Simulating roll clouds associated with low-level convergence in WRF

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Simulating roll clouds associated with low-level convergence in WRF Abhnil

Centre, University of New South Wales, Sydney, NSW, Australia UVSQ-CNRS-IPSL,

Australia 2 LATMOS, Acknowledgements: Prof Roger Smith, Meteorological

1 Simulating roll clouds associated with low-level convergence in WRF Abhnil Prasad1,3, Steven Sherwood1,3 and Hélène Brogniez2 1 Climate Change Research Centre, University of New South Wales, Sydney, NSW, Australia UVSQ-CNRS-IPSL, Guyancourt, France 3 ARC Centre of Excellence for Climate System Science, Australia 2 LATMOS, Acknowledgements: Prof Roger Smith, Meteorological Institute University of Munich, Germany Prof Michael Reeder, Monash University, Melbourne, Australia

Horizontal Convective Rolls Counter-rotating horizontal vortices within the planetary boundary-layer that arise from a combination of shearing instability and daytime heating.

2 Horizontal Convective Rolls Counter-rotating horizontal vortices within the planetary boundary-layer that arise from a combination of shearing instability and daytime heating. Rolls align with the vertical shear vector Air lifted by the roll updrafts can saturate, forming a regular arrangement of "cloud streets" aligned along the rolls. Convective initiation often takes place when two or more features such as fronts and/or rolls collide, merge or otherwise meet

3 Convective Initiation Atkins NT et al. (1995) Because HCRs and the sea breeze both represent regions of locally enhanced lifting and convergence, their interaction can lead to convective initiation.

Cloud lines in Australia Type 1 Type 2 Type 3 long, thin cloud lines, either straight or in the form of mesoscale, generally comprising small cumuli.

4 Cloud lines in Australia Type 1 Type 2 Type 3 long, thin cloud lines, either straight or in the form of mesoscale, generally comprising small cumuli. Extensive areas of broken cloud, either stratiform or convective with a sharp leading. overcast deep convective systems, such as tropical squall lines, comprising a sharp leading edge of deep convective cells and a trailing mesoscale stratiform anvil

5 Research Questions? Can current WRF capabilities simulate roll clouds associated with low-level convergence? Sensitivity to Initial and Boundary Conditions Sensitivity to PBL and CU schemes Evaluation of convective cloud line simulations with observational data for the instrumental accuracy required to constrain models. Himawari 8 animation over the Gulf of Carpentaria on 18 th January 2016

6 WRF Setup Cumulus-Kain-Fritsch (KF) Scheme MP-WRF Single Moment 3- Class Scheme LW-RRTM SW-Dudhia PBL-Yonsei University Scheme Resolution: 27km, 9km, 3km

7 Sensitivity Experiments Boundary Condition NCEP FNL Analysis ERA Interim CU Schemes (turned off for resolution < 4 km) Cumulus-Kain-Fritsch (KF) Betts-Miller-Janjic (BMJ) Grell-Devenyi (GD) ensemble Simplified Arakawa-Schubert (SAS) Tiedtke (TIE) scheme PBL Schemes Yonsei University (YSU) Mellor-Yamada-Janjic (MYJ) Quasi-Normal Scale Elimination (QNSE) Mellor-Yamada Nakanishi and Niino (MYNN) Level 2.5/3 Asymmetric Convective Model (ACM2)

8 Datasets NCEP FNL Analysis (GFS_FNL) available at 1 (spatial resolution) every 6 hours ERA Interim Project available at 0.71 (spatial resolution) every 6 hours Radiosonde data for various sites (especially Darwin) over Australia Megha-Tropiques RH 6-layer product

9 Simulation of Convergence Lines CONVERGENCE

$cloud fraction (right) at 950 hpa$

10 Snapshot Himawari Image Simulation of convergence lines (left) and cloud fraction (right) at 950 hpa for 3 km resolution on 18/01/2016 at 2330 UTC.

11 Cross-Section

12 More Cases 2016/01/ /01/ /01/ /01/ /01/ /01/ /01/ /01/ /01/ /01/ /01/ /01/ /01/18

13 Sensitivity to RH Pressure (hpa) (a) NCEP Radiosonde Pressure (hpa) NCEP YSU MYJ QNSE ACM2 MYNN2 MYNN3 (b) Pressure (hpa) NCEP KF BMJ GB SAS TIE (c) Mean RH (%) Mean Bias RH (%) Mean Bias RH (%) NCEP is drier compared to OBS

14 Sensitivity to QVAPOR Pressure (hpa) (a) NCEP Radiosonde Pressure (hpa) (b) NCEP YSU MYJ QNSE ACM2 MYNN2 MYNN3 Pressure (hpa) (c) NCEP KF BMJ GB SAS TIE Mean QVAPOR (g/kg) Mean Bias QVAPOR (g/kg) Mean Bias QVAPOR (g/kg) Moisture in the Boundary Layer???

15 SAPHIR instrument on Megha-Tropiques SAPHIR is a multi-channel passive microwave humidity sounder. Atmospheric humidity profiles can be obtained by measuring brightness temperatures in different channels situated close to the GHz water vapour absorption line RH retrieved in 6 layers: L1 : 100 hpa hpa L2 : 250 hpa hpa L3 : 400 hpa hpa L4 : 650 hpa hpa L5 : 750 hpa hpa L6 : 850 hpa hpa

16 Orbit

17 (a) Comparison (b) (c) Alice Springs Broome Darwin Gove Rockhampton Townsville Weipa Willis 100:200 hpa 250:350 hpa 400:600 hpa 650:700 hpa 750:800 hpa 850:950 hpa 100:200 hpa 250:350 hpa 400:600 hpa 650:700 hpa 750:800 hpa 850:950 hpa Overpass MBE (Satellite-Radiosonde (%)) RMBE (Satellite-Radiosonde (%)) (d) (e) (f) 100:200 hpa 250:350 hpa 400:600 hpa 650:700 hpa 750:800 hpa 850:950 hpa 100:200 hpa 250:350 hpa 400:600 hpa 650:700 hpa 750:800 hpa 850:950 hpa 100:200 hpa 250:350 hpa 400:600 hpa 650:700 hpa 750:800 hpa 850:950 hpa Standard Error (%) RMSE(%) Correlation Alice Springs Broome Darwin Gove Rockhampton Townsville Weipa Willis

18 MODEL UNDER-ESTIMATION RH Bias (Using SAPHIR)

19 What can we do to fix the Bias in RH? NCEP ERA Interim

20 Water Vapor Perturbations -5% -10% -15% -20% +5% +10% +15% +20%

21 After perturbation Control +20%

22 -20% +20% Effect of Perturbation

23 Conclusion Initial simulations for cloud lines observed on 18th October, 2016 over the Gulf of Carpentaria showed greater agreement in the timing and propagation of the disturbance and the low-level convergence. The current version (V2-00) of Megha-Tropiques (MT) appears to be too moist in the lowest retrieved layer by up to 30% over the dry continental interior, though mostly accurate to within ± 10%. Unperturbed WRF simulations for the test case examined here were 10-20% too dry in the region where cloud lines were observed. Compensating for the bias in RH via the model initialization produced more realistic simulations of roll clouds and convection. The importance of increased accuracy of observations in measuring water vapor is highly critical to properly constrain simulations of convective environments.

24 Future Work Compare Himawari Radiance with simulated Himawari radiance from WRF outputs. Explore very high resolution simulations.

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