Precipitation Radar Perspectives

on Air-Sea Interactions

During DYNAMO

Elizabeth Thompson

Corvallis PowWow

June 24, 2013

Objectives

Present hypotheses for why/how air-sea interactions are important/unique in the IO and to the MJO

... and how our DYNAMO datasets might be used to address these hypotheses

Air-Sea communication methods:1. Freshwater Flux2. Momentum Flux3. Radiative Fluxes

Important on what

time/space scales?

Radar Rainfall Estimation during Dynamo: Thompson et al. 2013, in prep

Motivation: Rain and absorbed IR are primarily

responsible for atmospheric (MJO) circulation and diabatic heating structure; vertical motion helps counterbalance tropical heating and maintains weak Temp gradients

Goals: Is DYNAMO rainfall different from

TOGA COARE? If so, why? microphysics dynamics large scale environment MJO maturity

Produce best rainfall estimation product possible for air-sea science applications limiting factor in parameterization

motivations/implementation Largest source of error from rain rate

to cumulative rainfall is sampling error,

Methodology: *** improve attenuation

correction

2DVD data Manus/Gan Islands

EM scattering calculations = radar variables

linear regression to fit power law estimators:

Z = a * R ^ b

Use dual-polarized radar data to train single-polarized radar estimation SPOL & SMART-R @ Gan

Determine statistical significance between rainfall PDFs: before vs. after

Freshwater Flux

Freshwater Flux What role does precipitation play on

upper ocean... stability, buoyancy? (horiz/vert) mixing coefficients? surface roughness?acceleration of sub-sfc jets? barrier layer & puddle

formation/maintenance/erosion?

Freshwater Flux

Gan vs. Manus Island 2DVD

Gan Island = subset of Manus Island, so rainfall should be same for DYNAMO and TOGA COARE...

So why are Z-R relationships different? Are they really different?

Freshwater Flux

< all 2DVD data

Bringi, V. N., C. R. Williams, M. Thurai, P. T. May, 2009: JTECH

log10(NW) = -0.3*D0 + 9.5

6/11/13

Freshwater Flux

CONV

STRAT

NCAR/MISMO/TC underestimating rain, not

representing C/S

zMISMO-NCAR = 178*R**1.44zTS96_C = 139*R**1.43zTS96_S = 367*R**1.30

zCSU_C = 61.12*R**1.58 zCSU_S = 200.26*R**1.51

6/11/13

Freshwater Flux

per day

per hour

Aerial Avg. Rainfall Time SeriesOld Coefficients

Freshwater Flux

Aerial Avg. Rainfall Time SeriesNew Coefficients

per hour

per day

***Rainfall rates between single- and dual-polarized radars agree more

other rainfall metrics: examples??

PDFs of rainfall/Zheight of maximum echo topsareal average rainfall

Freshwater Flux

Polar coordinate (high res) convective stratiform partitioning May have

different implications for puddles?

More trustworthy rainfall rates = more meaningful rainfall metrics already started

quantifying this for comparisons

What would a puddle map look like from a particular rain map?

Freshwater Flux

Fresh Water Puddle Hunts

How does freshwater flux affect stability of upper ocean and therefore diurnal thermocline cycle?

Are puddles we see at the ship representative of Equatorial Indian Ocean? of the entire radar domain?

Can 150 km radar feature ID / tracking explain observed puddle variability at ship? actually, let’s just look at a few easy cases, find parents to Aurelie’s orphan

puddles. You aren’t going to figure this out on every case, but you should be able to find at least a few cases and understand them really well. The history of the puddle’s parent’s life will be interesting.

How does rainfall contribute to puddle formation/lifecycle/lifetime? linear vs. MCS vs. popcorn convective vs. stratiform volume flux vs. surface flux

Develop/conduct this research WITH Aurelie because she understands the subjects and will see things I won’t have noticed, and vice versa.

~ 2 D advection model? move around in current (apply over whole domain?), mix together at night?

Freshwater Flux

Barrier Layers How do convective vs.

stratiform, organized vs. unorganized, etc. rainfalls contribute to barrier layer formation (at ship)?

What is accumulated effect of different rainfall morphologies (spectrum of convection) to barrier layer production, maintenance, erosion?

sequence, order matters

What is the role of advection?

Important because...

barrier layers favor the maintenance and displacement of WPWP into cent. pacific by isolating the ML from entrainment cooling @depth and by confining the momentum of WWB to shallow ML (Lukas and Lindstrom 1991)

Freshwater Flux

Freshwater FluxHypothesisTO-DO List

1. rainfall metrics wanted?2. Write and test puddle

detection algorithm (polar coordinates)

3. Barrier layer study status?4. How could we use precip radar

data in puddle model?5. Collaborate with LIDAR? W-

band? to close whole near ship, get upward velocity during stratiform rain?

