Tag: Sang-Ki Lee

Ocean Temperatures May Hold Key to Predicting Tornado Outbreaks

Tornadoes are one of nature’s most destructive forces. Recent violent and widespread tornado outbreaks in the United States, such as occurred in the spring of 2011, have caused significant loss of life and property. Currently, our capacity to predict tornadoes and other severe weather risks does not extend beyond seven days. Extending severe weather outlooks beyond seven days will assist emergency managers, businesses, and the public prepare the resources needed to prevent economic losses and protect communities. So how can scientists better predict when and where tornadoes are likely to strike, before the tornado season begins?

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(left column) Seasonality of precipitation and 850mb winds for the monsoon regions as measured by the difference between June-July-August-September (JJAS) minus annual mean precipitation and winds. (middle-column) shows the composite difference of JJAS precipitation (shaded) and 850mb wind for each monsoon region with respect to weak minus strong SAMHT at lead-time 20 years after the anomalous SAMHT. Blue stipples indicates regions where precipitation differences are significant at 95% confidence level based on a non-parametric Kolmogorov-Smirnov test. (right-column) Lag-lead Spearman ranked correlation between SAMHT and NH monsoon index. The blue dashed lines depict the 95% significance level based on a non-parametric Kendall-t test. Negative lag indicates periods when SAMHT leads the NH monsoon index. Periods with significant correlation between the SAMHT and monsoon are shaded blue. Image Credit: NOAA AOML.

Meridional heat transport in the South Atlantic reveals links with global monsoons

A recent paper published in the Journal of Climate led by PHOD researchers Hosmay Lopez, Shenfu Dong, Sang-Ki Lee, and Gustavo Goni provides a physical mechanism on how low frequency variability of the South Atlantic Meridional Heat Transport (SAMHT) associated with the Atlantic Meridional Overturning Circulation ( AMOC) may influence decadal variability of atmospheric circulation and monsoons. This is the first attempt to link the South Atlantic Overturning Circulation variability to weather and climate.

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Figure 3 Glider approximate location (black diamond) superimposed on Infrared image of Hurricane Gonzalo on October 14, 1500 UTC, when it travelled the closest to the location of the underwater glider. Credit: image obtained from the Cooperative Institute for Meteorological Satellite Studies.

Underwater gliders observations reveal the importance of salinity effects during passage of Hurricane Gonzalo (2014)

Hurricanes are known to drive the cooling of surface waters as they travel over the ocean, leaving a cooling swath where they pass. The sea surface cooling is mostly caused by mixing forced by the strong winds of the hurricane, which occurs as the mixture of warm surface waters with colder waters that can be as deep as 100 m below the surface.

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Research Shows Indian Ocean Plays Key Role in Global Warming Hiatus

The earth is warming, but atmospheric and oceanic temperatures that rose steadily over the last half century have leveled off and slowed this past decade, causing the appearance of an imbalance in the Earth’s heat budget. Scientists looking to the deep ocean for where the additional heat energy might be stored recently traced a pathway that leads to the Indian Ocean.

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Illustration of increased trade winds in the Pacific and Indian Oceans during the recent warming hiatus, which increased the inter-ocean pressure gradient and thus enhanced Indonesian throughflow. This resulted in an abrupt increase of Indian Ocean heat content. Image credit: NOAA/CIMAS

Indian Ocean Plays Key Role in Global Warming Hiatus

The earth is warming, but temperatures in the atmosphere and at the sea surface that steadily rose in the last half-century have leveled off and slowed in the past decade, causing the appearance of an imbalance in Earth’s heat budget. Scientists are looking into the deep ocean to determine where this additional heat energy could be stored, and recently traced a pathway that leads to the Indian Ocean.

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Time-longitude plots of (a) composite mean (CM) and (b and c) the two leading inter-event EOFs of the tropical Pacific SST anomalies averaged between 5°S and 5°N, for 21 El Ninos during 1949-2013. (d and e) Same as b and c except that the two EOFs are rotated by 90º. Units are in ºC. The dashed gray boxes indicate Nino 3.4 in DJF (0,+1), Nino 3 (150°W-90°W and 5°S-5°N) in AMJ (+1), Niño 3 in AMJ (0), and Niño 3.4 in OND (+1).

A new approach provides a holistic view of ENSO variability during the onset, peak and decay phases

From its onset to the decay, El Niño-Southern Oscillation (ENSO) plays an important role in forcing climate variability around the globe. A new study led by Sang-Ki Lee, a PhOD/CIMAS scientist, provides an efficient approach to explore the differences in the evolution of space-time patterns of sea surface temperature observed during El Niño events

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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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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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(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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