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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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?