scholarly journals Improving Ocean Model Initialization for Coupled Tropical Cyclone Forecast Models Using GODAE Nowcasts

2008 ◽  
Vol 136 (7) ◽  
pp. 2576-2591 ◽  
Author(s):  
G. R. Halliwell ◽  
L. K. Shay ◽  
S. D. Jacob ◽  
O. M. Smedstad ◽  
E. W. Uhlhorn
Keyword(s):  
Tropical Cyclone ◽  
Thermal Energy ◽  
Prediction Models ◽  
Three Dimensional ◽  
Heat Content ◽  
Ocean Model ◽  
Upper Ocean ◽  
Cold Bias ◽  
Sst Cooling ◽  
Free Running

Abstract To simulate tropical cyclone (TC) intensification, coupled ocean–atmosphere prediction models must realistically reproduce the magnitude and pattern of storm-forced sea surface temperature (SST) cooling. The potential for the ocean to support intensification depends on the thermal energy available to the storm, which in turn depends on both the temperature and thickness of the upper-ocean warm layer. The ocean heat content (OHC) is used as an index of this potential. Large differences in available thermal energy associated with energetic boundary currents and ocean eddies require their accurate initialization in ocean models. Two generations of the experimental U.S. Navy ocean nowcast–forecast system based on the Hybrid Coordinate Ocean Model (HYCOM) are evaluated for this purpose in the NW Caribbean Sea and Gulf of Mexico prior to Hurricanes Isidore and Lili (2002), Ivan (2004), and Katrina (2005). Evaluations are conducted by comparison to in situ measurements, the navy’s three-dimensional Modular Ocean Data Assimilation System (MODAS) temperature and salinity analyses, microwave satellite SST, and fields of OHC and 26°C isotherm depth derived from satellite altimetry. Both nowcast–forecast systems represent the position of important oceanographic features with reasonable accuracy. Initial fields provided by the first-generation product had a large upper-ocean cold bias because the nowcast was initialized from a biased older-model run. SST response in a free-running Isidore simulation is improved by using initial and boundary fields with reduced cold bias generated from a HYCOM nowcast that relaxed model fields to MODAS analyses. A new climatological initialization procedure used for the second-generation nowcast system tended to reduce the cold bias, but the nowcast still could not adequately reproduce anomalously warm conditions present before all storms within the first few months following nowcast initialization. The initial cold biases in both nowcast products tended to decrease with time. A realistic free-running HYCOM simulation of the ocean response to Ivan illustrates the critical importance of correctly initializing both warm-core rings and cold-core eddies to correctly simulate the magnitude and pattern of SST cooling.

scholarly journals Tropical Cyclones and Transient Upper-Ocean Warming

2008 ◽  
Vol 21 (1) ◽  
pp. 149-162 ◽  
Author(s):  
Claudia Pasquero ◽  
Kerry Emanuel
Keyword(s):  
Tropical Cyclone ◽  
Tropical Cyclones ◽  
Heat Content ◽  
Ocean Model ◽  
Ocean Heat Content ◽  
Upper Ocean ◽  
Cyclone Activity ◽  
Upper Ocean Heat Content ◽  
Vertical Temperature Profile ◽  
Thermodynamic Conditions

Abstract Strong winds affect mixing and heat distribution in the upper ocean. In turn, upper-ocean heat content affects the evolution of tropical cyclones. Here the authors explore the global effects of the interplay between tropical cyclones and upper-ocean heat content. The modeling study suggests that, for given atmospheric thermodynamic conditions, regimes characterized by intense (with deep mixing and large upper-ocean heat content) and by weak (with shallow mixing and small heat content) tropical cyclone activity can be sustained. A global general circulation ocean model is used to study the transient evolution of a heat anomaly that develops following the strong mixing induced by the passage of a tropical cyclone. The results suggest that at least one-third of the anomaly remains in the tropical region for more than one year. A simple atmosphere–ocean model is then used to study the sensitivity of maximum wind speed in a cyclone to the oceanic vertical temperature profile. The feedback between cyclone activity and upper-ocean heat content amplifies the sensitivity of modeled cyclone power dissipation to atmospheric thermodynamic conditions.

