Estimation of marine boundary layer heights over the western North Pacific using GPS radio occultation profiles

Transcription

1 Estimation of marine boundary layer heights over the western North Pacific using GPS radio occultation profiles Fang-Ching Chien National Taiwan Normal University Thanks to collaborators: Dr. Hong, Dr. Kuo, Dr. Sokolovskiy

2 Motivation It is found that the marine boundary layer height (MBLH) is in general too low over the western North Pacific in the WRF forecasts. The purpose of this study is to estimate the MBLH from Formosat- 3/COSMIC GPS RO data, and to provide a dataset for comparison with the WRF model. For the preliminary result, the GPS RO profiles in 2014 are used. In the future, more profiles in other years may be considered.

3 Methods MXP-BA: developed by Sokolovskiy et al. (2007), the altitude of maximum gradient of square of bending angle lapse is defined as MBLH. P = α 2 / z, P max MBLH MG-BA: the height of minimum gradient of bending angle MBLH (Xie et al. 2012; Ao et al. 2012). ( α/ z) min BP-Ref: estimates the MBLH by finding the break point in a refractivity profile (Sokolovskiy et al. 2006; Guo et al. 2011). MG-Ref: similar to MG-BA, but uses refractivity instead of bending angle. ( N/ z) min The above estimated MBLHs are compared with the observations from nearby sounding stations over islands, whenever available. Distance 200 km and the time window 3 h.

4 PBLH ~ 1.4 km Temp. inversion and sharp decrease of WVP break point in refractivity (N) profile PBL top (Sokolovskiy et al. 2006) Guo et al. (2011)

5 Year of 2014 Latitude Longitude 500-m Data amount 1000-m Data amount Total Season Data amount (566) Data amount (1669) DJF(winter) MAM(spring) JJA(summer) SON(autumn)

6 Bending angle Refractivity Confidence level (CL) from sounding OBS = (Ao et al. 2012) MXP-BA GPS RO MBLH MG- BP BA Ref MG- Ref Sounding MBLH CL(1-3) T Water Vapor P OBS sounding RO wetprf ERA

7 Bending angle Refractivity CL=2 MXP-BA GPS RO MBLH MG- BP BA Ref MG- Ref Sounding MBLH CL(1-3) T Water Vapor P OBS sounding RO wetprf ERA

8 Bending angle Refractivity CL=1 MXP-BA GPS RO MBLH MG- BP BA Ref MG- Ref Sounding MBLH CL(1-3) T Water Vapor P CL=3 CL=2 CL=1 N/A Total OBS sounding RO wetprf ERA

9 MBLH from GPS RO(m) MBLH from GPS RO(m) MBLH from GPS RO(m) MBLH from GPS RO(m) Cases filtered by Confidence level (CL=3) (intercept = 0) MXP-BA y = x R² = BP-Ref y = x R² = MBLH from sounding obs (m) MBLH from sounding obs (m) 4500 MG-BA y = x R² = MG-Ref y = x R² = MBLH from sounding obs (m) MBLH from sounding obs (m) *CL(3) *Data amount: 352

10 Cases filtered by CL=3 Mean absolute error MAE = H RO H sounding DJF Winter MAM Spring JJA Summer SON Autumn CL=3 Cl(3) MXP-BA MG-BA BP-Ref MG-Ref MAE DA MAE DA MAE DA MAE DA ALL Cl(3) MXP-BA MG-BA BP-Ref MG-Ref MAE DA DA: Data amount 1000-GPS RO

11 Cases filtered by CL=3 Mean error/standard deviation ME = CL=3 (H RO H sounding ) Cl(3) MXP-BA MG-BA BP-Ref MG-Ref DJF MAM JJA SON ME Sdv DA ME Sdv DA ME Sdv DA ME Sdv DA Sdv ME -1 Sdv Mean error (Confidence=3) Cl(3) MXP-BA MG-BA BP-Ref MG-Ref ALL ME Sdv DA DA: Data amount 1000-GPS RO

12 Cases filtered by CL=3 3-hly Averaged MBLH (diurnal variation) *Data amount: 352 DJF (LT) (DA) MAM (LT) (DA) JJA (LT) (DA) SON (LT) (DA) ALL (LT) (DA) (LT)Local time (DA)Data amount

13 MXP-BA has the best estimation of MBLH Cases filtered by CL=3 Would it still the best over the ocean when and where there is no sounding at all? to identify the quality of the estimated MBLH from GPS RO

14 Cases filtered by sha Mean error/standard deviation ME = sha (H RO H sounding ) Mean error Cases filtered by sha DJF MAM JJA SON ALL MXP-BA MG-BA BP-Ref MG-Ref ME Sdv DA ME Sdv DA ME Sdv DA ME Sdv DA ME Sdv DA DA: Data amount Total: 1669 Mean error (Confidence=3) Cases filtered by CL=3 for comparison

15 DJF MAM The averaged MBLH over the western North Pacific using MXP-BA (sha 3.0) ALL JJA SON

16 Conclusions The MBLHs estimated by the MXP-BA method have the smallest error. Those by the MG-BA method have the second lowest error. The BP-Ref method overestimates the MBLH, and the MG-Ref method underestimates the MBLH. Methods that use bending angle to determine MBLH produce better result than those use refractivity. Errors of the estimated MBLHs are the highest in summer. MBLHs have little diurnal variation. The MBLHs are much higher in winter than in summer over the ocean. The averaged MBLHs over the western North Pacific are higher in the subtropics than in the tropics and the mid-latitude regions.