The Structural Evolution of African Easterly Waves Matthew A. Janiga and Chris Thorncroft DEPARTMENT OF ATMOSPHERIC AND ENVIRONMENTAL SCIENCES University at Albany, State University of New York Northeast Tropical Conference 5/18/2011 Supported by NSF Grant: ATM

 Much is known about the mean kinematic and thermodynamic structure of African easterly waves (AEWs) (e.g. Reed et al., 1977). However, comparatively little is known about there mean structural evolution.  Relationships between AEWs and organized convection have been observed (Fink and Reiner, 2003). However, the role of the 3D flow and sub-synoptic scale features associated with the AEW in this relationship is poorly understood.  Lastly, while the importance of the upscale impact of convection on AEWs has been demonstrated in case studies (e.g. Berry and Thorncroft, 2005; Schwendike and Jones, 2010), the representativeness of these studies is not known. Background and Motivation

The Composite Evolution of African Easterly Waves

Methodology  Tracks of AEWs were determined by tracking long- lived synoptic-scale vorticity maxima at 700 hPa during JAS (see Hodges et al., 1999).  The composite structural evolution of AEWs was determined by compositing analyses and forecasts from the NCEP Climate Forecast System Reanalysis (CFSR) and TRMM 3B42 rainrate estimates. SV AEJ NV km Wavelength ~8 ms -1 surface jet-level Carlson (1969)

Composite Location for Developing Phase GATE Array MIT Radar 20°E

Composite Location for Mature Baroclinic Phase GATE Array MIT Radar 5°W5°W

Composite Location for Coastal Transition Phase GATE Array MIT Radar 15°W

Composite Location for Oceanic Phase GATE Array MIT Radar 30°W

Mid-Level Kinematic Structure: Developing Phase 700 hPa PV (0.1 PVU, shaded) and Streamfunction (x10 6 m 2 s -1, contours) 700 hPa PV (0.1 PVU, shaded) and Streamfunction (x10 6 m 2 s -1, contours) 1.0° CFSR Reanalysis

Mid-Level Kinematic Structure: Mature Baroclinic Phase 700 hPa PV (0.1 PVU, shaded) and Streamfunction (x10 6 m 2 s -1, contours) 700 hPa PV (0.1 PVU, shaded) and Streamfunction (x10 6 m 2 s -1, contours) 1.0° CFSR Reanalysis

Mid-Level Kinematic Structure: Coastal Transition Phase 700 hPa PV (0.1 PVU, shaded) and Streamfunction (x10 6 m 2 s -1, contours) 700 hPa PV (0.1 PVU, shaded) and Streamfunction (x10 6 m 2 s -1, contours) 1.0° CFSR Reanalysis

Mid-Level Kinematic Structure: Oceanic Phase 700 hPa PV (0.1 PVU, shaded) and Streamfunction (x10 6 m 2 s -1, contours) 700 hPa PV (0.1 PVU, shaded) and Streamfunction (x10 6 m 2 s -1, contours) 1.0° CFSR Reanalysis

Low-Level Kinematic Structure: Developing Phase 925 hPa Vorticity (x10 -5 s -1, shaded), Wind (ms -1, vectors), and Streamfunction (x10 6 m 2 s -1, contours) 1.0° CFSR Reanalysis

Low-Level Kinematic Structure: Mature Baroclinic Phase 925 hPa Vorticity (x10 -5 s -1, shaded), Wind (ms -1, vectors), and Streamfunction (x10 6 m 2 s -1, contours) 1.0° CFSR Reanalysis

Low-Level Kinematic Structure: Coastal Transition Phase 925 hPa Vorticity (x10 -5 s -1, shaded), Wind (ms -1, vectors), and Streamfunction (x10 6 m 2 s -1, contours) 1.0° CFSR Reanalysis

Low-Level Kinematic Structure: Oceanic Phase 925 hPa Vorticity (x10 -5 s -1, shaded), Wind (ms -1, vectors), and Streamfunction (x10 6 m 2 s -1, contours) 1.0° CFSR Reanalysis

Low-Level Thermodynamic Structure: Developing Phase 925 hPa 2-10 day Filtered θ (K, shaded), θ (K, contours), and 2-10 day Filtered Wind (ms -1, vectors) 1.0° CFSR Reanalysis

Low-Level Thermodynamic Structure: Mature Baroclinic Phase 925 hPa 2-10 day Filtered θ (K, shaded), θ (K, contours), and 2-10 day Filtered Wind (ms -1, vectors) 1.0° CFSR Reanalysis