scholarly journals Upper-Ocean Response to Hurricane Frances (2004) Observed by Profiling EM-APEX Floats*

2011 ◽  
Vol 41 (6) ◽  
pp. 1041-1056 ◽  
Author(s):  
Thomas B. Sanford ◽  
James F. Price ◽  
James B. Girton
Keyword(s):  
Drag Coefficient ◽  
Vertical Mixing ◽  
Ocean Model ◽  
Upper Ocean ◽  
Surface Mixed Layer ◽  
Wind Speeds ◽  
Sst Cooling ◽  
Ocean Response ◽  
Upper Ocean Response ◽  
The Right

Abstract Three autonomous profiling Electromagnetic Autonomous Profiling Explorer (EM-APEX) floats were air deployed one day in advance of the passage of Hurricane Frances (2004) as part of the Coupled Boundary Layer Air–Sea Transfer (CBLAST)-High field experiment. The floats were deliberately deployed at locations on the hurricane track, 55 km to the right of the track, and 110 km to the right of the track. These floats provided profile measurements between 30 and 200 m of in situ temperature, salinity, and horizontal velocity every half hour during the hurricane passage and for several weeks afterward. Some aspects of the observed response were similar at the three locations—the dominance of near-inertial horizontal currents and the phase of these currents—whereas other aspects were different. The largest-amplitude inertial currents were observed at the 55-km site, where SST cooled the most, by about 2.2°C, as the surface mixed layer deepened by about 80 m. Based on the time–depth evolution of the Richardson number and comparisons with a numerical ocean model, it is concluded that SST cooled primarily because of shear-induced vertical mixing that served to bring deeper, cooler water into the surface layer. Surface gravity waves, estimated from the observed high-frequency velocity, reached an estimated 12-m significant wave height at the 55-km site. Along the track, there was lesser amplitude inertial motion and SST cooling, only about 1.2°C, though there was greater upwelling, about 25-m amplitude, and inertial pumping, also about 25-m amplitude. Previously reported numerical simulations of the upper-ocean response are in reasonable agreement with these EM-APEX observations provided that a high wind speed–saturated drag coefficient is used to estimate the wind stress. A direct inference of the drag coefficient CD is drawn from the momentum budget. For wind speeds of 32–47 m s−1, CD ~ 1.4 × 10−3.

In Situ Data Biases and Recent Ocean Heat Content Variability*

2009 ◽  
Vol 26 (4) ◽  
pp. 846-852 ◽  
Author(s):  
Josh K. Willis ◽  
John M. Lyman ◽  
Gregory C. Johnson ◽  
John Gilson
Keyword(s):  
Heat Content ◽  
Ocean Heat Content ◽  
Rate Equations ◽  
Upper Ocean ◽  
Cold Bias ◽  
Sampling Errors ◽  
Upper Ocean Heat Content ◽  
Data Errors ◽  
In Situ Data

Abstract Two significant instrument biases have been identified in the in situ profile data used to estimate globally integrated upper-ocean heat content. A large cold bias was discovered in a small fraction of Argo floats along with a smaller but more prevalent warm bias in expendable bathythermograph (XBT) data. These biases appear to have caused the bulk of the upper-ocean cooling signal reported by Lyman et al. between 2003 and 2005. These systematic data errors are significantly larger than sampling errors in recent years and are the dominant sources of error in recent estimates of globally integrated upper-ocean heat content variability. The bias in the XBT data is found to be consistent with errors in the fall-rate equations, suggesting a physical explanation for that bias. With biased profiles discarded, no significant warming or cooling is observed in upper-ocean heat content between 2003 and 2006.

scholarly journals Restratification of the Upper Ocean after the Passage of a Tropical Cyclone: A Numerical Study

