MJO Modulation of Lightning in Mesoscale Convective Systems

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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
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Mesoscale Convective Systems (MCSs)
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Radar echoes showing the precipitation in the 3
MCSs
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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)
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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)

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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)

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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
  dBZup 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

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Indian Ocean
NW Western Pacific
SE Western Pacific
Image courtesy Barnes and Houze (2013)
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MJO modulation of lightning

• Out of phase with rain (Morita et al. 2006)

Image courtesy Morita et al. (2006)
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MJO active
MJO inactive
Image courtesy Kodama et al. (2006)
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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)

Break period (phases 8-1-2) minus active period
(phases 4-5-6)
Image courtesy Virts et al. (2013)
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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?

Break period (phases 8-1-2) minus active period
(phases 4-5-6)
Image courtesy Virts et al. (2013)
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Identifying MCSs using A-Train data

• MODIS 10.8 ?m brightness temperature
• AMSR-E rain rate
• Years included2007-2010

Details in Yuan and Houze 2010
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Separated HCS
Details in Yuan and Houze 2010
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Separated HCS
Details in Yuan and Houze 2010
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Separated HCS
Details in Yuan and Houze 2010
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Separated HCS
Details in Yuan and Houze 2010
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Separated active MCS
Separated HCS
Connected active MCS
Details in Yuan and Houze 2010
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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

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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)

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Indian Ocean Maritime Continent Western Pacific SPCZ
CMCSs 29.5 17.6 30.0 29.3
MCS lightning density
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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
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• CMCSs most frequent with peak precip.
• SMCS timing varies, reflects MJO stage
• CMCSs experience greater variability

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MJO modulation of lightning inMaritime Continent
SMCSs
More frequent lightning, broaderlightning
maximum during break period
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Lifted Index (LI)

• Measure of lower-tropospheric stability

• Negative LI ? parcel warmer than environment
• Calculate using ERA-Interim fields

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MCS environments more unstable during break period
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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

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TRMM radar precipitation features (RPFs)

• Contiguous areas with near-surfacerain rate gt 0
• Use features with maximum 30 dBZ height gt 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
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TRMM radar precipitation features (RPFs)

• Contiguous areas with near-surfacerain rate gt 0
• Use features with maximum 30 dBZ height gt 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
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MJO modulation of convective rain fraction

• Peak at end ofbreak period
• Varies strongly withRPF size

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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

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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

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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

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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

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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

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Similar evolution in 2-4 day wavesduring MJO
active period
Image courtesy Zuluaga and Houze (2013)
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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.

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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)

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This work was funded by NASA ( NNX13AQ37G)and
the Department of Energy (DE-SC0008452).