Tropopause Cirrus Variation by Equatorial Kelvin Waves

Transcription

1 Tropopause Cirrus Variation by Equatorial Kelvin Waves Masatomo Fujiwara Hokkaido University SOWER Meeting, 19 July 2006

2 Outline Kelvin waves in the TTL (10 min) Cirrus in the TTL (5 min) Results from R/V Mirai s MR04-08 Cruise (near Palau, in Dec 2004 Jan 2005) (10 min) Summary

3 Kelvin waves? (1/3) Coastal Kelvin waves [William Thomson (Lord Kelvin), 1879] Oceanic long gravity waves propagating parallel to a wall/coast Explanation for the coastal tides in the English Channel (Coriolis force by the flow) = (Pressure gradient force) Trapped near the coast (L: Rossby radius of deformation) [Gill, 1982; The Open University, 1989] (cf. Kelvin ship waves)

4 Kelvin waves? (2/3) Equatorial Kelvin waves [Taroh Matsuno, JMSJ, 1966] Matsuno theoretically investigated large-scale motions in the equatorial region, and found various types of equatorially trapped waves Also investigated forced stationary motion (the so-called Matsuno- Gill pattern) [Matsuno, 1966; vertical section by Fujiwara et al., 1998] The equator acts as the wall for a pair of coastal Kelvin waves only propagate eastward vertical section gravity waves U, W, P in phase; no V ; T by W

5 Kelvin waves? (3/3) In search of the zonal momentum source of the Quasi-Biennial Oscillation (QBO) Yanai-Maruyama wave (1966) Mixed Rossby- Gravity (MRG) waves Wallace-Kousky wave (1968) Kelvin waves QBO theory : Lindzen and Holton [1968; various gravity waves], Holton and Lindzen [1972; Kelvin and MRG] U T Twice daily radiosonde data above 100 hpa at Balboa (9N, 80W), Trinidad (11N, 61W), and Kwajalein (9N, 168E). (Note the prominent fluctuations around the tropopause.) [Wallace and Kousky, 1968]

6 Kelvin waves around the tropopause Madden and Julian [1972] found eastward-moving tropopause temperature anomalies associated with the intra-seasonal oscillations (ISO or MJO or day osc.) Parker [1973] discussed that most of the day oscillations found at 100 hpa can be regarded as equatorial Kelvin waves Suzuki and Shiotani [Madden and Julian, 1972]

7 Kelvin waves and STE (1/5) Kelvin waves cause significant (peak-to-peak ~ 10 K) temperature fluctuations in the TTL [Tsuda et al., 1994; ], but currently it seems they are only regarded as one of the agents which produce temperature flucturations Main dynamical processes (esp. for dehydration ) : slow ascent (Brewer-Dobson circ., extratropical pump); penetrating cumulonimbus clouds; large-scale horizontal flow; etc. Tropical clouds tend to be organized to larger-scale cloud disturbances [e.g., ISO] and above the top of these organized clouds, Kelvin waves develop to cause minor constituents variations Therefore the equatorial waves and organized clouds are both essential and constitute a large-scale system to cause the tropical STE [Fujiwara and Takahashi, 2001] some evidence for this statement

8 Kelvin waves and STE (2/5) [ ppbv ] Ozonesondes at Watukosek, Indonesia Large-amplitude Kelvin waves & associated ISO transport ozone Role of Kelvin waves in the transport and dynamics in the TTL [Fujiwara et al., 1998]

9 Kelvin waves and STE (2/5) Large-amplitude Kelvin waves & associated ISO transport ozone Role of Kelvin waves in the transport and dynamics in the TTL [Fujiwara et al., 1998]

10 Kelvin waves and STE (3/5) NOAA FPHs & Ozonesondes at the Galapagos water vapor m.r. Downward displacement phase ozone-rich, dry unsaturated air ozone m.r. saturation water vapor m.r. Upward displacement phase cold anomaly prevents TTL from excess water Meteorological data indicate the passage of Kelvin waves Role of Kelvin waves as a dehydration pump [Fujiwara et al., 2001]

11 Kelvin waves and STE (4/5) Kelvin waves in TTL often have large amplitudes breaking Turbulence generation by breaking Kelvin waves ( Spectral Width indicates the strength of the turbulence ) Equatorial Atmosphere Radar (EAR), Sumatra, Indonesia wind & turbulence up to LS 560 Yagi antennae (~in a 110-m field) since June 2001 Yamamoto et al. [Fujiwara et al., 2003] EAR observed turbulence generation in the breaking phase (eastward wind phase) of the Kelvin waves irreversible transport (mixing)

12 Kelvin waves and STE (5/5) (Equator) Eastward-moving large-scale disturbances are dominant at the equatorial tropopause Most of them are (breaking) equatorial Kelvin waves In the eastern hemisphere, these waves are associated with organized convective activity in the troposphere (MJO, convectively coupled Kelvin waves) Ozone & dry air transport Dehydration at the cold phase Irreversible transport, mixing [Fujiwara and Takahashi, 2001 : CCSR/NIES AGCM T42L60 + simple ozone chemistry] dz~550 m in UT/LS

13 Waves & flow in the TTL Matsuno-Gill pattern : response to large-scale tropical convective heating (Kelvin waves & equatorial Rossby waves) Characteristic flow pattern & zonal asymmetry in temperature in the TTL cold anomaly [Hatsushika and Yamazaki, 2003; see also Highwood and Hoskins, 1998]

14 Kelvin waves! - a short summary - Dynamical response in the TTL to the convective heating by large-scale tropical organized clouds Dynamical control of the TTL Significant temperature perturbations Large-scale horizontal flow (+ eq. Rossby waves) Vertical, irreversible transport & dehydration in the TTL Cirrus in the TTL?

