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an atmospheric “ mesoscale ”: where convection meets waves (rotation optional). Brian Mapes University of Miami. for oceanographers. In a moist convecting atmosphere, small scale vertical motions don’t just carry fluxes, they cause latent heating

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an atmospheric mesoscale where convection meets waves rotation optional

an atmospheric “mesoscale”:where convection meets waves(rotation optional)

Brian Mapes

University of Miami

for oceanographers
for oceanographers
  • In a moist convecting atmosphere, small scale vertical motions don’t just carry fluxes, they cause latent heating
      • OK, you can view it as a vertical flux of water substance upward past the condensation level.
  • Spectral space: energy injection across scales
  • Physical space: feedback small updrafts
      • UV catastrophe of conditional instability (Lilly 1961)
      • Smallest updrafts, broadest subsidence (Bjerknes 1938)
mesoscale convection
mesoscale convection
  • “Mesoscale” convection events (meso = middle, in between L~H “convective” scale and N/fH “Rossby radius”) are less theoretically tidy than parcel or exp(ikx) UV catastrophe, but profound & real
  • convectively coupled internal waves
convectively coupled gravity waves in 2d crm no preferred hor scale

5 decades

3 decades

Convectively coupled gravity waves in 2D CRMNo preferred hor. scale

}

Eureka! 5/3!

Stefan Tulich (Mapes et al. 2009 JMSJ)

mesoscale convection1
mesoscale convection
  • Are these things coherent aspects (the spectral tail) of the large-scale flow, or an emergent metaphenomenon bubbling up from convection?
  • Implication: is it better to spend computing DOFs to resolve the mesoscale? Or rather on little hi-res but periodic “sample” patches of convective-scale flow, coupled across an enforced scale separation?
    • (MMF or “super-parameterization”)
3d global simulations
3D global simulations
  • GEOS-5 global AGCM at 5km mesh size
          • by Bill Putman, Max Suarez, others at NASA GSFC
  • 20-day run analyzed here
  • Cubed sphere grid, nonhydrostatic
  • GCM physics left on – mostly
      • subgridscale plumes hobbled by entrainment
      • disabled subgridorographic gravity wave drag
comparison to satellite imagery
comparison to satellite imagery

http://earthobservatory.nasa.gov/IOTD/view.php?id=44246&src=eoa-iotd

predicted cloud features for February 6, 2010

2 weeks into simulation

5km gcm detailed examinations
5kmGCM: detailed examinations
  • 1. Tropical mesoscale rain events: case studies
    • One scale selected in to analysis: 250km events
      • Rebinrainrate to 2.5deg, find 10 largest maxima
        • in ~20 day simulation period (Jan-Feb 2010)
        • in 15N-15S, to minimize cyclone dominated cases
      • Extract space-time cubes around these events
        • (+/-18h, +/- 3 degrees)
        • 10 wettest cases, plus composite mean case
  • 2. Vertical flux [wq], partitioned by scale
          • through simple coarse-graining (rebinning)
http www rsmas miami edu personal ssong research hr 250kmevents htm
http://www.rsmas.miami.edu/personal/ssong/research/HR_250kmevents.htmhttp://www.rsmas.miami.edu/personal/ssong/research/HR_250kmevents.htm
http www rsmas miami edu personal ssong research hr 250kmevents htm1
http://www.rsmas.miami.edu/personal/ssong/research/HR_250kmevents.htmhttp://www.rsmas.miami.edu/personal/ssong/research/HR_250kmevents.htm
slide16

99% is from resolved condensation process: good

  • m

composite basis

HOURS RELATIVE TO MAX 250km RAIN

slide17
Tropical radar observations (EPIC 2001)Time scale is hours even for small space scalesMesoscale is real (if broadband)

96km radius

cell: <1h

8km radius

MCS: 10h

Mapes and Lin 2006 MWR

slide18

m

HOURS RELATIVE TO MAX 250km RAIN

t t p 250km area mean
T’(t,p): 250km area mean

p (hPa)

leading nose

HOURS RELATIVE TO MAX 250km RAIN

rh t p
RH(t,p)

p (hPa)

W

W

HOURS RELATIVE TO MAX 250km RAIN

slide23

trimodal: shallow, medium, deep similar to obs (if a bit off in exact heights)

