MJO Modulation of Lightning in Mesoscale Convective Systems
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Transcript of MJO Modulation of Lightning in Mesoscale Convective Systems
MJO Modulation of Lightning inMesoscale Convective Systems
Katrina S. Virts andRobert A. Houze, Jr.
University of Washington
Seminar, Pacific Northwest National Laboratory, Richland, WA, 4 June 2014
Mesoscale Convective Systems (MCSs)
ConvectivePrecipitation
StratiformPrecipitation
Radar echoes showing the precipitation in the 3 MCSs
Madden-Julian Oscillation
Intraseasonal time scales (~30-80 days)
Enhanced convection develops over equatorial Indian Ocean
Eastward propagation
Associated circulation anomalies
Image courtesy Madden and Julian (1972)
MJO modulation of cloud population
Field campaigns (TOGA COARE, DYNAMO/AMIE)
Satellite observations– Passive sensors
• “Superclusters” (Nakazawa 1988)
• MJO “modulates cloud clusters of all sizes, but larger clusters are proportionately more affected than smaller clusters” (Mapes & Houze 1993)
• MJO “associated with weaker or stronger mesoscale organization of deep convection” (Tromeur & Rossow 2010)
MJO modulation of cloud population
Satellite observations (continued)– TRMM
• Shallow cumulus and congestus prior to onset of deep convection (Benedict & Randall 2007)
• “The precipitating cloud population of the Madden-Julian Oscillation over the Indian and western Pacific Oceans” (Barnes and Houze 2013)
– CloudSat• “A familiar evolution of cloud type predominance” (Riley et al.
2011)
• “Shallow and congestus clouds in advance of the [MJO] peak, deep clouds near the peak, and upper level anvils after the peak” (Del Genio et al. 2012)
– Other A-Train satellites (Yuan and Houze 2013)
MJO modulation of cloud population(Barnes and Houze 2013)
Echo types:– Isolated shallow echoes (ISEs) — echo tops at least 1 km
below freezing level– Deep convective cores (DCCs) — radar echo ≥ 30 dBZ
up to at least 8 km– Wide convective cores (WCCs) — radar echo ≥ 30 dBZ
covering at least 800 km2
– Broad stratiform regions (BSRs) — stratiform echo covering at least 50,000 km2
Image courtesy Barnes and Houze (2013)
Indian Ocean NW Western Pacific SE Western Pacific
MJO modulation of lightning
Out of phase with rain (Morita et al. 2006)
Image courtesy Morita et al. (2006)
Image courtesy Kodama et al. (2006)
MJO inactive MJO active
MJO modulation of lightning
Out of phase with rain (Morita et al. 2006)
Suppressed over large islands during active period (Kodama et al. 2006)
Modulation of diurnal cycle (Virts et al. 2013)
Image courtesy Virts et al. (2013)
Break period (phases 8-1-2) minus active period (phases 4-5-6)
MJO modulation of lightning
Out of phase with rain (Morita et al. 2006)
Suppressed over large islands during active period (Kodama et al. 2006)
Modulation of diurnal cycle (Virts et al. 2013)
What about individual convective clouds?Image courtesy Virts et al. (2013)
Break period (phases 8-1-2) minus active period (phases 4-5-6)
Identifying MCSs using A-Train data
MODIS 10.8 m brightness temperature
AMSR-E rain rate
Years included:2007-2010
Details in Yuan and Houze 2010
260K
SeparatedHCS
Details in Yuan and Houze 2010
260KClosedcontour
SeparatedHCS
Details in Yuan and Houze 2010
260KClosedcontour
“HCS”
SeparatedHCS
Details in Yuan and Houze 2010
260KClosedcontour Rain
SeparatedHCS
Heavy Rain
“HCS”
Details in Yuan and Houze 2010
260KClosedcontour Rain
SeparatedHCS
“Connected” active MCS
“Separated” active MCS
Heavy Rain
“HCS”
Details in Yuan and Houze 2010
World-Wide Lightning Location Network (WWLLN)
Global network of 70+ sensors
Monitors very low frequency waves
Lightning strokes located to within 5 km and a few s
Preferentially detects cloud-to-ground lightning
World-Wide Lightning Location Network (WWLLN)
Lightning in one-hour window– Separate coordinate system for each MCS, centered on
largest raining core– Lightning in cloudy grid boxes (lightning density)
Indian Ocean
Maritime Continent
Western Pacific
SPCZ
% CMCSs 29.5 17.6 30.0 29.3
MCS lightning density
Indian Ocean
Maritime Continent
Western Pacific
SPCZ
% CMCSs 29.5 17.6 30.0 29.3
MCS lightning density 2.9 26.5 2.5 7.6
CMCSs most frequent with peak precip.
