3km at 60hr. CNTL B15 Center of Jet [m/s] [m/s] [m/h] [m/h] ●Horizontal structure changed Because of vertical shear becomes strong.

  19. Vertical Structure P’ (contour, 0.2hPa) and positive θ’(shadowed) at70hr CNTL B15 Z [km] Y [km] ●Vertical trough still tilts eastward with increasing height

  20. Energetics Budget of Eddy Kinetic Energy : [K,K’]y [K,K’]z redistributio [P’,K’] dissipation Budget of Eddy Available Potential Energy : [P,P’] [K’,P’] [Q,P’] Ek=ρ0(u’2+v’2+w’2)/2, Ep=αθ’2/2 V : velocity (vector), p:pressure, Cs : sound velocity, Q : condensational heating q : condensational water Ek : Eddy Kinetic Energy, Ep: Eddy Available Potential Energy (￣): zonal mean, ( )’ : deviation from zonal mean res: residual terms、diff : diffusion

  21. Tendency of EKE[J m-3] averaged over whole region Difference of Developing Process Developing rate becomes small because qv becomes small amount Energy Diagram between 50-60hour CNTL B15 ●Contribution of Q becomes weak ●Effect of Basic Field becomes strong ●mainly depends on Q

  22. Mechanism of Trailing Portion 1 Mixing ratio of water vapor [g/kg] at z=0.5km dry air advection from above large gradient of qv

  23. Mechanism of Trailing Portion 2 Each Terms of Front Genesis at 19hr • Condensation • Divergence • Deformation • Tilting Term Deformation and Tilting are much strong!! Mechanism: 1:dry air advection from above with down draft 2:deformation and tilting strengthen

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