Vertical structure and precipitation properties in typhoon rainbands

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1 The 4 th THORPEX-Asia Science workshop, Kunming, China on 31 Oct.-2 Nov Vertical structure and precipitation properties in typhoon rainbands Dong-Kyun Kim, Yeon-Hee Kim, Kwan-Young Chung Forecast research lab., NIMR, Korea

2 KMA and NCIO Outline wind profilers National center for intensive observation of severe weather (NCIO) Backgrounds: wind profiler radar Retrieval methodology Ground-based remote sensing measurements of Typhoon Meari (2011) and Typhoon Bolaven (2012) Results -Vertical structure and precipitation properties -Comparison of mean vertical profiles Summary

3 National center for intensive observation of severe weather (NCIO) Purposes: Observe severe weather phenomena (e.g., storms and typhoons), understand their mechanisms by investigating vertical structures and microphysical characteristics, and enhance the predictability of HIW over the Korean peninsular 1290-MHz wind profiler : SNR, Doppler velocity, Doppler power spectra, wind, etc. K-band micro rain radar : Z, R, DSD, etc. Parsivel disdrometer : Z, R, Drop size spectra, etc. Optical rain gauge : R 22-channel microwave radiometer : T, RH, PWV, LWP, etc. Ceilometer : cloud base height, etc. K-band cloud radar (installed by March 2013) : Z, R, Doppler power spectra and velocity, LDR, etc. NCIO Seoul

4 KMA Wind and NCIO profiler wind radar profilers North West Zenith South 15 o East Profiler-observed Doppler power spectrum Sampling volume From clear air From rain Wind profiler radar can measure backscatter echoes both from turbulence in the upper air and hydrometeors (ices and raindrops). Wind profiler radar

5 Profiler-observed KMA observed and NCIO spectra wind profilers with height Ice/snow Melting layer Rain Height resolution : 100 m Gage et al. (1994)

6 KMA Drop and size NCIO distribution wind profilers We use a gamma DSD of the form: μ N( D) = NoD exp( ΛD) : can describe the fluctuations of the DSDs observed on small time scales and spaces. : To retrieve the DSDs, we must obtain three unknowns : N 0, μ (shape), Λ (slope), which are called DSD parameters. μ=0 μ > 0 μ < 0 D m (mass-weighted mean diameter) Decrease of Λ Increase of Λ

7 KMA and Spectra NCIO method wind profilers Sobs ( v) = SBragg + SRayleigh + Noise = Pair S air ( v w) + S air ( v w) S hyd ( v) + Noise Profiler-observed spectrum consists of clear-air spectrum, Rayleigh spectrum, and Noise. S S Bragg Rayleigh P air ( v w) ( v) = Pair S air ( v w) = exp 2 2πσ 2σ air air ( v) = S ( v w) S ( v) air hyd 2 : Gaussian shape = 1 2πσ air ( v w) exp 2 2σ air 2 S hyd ( v) Raindrop size spectra (i.e., hydrometeor size distribution) LSE N [ ] 2 log( S ( v )) log( S ( v )) = i obs i convolved i

8 Wind profiler measurements during the typhoon periods 1) Typhoon Meari (25 June 2011) 2) Typhoon Bolaven (27-28 August 2012)

KMA Typhoon and NCIO Meari wind (2011) profilers Track of Meari Bright band Presence of

has pre-existed for 2~3 days before Typhoon Meari started to affect the southern coast

Vertical structure in the successive rainbands of Typhoon Meari (about 250 km away from

9 KMA Typhoon and NCIO Meari wind (2011) profilers Track of Meari Bright band Presence of large drops Frontal system NCIO Vortex center 0100 The Changma(Meiyu) frontal system has pre-existed for 2~3 days before Typhoon Meari started to affect the southern coast area directly. Typhoon Meari moved north over the Yellow sea and dissipated on 27 June. Vertical structure in the successive rainbands of Typhoon Meari (about 250 km away from the vortex center) was observed by the wind profiler radar at NCIO from 1400 UTC 25 June.

profiler and MRR suggests that the profiler-retrieved parameters are reliable up to ~4 km

10 KMA Retrieved and NCIO rainfall wind parameters profilers Z R Gray-colored regions indicate rain rates greater than 80 mm/hr D m The good agreement in the D m time series between the profiler and MRR suggests that the profiler-retrieved parameters are reliable up to ~4 km AGL below the melting layer. (although we need to think about the effects of vertical air motion.)

