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Yukiko YAMADA, Takeaki SAMPE, Yoshiyuki O. TAKAHASHI, Mayumi K. YOSHIOKA,

A resolution dependence of equatorial precipitation activities represented in a general circulation model. Yukiko YAMADA, Takeaki SAMPE, Yoshiyuki O. TAKAHASHI, Mayumi K. YOSHIOKA, Wataru OHFUCHI, Masaki ISHIWATARI, Kensuke NAKAJIMA, Yoshi-Yuki HAYASHI. APE Workshop 20/04/2005.

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Yukiko YAMADA, Takeaki SAMPE, Yoshiyuki O. TAKAHASHI, Mayumi K. YOSHIOKA,

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  1. A resolution dependence of equatorial precipitation activities represented in a general circulation model Yukiko YAMADA, Takeaki SAMPE, Yoshiyuki O. TAKAHASHI, Mayumi K. YOSHIOKA, Wataru OHFUCHI, Masaki ISHIWATARI, Kensuke NAKAJIMA, Yoshi-Yuki HAYASHI APE Workshop 20/04/2005

  2. Outline and Introduction

  3. 1. Outline • Resolution dependence experiments • We, “AGU for APE” performed GCM runs with various horizontal and vertical resolutions. • This presentation show … • We will focus our attention on the model representation of organized way of equatorial precipitation activities and their hierarchical appearances. • We will try to consider on generation and maintenance mechanism of precipitation structures in these runs. APE project by AGU for APE http://www.gfd-dennou.org/arch/ape/

  4. 2. Background • Equatorial hierarchical structure of precipitation activity • It has been argued that there exists three types of structure with different time and spatial scales; MJO, super cloud cluster and cloud cluster. • They seem to form hierarchical structures. super cloud cluster MJO Schematic diagram for hierarchy of ISV. (Nakazawa, 1988) Time-longitude section of transient OLR averaged between the equator and 5N from May to July in 1980. (Nakazawa, 1988)

  5. 3. Purpose • Aqua-planet experiments in past • Exp.) Hayashi and Sumi (1986): T42L16 • They suggested that super cloud clusters and a MJO-like modulation of the intensity of these super cloud clusters with a structure of wavenumber one are spontaneously excited in an aqua planet GCM. • With higher resolution, … • How is the their hierarchical structure represented? 0day super cloud cluster !?? MJO !?? Time-longitude section of transient precipitation in GCM (Hayashi and Sumi, 1986) 90day 360 720 0deg

  6. Model and Experimental design

  7. 4. Model • AFES • Based on CCSR-NIES AGCM version 5.4.02 tuned for efficient parallel computing at the Earth Simulator Center • Dynamical core: • Primitive eq.(sigma coodinate) with hydrostatic approx. • Horizontal : Spectral (spherical harmonics) • Vertical : Finite difference (Lorenz grid) • Time integration : Semi-implicit method • The physical processes: • Radiative transfer scheme : Nakajima and Tanaka (1986) • Vertical diffusion scheme : Mellor-Yamada (1974) level-2 • Cumulus scheme: • Not used and Emanuel (1991) convective scheme

  8. 5. Experimental design • SST • SST is used in APE control experiment. • Resolution • Standard run : T39L48 • Horizontal resolution : from T39to T319 • Vertical resolution : from L24 to L96 • In results, we focus attention on … • The runs that the cumulus convective scheme is not used. • Horizontal resolution dependences (T39L48, T79L48, T159L48, T319L48)

  9. Results(no cumulus scheme run)

  10. 6. Zonally and temporally averaged precipitation T159, T319 T79 T39 When the horizontal resolution is increased from T39L48 to T319L48, precipitation increases in the vicinity of the equator.

  11. 7. Movie: T39L48 T39L48

  12. 8. Movie: T319L48 T319L48

  13. ←From the next slide, these experiments are described in detail. 9. Longitude-time section of equatorial precipitation T39L48 T79L48 T159L48 T319L48

  14. 10. T39L48 T39L48

  15. 16m/s 11. T39L48 T39L48 T39L48 wavenumber-frequency power spectrum calculated as Wheeler and Kiladis (1999) • Eastward moving precipitation areas • Phase speed is about 16 ~ 25 m/s • The spectral power signals appear along the dispersion curves of the equatorial Kelvin waves. • Westward moving precipitation areas • The signals are broadly distributed in spectrum diagram.

  16. 12. T159L48 T159L48 The area surrounded by a blue border is magnified.

  17. 13. T159L48 • In the high horizontal resolution run, • The eastward propagating structures with the horizontal scale of 4,000 km are actually composed of some smaller scale westward moving structures. • A hierarchical structure appears !

  18. 14. Eastward propagating structures in T159L48 The eastward propagating structure (blue line) is focused on.