6. How to evaluate integrated effects, for “ocean memory”: Jim Edson’s capacitor idea

Colliding Gust Fronts: 22 Nov 2011

Gust fronts are interesting because: up-scale growth of smaller features into larger MCSs became more

frequent before/during MJO initiation Anecdotally, Gust fronts more frequently noticed at night? part of erratic storm motion implications for environmental wind shear and BL recovery

Radial Velocity (m/s) Reflectivity (dBZ)

Momentum Flux

Gust Front Detection Algorithm

END RESULT: Feature ID and

tracking history of: frequency intensity duration speed, direction shape, asymmetry precip parent storm storm initiation/mergers

Nuts and Bolts: Scott Collis (ARM)

provided automatic unfolding algorithm

Implement special polar coord QC

Look for convergence along gust fronts look for gradients against

smoothed background flow Only close to radar...

close gap at ship with LIDAR

CYLBIN? Solve for 2D wind field?

Momentum Flux

Wind Stress Hypothesis TO-DO List

1. wind stress/gustiness/wind metrics wanted?

2. Implement gust front detection, tracking, and feature ID

3. collaborate with existing DYNAMO cold pool studies

4. collaborate with LIDAR? W-band?

5. how to collaborate with ocean mixing, currents, and ADCP profilers?

6. how to use ADCP spatial data?7. clear air return? N?8. contribution to diurnal jets,

wrytki jets, EUC, mixing coefficients, turbulence?

Radiative Fluxes @ interfaceImportance/Focus of

air-sea fluxes for MJO:

“For ocean to play a major role in the dynamics of the propagating (initiating) MJO, SFC flux variation must induce SST variation

peak warming anomaly < peak cooling anomaly but suppressed phase lasts longer than active phase and has greater zonal extent. So over life cycle of MJO, WPWP has net heat flux > 0.

IDEAS: assess buoyancy flux into the ML thru air-sea

interface (5.10) insolation, LW flux, latent/sensible heat fluxes buoyancy flux due to sfc salinity change b/c of

evap and rain buoyancy flux due to heat flux b/c T difference

rain vs. sea stability as a function of depth ML depth and diurnal cycle of thermocline

with metrics of precipitation/clouds ML depth may have some optimal value... eq. 5.22 has variation of ML density due to

precip, linking horiz mixing coefficient with atm forcing (precip) ... cumulative precip during rain event

composite air-sea fluxes with certain radar resolved “features,” as in RICO, etc.

Assess relative strengths and directions of identified feedback mechanisms Diurnal cycle of RH >> LHF SST-Convection wind-evap-entrainment cloud-raidative

RadiativeFluxes

Radiative Fluxes @ interface IINull hypothesis: extent, frequency, organization, intesity of precipitating

systems cannot explain variability (on interannual, accumulated diurnal cycle, diurnal cycle, convective life cycle time scales) in air-sea fluxes.

convective rains induce patchy spatial patterns in sea surface temp/salinity multi-cloud structures are involved in MJO disturbances Eq 5.19-5.21 : estimate inhomogeneity of the buoyancy or density field in the

upper ocean induced by atm forcing Is the wind stress/precip timing the same as for TOGA COARE? If not, why?

Implications for MJO dynamical theories? Are diurnal warm layers critical for afternoon atm. convection? Postulated to

progressively moisten lower trop, setting up favorable conditions for onset of organized convection w/in MJO (Godfrey et al. 1998).

use of microprofiler data? Rainfalls are in fact the major contributor to the temporal and spatial

intermittency of the buoyancy flux between atm and ocean in WPWP – so what is the intermittency of the buoyancy flux?

subgrid scale precip statistics w/in 1 km resolution can, in principle, be used to implement horizontal mixing parameterizations in an ocean GCM

RadiativeFluxes

Radiative FluxHypothesisTO-DO list

1. What kind of rainfall POINT metrics do you want?

2. Implement cell tracking and feature ID

3. Collaborate with flux group4. Robust statistical treatment of

multivariate datasets?5. explore text files and

equations

SummaryPrecipitation Radar Perspective on

Air-Sea Interaction during DYNAMO

Momentum Flux

RadiativeFluxes

Freshwater Flux

Important &

Quantifiable

...on what time/space

scales?

** save something for my PhD prospectus!

Lots more ideas and lots more questions

Mirror Mirai Study ISV of SST during boreal winters is large of IO south of Eq.,

where shallow thermocline induces a shallow ML (de Boyer Montegut et al. 2004, Yokoi et al. 2008). This region is called the Seychelles-Chagos Thermocline Ridge.