2012 ◽  
Vol 42 (9) ◽  
pp. 1377-1401 ◽  
Author(s):  
Wei Mei ◽  
Claudia Pasquero
Keyword(s):  
Tropical Cyclone ◽  
Water Column ◽  
Numerical Study ◽  
Baroclinic Instability ◽  
Relative Size ◽  
Heat Content ◽  
Heat Fluxes ◽  
Upper Ocean ◽  
Regional Ocean Modeling System ◽  
Eddy Structures

Abstract The role of baroclinic instability in the restratification of the upper ocean after the passage of a tropical cyclone (TC) is determined by means of numerical simulations. Using a regional ocean model, the Regional Ocean Modeling System (ROMS), a high-resolution three-dimensional simulation that includes the process of baroclinic instability and is initialized with moderate-amplitude eddy structures reproduces the satellite-observed decay rate of the TC-induced sea surface temperature (SST) anomaly and is also in qualitative agreement with published observations after the passage of Hurricane Fabian in 2003 that showed decaying cold and warm anomalies located in the climatological mixed layer (CML) and upper thermocline, respectively. The model ocean is restratified after approximately one month with a net heat gain in the water column due to anomalous air–sea heat fluxes. The model shows, however, that vertical heat fluxes associated with baroclinic instability dominate over air–sea heat fluxes in restoring the CML heat content during the first month. A comparison with two-dimensional simulations that exclude baroclinic adjustment further highlights the importance of baroclinic instability: it can not only input a considerable amount of heat into the CML, but also establish strong stratification there, inhibiting the downward penetration of heat contributed by diabatic heating at the surface; both effects hasten the recovery of the SST. Additional experiments were performed to examine the sensitivity of the model results to changes in Newtonian cooling rate, changes in the magnitude of the eddy structures used to initialize the simulation, and changes in poststorm wind strength; the results indicate that, although some of them may have a significant effect on the recovery time of the SST, their influence on the contribution of baroclinic instability to the recovery of the CML heat content is modest. However, the contribution of baroclinic instability exhibits pronounced positive dependence on the depth of the mixing layer relative to the CML depth and the relative size of the area with unperturbed water. Its dependence on the shape of the spatial variation of the mixing depth is relatively weak but in a more complicated manner. These dependencies are consistent with those predicted by a simple front adjustment model, whereas the latter also suggest that the contribution of baroclinic instability is independent of the prestorm stratification below the CML. Overall, the idealized simulations in this study suggest that, for a typical situation in the real ocean, baroclinic instability can account for approximately 50% of the full recovery of the CML heat content, whereas under specific conditions the contribution can be significantly smaller. Those estimates provide a limit to the maximum net warming of the water column after the initial mixing event and thus have important implications regarding estimating the long-term effect of TCs on the upper-ocean heat budget.

scholarly journals Application of Oceanic Heat Content Estimation to Operational Forecasting of Recent Atlantic Category 5 Hurricanes

2008 ◽  
Vol 23 (1) ◽  
pp. 3-16 ◽  
Author(s):  
Michelle Mainelli ◽  
Mark DeMaria ◽  
Lynn K. Shay ◽  
Gustavo Goni
Keyword(s):  
Tropical Cyclone ◽  
Positive Impact ◽  
Thermal Structure ◽  
Heat Content ◽  
Intensity Change ◽  
Upper Ocean ◽  
Average Intensity ◽  
Hurricane Intensity ◽  
Structure Information ◽  
Maximum Improvement