Low-Level Thermodynamic Structure: Coastal Transition Phase 925 hPa 2-10 day Filtered θ (K, shaded), θ (K, contours), and 2-10 day Filtered Wind (ms -1, vectors) 1.0° CFSR Reanalysis +θ΄ no longer ahead of SV

Low-Level Thermodynamic Structure: Oceanic Phase 925 hPa 2-10 day Filtered θ (K, shaded), θ (K, contours), and 2-10 day Filtered Wind (ms -1, vectors) 1.0° CFSR Reanalysis Northerly flow out of phase with +θ΄

Sub-Synoptic-Scale Structures in AEWs Helene AEW (2006)

 N = 925 hPa NV.  M = 700 hPa SV.  L = 925 hPa SV.  Dashed lines denote trough axes defined at 700 hPa.  Except for being stronger than most AEWs the evolution of the AEW associated with Hurricane Helene (2006) was somewhat typical of the composite evolution.  The 0.5° AMMA reanalysis is used to highlight sub-synoptic scale features which are “washed out” in the composites.

IR (shaded) and 700 hPa Streamfunction (x10 6 m 2 s -1, contours) IR (shaded) and 700 hPa Streamfunction (x10 6 m 2 s -1, contours) 700 hPa PV (0.1 PVU, shaded), Streamfunction (x10 6 m 2 s -1, contours), and Winds (ms -1, vectors) Sep. 5, 0000Z Developing

IR (shaded) and 700 hPa Streamfunction (x10 6 m 2 s -1, contours) IR (shaded) and 700 hPa Streamfunction (x10 6 m 2 s -1, contours) 700 hPa PV (0.1 PVU, shaded), Streamfunction (x10 6 m 2 s -1, contours), and Winds (ms -1, vectors) Sep. 6, 0000Z Developing

IR (shaded) and 700 hPa Streamfunction (x10 6 m 2 s -1, contours) IR (shaded) and 700 hPa Streamfunction (x10 6 m 2 s -1, contours) 700 hPa PV (0.1 PVU, shaded), Streamfunction (x10 6 m 2 s -1, contours), and Winds (ms -1, vectors) Sep. 7, 0000Z Developing

IR (shaded) and 700 hPa Streamfunction (x10 6 m 2 s -1, contours) IR (shaded) and 700 hPa Streamfunction (x10 6 m 2 s -1, contours) 700 hPa PV (0.1 PVU, shaded), Streamfunction (x10 6 m 2 s -1, contours), and Winds (ms -1, vectors) Sep. 8, 0000Z Developing

IR (shaded) and 700 hPa Streamfunction (x10 6 m 2 s -1, contours) IR (shaded) and 700 hPa Streamfunction (x10 6 m 2 s -1, contours) 700 hPa PV (0.1 PVU, shaded), Streamfunction (x10 6 m 2 s -1, contours), and Winds (ms -1, vectors) Sep. 9, 0000Z Mature Baroclinic

IR (shaded) and 700 hPa Streamfunction (x10 6 m 2 s -1, contours) IR (shaded) and 700 hPa Streamfunction (x10 6 m 2 s -1, contours) 700 hPa PV (0.1 PVU, shaded), Streamfunction (x10 6 m 2 s -1, contours), and Winds (ms -1, vectors) Sep. 10, 0000Z Mature Baroclinic

IR (shaded) and 700 hPa Streamfunction (x10 6 m 2 s -1, contours) IR (shaded) and 700 hPa Streamfunction (x10 6 m 2 s -1, contours) 700 hPa PV (0.1 PVU, shaded), Streamfunction (x10 6 m 2 s -1, contours), and Winds (ms -1, vectors) Sep. 11, 0000Z Coastal Transition

IR (shaded) and 700 hPa Streamfunction (x10 6 m 2 s -1, contours) IR (shaded) and 700 hPa Streamfunction (x10 6 m 2 s -1, contours) 700 hPa PV (0.1 PVU, shaded), Streamfunction (x10 6 m 2 s -1, contours), and Winds (ms -1, vectors) Sep. 12, 0000Z Coastal Transition

IR (shaded) and 925hPa Streamfunction (x10 6 m 2 s -1, contours) IR (shaded) and 925hPa Streamfunction (x10 6 m 2 s -1, contours) 925 hPa θv (K, shaded), Streamfunction (x10 6 m 2 s -1, contours), Winds (ms -1, vectors), and Vorticity (> 2.5x10 -5 s -1, pattern) Sep. 5, 0000Z Developing