ISV of SSTs decreases when wind stress increases to deepen ML

Stronger DWLs tend to appear where ISV of SST is greater (Bellenger and Duvel 2009) ... so mirai ≠ revelle

with statistically different rainfall time series, convection populations, DWLs, ocean ML dynamics?...

How are ocean ML and air-sea fluxes different? What does this say about SCTR? synoptic scale general

circulation? equatorial dynamics? same time period :: 2 locations, regimes, dynamics ~

quasi independent samples?

Future: Build Parameterizations Ground based precipitation radar results can be applied to

TRMM and GPM satellite radars, although they glaze over the mesoscale because of insufficient resolution

spray/rain-mediated, component of air-sea fluxes - microscale Transfers energy from sensible to latent heat flux and enhances

momentum flux into ocean (for high winds), modifies precip/evap/momentum in atm. BL

Fairall 1994 attempted - how well did you do? Is it a fruitful endeavor to revisit? If so, how?

get rain rate/rainfall right first: large error from space? Use sea “clutter” to study this in CALWATER2?

Interactive air/sea process parameterizations & sub-models precipitating systems :: upper ocean

How can we make these subgrid scale process studies relevant and useful to GCMs?

JPL summer school application:

satellite/ climate models

RadiativeFluxes

Freshwater Flux

Momentum Flux

extra unorganized

thoughts

Freshwater Flux NOTES Null hypothesis: the nature of freshwater

pools does not depend on the characteristics/spectrum of rainfall events.

“A hallmark of the MJO is (nearly) coincident westerly wind stress maxima with max freshwater flux into ocean, Hence their individual influence on the buoyancy forcing of the warm pool ML tends to cancel” – Anderson et al 1996, Zhang and Anderson 2003.

Freshwater input produces buoyancy flux from air to sea, which tends to suppress convection initially b/c rainT < SST, but may superheat later

since there is a frequent freshwater flux into the ocean, there is a continuous creation, evolution, and dissipation of the density anomalies in the WPWP ~ working toward equilibrium buoyancy spectrum?

turbulent mixing is mainly localized within this stably stratified near-sfc layer. subsequent diurnal warming develops within this freshwater lens.

Freshwater Flux

Gust Front Detection NOTES Null hypothesis: gust fronts, as

indicated on PPI radar scans, behave similarly in the eq. IO throughout the MJO lifecycle

We know cold pools are characteristic of their environment and it’s perturbations

How do nature of atmospheric cold pools change with MJO? Convective morphology/lifecycle/intensity? diurnal cycle?

Can radar detected (Lagrangian) gust fronts explain observed variability of gust fronts at Revelle (Eulerian)?

Does gust front detection/evolution provide metrics for boundary layer recovery?

Circulation and mass transport in upper 1 km of ocean is direction related to the curl of the wind stress, then wind driven circulations vanish at a certain depth.

What systematic/anomalous contribution do atmospheric cold pools make to surface wind stress? isotropic in space/time? how often? what direction? >> conv/div mixing? TKE?

What is the systematic influence of cold pools on the ocean? Do they cancel out over time, Conv/div, wind stress, direction? Romeo and Juliet or Grandpa?

Is there something to be learned/garnered from wave field w/r/t wind forcing?

low level winds and wind stress are correlated to currents on 30-60 day time scale (mcphaden 1982, mysak and pertz)

Anomalous westerlies and easterlies of MJO can excite downwelling and upwelling oceanic KWs, respectively, that in turn affect SST (McPhaden 1999)

Momentum Flux

Radiative Fluxes NOTES Net IR flux depends on cloud thickness, height/depth, Atm. WV

content diurnal cycle is more prominent in suppressed phase, so are diurnal

warm layers, fresh water puddles, and diurnal jets clouds/precip are major contributor to horiz temp/salinity gradients. How much cooling does it take to convect? Rayleigh number. surface evap plays controversial role in MJO (Zhange 2005, Sobel et

al. 2010), may help increase low-level moisture east of conv. centers thru zonal advection

TOGA COARE provided firm evidence that MJO had coupled atm-ocean structures, which led to surge of theoretical and numerical model studies on the nature of air-sea interactions and their role in maintnating and developing the ISO.

models operate with integrals rather than instantaneous values of fluxes, so the diurnal amplitudes depend on the history of fluxes; connect mean quantities and gradients to “accumulated fluxes” at air-sea surface.

Heat capacity of top 2-3 m of ocean is as much as the that of the entire atm!! Density is 1000X greater, viscosity 30X greater, vertical length scale 30x smaller === takes much much more time for heat and momentum fluxes from the ocean surface to propagate the same distance they might in atm BL.

RadiativeFluxes