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Intraseasonal variations of upper tropospheric water vapor in Asian monsoon region

Intraseasonal variations of upper tropospheric water vapor in Asian monsoon region. Jianping Li 1 , Ruifen Zhan 2 and A. Gettelman 3 1. LASG, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing;

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Intraseasonal variations of upper tropospheric water vapor in Asian monsoon region

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  1. Intraseasonal variations of upper tropospheric water vapor in Asian monsoon region Jianping Li1, Ruifen Zhan2 and A. Gettelman3 1. LASG, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing; 2. Shanghai Typhoon Institute of China Meteorological Administration, Shanghai; 3. National Center for Atmospheric Research, Boulder, CO, USA International Workshop on Asian Summer Monsoon and Its Role in Global Stratosphere-Troposphere Exchange (ASM-STE) July 21-23, 2010, Lhasa, China ACPD, 2006

  2. Outline • Introduction • Data and methodology • The UTWV distribution • UTWV characteristics associated with ISO in Asian monsoon region • Relationship with the Asian summer monsoon • Conclusions

  3. Introduction Why concern intraseasonal oscillation (ISO) of upper troposphere water vapor (UTWV)? • UTWV is one of the key greenhouse gases • UTWV is a major source of the hydroxyl radical • UTWV is also a valuable tracer of atmospheric motions and transports significant amounts of energy in the form of latent heat. • The ISO can affect not only the humidity field in the troposphere but also stratosphere-troposphere exchange.

  4. Why focus on the Asian summer monsoon region? • The Asian monsoon region is believed as the main source of the UTWV between May and September (Dethof et al. 1999; Gettelman et al., 2004; Randel and Park, 2005). About 75% of the total net upward WV flux at tropopause levels is contributed by the Asian monsoon circulation from July to September (Gettelman et al., 2004). • The Asian summer monsoon is well known for its prominent ISO. Since the summertime WV field in the upper troposphere often exhibits a monsoon signature, it seems significant to document UTWV seasonal variability associated with the ISO in the Asian monsoon region.

  5. Questions • What are the seasonal characteristics of UTWV associated with ISO in Asian monsoon region? • What are the relationships between UTWV and Asian summer monsoon on the intraseasonal time scale?

  6. Data & methodology AIRS Water Vapor: May-September in 2003 and 2004, 1°x1° grid, available on 12 standard pressure levels over 1000-100 hPa NCEP/NCAR u, w and OLR: May-September of 2004, 2.5° x2.5° grid • Continuous Spectrum Analysis • Butterworth Band-Pass Filter • Lag correlation

  7. Asian monsoon region EASM SASM South Asia East Asia

  8. UTWV distribution UTWV global distribution Global distribution of water vapor (ppmv) from AIRS data at 200 hPa averaged in 15-30 August 2004. White solid lines indicate contours of tropopause pressure (150, 120 hPa).

  9. UTWV distribution HovmÖller plot of daily AIRS WV at 200 hPa averaged over 2030N from May to September 2004. The black sold contours are 35 ppmv.

  10. UTWV characteristics associated with ISO in Asian monsoon region Power spectra of the UTWV 30-60 day mode: 67% 10-20 day mode: 14% Total: ~81% 30-60 day mode: 61% 10-20 day mode: 13% Total: ~74% South Asia East Asia Power spectra (thick solid line) for 5-day running mean 200 hPa WV from May to September 2004 based on AIRS.

  11. Longitude-time sections of the UTWV associated with the ISO 30-60d mode in 2004 30-60d mode in 2003 0 3 6 9 12 0 3 6 9 Averaged over 15-25N

  12. Source of the UTWV (a) South Asia (b) East Asia East Asian pattern South Asian pattern Time-longitude cross-section of lag correlations of 1025N 5-day running mean WV (without the band-pass filter) at 200 hPa with WV averaged over (a) 6575E and (b) 120130E based on AIRS. Positive lags correspond to WV averaged over 1025N leading. Influence of monsoon sub-system is independent?

  13. Relationship with the Asian summer monsoon • Is the longitudinal 3060d oscillation of UTWV related to ISO of Asian monsoon deep convection? • If so, what is the relationship between monsoon convection and UTWV?

  14. Source of monsoon convection South Asia East Asia Lag correlations of 1025N 5-day running mean OLR with OLR averaged over (a) 6575E and (b) 120130E. Like the UTWV, the convective fields also exhibit the pronounced regional reverse ISO patterns in two monsoon systems.

  15. Characteristics of UTWV associated with 30-60d oscillation in Asian monsoon region UTWV Longitude-pressure sections of 30-60d filtered WV (ppmv, shading) based on AIRS and vertical wind components (vectors) from Pentad 40 (15~19 Jul) to Pentad 48 (24~28 Aug) in 2004. The longitudinal distribution of 30-60d filtered OLR for the same period. The red line represents the enhanced convection. All plots are for 15-25N. OLR SASM EASM

  16. Lag correlations between OLR and UTWV South Asia East Asia Lag correlations between OLR and AIRS WV on 3060 day band in (a) South Asia (3597.5E, 522.5N) and (b) East Asia (110140E, 020N) during May-September 2004. Positive lags refer to OLR leading WV. • The high UTWV lags the enhanced monsoon convection by about 1-2 pentads, suggesting that the upper troposphere is generally moistened following intense monsoon convection.

  17. Conclusions • The pronounced regionally propagating features of UTWV associated with an ISO in the Asian summer monsoon region with an emphasis on relationship to the Asian monsoon. The UTWV peak in summer lies not only in South Asia but also in East Asia. • The ISO of UTWV has two significant periods, a 30-60d mode and a 10-20d mode, respectively. The 30-60d mode is dominant in the intraseasonal variability of UTWV over the Asian monsoon region in summer. The mode exhibits two distinct patterns in the two monsoon sub-systems, defined as the South Asian pattern and East Asian pattern, respectively.

  18. Conclusions • Like the UTWV, the convection also exhibits the pronounced regional ISO patterns in two monsoon systems. • The lag correlation pattern between OLR and the UTWV on 30-60d band shows that the upper troposphere is moistened following the enhanced monsoon convection with lags about 5-10 days. The result shows that the Asian summer monsoon plays an important role in the intraseasonal variations of UTWV.

  19. Thank you!

  20. AIRS global distribution The peak (~18 ppmv) is a widely elongated belt stretching eastward from the Indian subcontinent to the East Asia, including China and south of Japan Global distribution of water vapor (ppmv) from AIRS data at 150 hPa averaged in 15-30 August 2004. White solid lines indicate contours of tropopause pressure (150, 120 hPa).

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