Kaustav Chakravarty Richard H Johnson Paul E Ciesielski Colorado State University The MaddenJulian Oscillation Observations Theoretical Understanding Modeling and Prediction AGU Fall Meeting ID: 1045456
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1. Multiscale Variability of the Atmospheric Boundary Layer during DYNAMOKaustav ChakravartyRichard H. JohnsonPaul E. CiesielskiColorado State UniversityThe Madden-Julian Oscillation: Observations, Theoretical Understanding, Modeling, and Prediction; AGU Fall Meeting, New Orleans, 11-15 December 2017
2. DYNAMO/CINDY/AMIE Sounding DomainAmplitude of MJO signal (20-day low-pass filtered 450-hPa hPa h-1) Boundary layer properties investigated at 3 sites(Johnson and Ciesielski 2017, JAS)
3. 4 October Soundings at R/V Revelle08 L14 LθθqqProcedure for determining mixed layers: soundingsEach sounding evaluated subjectively (5-hPa resolution)Mixed layers: θ and q have approximately well-mixed structure over same depth, capped by distinct increase in stability, drying above; entrainment zone evident in majority of casesResults backed up by recently developed objective procedure07 L 13 LmhPaENTRAINMENT ZONEθθqq
4. 4 October Soundings at R/V Revelle07 L13 Lθθqq07 L13 LShallow cumulus layers frequently observed“trade-like” stable layerCumulus cloud bases are at the top of the entrainment zone, so arguably it is important to accurately predict mixed layer properties in order to properly represent cumulus cloud populations
5. Many soundings show indication of “trade-like” stable layer near 2 km or 800 hPa, especially during buildup phase of MJORevelle Soundings4 October 2011Terra/MODIS Visible Image (250 m)Terra/MODIS visible image (250 m)
6. 0729 LT 22 Nov1859 LT 22 NovRecovering Boundary Layer Wake at R/V Revelle22 November 2011 9-12 hComparable to wake recovery periods found in TOGA COARE (Young, Perugini, Fairall 1995)θ 07 10 13 16 1904 LT TOGA radar on Revelle
7. Mean Mixed Layer StatisticsMean zi ML Gan Mal Revelle Undist. Trades ~600 * Johnson et al. (2001)** Fitzjarrald and Garstang (1981)(m) frequency (%)GATE** 424 79COARE* 512 72(1 Oct–15 Dec)503695357249164
8. Two prominent MJO events: October and NovemberSUMATRADYNAMO ARRAYBORNEOTime MJO envelopes consists of westward- and eastward-moving disturbancesEAST AFRICAMJO 1MJO 2
9. Mixed Layers at Mal, Gan, and Revelle Shallower MLs during rainy periods, less so at GanOct/Nov MJO modulation of ML depth greatest at Mal and RevelleGreatest ML depths at Gan during dry, suppressed period in Jan and Feb MJO1MJO2
10. 10 kmllAddu AtollGan sounding siteWhy is MJO modulation of ML depth less at Gan Island?Diurnal heating/cooling of atoll makes lower portion of Gan soundings less representative of open oceanMal is much smaller Mal & especially Revelle more representative of open ocean
11. ML deepens during SST warming phasesBuoyancy flux F nearly constant during early Oct: weakening L-S subsidence promoted ML growthML grows above LCL, promoting cloud growthSST diurnal cycle during ocean warming phases?data courtesy Edson, Fairall, de SzoekeML depths, LCLSurface buoyancy flux, wind speedR/V Revelle
12. 04 L07101316192301Diurnal cycle of mixed layer at Gan Island- 8 October -θq 250 m diurnal variationGan ARM Sounding SiteLarge diurnal cycle during suppressed periodsHowever, Gan soundings influenced by atoll heating/cooling
13. Diurnal Cycle at Revelle, 11-21 NovemberAfternoon SST peak leads to increased F, reduction in zLCL – zi , more BL thermals can reach condensation levels, afternoon cloud cover and rainfall maximumNocturnal rainfall peak still present, typical of open oceanExplains semi-diurnal rainfall maximaMixed layer at Revelle more representative of open ocean
14. SUMMARYAtmospheric mixed layers observed for ~70% of soundings; mean depth ~475-525 m; findings similar to TOGA COARE, GATEMixed layers modulated on multiple time scalesMLs deepen during MJO suppressed phaseModulation of ML by MJO less distinct at Gan: possible explanation – atoll heating/cooling effectsAfternoon ML peak on suppressed days at Revelle associated with SST diurnal warm layer; concurrent afternoon peaks in rainfall/echo area coverageIncrease in cloudiness/rain on MJO-to-diurnal time scales a result of ML growth, allowing more BL thermals to reach condensation levelsRisky to generalize atoll/island BL properties to open ocean
15. Extra slides
16. TOGA COARE Mixed layer deepest during light-rain periods, shallowest during rain periods ML depth varies on MJO time scale(Johnson et al. 2001)