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  • Li, Tim  (10)
  • 2010-2014  (10)
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  • 2010-2014  (10)
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  • 1
    Online Resource
    Online Resource
    Moisture Asymmetry and MJO Eastward Propagation in an Aquaplanet General Circulation Model*
    American Meteorological Society ; 2014
    In:  Journal of Climate Vol. 27, No. 23 ( 2014-12-01), p. 8747-8760
    Details
    In: Journal of Climate, American Meteorological Society, Vol. 27, No. 23 ( 2014-12-01), p. 8747-8760
    Abstract: The role of zonal moisture asymmetry in the eastward propagation of the Madden–Julian oscillation (MJO) is investigated through a set of aquaplanet atmospheric general circulation model (AGCM) experiments with a zonally symmetric sea surface temperature distribution. In the control experiment, the model produces eastward-propagating MJO-like perturbations with a dominant period of 30–90 days. The model MJO exhibits a clear zonal asymmetry in the lower-tropospheric specific humidity field, with a positive (negative) anomaly appearing to the east (west) of the MJO convection. A diagnosis of the lower-tropospheric moisture budget indicates that the asymmetry primarily arises from vertical moisture advection associated with boundary layer convergence, while horizontal moisture advection has the opposite effect. In a sensitivity experiment, the lower-tropospheric specific humidity field is relaxed toward a zonal-mean basic state derived from the control simulation. In this case, the model’s mean state remains the same, but its intraseasonal mode becomes quasi-stationary. The numerical model experiments clearly demonstrate the importance of the zonal moisture asymmetry in MJO eastward propagation.
    Type of Medium: Online Resource
    ISSN: 0894-8755 , 1520-0442
    URL: Article
    DOI: 10.1175/JCLI-D-14-00148.1
    RVK:
    UA 4548
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2014
    detail.hit.zdb_id: 246750-1
    detail.hit.zdb_id: 2021723-7
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  • 2
    Online Resource
    Online Resource
    Increase of global monsoon area and precipitation under global warming: A robust signal? : CHANGES IN GLOBAL MONSOON
    American Geophysical Union (AGU) ; 2012
    In:  Geophysical Research Letters Vol. 39, No. 6 ( 2012-03-28), p. n/a-n/a
    Details
    In: Geophysical Research Letters, American Geophysical Union (AGU), Vol. 39, No. 6 ( 2012-03-28), p. n/a-n/a
    Type of Medium: Online Resource
    ISSN: 0094-8276
    URL: Article
    DOI: 10.1029/2012GL051037
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 2012
    detail.hit.zdb_id: 2021599-X
    detail.hit.zdb_id: 7403-2
    SSG: 16,13
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    Online Resource
  • 3
    Online Resource
    Online Resource
    Future change of the global monsoon revealed from 19 CMIP5 models
    American Geophysical Union (AGU) ; 2013
    In:  Journal of Geophysical Research: Atmospheres Vol. 118, No. 3 ( 2013-02-16), p. 1247-1260
    Details
    In: Journal of Geophysical Research: Atmospheres, American Geophysical Union (AGU), Vol. 118, No. 3 ( 2013-02-16), p. 1247-1260
    Abstract: The CMIP5 models project enhanced global monsoon activity under RCP4.5 scenario The causes of monsoon rainfall change were examined by a moisture budget
    Type of Medium: Online Resource
    ISSN: 2169-897X , 2169-8996
    URL: Issue
    URL: Article
    DOI: 10.1002/jgrd.v118.3
    DOI: 10.1002/jgrd.50145
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 2013
    detail.hit.zdb_id: 710256-2
    detail.hit.zdb_id: 2016800-7
    detail.hit.zdb_id: 2969341-X
    SSG: 16,13
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  • 4
    Online Resource
    Online Resource
    Interactions between Boreal Summer Intraseasonal Oscillations and Synoptic-Scale Disturbances over the Western North Pacific. Part I: Energetics Diagnosis*