107 Relatively large updrafts were found in the regions of high

11 KMA Retrieved and NCIO rainfall wind parameters profilers Z Strong Z streaks R Large updrafts w w = W V f, V f =2.6Z Relatively large updrafts were found in the regions of high Z and R values. Also, high Z values were found in the weak downdraft regions.

observed by the wind profiler at NCIO from 0800 UTC 27 August.

12 KMA Typhoon and NCIO Bolaven wind (2012) profilers Track of Bolaven 2000 UTC 0827 NCIO Vertical structure in the rainband of Typhoon Bolaven was observed by the wind profiler at NCIO from 0800 UTC 27 August. At around this time, Bolaven showed a broken eyewall structure in a weakening stage.

13 KMA and Radar NCIO images wind profilers NCIO a b c Vortex center a b c

14 KMA and Radar NCIO images wind profilers a b c a b c

15 KMA Wind and profiler NCIO measurements wind profilers Intense bright band Elevated bright band Large Doppler velocities (downdrafts!) As the vortex center gets nearer, the rain rates increase while the bright band intensity gets weaker. The bright band level was raised by ~500 m on around 1530 UTC.

km AGL and the bright band intensity gets weaker.

16 KMA Wind and profiler NCIO measurements wind profilers As the vortex center gets closer to the NCIO, the winds become stronger at lower levels near 2~4 km AGL and the bright band intensity gets weaker. The elevated BB on ~1530 UTC may be associated with the strong southeasterly winds below the melting layer.

R D m Rain rates were higher in the regions of stronger updrafts.

17 Time-height KMA and sections NCIO wind of the profilers parameters Z As the vortex center gets nearer, vertical air motion (i.e., updrafts) at lower levels (2~4 km AGL) became to be stronger. R D m Rain rates were higher in the regions of stronger updrafts. That is, a high correlation between R and updrafts in this case. The high rainfall rates could be overestimated by the updrafts. N 0 w Vertical air motion(w) was estimated from w = W V f where V f =2.6Z

The frequency distributions of reflectivity and Doppler velocity were broader in the rainbands of Meari, compared to those of

18 Contoured KMA frequency and NCIO distributions wind profilers by height Basically both the rainbands had a stratiform structure with a bright band near the melting layer. The frequency distributions of reflectivity and Doppler velocity were broader in the rainbands of Meari, compared to those of Bolaven. This indicates that there are larger distributions in raindrop sizes for Meari. Higher mean reflectivity and Doppler velocity profiles below the melting layer are observed in the rainbands of Bolaven.

19 KMA Vertical and NCIO mean wind profiles profilers w = W V f, V f =2.6Z There were higher reflectivity and Doppler velocity profiles were found in the rainbands of Bolaven, compared to those of Meari. The larger spectral width profile in Bolaven is attributed to stronger horizontal wind speeds. Mean updraft profiles of about 2 m s -1 below the melting layer were analyzed in both the rainbands.

20 Comparisons KMA and of NCIO mean wind vertical profilers parameters Compared to Meari, the higher Z and R profiles were found in the rainbands of Bolaven. The higher D m profile indicates that there were relatively larger raindrops in the rainbands of Bolaven. As shown in the previous slide, there were mean updrafts below the melting layer. Stdev The standard deviations (Stdev) of the parameters except for rain rate were relatively larger in the rainbands of Meari. 25 th mean 75 th percentile

21 KMA and NCIO Summary wind profilers Vertical structure and rainfall properties within Typhoon Meari and Bolaven were investigated primarily from wind profiler measurements and retrievals. Basically both the rainbands had a stratiform structure with a bright band near the melting layer. The frequency distributions of reflectivity and Doppler velocity were broader in the rainbands of Meari, compared to those of Bolaven. This indicates the wide size distributions of raindrops in the rainbands of Meari. With the higher Z and R profiles, the higher D m profile indicates that there were relatively larger raindrops in the rainbands of Bolaven, compared to those of Meari The updraft profiles with a mean of about 2 m s -1 below the melting layer were analyzed in both the rainbands. The relatively larger standard deviations (Stdev) of the parameters except for rain rate indicate larger variations of the rainfall parameters in the rainbands of Meari. More hurricane studies will be conducted to analyze rainfall properties in different rain regimes.

22 Thank you!! Contact:

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