scholarly journals Upper-Ocean Thermal Structure and the Western North Pacific Category 5 Typhoons. Part II: Dependence on Translation Speed

2009 ◽  
Vol 137 (11) ◽  
pp. 3744-3757 ◽  
Author(s):  
I-I. Lin ◽  
Iam-Fei Pun ◽  
Chun-Chieh Wu
Keyword(s):  
Mixed Layer ◽  
North Pacific ◽  
Western North Pacific ◽  
Thermal Structure ◽  
Subsurface Layer ◽  
Heat Content ◽  
Correlation Coefficients ◽  
Upper Ocean ◽  
Translation Speed

Abstract Using new in situ ocean subsurface observations from the Argo floats, best-track typhoon data from the U.S. Joint Typhoon Warning Center, an ocean mixed layer model, and other supporting datasets, this work systematically explores the interrelationships between translation speed, the ocean’s subsurface condition [characterized by the depth of the 26°C isotherm (D26) and upper-ocean heat content (UOHC)], a cyclone’s self-induced ocean cooling negative feedback, and air–sea enthalpy fluxes for the intensification of the western North Pacific category 5 typhoons. Based on a 10-yr analysis, it is found that for intensification to category 5, in addition to the warm sea surface temperature generally around 29°C, the required subsurface D26 and UOHC depend greatly on a cyclone’s translation speed. It is observed that even over a relatively shallow subsurface warm layer of D26 ∼ 60–70 m and UOHC ∼ 65–70 kJ cm−2, it is still possible to have a sufficient enthalpy flux to intensify the storm to category 5, provided that the storm can be fast moving (typically Uh ∼ 7–8 m s−1). On the contrary, a much deeper subsurface layer is needed for slow-moving typhoons. For example at Uh ∼ 2–3 m s−1, D26 and UOHC are typically ∼115–140 m and ∼115–125 kJ cm−2, respectively. A new concept named the affordable minimum translation speed Uh_min is proposed. This is the minimum required speed a storm needs to travel for its intensification to category 5, given the observed D26 and UOHC. Using more than 3000 Argo in situ profiles, a series of mixed layer numerical experiments are conducted to quantify the relationship between D26, UOHC, and Uh_min. Clear negative linear relationships with correlation coefficients R = −0.87 (−0.71) are obtained as Uh_min = −0.065 × D26 + 11.1, and Uh_min = −0.05 × UOHC + 9.4, respectively. These relationships can thus be used as a guide to predict the minimum speed a storm has to travel at for intensification to category 5, given the observed D26 and UOHC.

scholarly journals Upper-Ocean Thermal Structure and the Western North Pacific Category 5 Typhoons. Part I: Ocean Features and the Category 5 Typhoons’ Intensification

2008 ◽  
Vol 136 (9) ◽  
pp. 3288-3306 ◽  
Author(s):  
I-I. Lin ◽  
Chun-Chieh Wu ◽  
Iam-Fei Pun ◽  
Dong-Shan Ko
Keyword(s):  
Hurricane Katrina ◽  
North Pacific ◽  
Western North Pacific ◽  
Thermal Structure ◽  
Heat Content ◽  
Ocean Heat Content ◽  
Upper Ocean ◽  
Upper Ocean Heat Content ◽  
Typhoon Season ◽  
Region 10

Abstract Category 5 cyclones are the most intense and devastating cyclones on earth. With increasing observations of category 5 cyclones, such as Hurricane Katrina (2005), Rita (2005), Mitch (1998), and Supertyphoon Maemi (2003) found to intensify on warm ocean features (i.e., regions of positive sea surface height anomalies detected by satellite altimeters), there is great interest in investigating the role ocean features play in the intensification of category 5 cyclones. Based on 13 yr of satellite altimetry data, in situ and climatological upper-ocean thermal structure data, best-track typhoon data of the U.S. Joint Typhoon Warning Center, together with an ocean mixed layer model, 30 western North Pacific category 5 typhoons that occurred during the typhoon season from 1993 to 2005 are systematically examined in this study. Two different types of situations are found. The first type is the situation found in the western North Pacific south eddy zone (SEZ; 21°–26°N, 127°–170°E) and the Kuroshio (21°–30°N, 127°–170°E) region. In these regions, the background climatological warm layer is relatively shallow (typically the depth of the 26°C isotherm is around 60 m and the upper-ocean heat content is ∼50 kJ cm−2). Therefore passing over positive features is critical to meet the ocean’s part of necessary conditions in intensification because the features can effectively deepen the warm layer (depth of the 26°C isotherm reaching 100 m and upper-ocean heat content is ∼110 kJ cm−2) to restrain the typhoon’s self-induced ocean cooling. In the past 13 yr, 8 out of the 30 category 5 typhoons (i.e., 27%) belong to this situation. The second type is the situation found in the gyre central region (10°–21°N, 121°–170°E) where the background climatological warm layer is deep (typically the depth of the 26°C isotherm is ∼105–120 m and the upper-ocean heat content is ∼80–120 kJ cm−2). In this deep, warm background, passing over positive features is not critical since the background itself is already sufficient to restrain the self-induced cooling negative feedback during intensification.