    American Meteorological Society ; 2011
    In:  Journal of Climate Vol. 24, No. 3 ( 2011-02-01), p. 927-941
    Details
    In: Journal of Climate, American Meteorological Society, Vol. 24, No. 3 ( 2011-02-01), p. 927-941
    Abstract: The role of scale interactions in the maintenance of eddy kinetic energy (EKE) during the extreme phases of the intraseasonal oscillation (ISO) is examined through the construction of a new eddy energetics diagnostic tool that separates the effects of ISO and a low-frequency background state (LFBS; with periods longer than 90 days). The LFBS always contributes positively toward the EKE in the boreal summer, regardless of the ISO phases. The synoptic eddies extract energy from the ISO during the ISO active phase. This positive barotropic energy conversion occurs when the synoptic eddies interact with low-level cyclonic and convergent–confluent ISO flows. This contrasts with the ISO suppressed phase during which the synoptic eddies lose kinetic energy to the ISO flow. The anticyclonic and divergent–diffluent ISO flows during the suppressed phase are responsible for the negative barotropic energy conversion. A positive (negative) EKE tendency occurs during the ISO suppressed-to-active (active-to-suppressed) transitional phase. The cause of this asymmetric EKE tendency is attributed to the spatial phase relation among the ISO vorticity, eddy structure, and EKE. The southwest–northeast-tilted synoptic disturbances interacting with cyclonic (anticyclonic) vorticity of ISO lead to a positive (negative) EKE tendency in the northwest region of the maximum EKE center. The genesis number and location and intensification rate of tropical cyclones in the western North Pacific are closely related to the barotropic energy conversion. The enhanced barotropic energy conversion favors the generation and development of synoptic seed disturbances, some of which eventually grow into tropical cyclones.
    Type of Medium: Online Resource
    ISSN: 1520-0442 , 0894-8755
    URL: Article
    DOI: 10.1175/2010JCLI3833.1
    RVK:
    UA 4548
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2011
    detail.hit.zdb_id: 246750-1
    detail.hit.zdb_id: 2021723-7
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  • 5
    Online Resource
    Online Resource
    Contributing Factors to the Recent High Level of Accumulated Cyclone Energy (ACE) and Power Dissipation Index (PDI) in the North Atlantic*
    American Meteorological Society ; 2014
    In:  Journal of Climate Vol. 27, No. 8 ( 2014-04-15), p. 3023-3034
    Details
    In: Journal of Climate, American Meteorological Society, Vol. 27, No. 8 ( 2014-04-15), p. 3023-3034
    Abstract: In recent decades, tropical cyclone (TC) activity in the North Atlantic has shown a marked positive anomaly in genesis number, mean lifespan, number of intense hurricanes, and mean maximum intensity. The accumulated cyclone energy (ACE), which is defined as the sum of the square of the maximum surface wind velocity throughout the lifetime of a TC, is one of the measures that can be used to synthesize these factors. Similar to the ACE, the power dissipation index (PDI), which is defined as the integrated third power of maximum surface wind velocity, has also been used to describe TC activity. The basin-total ACE and PDI for the North Atlantic have also followed a large positive anomaly during the period 1995–2012; however, the relative importance of factors such as TC genesis number, TC track property (e.g., duration and lifespan), and TC intensity remains unclear in terms of their contribution to the positive anomalies in ACE and PDI. This study uses a new empirical statistical approach to analyze the TC data and finds that the increase in the TC genesis number is primarily responsible for the positive anomalies in ACE and PDI. Other factors, such as TC track property and TC intensity, appear to be minor influences.