Abstract Research investigating the importance of the subsurface ocean structure on tropical cyclone intensity change has been ongoing for several decades. While the emergence of altimetry-derived sea height observations from satellites dates back to the 1980s, it was difficult and uncertain as to how to utilize these measurements in operations as a result of the limited coverage. As the in situ measurement coverage expanded, it became possible to estimate the upper oceanic heat content (OHC) over most ocean regions. Beginning in 2002, daily OHC analyses have been generated at the National Hurricane Center (NHC). These analyses are used qualitatively for the official NHC intensity forecast, and quantitatively to adjust the Statistical Hurricane Intensity Prediction Scheme (SHIPS) forecasts. The primary purpose of this paper is to describe how upper-ocean structure information was transitioned from research to operations, and how it is being used to generate NHC’s hurricane intensity forecasts. Examples of the utility of this information for recent category 5 hurricanes (Isabel, Ivan, Emily, Katrina, Rita, and Wilma from the 2003–05 hurricane seasons) are also presented. Results show that for a large sample of Atlantic storms, the OHC variations have a small but positive impact on the intensity forecasts. However, for intense storms, the effect of the OHC is much more significant, suggestive of its importance on rapid intensification. The OHC input improved the average intensity errors of the SHIPS forecasts by up to 5% for all cases from the category 5 storms, and up to 20% for individual storms, with the maximum improvement for the 72–96-h forecasts. The qualitative use of the OHC information on the NHC intensity forecasts is also described. These results show that knowledge of the upper-ocean thermal structure is fundamental to accurately forecasting intensity changes of tropical cyclones, and that this knowledge is making its way into operations. The statistical results obtained here indicate that the OHC only becomes important when it has values much larger than that required to support a tropical cyclone. This result suggests that the OHC is providing a measure of the upper ocean’s influence on the storm and improving the forecast.

Limitation of One-Dimensional Ocean Models for Coupled Hurricane–Ocean Model Forecasts

2009 ◽  
Vol 137 (12) ◽  
pp. 4410-4419 ◽  
Author(s):  
Richard M. Yablonsky ◽  
Isaac Ginis
Keyword(s):  
North Atlantic Ocean ◽  
Three Dimensional ◽  
Ocean Model ◽  
Sea Surface ◽  
Upper Ocean ◽  
Surface Cooling ◽  
One Dimensional ◽  
Sea Surface Cooling ◽  
Ocean Models ◽  
The One

Abstract Wind stress imposed on the upper ocean by a hurricane can limit the hurricane’s intensity primarily through shear-induced mixing of the upper ocean and subsequent cooling of the sea surface. Since shear-induced mixing is a one-dimensional process, some recent studies suggest that coupling a one-dimensional ocean model to a hurricane model may be sufficient for capturing the storm-induced sea surface temperature cooling in the region providing heat energy to the hurricane. Using both a one-dimensional and a three-dimensional version of the same ocean model, it is shown here that the neglect of upwelling, which can only be captured by a three-dimensional ocean model, underestimates the storm-core sea surface cooling for hurricanes translating at <∼5 m s−1. For hurricanes translating at <2 m s−1, more than half of the storm-core sea surface cooling is neglected by the one-dimensional ocean model. Since the majority of hurricanes in the western tropical North Atlantic Ocean translate at <5 m s−1, the idealized experiments presented here suggest that one-dimensional ocean models may be inadequate for coupled hurricane–ocean model forecasting.

scholarly journals Impact of Sea-State-Dependent Langmuir Turbulence on the Ocean Response to a Tropical Cyclone

2016 ◽  
Vol 144 (12) ◽  
pp. 4569-4590 ◽  
Author(s):  
Brandon G. Reichl ◽  
Isaac Ginis ◽  
Tetsu Hara ◽  
Biju Thomas ◽  
Tobias Kukulka ◽  
...  
Keyword(s):  
Tropical Cyclone ◽  
Three Dimensional ◽  
Ocean Model ◽  
Stokes Drift ◽  
Langmuir Turbulence ◽  
Sea State ◽  
Near Surface ◽  
Ocean Response ◽  
State Dependent ◽  
The Impact