Exploratory Analysis of Upper-Ocean Heat Content and Sea Surface Temperature Underlying Tropical Cyclone Rapid Intensification in the Western North Pacific

2020 ◽  
Vol 33 (3) ◽  
pp. 1031-1050 ◽  
Author(s):  
Cheng-Hsiang Chih ◽  
Chun-Chieh Wu
Keyword(s):  
Surface Temperature ◽  
Sea Surface Temperature ◽  
North Pacific ◽  
Western North Pacific ◽  
Heat Content ◽  
Ocean Heat Content ◽  
Sea Surface ◽  
Upper Ocean ◽  
Rapid Intensification ◽  
Upper Ocean Heat Content

AbstractThe statistical relationships between tropical cyclones (TCs) with rapid intensification (RI) and upper-ocean heat content (UOHC) and sea surface temperature (SST) from 1998 to 2016 in the western North Pacific are examined. RI is computed based on four best track datasets in the International Best Track Archive for Climate Stewardship (IBTrACS). The statistical analysis shows that the UOHC and SST are higher in the RI duration than in non-RI duration. However, TCs with high UOHC/SST do not necessarily experience RI. In addition, the UOHC and SST are lower in the storm inner-core region due to storm-induced ocean cooling, and the UOHC reduces more significantly than the SST along the passages of TCs in the lower-latitude regions. Moreover, most of the RI (non-RI) duration is associated with the higher (lower) UOHC, but this is not the case for the SST pattern. Meanwhile, the TC intensification rate during the RI period does not appear to be sensitive to the SST, but shows statistically significant differences in the UOHC. In addition, there is a statistically significant increasing trend in the UOHC underlying TCs from 1998 to 2016. It is also noted that the percentages of the TCs with RI show different polynomial and linear trends based on different calculations of the RI events and RI durations. Finally, it is shown that there is no statistically significant difference in the UOHC, SST, and the percentage of RI among the five categories of ENSO events (i.e., strong El Niño, weak El Niño, neutral, weak La Niña, and strong La Niña).

scholarly journals Global distribution and variability of subsurface chlorophyll a concentration

2021 ◽  
Author(s):  
Sayaka Yasunaka ◽  
Tsuneo Ono ◽  
Kosei Sasaoka ◽  
Kanako Sato
Keyword(s):  
Chlorophyll A ◽  
Mixed Layer ◽  
Net Primary Production ◽  
Thermal Structure ◽  
Mixed Layer Depth ◽  
Subsurface Layer ◽  
Spatiotemporal Variability ◽  
Shortwave Radiation ◽  
Concentration Data ◽  
Chl A

Abstract. Chlorophyll a (Chl-a) often retains its maximum concentration not at the surface but in the subsurface layer. The depth of the Chl-a maximum primarily depends on the balance between light penetration from the surface and nutrient supply from the deep ocean. However, a global map of subsurface Chl-a concentrations based on observations has not been presented yet. In this study, we integrate Chl-a concentration data not only from recent biogeochemical floats but also from historical ship-based and other observations, and present global maps of subsurface Chl-a concentration with related variables. The subsurface Chl-a maximum deeper than the mixed layer depth was stably observed in the subtropics and tropics (30° S to 30° N), only in summer in midlatitudes (30–40° N/S), and rarely at 45–60° S of the Southern Ocean and in the northern North Atlantic (north of 45° N). The depths of the subsurface Chl-a maxima are deeper than those of the euphotic layer in the subtropics and shallower in the tropics and midlatitudes. In the subtropics, seasonal oxygen increases below the mixed layer implied substantial biological new production, which corresponds to 10 % of the net primary production there. During El Niño, the subsurface Chl-a concentration in the equatorial Pacific is higher in the middle to the east and lower in the west than that during La Niña, which is opposite that on the surface. The spatiotemporal variability of the Chl-a concentration described here would be suggestive results not only for the biogeochemical cycle in the ocean but also for the thermal structure and the dynamics of the ocean via the absorption of shortwave radiation.

