Category: Physical Oceanography

Distribution of long-term mean observed (a)-(b) and simulated (c)-(d) meridional velocity along 23°W and 10°W. Gray dots in (a)-(b) indicate statistically significant values. Contour interval is 2.5 cm s-1. Figure reproduced from Perez et al., (2013). Image Credit: NOAA AOML.

Mean Meridional Currents in the Central and Eastern Equatorial Atlantic

In an article recently published in Climate Dynamics (Perez et al., 2013) , scientists in PhOD (R. Perez, R. Lumpkin, C. Schmid) described for the first time the mean vertical and cross-equatorial structure of the upper-ocean meridional currents in the Atlantic cold tongue region, using in situ observations including drifters, Argo, shipboard/lowered ADCP, and moored ADCP. This study involves collaborations with scientists from the University of Miami, Scripps Institution of Oceanography, and several international institutions and makes use of data from several major tropical Atlantic field programs including NOAA’s PIRATA Northeast Extension.

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AOML Tests New Deep Water Data Pod System  “ABIISS” 

The AOML technology test of a system to autonomously retrieve data from subsurface moored instruments has had a major success. The Adaptable Bottom Instrument Information Shuttle System (ABIISS) is in the midst of its first 4000+ meter test, and on November 6th, 2015 the first data pod surfaced and successfully transmitted its daily data record from the ocean bottom pressure-equipped inverted echo […]

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Sketch of the physical processes linking the major summer monsoons in the NH and the southern subtropical anticyclones. The three regions of rising motion, the three regions of sinking motion and the regions of southern subtropical anticyclones affected are filled with gray, sky blue and red colors, respectively. The sinking regions in the southeastern tropical Pacific and the southeastern tropical Atlantic are indicated by sky blue borderlines. Thick black arrows represent divergent winds in the upper level, while light green arrows represent the paths of the stationary barotropic Rossby waves forced by diabatic cooling over the three regions of sinking motion and by diabatic heating in the Indian summer monsoon region. Image Credit: NOAA AOML.

Inter-hemispheric Influence of the Northern Summer Monsoons on the Southern Subtropical Anticyclone

In a recent article accepted for publication in the Journal of Climate, scientists in PhOD, S.-K. Lee (CIMAS) and C. Wang collaborated with R. Mechoso and D. Neelin, both at UCLA, to explore why the southern subtropical anticyclones are notably stronger in the austral winter than in summer, which is in contrast with the Northern Hemisphere (NH) in which subtropical anticyclones are more intense in summer according to the monsoon heating paradigm. They performed model experiments to show that during the boreal summer enhanced tropical convection activity in the NH plays important roles in strengthening the southern subtropical anticyclones.

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The evolution of the tropical Pacific ocean/atmosphere system concurrent with and following atmospheric variability in the SLPI region in the year preceding an El Nino event. Shading: Composite of normalized monthly-mean heat content anomalies in the upper 300m. Shading interval is from 0.4 (yellow) to 1.0 (maroon) in increments of 0.1. Black contours: Composite of normalized monthly mean near-surface temperature anomalies at 5 m depth. Contour interval is 0.1; minimum contour is ±0.4. White contours: Composite of normalized monthly mean zonal wind stress anomalies. Positive (negative) values have solid (dashed) contours. See Anderson et al. (2013) for more details. Image Credit: NOAA AOML.

Triggering of El Nino through trade-wind induced charging of the equatorial Pacific

In a recent study by scientists at Boston University, PHOD, and NCAR, a new mechanism was uncovered for initiating ENSO events wherein SLP-generated North Pacific trade winds induce subsurface heat content changes that serve as precursors to El Ninos. This trade-wind charging mechanism of the equatorial Pacific is fundamentally different from any previously diagnosed, and studies examining the surface and subsurface ocean dynamics associated with this mechanism are underway.

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(a) Correlation between the NEUC transport and the SST and pseudo-wind stress in the Tropical Atlantic. The boxes are regions of high magnitude of correlation, where a SST index (SST2) and a meridional wind index (y-wind2) are taken (b). (c) Lagged correlation between the indices timeseries and the NEUC transport index. Image Credit: NOAA AOML.