Mapes et al. 2006 DAO

gcrm detailed examinations
GCRM detailed examinations
  • 1. Tropical mesoscale rain events: case studies
    • One scale built in to analysis: 250km
    • Rebinrainrate to 2.5deg, find 10 largest maxima
      • in ~20 day simulation period (Jan-Feb 2010)
      • in 15N-15S, to minimize cyclone dominated cases
    • Extract space-time cubes around these
      • (+/-18h, +/- 3 degrees)
      • 10 cases, and composite mean case
  • 2. Vertical enthalpy flux, partitioned by scale
          • through simple coarse-graining (rebinning)
2 enthalpy flux
2. Enthalpy flux
  • Enthalpy = sensible heat + latent heat
    • CpT + Lqv
    • Flux thru 500mb level balances ~23 Wm-2 radiativecooling above that level
    • sensible heat flux Cp [wT] ~ 7 Wm-2
    • latent heat flux L [wq]: ~ 16 Wm-2
                  • destined to condense up there
slide26

Latent flux across 500mb

snapshot

by scales resolved in 80kmrebinning

sub-80km = total flux minus the above

slide27

Latent flux

snapshot

by scales resolved in 250kmrebinning

sub-250km = total explicit flux minus above

slide28

Latent flux

snapshot

by scales resolved in 500 km rebinning

sub-500km =

total explicit flux minus above

sub 80km and super 80km scales conspire to carry flux convection occurs in mesoscale clusters
sub-80km and super-80km scales conspire to carry flux: convection occurs in mesoscale clusters
flux partitoned by scales
Flux partitoned by scales
  • Vapor flux by convective (5-80km) scales is colocated with flux in >80km scale mesoscale updrafts.
  • Small scales mainly just add a bit (10 - 40%) to the flux by mesoscale mean updrafts
  • Might this be true at still-finer scales?
  • Borrowed slides (with permission, and email discussion last 2 days) from Chin-Hoh Moeng (NCAR)
slide32

Split the LES flow into: “resolvable” grid-scale (GS)

& “unresolved” scale (SGS)

apply

“smoothing”

Giga-LES

CRM resolvable

SGS is the difference.

Moeng et al. 2010 JAMES

apply smoothing with a width of 4 km

GS: CRM-grid scales

SGS: CRM-SGS

SGS(w-var)

Apply “smoothing” with a width of 4 km

GS

most of w-kinetic energy in SGS

SGS(q-var)

GS

SGS (wq-cov)

~ half of moisture flux in SGS

GS

large scales

small scales

Moeng et al. 2010 JAMES

slide34

SGS flux

Moeng et al. 2010- JAMES

slide35

SGS flux is in clouds

  • condensedwater path (vertical integral)

Moeng et al. 2009 JAMES

flux partitoned by scales1
Flux partitoned by scales
  • Vapor flux by convective (5-80km) scales is colocated with flux in >80km scale mesoscale cloud system updrafts.
  • Small scales mainly just add a bit (up to 40%) to the flux by mesoscale mean updrafts
  • Vapor flux by sub-convective (0.1-4km) scales is colocated with >4km scale convective cloud updrafts.
  • Small scales mainly just add a bit (~40%) to the flux by convective mean updrafts
flux part summary
Flux part summary
  • Mesoscale updrafts are moist, fluxing q up
  • Convective updrafts are inside, adding to it
  • Sub-drafts inside the convective drafts: ditto
  • Q: How might poorly-resolved convection be distorted by having to carry the flux of missing sub-scales? (and can param’z’n fix it?)
  • Q2: Is subgridparam’z’n a flux amplifier? Is that safe numerically?
summary
Summary
  • Deep convection – gravity wave interactions are common: a “mesoscale”
  • Broadband (meso synoptic, in tropics)
    • -5/3, but NOT a swirls-advecting-vorticity cascade
    • has a velocity scale, not a length scale
    • multicellular: hours, not minutes (not just H/w)
  • “Mesoscale convection”, convective cells, and sub-cellular drafts all conspire to carry geophysically (radiatively) demanded vertical energy flux
    • Do we need to resolve them all? Or might truncation + parameterization suffice?