    Type of Medium: Online Resource
    ISSN: 0894-8755 , 1520-0442
    URL: Article
    DOI: 10.1175/JCLI-D-13-00394.1
    RVK:
    UA 4548
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2014
    detail.hit.zdb_id: 246750-1
    detail.hit.zdb_id: 2021723-7
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  • 6
    Online Resource
    Online Resource
    Influence of Model Biases on Projected Future Changes in Tropical Cyclone Frequency of Occurrence*
    American Meteorological Society ; 2014
    In:  Journal of Climate Vol. 27, No. 5 ( 2014-03-01), p. 2159-2181
    Details
    In: Journal of Climate, American Meteorological Society, Vol. 27, No. 5 ( 2014-03-01), p. 2159-2181
    Abstract: The influence of model biases on projected future changes in the frequency of occurrence of tropical cyclones (FOCs) was investigated using a new empirical statistical method. Assessments were made of present-day (1979–2003) simulations and future (2075–99) projections, using atmospheric general circulation models under the Intergovernmental Panel on Climate Change (IPCC) A1B scenario and phase 5 of the Coupled Model Intercomparison Project (CMIP5) models under the representative concentration pathway (RCP) 4.5 and 8.5 scenarios. The models project significant decreases in global-total FOCs by approximately 6%–40%; however, model biases introduce an uncertainty of approximately 10% in the total future changes. The influence of biases depends on the model physics rather than model resolutions and emission scenarios. In general, the biases result in overestimates of projected future changes in basin-total FOCs in the north Indian Ocean (by +18%) and South Atlantic Ocean (+143%) and underestimates in the western North Pacific Ocean (−27%), eastern North Pacific Ocean (−29%), and North Atlantic Ocean (−53%). The calibration of model performance using the smaller bias influence appears crucial to deriving meaningful signals in future FOC projections. To obtain more reliable projections, ensemble averages were calculated using the models less influence by model biases. Results indicate marked decreases in projected FOCs in the basins of the Southern Hemisphere, Bay of Bengal, western North Pacific Ocean, eastern North Pacific, and Caribbean Sea and increases in the Arabian Sea and the subtropical central Pacific Ocean.
    Type of Medium: Online Resource
    ISSN: 0894-8755 , 1520-0442
    URL: Article
    DOI: 10.1175/JCLI-D-13-00436.1
    RVK:
    UA 4548
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2014
    detail.hit.zdb_id: 246750-1
    detail.hit.zdb_id: 2021723-7
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  • 7
    Online Resource
    Online Resource
    Is “rich-get-richer” valid for Indian Ocean and Atlantic ITCZ? : RAINFALL CHANGES IN IO AND ATLANTIC ITCZ
    American Geophysical Union (AGU) ; 2012
    In:  Geophysical Research Letters Vol. 39, No. 13 ( 2012-07), p. n/a-n/a
    Details
    In: Geophysical Research Letters, American Geophysical Union (AGU), Vol. 39, No. 13 ( 2012-07), p. n/a-n/a
    Type of Medium: Online Resource
    ISSN: 0094-8276
    URL: Article
    DOI: 10.1029/2012GL052399
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 2012
    detail.hit.zdb_id: 2021599-X
    detail.hit.zdb_id: 7403-2
    SSG: 16,13
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  • 8
    Online Resource
    Online Resource
    Interactions between Boreal Summer Intraseasonal Oscillations and Synoptic-Scale Disturbances over the Western North Pacific. Part II: Apparent Heat and Moisture Sources and Eddy Momentum Transport*
    American Meteorological Society ; 2011
    In:  Journal of Climate Vol. 24, No. 3 ( 2011-02-01), p. 942-961
    Details
    In: Journal of Climate, American Meteorological Society, Vol. 24, No. 3 ( 2011-02-01), p. 942-961
    Abstract: The interactions between the boreal summer intraseasonal oscillation (ISO) and synoptic-scale variability (SSV) are investigated by diagnosing the atmospheric apparent heat source (Q1), apparent moisture sink (Q2), and eddy momentum transport. It is found that the synoptic Q1 and Q2 heating (cooling) anomalies are in phase with cyclonic (anticyclonic) vorticity disturbances, aligned in a southeast–northwest-oriented wave train pattern over the western North Pacific (WNP). The wave train is well organized and strengthened (loosely organized and weakened) during the ISO active (suppressed) phase. The nonlinearly rectified Q1 and Q2 fields due to the eddy–mean flow interaction account for 10%–30% of the total intraseasonal Q1 and Q2 variabilities over the WNP. During the ISO active (suppressed) phase, the nonlinearly rectified intraseasonal Q1 and Q2 heating (cooling) appear to the northwest of the ISO enhanced (suppressed) convection center, favoring the northwestward propagation of the ISO. A diagnosis of the zonal momentum budget shows that the eddy momentum flux convergence forces an intraseasonal westerly (easterly) tendency to the north of the ISO westerly (easterly) center during the ISO active (suppressed) phase. As a result, the eddy momentum transport may contribute to the northward propagation of the boreal summer ISO over the WNP.