Using a novel combination of autonomous vehicles for air-sea interaction studies: Results from the Eurec4a campaign 

2021 ◽  
Author(s):  
Elizabeth Siddle ◽  
Karen J. Heywood ◽  
Ben Webber ◽  
Peter Bromley
Keyword(s):  
Time Series ◽  
North Atlantic ◽  
Heat Budget ◽  
Heat Content ◽  
Flux Measurement ◽  
Extreme Weather Events ◽  
Upper Ocean ◽  
Momentum Exchange ◽  
Tropical North Atlantic

<div> <p>The Tropical North Atlantic region is a key driver of climate variability and extreme weather events, driven largely by heat and momentum exchanges across the air-sea boundary. Observations of these fluxes by satellites and vessels are limited in their spatial resolution and length of time series respectively. In-situ samples across long time periods are needed, which can be obtained through developing a network of in-situ flux measurement platforms. UEA and AutoNaut have worked to address this challenge with the deployment of <em>Caravela</em> - an AutoNaut uncrewed surface vessel. <em>Caravela</em> is a wave and solar powered autonomous vessel, equipped with meteorological and oceanographic sensors and the ability to transport a Seaglider. <em>Caravela</em> successfully completed its first scientific deployment as part of the Eurec<sup>4</sup>a campaign. </p> </div><div> <p>Eurec<sup>4</sup>a ran from January—March 2020 from Barbados, investigating climate change feedback in the Tropical North Atlantic and the role of cloud systems. <em>Caravela</em> spent 11 days of her 33-day deployment occupying a 10 km square, co-located with other Eurec<sup>4</sup>a platforms to gather in-situ surface data on heat and momentum exchange. Preliminary results from <em>Caravela</em> give us an insight into heat exchange at the surface, downwelling radiation and wind conditions during deployment. There is an identifiable diurnal cycle during the deployment, particularly visible in temperature data, which will feed into our understanding of changes in fluxes at a local scale. Profiling ocean gliders at the study site allow us to determine a time series of upper ocean heat content changes. These data, alongside that collected by other platforms during Eurec<sup>4</sup>a, should enable an upper ocean heat budget to be calculated at <em>Caravela’s</em> study site. </p> </div>

Upper ocean responses to category 5 typhoon Megi in the western north Pacific

2012 ◽  
Vol 31 (1) ◽  
pp. 51-58 ◽  
Author(s):  
Xiaoyan Chen ◽  
Delu Pan ◽  
Xianqiang He ◽  
Yan Bai ◽  
Difeng Wang
Keyword(s):  
North Pacific ◽  
Western North Pacific ◽  
Upper Ocean

scholarly journals Satellite-Derived Ocean Thermal Structure for the North Atlantic Hurricane Season

2016 ◽  
Vol 144 (3) ◽  
pp. 877-896 ◽  
Author(s):  
Iam-Fei Pun ◽  
James F. Price ◽  
Steven R. Jayne
Keyword(s):  
Mixed Layer ◽  
North Atlantic ◽  
Thermal Structure ◽  
Estimation Error ◽  
Mixed Layer Depth ◽  
Heat Content ◽  
Height Anomaly ◽  
The North ◽  
Hurricane Season ◽  
The North Atlantic

Abstract This paper describes a new model (method) called Satellite-derived North Atlantic Profiles (SNAP) that seeks to provide a high-resolution, near-real-time ocean thermal field to aid tropical cyclone (TC) forecasting. Using about 139 000 observed temperature profiles, a spatially dependent regression model is developed for the North Atlantic Ocean during hurricane season. A new step introduced in this work is that the daily mixed layer depth is derived from the output of a one-dimensional Price–Weller–Pinkel ocean mixed layer model with time-dependent surface forcing. The accuracy of SNAP is assessed by comparison to 19 076 independent Argo profiles from the hurricane seasons of 2011 and 2013. The rms differences of the SNAP-estimated isotherm depths are found to be 10–25 m for upper thermocline isotherms (29°–19°C), 35–55 m for middle isotherms (18°–7°C), and 60–100 m for lower isotherms (6°–4°C). The primary error sources include uncertainty of sea surface height anomaly (SSHA), high-frequency fluctuations of isotherm depths, salinity effects, and the barotropic component of SSHA. These account for roughly 29%, 25%, 19%, and 10% of the estimation error, respectively. The rms differences of TC-related ocean parameters, upper-ocean heat content, and averaged temperature of the upper 100 m, are ~10 kJ cm−2 and ~0.8°C, respectively, over the North Atlantic basin. These errors are typical also of the open ocean underlying the majority of TC tracks. Errors are somewhat larger over regions of greatest mesoscale variability (i.e., the Gulf Stream and the Loop Current within the Gulf of Mexico).

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