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).