Comparison of Multi-Day Convective-Environmental Evolution between TC Developing vs. Non-Developing Disturbances over the Western North Pacific Minhee Chang ( 張敏姬 ) 1 , Chang-Hoi Ho 1 , Myung-Sook Park 2 1 School of Earth and Environmental Sciences, Seoul National University, Seoul, Korea 2 Korea Institute of Ocean Science & Technology, Busan, South Korea Climate Physics Laboratory Seoul National University
TC developing vs. non-developing disturbances Yes Developing disturbance TC Tropical developing? disturbances Non- No developing disturbance • Every year in the western North Pacific, more than a hundred of tropical disturbances exists, but only a few of them develop into tropical cyclone. • Previous studies have suggested different pathways regarding how the tropical disturbance can develop into a tropical cyclone; top-down hypothesis (Simpson et al. 1997; Bister and Emanuel 1997) and bottom-up hypothesis (Hendricks et al. 2004; Montgomery et al. 2006). | Introduction | Motivation | Objective | Data and methodology | Result | Summary | 2
Recent studies on deep convective features • Different elements (rainfall area and frequency by Zawislak and Zipser 2014a; mid-level vorticity strength by Zawislak and Zipser 2014b; latent heating maximum location by Park and Elsberry 2013) of deep convective cloud have been emphasized by previous researches. • TC formation process is known to be associated with a Satellite Aircraft radar series of diurnal convective bursts (Zehr 1992; Davis TRMM and Ahijevych 2012) . (non-sun- synchronous satellite) Hurricane Matthew (2010) Convection Convection area (radius) area (fraction) Time (Davis and Ahijevych 2012) Time (Zehr 1992) | Introduction | Motivation | Objective | Data and methodology | Part 1 | Part 2 | Summary | 3
Physical mechanism and meaning of multiple diurnal convective bursts Relative vorticity [x10 -5 s -1 ] <Diurnal radiative forcing> Diurnal large-scale Height convective environment Convection instability cooling area (fraction) Nighttime differential cooling Time (Zehr 1992) Height • Multiple diurnal convective bursts are mostly attributed to diurnal variation of radiative forcing (Webster and Stephens 1980; Gray and Jacobson 1977; Melhouser Daytime and Zhang 2013; Tang and Zhang 2016) , thus, tend to have morning maxima and afternoon minima (Gray and Jacobson 1977) . Height • In the idealized simulations, nighttime destabilization through radiative cooling turns out to promote deep moist convection that leads to vortex intensification as well as to TC genesis (Melhauser and Zhang 2013; Tang and Zhang 2016) . (Tang and Zhang 2016) Local Standard Time | Introduction | Motivation | Objective | Data and methodology | Result | Summary | 4
Objective : Scientific questions (1) In what percentage, mCB is related to TC development and non-development processes? ? mCB TC formation (2) If mCB and TC development does not have one-to-one relationship, what other element modulates TC development and non-development processes? ? mCB & large-scale condition TC formation (3) Can a tropical cyclone develop without mCB and how? ? Without mCB TC formation (4) What are the characteristics of TC development without mCB? ? Without mCB & large-scale condition TC formation | Introduction | Motivation | Objective | Data and methodology | Result | Summary | 5
Data Domain : western North Pacific (100 –180˚E, 0–35˚N ) • Developing disturbances (80) • Non-developing disturbances (383) Period : Year of 2007 – 2009 Type Time Space Variables Name resolution resolution 4km × 4km IR(10.8 μ m), WV(6.7 μ m) Geostationary satellite data 1 hourly MTSAT-1R brightness temperature 1.25⁰ × 1.25⁰ Reanlaysis data 3 hourly MERRA reanalysis 1 u, v, omega, T, PV, height, 0.5⁰ × 0.625⁰ RH, q 3 hourly MERRA reanalysis 2 0.25 × 0.25 1 daily SST OISST – Track data 6 hourly TD formation time JTWC best track – 6 hourly LAT, LON IBTrACS best track – 3hourly LAT, LON Tropical cloud cluster track | Introduction | Motivation | Objective | Data and methodology | Result | Summary | 6
Methodology: Vortex tracking Developing disturbances (80) 600 hPa Potential Vorticity : 5 days prior to TC formation TC Peipah (2007) vortex track Day Day Day Day Day Day Day 1 2 3 4 5 6 7 TC formation Vortex tracking Latitude day Non-developing disturbances (383) : 5 days including decay of disturbances. Day Day Day Day Day 1 2 3 4 5 Largest Vortex Vortex CB day tracking tracking Longitude • By following the 600 hPa PV centers five day pre-genesis and two-day post-genesis positions are obtained. | Introduction | Motivation | Objective | Data and methodology | Result | Summary | 7