    Type of Medium: Online Resource
    ISSN: 1520-0442 , 0894-8755
    URL: Article
    DOI: 10.1175/2010JCLI3834.1
    RVK:
    UA 4548
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2011
    detail.hit.zdb_id: 246750-1
    detail.hit.zdb_id: 2021723-7
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  • 9
    Online Resource
    Online Resource
    Role of the Boundary Layer Moisture Asymmetry in Causing the Eastward Propagation of the Madden–Julian Oscillation*
    American Meteorological Society ; 2012
    In:  Journal of Climate Vol. 25, No. 14 ( 2012-07-15), p. 4914-4931
    Details
    In: Journal of Climate, American Meteorological Society, Vol. 25, No. 14 ( 2012-07-15), p. 4914-4931
    Abstract: The moisture budget associated with the eastward-propagating Madden–Julian oscillation (MJO) was diagnosed using 1979–2001 40-yr ECMWF Re-Analysis (ERA-40) data. A marked zonal asymmetry of the moisture relative to the MJO convection appears in the planetary boundary layer (PBL, below 700 hPa), creating a potentially more unstable stratification to the east of the MJO convection and favoring the eastward propagation of MJO. The PBL-integrated moisture budget diagnosis indicates that the vertical advection of moisture dominates the low-level moistening ahead of the convection. A further diagnosis indicates that the leading term in the vertical moisture advection is the advection of the background moisture by the MJO ascending flow associated with PBL convergence. The cause of the zonally asymmetric PBL convergence is further examined. It is found that heating-induced free-atmospheric wave dynamics account for 75%–90% of the total PBL convergence, while the warm SST anomaly induced by air–sea interaction contributes 10%–25% of the total PBL convergence. The horizontal moisture advection also plays a role in contributing to the PBL moistening ahead of the MJO convection. The leading term in the moisture advection is the advection across the background moisture gradient by the MJO flow. In the western Indian Ocean, Maritime Continent, and western Pacific, the meridional moisture advection by the MJO northerly flow dominates, while in the eastern Indian Ocean the zonal moisture advection is greater. The contribution of the moisture advection by synoptic eddies is in general small; it has a negative effect over the tropical Indian Ocean and western Pacific and becomes positive in the Maritime Continent region.
    Type of Medium: Online Resource
    ISSN: 0894-8755 , 1520-0442
    URL: Article
    DOI: 10.1175/JCLI-D-11-00310.1
    RVK:
    UA 4548
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2012
    detail.hit.zdb_id: 246750-1
    detail.hit.zdb_id: 2021723-7
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  • 10
    Online Resource
    Online Resource
    Trends in global monsoon area and precipitation over the past 30 years : CHANGES IN GLOBAL MONSOON
    American Geophysical Union (AGU) ; 2011
    In:  Geophysical Research Letters Vol. 38, No. 8 ( 2011-04-28), p. n/a-n/a
    Details
    In: Geophysical Research Letters, American Geophysical Union (AGU), Vol. 38, No. 8 ( 2011-04-28), p. n/a-n/a
    Type of Medium: Online Resource
    ISSN: 0094-8276
    URL: Article
    DOI: 10.1029/2011GL046893
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 2011
    detail.hit.zdb_id: 2021599-X
    detail.hit.zdb_id: 7403-2
    SSG: 16,13
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