Observations of the marine boundary layer under a cutoff low over the southeast Pacific Ocean
- 167 Downloads
Stratocumulus is often present offshore of Peru and northern Chile and exists at the top of a cool, moist and well-mixed marine boundary layer (MBL) under a marked temperature inversion maintained by large-scale subsidence. The subtropical MBL and stratocumulus has been the focus of many recent studies, but mid-latitude systems can exert a strong influence. However, this connection is not well established due to debatable model results and few in situ measurements south of 20°S. During a 2-week field campaign in August 2011 at Robinson Crusoe Island (~700 km offshore at 33.6°S), radiosondes were launched to observe the response of the MBL to mid-latitude synoptic forcing. During the observation period a broad, slow-moving cutoff low (COL) passed over the region. Other observations include COSMIC GPS, infrared satellite imagery, TRMM radar reflectivity, and operational radiosondes from the Chilean weather service. A numerical simulation is included to diagnose the synoptic features. The inversion prior to the COL was maintained and lifted above 5 km as the COL passed over the island. Soon after the COL center passed the island, the MBL top did not descend or reform near the surface and then deepen, but rather an inversion reformed at ~2.7 km. Using a variety of datasets, the height of the reformation of the inversion is related to the cloud top height of the scattered shallow cumulus convection under the COL, which coincides with the level of maximum convergence of the vertical velocity.
KeywordsGlobal Position System Brightness Temperature Temperature Inversion Vertical Wind Shear Marine Boundary Layer
This project was supported by the Chilean Fondo Nacional de Desarrollo Científico y Tecnológico (FONDECYT) 3110100 and New Faculty Startup funds at KU. Thanks to José Rutllant, Carlos Parra of the Dirección Meteorológica de Chile, and Rosa Zamora for their help during the field campaign on RCI. Roberto Rondanelli helped with processing the satellite data. I also thank two anonymous reviewers for their comments.
- Allen G, Coe H, Clarke A, Bretherton C, Wood R, Abel SJ, Barrett P, Brown P, George R, Freitag S, McNaughton C, Howell S, Shank L, Kapustin V, Brekhovskikh V, Kleinman L, Lee Y-N, Springston S, Toniazzo T, Krejci R, Fochesatto J, Shaw G, Krecl P, Brooks B, McMeeking G, Bower KN, Williams PI, Crosier J, Crawford I, Connolly P, Allan JD, Covert D, Bandy AR, Russell LM, Trembath J, Bart M, McQuaid JB, Wang J, Chand D (2011) South East Pacific atmospheric composition and variability sampled along 20°S during VOCALS-Rex. Atmos Chem Phys 11:5237–5262. doi: 10.5194/acp-11-5237-2011 CrossRefGoogle Scholar
- Anthes RA, Bernhardt PA, Chen Y, Cucurull L, Dymond KF, Ector D, Healy SB, Ho SP, Hunt DC, Kuo YH, Liu H, Manning K, McCormick C, Meehan TK, Randel WJ, Rocken C, Schreiner WS, Sokolovskiy SV, Syndergaard S, Thompson DC, Trenberth KE, Wee TK, Yen NL, Zhang Z (2008) The COSMIC/FORMOSAT-3 mission: early results. Bull Am Meteorol Soc 89:313–333. doi: 10.1175/BAMS-89-3-313 CrossRefGoogle Scholar
- Hill EF, Browning KA (1987) Case study of a persistent mesoscale cold pool. Meteorol Mag 116:297–309Google Scholar
- Matsumoto SK, Ninomiya K, Hasegawa R, Miki Y (1982) The structure and role of a subsynoptic cold vortex on the heavy precipitation. J Meteorol Soc Jpn 60:339–353Google Scholar
- Mechoso CR, Robertson AW, Barth N, Davey MK, Delecluse P, Gent PR, Ineson S, Kirtman B, Latif M, Le Treut H, Nagai T, Neelin JD, Philaner SGH, Polcher J, Schopt PS, Stockdale T, Suarez MJ, Terray L, Thual O, Tribbia JJ (1995) The seasonal cycle over the tropical Pacific in coupled ocean-atmosphere general circulation models. Mon Weather Rev 123:2825–2838CrossRefGoogle Scholar
- Palmén E, Newton CW (1969) Atmospheric circulation systems: their structure and physical interpretation. Academic Press, New YorkGoogle Scholar
- Skamarock WC, Klemp JB, Dudhia J, Gill DO, Barker DM, Wang W, Powers JG (2008) A description of the advanced research WRF version 3, NCAR Tech Note, NCAR/TN–475+STRGoogle Scholar
- Wood R, Mechoso CR, Bretherton CS, Weller RA, Huebert B, Straneo F, Albrecht BA, Coe H, Allen G, Vaughan G, Daum P, Fairall C, Chand D, Gallardo Klenner L, Garreaud R, Grados C, Covert DS, Bates TS, Krejci R, Russell LM, de Szoeke S, Brewer A, Yuter SE, Springston SR, Chaigneau A, Toniazzo T, Minnis P, Palikonda R, Abel SJ, Brown WOJ, Williams S, Fochesatto J, Brioude J, Bower KN (2011) The VAMOS Ocean-Cloud-Atmosphere-Land Study Regional Experiment (VOCALS-REx): goals, platforms, and field operations. Atmos Chem Phys 11:627–654. doi: 10.5194/acp-11-627-2011 CrossRefGoogle Scholar