  19. 15. Eastward propagating structures in T159L48 15m/s wavenumber-frequency power spectrum calculated as Wheeler and Kiladis (1999) • Eastward propagating structure • The phase speed is about 15 m/s. • The spectral power signals appear along the dispersion curves of the equatorial Kelvin waves.

  20. 16. Eastward propagating structures in T159L48 sigma=0.85 Zonal mean values are subtracted • Composite analysis • In order to examine the circulation structures associated with the eastward propagating structure, composite analysis is adopted. • Reference points for composite are chosen along the convergence lines with the zonal wind of sigma=0.85 (black line).

  21. 17. Eastward propagating structures in T159L48 The equatorial longitude-height section of the composite circulation structure. Zonal mean values are subtracted. • The composite circulation structure • Phase slant of temperature and zonal wind can be observed. • The eastward propagating structures are maintained by the equatorial Kelvin wave-CISK?

  22. 18. Westward propagating structures in T159L48 The westward propagating structures are examined.

  23. 19. Westward propagating structures in T159L48 wavenumber-frequency power spectrum calculated as Wheeler and Kiladis (1999) • Westward propagating structure • There are two types of structures with different phase speed; 8~10 m/s and 15 ~ 20 m/s. • The spectral power signals of the structures whose phase speed is 15 ~ 20 m/s appear along the dispersion curves of westward gravity waves.

  24. 7m/s 20. Westward propagating structures in T159L48 • Vertical distributions of zonally averaged eastward wind at equator. • The phase speed of westward propagating structures, 8 ~ 10 m/s is almost equal to zonally averaged background zonal wind speed. • The structures whose phase speed is 8 ~ 10 m/s is maintained by conditional instability of the first kind (CIFK). • These westward moving precipitation areas are regarded as CIFK structure advected by the background wind.

  25. Summary

  26. 21. Summary:AFES no cumulus scheme runs • In the high horizontal resolution run (T39 ⇒ T159) • The large scale eastward propagating structures are composed of some smaller scale westward moving structures. • A hierarchical structure appears clearly. • Eastward propagating structures • The eastward propagating structures seem to be maintained by the equatorial Kelvin wave-CISK. • Westward propagating structures • There are two types of structures with different phase speed in the westward propagating structures. • One may be may be related to westward gravity waves. • The other is regarded as CIFK structure advected by the background wind. APE project by AGU for APE http://www.gfd-dennou.org/arch/ape/

  27. Results(Emaluel scheme run)

  28. 22.Emanuel scheme experiment • Emanuel scheme experiment • We also performed various resolution runs similar as no cumulus runs. • NetCDF file of T39L48 runs is submitted to PCMDI.

  29. 23. Zonally and temporally averaged precipitation T79,T159, T319 T39 Precipitation around the equator increases up to T79. With heigher resolution than T79, it hardly changes.

  30. 24. Longitude-time section of equatorial precipitation T39L48_non T39L48_eml • No cumulus scheme run • Eastward moving structures appear. • Emanuel scheme run • Westward moving structures appear clearly.

  31. 25. Longitude-time section of equatorial precipitation T39L48_eml T79L48_eml T319L48_eml T159L48_eml

  32. 26. Magnified view of X-T diagram: T159L48 16 m/s 12.5 m/s • In the higher horizontal resolution run • The eastward propagating structures with the horizontal scale of 4,000 ~ 6,000 km are actually composed of some smaller scale westward moving structures. • A hierarchical structure appears as in no cumulus scheme runs.

  33. 27. Summary: AFES Emanuel scheme runs • In the Emanuel scheme run, • Westward moving structures appear clearly unlike in the no cumulus scheme runs. • With higher resolution runs, a hierarchical structure appears as in the no cumulus runs. APE project by AGU for APE http://www.gfd-dennou.org/arch/ape/

  34. Appendix

  35. appendix

  36. Cumulus scheme dependence: Emanuel scheme

  37. Cumulus scheme dependence: Emanuel scheme wave-CISK っぽくない. 東西空間スケールが大きい構造をしてる

  38. 10. Higher horizontal resolution run: T159L48 T159L48 T159L48 12.5 m/s 16 m/s 12.5 m/s • Eastward moving precipitation areas • Phase speed is about 16 ~ 25 m/s. • The spectral power signals appear along the dispersion curves of Kelvin waves. • Westward moving (grid scale) precipitation areas • Phase speed is about 12.5 m/s. • This value of phase speed is almost equal to zonally averaged background zonal wind speed.

  39. 25. Standard run: T39L48 T39L48 T39L48 7.5 m/s 7.5 m/s • Eastward moving precipitation areas • Eastward moving structures do not appear clearly. • Westward moving (grid scale) precipitation areas • Phase speed is about 7.5 m/s. • This value of phase speed is almost equal to zonally averaged background zonal wind speed.

  40. Cumulus scheme dependence: Emanuel scheme

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