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An investigation of tropical wave activity and its interaction with deep convection based on ISCCP products
Ademe Mekonnen1 and William B. Rossow2
1) EES, North Carolina A&T State University2) CREST Institute, The City College of New York
ISCCP at 30:What Do We Know and What Do We Still Need to Know?
CREST at City College, New York, NY22-25 April 2013
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Goals:
• Understand the process of convectively active events, transitions (WS perspective)
• Investigate the role of deep convection on wave initiation
• Investigate the interaction between deep convection and tropical easterly waves
effects of waves on convection: quantitative description?
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3
Area of interestElevation map
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Current work: AEWs and deep convection
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Data and methods• Data
- Weather state (WS) data from ISCCP D1 - Wind from ECMWF reanalysis
- CS/CT dataWS: 2.5o, 3-hrlyERA-Interim: 1.5o, 6-hrly, 37-pressure levelsperiod of record: 1983-2005
• Methods- time-filtering, space-time filtering (WK99)- regression analysis as in Wheeler et al (2000)
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The WS data:
Identified objectively by distinctive patterns in a joint frequency distributions of cloud top pressure and cloud optical thickness values using a K-means cluster analysis method (Rossow et al 2005; Jakob and Tselioudis 2003; Rossow and Schiffer 1991, 1999).
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Cloud top pressure vs. optical thickness patterns of Weather States (07/1983-12/2004; 35S-35N).
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Weather states (JAS 1984-2004)
WS1
WS2
WS3
WS4
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some Results
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Lag
(day
s)WS1, V’ WS3, V’
WS RFO and 700V' based on 2-10 day filtered 700hPa V’ at 12.5N, 30E. (WS shaded and V’ contoured; 0.3ms-1). The cross-sections are for 7.5-12.5N.
JAS
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Lag
(day
s)
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WS1 shaded WS3 contoured
*Only positive anomalies are shown
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Daily frequency of occurrences of WS and 200-hPa Divergence regressed onto 2-10-day filtered 700-v at 12.5N, 30E. WS anomalies (shaded), divergence (contoured)
WS1, 200D WS3, 200D
Daily frequency of occurrences of WS and 200-hPa wind regressed onto 2-10-day filtered 200-v at 12.5N, 30E. WS anomalies (shaded), wind (contoured)
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Questions:• Mechanisms for WS transition
o WS3 leading to WS1 and then easterly waves develop downstream?
or
o WS3 leading to easterly wave genesis and waves organize WS1?
• AEW phase variation vs. WS• The role of mountains & diurnal cycle
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Magnitude of wind shear (m/s; JAS 1984-2005)
Mean shear (200-850-hPa)
Daily frequency of occurrences of WS1 and wind shear regressed onto 2-10-day filtered 700-v at 12.5N, 30E. WS1 anomalies (shaded), wind shear (contoured)
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Daily frequency of occurrences of WS3 and wind shear regressed onto 2-10-day filtered 700-v at 12.5N, 30E. WS3 anomalies (shaded), wind shear (contoured)
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Mean shear (200-850-hPa)
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Thanks.
Questions? Comments?