the structural evolution of african easterly waves
DESCRIPTION
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: ATM0507976. - PowerPoint PPT PresentationTRANSCRIPT
The Structural Evolution of African Easterly Waves
Matthew A. Janiga and Chris ThorncroftDEPARTMENT OF ATMOSPHERIC AND
ENVIRONMENTAL SCIENCESUniversity at Albany, State University of New York
Northeast Tropical Conference5/18/2011
Supported by NSF Grant: ATM0507976
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 1998-2009 (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
2000-3000 km Wavelength~8 ms-1surface
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°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 (x106m2s-1, contours)
1.0° CFSR Reanalysis
Mid-Level Kinematic Structure: Mature Baroclinic Phase
700 hPa PV (0.1 PVU, shaded) and Streamfunction (x106m2s-1, contours)
1.0° CFSR Reanalysis
Mid-Level Kinematic Structure: Coastal Transition Phase
700 hPa PV (0.1 PVU, shaded) and Streamfunction (x106m2s-1, contours)
1.0° CFSR Reanalysis
Mid-Level Kinematic Structure: Oceanic Phase
700 hPa PV (0.1 PVU, shaded) and Streamfunction (x106m2s-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 (x106 m2s-1, contours)
1.0° CFSR Reanalysis
NV
Low-Level Kinematic Structure: Mature Baroclinic Phase
925 hPa Vorticity (x10-5 s-1, shaded), Wind (ms-1, vectors), and Streamfunction (x106 m2s-1, contours)
1.0° CFSR Reanalysis
NV
Low-Level Kinematic Structure: Coastal Transition Phase
925 hPa Vorticity (x10-5 s-1, shaded), Wind (ms-1, vectors), and Streamfunction (x106 m2s-1, contours)
1.0° CFSR Reanalysis
NV
Low-Level Kinematic Structure: Oceanic Phase
925 hPa Vorticity (x10-5 s-1, shaded), Wind (ms-1, vectors), and Streamfunction (x106 m2s-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
NV
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
NV
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
NV
+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 (x106 m2s-1, contours)
700 hPa PV (0.1 PVU, shaded), Streamfunction (x106 m2s-1, contours),
and Winds (ms-1, vectors)
Sep. 5, 0000ZDeveloping
IR (shaded) and 700 hPa Streamfunction (x106 m2s-1, contours)
700 hPa PV (0.1 PVU, shaded), Streamfunction (x106 m2s-1, contours),
and Winds (ms-1, vectors)
Sep. 6, 0000ZDeveloping
IR (shaded) and 700 hPa Streamfunction (x106 m2s-1, contours)
700 hPa PV (0.1 PVU, shaded), Streamfunction (x106 m2s-1, contours),
and Winds (ms-1, vectors)
Sep. 7, 0000ZDeveloping
IR (shaded) and 700 hPa Streamfunction (x106 m2s-1, contours)
700 hPa PV (0.1 PVU, shaded), Streamfunction (x106 m2s-1, contours),
and Winds (ms-1, vectors)
Sep. 8, 0000ZDeveloping
IR (shaded) and 700 hPa Streamfunction (x106 m2s-1, contours)
700 hPa PV (0.1 PVU, shaded), Streamfunction (x106 m2s-1, contours),
and Winds (ms-1, vectors)
Sep. 9, 0000ZMature Baroclinic
IR (shaded) and 700 hPa Streamfunction (x106 m2s-1, contours)
700 hPa PV (0.1 PVU, shaded), Streamfunction (x106 m2s-1, contours),
and Winds (ms-1, vectors)
Sep. 10, 0000ZMature Baroclinic
IR (shaded) and 700 hPa Streamfunction (x106 m2s-1, contours)
700 hPa PV (0.1 PVU, shaded), Streamfunction (x106 m2s-1, contours),
and Winds (ms-1, vectors)
Sep. 11, 0000ZCoastal Transition
IR (shaded) and 700 hPa Streamfunction (x106 m2s-1, contours)
700 hPa PV (0.1 PVU, shaded), Streamfunction (x106 m2s-1, contours),
and Winds (ms-1, vectors)
Sep. 12, 0000ZCoastal Transition
IR (shaded) and 925hPa Streamfunction
(x106 m2s-1, contours)
925 hPa θv (K, shaded), Streamfunction (x106 m2s-1, contours), Winds (ms-1, vectors), and
Vorticity (> 2.5x10-5 s-1, pattern)
Sep. 5, 0000ZDeveloping
IR (shaded) and 700 hPa Streamfunction (x106 m2s-1, contours)
925 hPa θv (K, shaded), Streamfunction (x106 m2s-1, contours), Winds (ms-1, vectors), and