IR (shaded) and 700 hPa Streamfunction (x10 6 m 2 s -1, contours) IR (shaded) and 700 hPa Streamfunction (x10 6 m 2 s -1, contours) 925 hPa θv (K, shaded), Streamfunction (x10 6 m 2 s -1, contours), Winds (ms -1, vectors), and Vorticity (> 2.5x10 -5 s -1, pattern) Sep. 6, 0000Z Developing

IR (shaded) and 700 hPa Streamfunction (x10 6 m 2 s -1, contours) IR (shaded) and 700 hPa Streamfunction (x10 6 m 2 s -1, contours) 925 hPa θv (K, shaded), Streamfunction (x10 6 m 2 s -1, contours), Winds (ms -1, vectors), and Vorticity (> 2.5x10 -5 s -1, pattern) Sep. 7, 0000Z Developing

IR (shaded) and 700 hPa Streamfunction (x10 6 m 2 s -1, contours) IR (shaded) and 700 hPa Streamfunction (x10 6 m 2 s -1, contours) 925 hPa θv (K, shaded), Streamfunction (x10 6 m 2 s -1, contours), Winds (ms -1, vectors), and Vorticity (> 2.5x10 -5 s -1, pattern) Sep. 8, 0000Z Developing

IR (shaded) and 700 hPa Streamfunction (x10 6 m 2 s -1, contours) IR (shaded) and 700 hPa Streamfunction (x10 6 m 2 s -1, contours) 925 hPa θv (K, shaded), Streamfunction (x10 6 m 2 s -1, contours), Winds (ms -1, vectors), and Vorticity (> 2.5x10 -5 s -1, pattern) Sep. 9, 0000Z Mature Baroclinic

IR (shaded) and 700 hPa Streamfunction (x10 6 m 2 s -1, contours) IR (shaded) and 700 hPa Streamfunction (x10 6 m 2 s -1, contours) 925 hPa θv (K, shaded), Streamfunction (x10 6 m 2 s -1, contours), Winds (ms -1, vectors), and Vorticity (> 2.5x10 -5 s -1, pattern) Sep. 10, 0000Z Mature Baroclinic

IR (shaded) and 700 hPa Streamfunction (x10 6 m 2 s -1, contours) IR (shaded) and 700 hPa Streamfunction (x10 6 m 2 s -1, contours) 925 hPa θv (K, shaded), Streamfunction (x10 6 m 2 s -1, contours), Winds (ms -1, vectors), and Vorticity (> 2.5x10 -5 s -1, pattern) Sep. 11, 0000Z Coastal Transition

IR (shaded) and 700 hPa Streamfunction (x10 6 m 2 s -1, contours) IR (shaded) and 700 hPa Streamfunction (x10 6 m 2 s -1, contours) 925 hPa θv (K, shaded), Streamfunction (x10 6 m 2 s -1, contours), Winds (ms -1, vectors), and Vorticity (> 2.5x10 -5 s -1, pattern) Sep. 12, 0000Z Coastal Transition

Upscale Impact of Moist Convection on AEWs

Climatological Latent Heating and PV Generation in CFSR TRMM 3B42 Rainrate (mm day -1, shaded) CFSR Rainrate Bias (mm day -1, shaded) Relative to 3B42 CFSR Rainrate Bias (mm day -1, shaded) Relative to 3B42 [mm day -1 ]

Climatological Latent Heating and PV Generation in CFSR Resolved heating (K day -1, shaded) and ω (hPa hr -1, contours) PV Tendency due to resolved latent heating (PVU day -1, shaded) Cross-Sections 5-15°N JAS Total PV tendency (PVU day -1, shaded) Total PV tendency (PVU day -1, shaded)

Heating over Land: Comparison with Radar Observations Pressure (hPa) Regression between rain rate (derived from ZR relationship, Russell et al., 2010) and divergence estimated from the radial wind (Mapes and Lin, 2005). Divergence (x10 -5 s -1 per mm hr -1 ) JAS  MIT C-Band radar operated in Niamey, Niger during JAS  Radar observations suggest a peak heating rate ~ hPa.  Low-level divergence was much stronger than other tropical sites examined in Mapes and Lin, (2005). Approx. Peak Heating

Heating over East Atlantic: Comparison with GATE Apparent heat source (Q 1 ) derived from Global Atmospheric Research Program Atlantic Tropical Experiment During Aug. 30 Sep. 18, Apparent heat source (Q 1 ) derived from Global Atmospheric Research Program Atlantic Tropical Experiment During Aug. 30 Sep. 18,  The level of peak heating over the East Atlantic is also qualitatively similar to the results from GATE.  Peak heating near ~600 hPa.