15 Cirrus in the TTL (1/4) Dehydration needs water vapor to condense and resulting cloud particles to fall out TTL should not be a clear sky Cirrus clouds influence the radiative balance and vertical motion (hence, the age of the TTL air) Supersaturation is needed for clouds to form; then, how much supersaturation is actually needed? Observations of both large-scale cirrus distribution and cloud microphysical properties in the TTL are necessary

16 Cirrus in the TTL (2/4) Only (?) in situ photos of TTL cirrus crystals [Heymsfield, 1986] Aircraft sampling from tropopause thin cirrus, Marchall Is., 17 Dec 1973 Marshall Is. (Kwajalein), 17 December 1973, WB57F Radius of the ice particles :10~30μm

17 Cirrus in the TTL (3/4) Wide-spread TTL cirrus & tropical STE Aircraft, satellite, and lidar observations SAGE II [Wang et al., 1996] LITE Sep.9-20, 94 [Winker and Trepte, 1998]

18 Cirrus in the TTL (4/4) TTL cirrus variation & Kelvin waves [Boehm and Verlinde, 2000] Lidar & radiosonde temperature anomalies at Nauru (0.5S, 166.9E) (June-July 1999) Cirrus appears selectively at the cold anomalies due to Kelvin waves. but Comstock et al. (2002) extended the analysis period for April-November 1999 Correlation between cloud occurrence and cold anomaly is not universal ( Why? analysis method?; ignoring the strong connection btwn. the lower and higher clouds?)

19 Results from R/V Mirai s MR04-08 Cruise (near Palau, in Dec 2004 Jan 2005) - Cirrus and Kelvin waves - M. Fujiwara (Hokkaido U.) I. Matsui, A. Shimizu, N. Sugimoto (NIES) K. Yoneyama (JAMSTEC) H. Okamoto (Tohoku U.), S. Iwasaki (NDA) SOWER members

20 R/V Mirai & NIES Lidar R/V Mirai : (Japan Agency for Marine-Earth Science and Technology, JAMSTEC) Atmospheric and Oceanic Research Vessel Doppler Radar RS92 radiosonde (every 3 hours) MR04-08: near Palau (7N, 134E) Dec. 04 Jan. 05 (+ SW+ECC soundings Inai et al.) 2-wavelength dual polarization lidar (National Institute for Environmental Studies, NIES) Nd:YAG laser (1064 nm & 532 nm) Range resolution : 3.75 m Temporal resolution : 10 sec ( For previous cruises, see Iwasaki et al. [GRL, 2004], and Shiotani et al.)

21 Subvisual cirrus was visible Left : Photo taken at 9:16UT (18:16LT), 2 January 2005 Bottom : Lidar quick look plot during the first half of 2 Jan. (UT) 00UT 06UT 12UT Cirrus could be seen even during the daytime with polarizing sunglasses SVC can be sometimes seen at the sunset

22 Large-scale field Eastward-moving large-scale disturbances (Kelvin waves) at 100 hpa At Longitude of R/V Mirai (white line) : Warm anomaly in mid DEC, Cold anom. in late DEC, Warm anom. in early JAN

23 Lidar Cirrus Observation (1/2) Tropopause/Top of TTL : ~370 K, or, cold point 370 K/CP 355 K Bottom of TTL : ~350 K 350 K Mid December : No cloud in TTL (UT clouds) Late December : Clouds in TTL (& cold anomaly) Early January : Clouds still in TTL (but warm anomaly) Descending at night

24 Lidar Cirrus Observation (2/2) Descending motion at night in January Particle depolarization ratio : an indicator for shape or non-sphericity TTL clouds are different from UT clouds (in the formation process?)

25 Interpretation Mid December : No cloud in TTL warm & descending phase of the Kelvin wave Late December : Clouds in TTL cold & ascending phase of the Kelvin wave Early January : Clouds still in TTL Descending at night Cloud particles were transported? ; Humidity was still supplied?

26 Mirai MR a summary - Cirrus variation associated with Kelvin waves in the TTL Temperature variation and flow pattern controlled by Kelvin waves Transport of cloud particles and water vapor TTL cirrus and UT cirrus may be different

27 Summary of the Talk Equatorial Kelvin (& Rossby) waves in the TTL Dynamical response to the convective heating by large-scale tropical organized clouds Dynamical control of the TTL Significant temperature perturbations (Kelvin) Large-scale horizontal flow (Kelvin + Rossby) Vertical, irreversible transport & dehydration in the TTL Cirrus variation (Nauru, MR04-08 near Palau)

28 Some Tropical Lidar Sites Blue Star : R/V Mirai (MR04-08), Dec 2004 to Jan 2005 (NIES) Red Star : Kototabang (EAR), since 2004 (Tokyo M. U.) Red Star : Bandung, 1990s (MRI-JMA), 2003 to 2005 (Nagoya U./SOWER) Red Star : Biak, since Jan (Nagoya U./SOWER) Red Star : Tarawa, since Jan (NIES/SOWER) Red Star : Surinam, 2004 to 2005 (AWI) Black Circle : Kwajalein (Marshall Is.),? Black Circle : Nauru, 1999 (to?), (ARM)

29 Surinam, Oct-Nov 2004 [Fortuin et al., 2006]

30 Tarawa, January 2006 [Iwasaki et al., 2006]

31 Summary of the Talk Equatorial Kelvin (& Rossby) waves in the TTL Dynamical response to the convective heating by large-scale tropical organized clouds Dynamical control of the TTL Significant temperature perturbations (Kelvin) Large-scale horizontal flow (Kelvin + Rossby) Vertical, irreversible transport & dehydration in the TTL Cirrus variation (Nauru, MR04-08 near Palau)