Methodology: Convective area time series e.g., Pre-Higos (24-30 Sep 2008) 500 km IR – WV 600 hPa radius PV max(A) Δ A ` Δ t TC formation mCB • Deep convective area (IR minus WV < 0) time series (solid line) and its 7-h running mean (thick solid line). • Definition of multi-day diurnal convective bursts (mCB): deep convective area increment satisfying four thresholds ( Δt ≥ 6 h, ΔA ≥ 5,000 km 2 , max(A) ≥ 15,000 km 2 , and Δ A/ Δt ≥ 500 km 2 h 1 ) for at least two consecutive days. | Introduction | Motivation | Objective | Data and methodology | Result | Summary | 8
Categorization of tropical disturbances • Developing/nondeveloping disturbances are sub-categorized based on the presence/absence of mCB. 67.5% (54 / 80) Yes D_w mCB Developing Yes occurrence? 32.5% (26 / 80) disturbance D_wo TC No Tropical developing? disturbances 13.8% (53 / 383) Yes ND_w Non- mCB No developing occurrence? 86.2% (330 / 383) disturbance ND_wo No “D” : Developing “ND” : Non-developing A. D_w A. D_w “_w” : with mCB Deep convective area [10 4 km 2 ] “_wo” : without mCB B. D_wo C. ND_w • Tropical cyclone formation is mostly (67.5%) associated with mCB (D_w). • A small fraction (32.5%) of tropical cyclones develop D. ND_wo without active convection (D_w/o). • But some (13.8%) of non-developers also accompany mCB (ND_w). Time | Introduction | Motivation | Objective | Data and methodology | Result | Summary | 9
Composite analysis: Relative vorticity, divergence (Shading) (contour line) A. D_w Potential vorticity strengthens due to deep convective updrafts. (Wang 2014) B. D_wo C. ND_w • Low-level vorticity continuously intensifies for both D_w and ND_w. But the strength for D_w is significantly stronger than ND_w on Days 3 – 5. D. ND_wo • The low-level convergent inflows for D_w are persistently maintained. But that for p ND_w are maintained in diurnal signal. • For D_w/o weak initial vorticity on Days 1 – 2 Time [10 -6 s -1 ] suddenly strengthens prior to TC genesis. | Introduction | Motivation | Objective | Data and methodology | Result | Summary | 10
Composite analysis: Relative humidity A. D_w B. D_wo C. ND_w • For D_w and ND_w, very moist (> 80%) mid- level from Day 1 to 5 is maintained. • For D_w/o, atmospheric conditions remain extremely dry (< 70%) until Day 2. D. ND_wo p Time [%] | Introduction | Motivation | Objective | Data and methodology | Result | Summary | 11
Composite analysis: Vertical wind shear A. D_w × : vortex center B. D_wo 3⁰ radius circle 8⁰ radius circle C. ND_w • For D_w on Days 1 – 3, vws magnitude is mostly under 14 m s -1 within 8 ⁰ radius circle. • For D_w/o on Day 1 – 2, vws around D. ND_wo vortex center is larger than 14 m s -1 , which significantly decrease on Days 4 – 5. • For ND_w on Days 1 – 3, about half of 8 ⁰ radius circle is covered with vws larger [m s – 1 ] than 14 m s -1 . | Introduction | Motivation | Objective | Data and methodology | Result | Summary | 12
Composite analysis summary A. D_w B. D_wo 67.5% (54 / 80) 32.5% (26 / 80) Vertical wind ? shear mCB Low-level inflow Relative vorticity C. ND_w D. ND_wo 13.8% (53 / 383) 86.2% (330 / 383) mCB • MCB within the environment of weak vertical wind shear is critical in vorticity strengthening for tropical cyclogenesis. Difference in D_w and ND_w. • A small number of tropical cyclones develop abruptly without mCB. More analysis is needed for D_wo. (Chang, M., Ho, C.-H., Park, M.-S., Kim, J., & Ahn, M.-H., 2017, JGR) | Introduction | Motivation | Objective | Data and methodology | Result | Summary | 13
A case study on developing disturbance without mCB TC Peipah (formed on Nov 3, 2007), a case with the B. D_wo 32.5% (26 / 80) • Major characteristics of D_w/o are .. most representative feature, is chosen for a case study. (i) suppressed convection in the preceding days (ii) sudden intensification of low-to-mid relative vorticity (iii) strong vertical wind shear diminishes later Abrupt TC formation may possibly induced by external forcing. 27 28 29 30 31 1 2 3 4 October November 14 | Introduction | Motivation | Objective | Data and methodology | Result | Summary |
TC formation influenced by upper-tropospheric disturbance • TUTT-induced TC formation (Sadler 1967; 1976; 1978) • Tropical transition (Davis and Bosart 2003; 2004) • Baroclinically induced TC formation (McTaggart- Cowan et al. 2008; 2013) • Anticyclonic Rossby wave breaking (Galarneau et al. 2015; Bentley et al. 2017) (Bentley et al. 2017) 15
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