Rainrate in CFSR and TRMM: Developing Phase TRMM 3B42 CFSR F06 h Total Rainrate (mm day -1, shaded), 2-10 day Filtered Rainrate (contours at 0.5, 2.5, 5, 10 mm day -1 )

Rainrate in CFSR and TRMM: Mature Baroclinic Phase TRMM 3B42 CFSR F06 h Total Rainrate (mm day -1, shaded), 2-10 day Filtered Rainrate (contours at 0.5, 2.5, 5, 10 mm day -1 )

Rainrate in CFSR and TRMM: Coastal Transition Phase TRMM 3B42 CFSR F06 h Total Rainrate (mm day -1, shaded), 2-10 day Filtered Rainrate (contours at 0.5, 2.5, 5, 10 mm day -1 )

Rainrate in CFSR and TRMM: Oceanic Phase TRMM 3B42 CFSR F06 h Total Rainrate (mm day -1, shaded), 2-10 day Filtered Rainrate (contours at 0.5, 2.5, 5, 10 mm day -1 )

PV Production Sources: Developing Phase Cumulus + Diff Diabatic Friction + Mom. Flux Resolved LH Radiation Cumulus + Diff Diabatic Friction + Mom. Flux Resolved LH Radiation Underground ~ hPa Diabatic PV Tendency (PVU day -1 ) and 700 hPa Streamfunction (x10 6 m 2 s -1, contours), Circle defines averaging domain of profile (3° radius from SV).

PV Production Sources: Mature Baroclinic Phase Cumulus + Diff Diabatic Friction + Mom. Flux Resolved LH Radiation Cumulus + Diff Diabatic Friction + Mom. Flux Resolved LH Radiation 900 hPa Diabatic PV Tendency (PVU day -1 ) and 700 hPa Streamfunction (x10 6 m 2 s -1, contours), Circle defines averaging domain of profile (3° radius from SV).

PV Production Sources : Coastal Transition Phase Cumulus + Diff Diabatic Friction + Mom. Flux Resolved LH Radiation Cumulus + Diff Diabatic Friction + Mom. Flux Resolved LH Radiation ~ hPa Diabatic PV Tendency (PVU day -1 ) and 700 hPa Streamfunction (x10 6 m 2 s -1, contours), Circle defines averaging domain of profile (3° radius from SV).

PV Production Sources: Oceanic Phase Cumulus + Diff Diabatic Friction + Mom. Flux Resolved LH Radiation Cumulus + Diff Diabatic Friction + Mom. Flux Resolved LH Radiation ~ hPa Diabatic PV Tendency (PVU day -1 ) and 700 hPa Streamfunction (x10 6 m 2 s -1, contours), Circle defines averaging domain of profile (3° radius from SV).

Summary and Conclusions  Recent observations show a much richer structure in AEWs. These results highlight sub-synoptic scale structures within AEWs.  A qualitative picture of the upscale impact of moist convection on AEWs is beginning to emerge. There are strong contrasts between convection over interior Africa and the East Atlantic. These effect the levels that PV production occurs at.  Future work will focus on quantitative estimates of the upscale impact of convection on AEWs and exploring the variability of AEW-convection relationships.

Total Radiation Heat Diffusion Cumulus Momentum Friction Advection Cumulus Microphysics

Time Tendency Diabatic Residual Advection Time Tendency Diabatic Residual Advection PV Budget: Developing Phase Cumulus + Diff Diabatic Friction + Mom. Flux Resolved LH Radiation Cumulus + Diff Diabatic Friction + Mom. Flux Resolved LH Radiation Underground ~

Time Tendency Diabatic Residual Advection Time Tendency Diabatic Residual Advection PV Budget: Mature Baroclinic Phase Cumulus + Diff Diabatic Friction + Mom. Flux Resolved LH Radiation Cumulus + Diff Diabatic Friction + Mom. Flux Resolved LH Radiation ~

Time Tendency Diabatic Residual Advection Time Tendency Diabatic Residual Advection PV Budget: Developing Phase Cumulus + Diff Diabatic Friction + Mom. Flux Resolved LH Radiation Cumulus + Diff Diabatic Friction + Mom. Flux Resolved LH Radiation ~850

Time Tendency Diabatic Residual Advection Time Tendency Diabatic Residual Advection PV Budget: Developing Phase Cumulus + Diff Diabatic Friction + Mom. Flux Resolved LH Radiation Cumulus + Diff Diabatic Friction + Mom. Flux Resolved LH Radiation ~950