Multiyear measurements of the oceanic and atmospheric boundary layers at the Brazil‐Malvinas confluence region

Abstract

[1] This study analyzes and discusses data taken from oceanic and atmospheric measurements performed simultaneously at the Brazil-Malvinas Confluence (BMC) region in the southwestern Atlantic Ocean. This area is one of the most dynamical frontal regions of the world ocean. Data were collected during four research cruises in the region once a year in consecutive years between 2004 and 2007. Very few studies have addressed the importance of studying the air-sea coupling at the BMC region. Lateral temperature gradients at the study region were as high as 0.3°C km À1 at the surface and subsurface. In the oceanic boundary layer, the vertical temperature gradient reached 0.08°C m À1 at 500 m depth. Our results show that the marine atmospheric boundary layer (MABL) at the BMC region is modulated by the strong sea surface temperature (SST) gradients present at the sea surface. The mean MABL structure is thicker over the warmside of the BMC where Brazil Current (BC) waters predominate. The opposite occurs over the coldside of the confluence where waters from the Malvinas (Falkland) Current (MC) are found. The warmside of the confluence presented systematically higher MABL top height compared to the coldside. This type of modulation at the synoptic scale is consistent to what happens in other frontal regions of the world ocean, where the MABL adjusts itself to modifications along the SST gradients. Over warm waters at the BMC region, the MABL static instability and turbulence were increased while winds at the lower portion of the MABL were strong. Over the coldside of the BC/MC front an opposite behavior is found: the MABL is thinner and more stable. Our results suggest that the sea-level pressure (SLP) was also modulated locally, together with static stability vertical mixing mechanism, by the surface condition during all cruises. SST gradients at the BMC region modulate the synoptic atmospheric pressure gradient. Postfrontal and prefrontal conditions produce opposite thermal advections in the MABL that lead to different pressure intensification patterns across the confluence.

Equatorially Antisymmetric Features in the Initiation Processes of the Madden-Julian Oscillation Observed in Late October during CINDY2011

“…4 and the low (high) SST in Fig. 5 supports the notion that the surface convergence of the s-ITCZ is due to the pressure adjustment mechanism (Lindzen and Nigam 1987;Kessler and Kleeman 2000;Pezzi et al 2009). The pressure adjustment mechanism is a well-known explanation for the cause of the surface convergence over the tropics: an SST-induced SAT difference hydrostatically adjusts the pressure gradient that drives the surface winds to produce the surface convergence.…”

Continuous Daily Observation of the Marine Atmospheric Boundary Layer over the Kuroshio by a Helicopter Shuttle Service

“…Given future longer-period TIS observations, we will be able to examine the spatial transitions of the MABL across the SST front and their modulations under the cold and dry northerlies and warm and moist southerlies. Such an investigation has been conducted by Pezzi et al (2009) based on the multiyear measurements of the MABL in the Brazil-Malvinas Confluence region. On a basis of the longer-period TIS observation, it will be interesting and challenging to properly model cases of stable stratification for better numerical weather prediction (NWP).…”

“…Several previous studies, however, have conducted shipboard atmospheric soundings along a single cross section using a global positioning system (GPS) sonde. These studies have been successful in showing the distinct transition of temperature and moisture in the MABL across the steep front of sea surface temperature (SST) formed along western boundary currents, such as the Kuroshio and its extension (Tokinaga et al 2006;Tanimoto et al 2009;Tokinaga et al 2009), the Gulf Stream (Sweet et al 1981), and the Brazil-Malvinas Confluence region (Pezzi et al 2005). While these observations have revealed the active effect of the SST front on the overlying MABL, our understanding of the ocean's role in affecting synoptic weather systems is still poor.…”

Análise Do Acoplamento Oceano-Atmosfera Em Escala Sinótica Ao Longo De 33 °s Nos Dias 19 E 20 De Junho De 2012

“…Até o presente, os efeitos causados pelos contrastes horizontais termais entre as massas d'água transportadas pela Corrente do Brasil (CB) e pela Corrente Costeira do Brasil (CCB) durante o inverno sobre a atmosfera imediatamente acima na costa do RS são praticamente desconhecidos. Por conta dos processos típicos de acoplamento oceano-atmosfera em regiões de alto gradiente termal horizontal de TSM nos oceanos e, em especial, no Atlântico Sul (PEZZI et al, 2005(PEZZI et al, , 2009Acevedo et al, 2010, Camargo et al, 2013, especula-se que a camada limite atmosférica (CLA) ao longo de transectos perpendiculares à costa do RS tenha características distintas sobre a CB e sobre a CCB. Souza e Robinson (2004) descreveram a CCB como uma corrente de natureza sazonal que domina a plataforma continental da região sul-sudeste brasileira durante o inverno.…”