SMCS timing varies, reflects MJO stage
CMCSs experience greater variability
MJO modulation of lightning inMaritime Continent SMCSs
More frequent lightning, broaderlightning maximum during break period
Lifted Index (LI)
Measure of lower-tropospheric stability
Negative LI parcel warmer than environment
Calculate using ERA-Interim fields
MCS environments more unstable during break period
MJO modulation of lightning density
Peak lightning at end of break period
SPCZ: peak lightning at beginning of break period
Lower lightning density in CMCSs
TRMM radar precipitation features (RPFs)
Contiguous areas with near-surfacerain rate > 0
Use features with maximum 30 dBZ height > 6 km
Size equivalent to smallest and largest 50% of MCSs
Years included: 1998-2012
RPF data obtained from University of Utah TRMM database. Details in Liu et al. 2008
TRMM radar precipitation features (RPFs)
Contiguous areas with near-surfacerain rate > 0
Use features with maximum 30 dBZ height > 6 km
Size equivalent to smallest and largest 50% of MCSs
Years included: 1998-2012
RPF data obtained from University of Utah TRMM database. Details in Liu et al. 2008
MJO modulation of convective rain fraction
Peak at end ofbreak period
Varies strongly withRPF size
MJO modulation of MCS characteristics
Isolated deep convection begins to aggregate– Strong instability strong updrafts more lightning– Dry mid/upper troposphere smaller stratiform areas
MCSs become more numerous– Stability increases less lightning– Increasingly extensive stratiform rain areas
MCSs increasingly more connected– CMCS occurrence peaks with precipitation
MCSs decrease in number, size, connectedness– Smaller stratiform areas rain is more convective– Increasing instability during break period more lightning
MJO modulation of MCS characteristics
Isolated deep convection begins to aggregate– Strong instability strong updrafts more lightning– Dry mid/upper troposphere smaller stratiform areas
MCSs become more numerous– Stability increases less lightning– Increasingly extensive stratiform rain areas
MCSs increasingly more connected– CMCS occurrence peaks with precipitation
MCSs decrease in number, size, connectedness– Smaller stratiform areas rain is more convective– Increasing instability during break period more lightning
MJO modulation of MCS characteristics
Isolated deep convection begins to aggregate– Strong instability strong updrafts more lightning– Dry mid/upper troposphere smaller stratiform areas
MCSs become more numerous– Stability increases less lightning– Increasingly extensive stratiform rain areas
MCSs increasingly more connected– CMCS occurrence peaks with precipitation
MCSs decrease in number, size, connectedness– Smaller stratiform areas rain is more convective– Increasing instability during break period more lightning
MJO modulation of MCS characteristics
Isolated deep convection begins to aggregate– Strong instability strong updrafts more lightning– Dry mid/upper troposphere smaller stratiform areas
MCSs become more numerous– Stability increases less lightning– Increasingly extensive stratiform rain areas
MCSs increasingly more connected– CMCS occurrence peaks with precipitation
MCSs decrease in number, size, connectedness– Smaller stratiform areas rain is more convective– Increasing instability during break period more lightning
MJO modulation of MCS characteristics(simplified)
Few MCSs, mainly shallow or isolated deep convection
“Younger” MCSs with strong convection
“Older” MCSs with mature stratiform rain areas
Familiar…
Similar evolution in 2-4 day wavesduring MJO active period
Image courtesy Zuluaga and Houze (2013)
Stretched building block model(Mapes et al. 2006)
Convective clouds and MCSs “in different stages of a large-scale wave have different durations of shallow convective, deep convective, and stratiform anvil stages in their life cycles,” such that evolution of mean characteristics of convective clouds aligns with the evolution of individual clouds.
Conclusions
MCSs over land contain more vigorous convection, more lightning
MCSs over the ocean are more connected
Larger, more connected, and more numerous MCSs during MJO active period
Peak lightning and convective rain fraction just prior to active period (except over SPCZ)
Evolution of mean MCS characteristics aligns with MCS lifecycle (stretched building block)
This work was funded by NASA (# NNX13AQ37G)and the Department of Energy (#DE-SC0008452).