Relationship between the Off-equatorial Current System and the Tropical Atlantic Variability

Scientists at PHOD developed a synthetic method, which combines high-density expendable bathythermograph (XBT) temperature data along the AX08 XBT transect (which runs between Cape Town and NYC) with altimetric sea level anomalies, to estimate the variability of the off-equatorial currents, such as the North Equatorial Countercurrent and the North Equatorial Undercurrent, on seasonal to interannual timescales. Understanding how the ocean dynamics is liked to anomalies of temperature and wind-stress in the tropical Atlantic is critical to understand the climate and weather variability in the adjacent continental areas.

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Global Ocean Surface Velocities from Drifters: Mean, Variance, ENSO Response, and Seasonal Cycle

Using over 30 years of observations from drogued, satellite-tracked surface drifting buoys, Lumpkin and Johnson (2013) developed a methodology to map seasonally-varying surface currents at 1/2 degree resolution. Results from this study can be used to better understand how the ocean transports properties like heat, salt, and passive tracers, and serves as a reference to study changes in ocean currents over time. One key result from this study is the global distribution of mean, seasonal and eddy kinetic energy, which totals 4.6x1017J in the upper 30 m of the ocean and reveals the presence of three large eddy “deserts”, one in the Atlantic Ocean and the other two in the Pacific.

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30 Years of Drifter Data Allow Scientists to Create a Visual Climatology of Ocean Currents

Using over 30 years of observations from satellite-tracked surface drifting buoys, NOAA oceanographers derived a global climatology of seasonally-varying ocean surface currents at one-half degree resolution. This data set can be used to better understand how the ocean transports properties like heat, salt, and passive tracers, and as a reference to study changes in ocean […]

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Incidents of intense (Fujita scale F3-F5) U.S. tornadoes in April-May for (a) the top ten positive Trans-Niño years, (b) ten neutral Trans-Niño years, and (c) the top ten negative Trans-Niño years during 1950-2010 obtained from Severe Weather Database (SWD). Green color is for F3, blue color for F4 and red color for F5 tornadoes. Image Credit: NOAA AOML.

Is there an optimal ENSO pattern that enhances large-scale atmospheric processes conducive to tornado outbreaks in the U.S?

The record-breaking U.S. tornado outbreaks in the spring of 2011 prompt the need to identify long-term climate signals that could potentially provide seasonal predictability for U.S. tornado outbreaks. A new research led by scientists in the Physical Oceanography Division of NOAA-AOML used both observations and model experiments to show that a positive phase Trans-Niño may be one such climate signal.

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Upper Ocean Heat content during the intensification of Hurricanes Katrina (left) and Isaac (right) Image Credit: New York Times

Satellite-derived Heat Content Product Developed at AOML Helps to Understand The Differences in Intensity Between Tropical Storm Isaac and Hurricane Katrina

A news article that appeared on August 27 shows the ocean conditions in the Gulf of America during hurricanes Katrina (August 2005) and Isaac (August 2012). The ocean conditions are depicted by the upper ocean heat content derived from satellite altimetry using a methodology developed at NOAA/AOML. The upper ocean heat content had larger values during Katrina mainly due to an anticyclonic warm ring and an extended Loop Current. These conditions, not found during the passage of Hurricane Isaac, partly contributed to the intensification of Katrina.

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(a) Simulated pathways of the northward heat transport (contours) and heat transport vector (vectors) in the upper 3000 m for 1979-2008 obtained from the control experiment (EXP_CTR). The unit is 1x109 W/m. (b) Differences in the simulated northward heat transport (contours) and heat transport vector (vectors) between 1979-2008 and 1871-1900 periods, obtained from EXP_CTR. Red color indicates northward heat transport, while blue color indicates southward heat transport. (c) Globally averaged zonal wind stress for 1871-1900 and for 1979-2008 periods, obtained from the 20th Century Reanalysis. Image Credit: NOAA AOML.

What Caused the Significant Increase in Atlantic Ocean Heat Content Since the mid-20th Century?

A new study led by researchers from University of Miami, NOAA-AOML, IFM-GEOMAR, and NCAR explores why the Atlantic Ocean has warmed substantially more than any other ocean basin since the 1950s. The research article published in the Geophysical Research letters evidences that the observed large warming of the Atlantic Ocean since the 1950s is largely induced by an increase in the inter-ocean heat transport from the Indian Ocean via the Agulhas leakage. The study points to an important role played by the Atlantic meridional overturning circulation (AMOC) in the South Atlantic in enhancing the secular warming of the Atlantic Ocean.

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