Vorticity (> 2.5x10-5 s-1, pattern)
Sep. 6, 0000ZDeveloping
IR (shaded) and 700 hPa Streamfunction (x106 m2s-1, contours)
925 hPa θv (K, shaded), Streamfunction (x106 m2s-1, contours), Winds (ms-1, vectors), and
Vorticity (> 2.5x10-5 s-1, pattern)
Sep. 7, 0000ZDeveloping
IR (shaded) and 700 hPa Streamfunction (x106 m2s-1, contours)
925 hPa θv (K, shaded), Streamfunction (x106 m2s-1, contours), Winds (ms-1, vectors), and
Vorticity (> 2.5x10-5 s-1, pattern)
Sep. 8, 0000ZDeveloping Modified
Monsoon Dry
Moist
IR (shaded) and 700 hPa Streamfunction (x106 m2s-1, contours)
925 hPa θv (K, shaded), Streamfunction (x106 m2s-1, contours), Winds (ms-1, vectors), and
Vorticity (> 2.5x10-5 s-1, pattern)
Sep. 9, 0000ZMature Baroclinic
IR (shaded) and 700 hPa Streamfunction (x106 m2s-1, contours)
925 hPa θv (K, shaded), Streamfunction (x106 m2s-1, contours), Winds (ms-1, vectors), and
Vorticity (> 2.5x10-5 s-1, pattern)
Sep. 10, 0000ZMature Baroclinic
SV
NV
IR (shaded) and 700 hPa Streamfunction (x106 m2s-1, contours)
925 hPa θv (K, shaded), Streamfunction (x106 m2s-1, contours), Winds (ms-1, vectors), and
Vorticity (> 2.5x10-5 s-1, pattern)
Sep. 11, 0000ZCoastal Transition
SV
NV
IR (shaded) and 700 hPa Streamfunction (x106 m2s-1, contours)
925 hPa θv (K, shaded), Streamfunction (x106 m2s-1, contours), Winds (ms-1, vectors), and
Vorticity (> 2.5x10-5 s-1, pattern)
Sep. 12, 0000ZCoastal Transition
SVNV
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
[mm day-1]
[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 1998-2009
Total PV tendency (PVU day-1, shaded)
Heating over Land: Comparison with Radar Observations
Pre
ssur
e (h
Pa)
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 2006-2007
MIT C-Band radar operated in Niamey, Niger during JAS 2006-2007.
Radar observations suggest a peak heating rate ~300-500 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 (Q1) derived from Global Atmospheric Research Program Atlantic Tropical Experiment
During Aug. 30 Sep. 18, 1974.
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 DiabaticFriction + Mom. FluxResolved LHRadiation
Underground
~600-750
700 hPa Diabatic PV Tendency (PVU day-1) and 700 hPa Streamfunction
(x106 m2s-1, contours),
Circle defines averaging domainof profile (3° radius from SV).
PV Production Sources: Mature Baroclinic Phase
Cumulus + Diff DiabaticFriction + Mom. FluxResolved LHRadiation
900 hPa Diabatic PV Tendency (PVU day-1) and 700 hPa Streamfunction
(x106 m2s-1, contours),
Circle defines averaging domainof profile (3° radius from SV).
PV Production Sources : Coastal Transition Phase
Cumulus + Diff DiabaticFriction + Mom. FluxResolved LHRadiation
~850
850 hPa Diabatic PV Tendency (PVU day-1) and 700 hPa Streamfunction
(x106 m2s-1, contours),
Circle defines averaging domainof profile (3° radius from SV).
PV Production Sources: Oceanic Phase
Cumulus + Diff DiabaticFriction + Mom. FluxResolved LHRadiation
~950
950 hPa Diabatic PV Tendency (PVU day-1) and 700 hPa Streamfunction
(x106 m2s-1, contours),
Circle defines averaging domainof 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
CumulusMomentum
Friction
Advection
Cumulus
Microphysics
Time Tendency DiabaticResidualAdvection
PV Budget: Developing Phase
Cumulus + Diff DiabaticFriction + Mom. FluxResolved LHRadiation
Underground Underground
~600-750
Time Tendency DiabaticResidualAdvection
PV Budget: Mature Baroclinic Phase
Cumulus + Diff DiabaticFriction + Mom. FluxResolved LHRadiation
~750-1000
Time Tendency DiabaticResidualAdvection
PV Budget: Developing Phase
Cumulus + Diff DiabaticFriction + Mom. FluxResolved LHRadiation
~850
Time Tendency DiabaticResidualAdvection
PV Budget: Developing Phase
Cumulus + Diff DiabaticFriction + Mom. FluxResolved LHRadiation
~950