Abstract Tropical cyclones are fueled by the air–sea heat flux, which is reduced when the ocean surface cools due to mixed layer deepening and upwelling. Wave-driven Langmuir turbulence can significantly modify these processes. This study investigates the impact of sea-state-dependent Langmuir turbulence on the three-dimensional ocean response to a tropical cyclone in coupled wave–ocean simulations. The Stokes drift is computed from the simulated wave spectrum using the WAVEWATCH III wave model and passed to the three-dimensional Princeton Ocean Model. The Langmuir turbulence impact is included in the vertical mixing of the ocean model by adding the Stokes drift to the shear of the vertical mean current and by including Langmuir turbulence enhancements to the K-profile parameterization (KPP) scheme. Results are assessed by comparing simulations with explicit (sea-state dependent) and implicit (independent of sea state) Langmuir turbulence parameterizations, as well as with turbulence driven by shear alone. The results demonstrate that the sea-state-dependent Langmuir turbulence parameterization significantly modifies the three-dimensional ocean response to a tropical cyclone. This is due to the reduction of upwelling and horizontal advection where the near-surface currents are reduced by Langmuir turbulence. The implicit scheme not only misses the impact of sea-state dependence on the surface cooling, but it also misrepresents the impact of the Langmuir turbulence on the Eulerian advection. This suggests that explicitly resolving the sea-state-dependent Langmuir turbulence will lead to increased accuracy in predicting the ocean response in coupled tropical cyclone–ocean models.

scholarly journals Upper Oceanic Energy Response to Tropical Cyclone Passage

2013 ◽  
Vol 26 (8) ◽  
pp. 2631-2650 ◽  
Author(s):  
John A. Knaff ◽  
Mark DeMaria ◽  
Charles R. Sampson ◽  
James E. Peak ◽  
James Cummings ◽  
...  
Keyword(s):  
Tropical Cyclone ◽  
Energy Content ◽  
Energy Conditions ◽  
Upper Ocean ◽  
Ocean Energy ◽  
Translation Speed ◽  
Structure Information ◽  
Sst Cooling ◽  
Ocean Response ◽  
Upper Ocean Response

Abstract The upper oceanic temporal response to tropical cyclone (TC) passage is investigated using a 6-yr daily record of data-driven analyses of two measures of upper ocean energy content based on the U.S. Navy’s Coupled Ocean Data Assimilation System and TC best-track records. Composite analyses of these data at points along the TC track are used to investigate the type, magnitude, and persistence of upper ocean response to TC passage, and to infer relationships between routinely available TC information and the upper ocean response. Upper oceanic energy decreases in these metrics are shown to persist for at least 30 days—long enough to possibly affect future TCs. Results also indicate that TC kinetic energy (KE) should be considered when assessing TC impacts on the upper ocean, and that existing TC best-track structure information, which is used here to estimate KE, is sufficient for such endeavors. Analyses also lead to recommendations concerning metrics of upper ocean energy. Finally, parameterizations for the lagged, along-track, upper ocean response to TC passage are developed. These show that the sea surface temperature (SST) is best related to the KE and the latitude whereas the upper ocean energy is a function of KE, initial upper ocean energy conditions, and translation speed. These parameterizations imply that the 10-day lagged SST cooling is approximately 0.7°C for a “typical” TC at 30° latitude, whereas the same storm results in 10-day (30-day) lagged decreases of upper oceanic energy by about 12 (7) kJ cm−2 and a 0.5°C (0.3°C) cooling of the top 100 m of ocean.

Uncertainty of Tropical Cyclone Wind Radii on Sea Surface Temperature Cooling

2021 ◽  
Author(s):  
Iam-Fei Pun ◽  
John Knaff ◽  
Charles Sampson
Keyword(s):  
Tropical Cyclone ◽  
Surface Temperature ◽  
Sea Surface Temperature ◽  
Prediction Models ◽  
Weather Prediction ◽  
Sea Surface ◽  
Weather Research And Forecasting ◽  
Translation Speed ◽  
Ocean Stratification ◽  
Sst Cooling

<p>The sea surface temperature (SST) beneath a tropical cyclone (TC) is of great importance to its dynamics; therefore, understanding and accurately estimating the magnitude of SST cooling is of vital importance.  Existing studies have explored important influences on SST such as TC translation speed, maximum surface winds, ocean thermal condition and ocean stratification.  But the influence of the TC wind radii (or collectively called the TC size) on SST has been largely overlooked.  In this study we assess the influence of wind radii uncertainty on SST cooling by a total of 15,983 numerical simulations for the western North Pacific during the 2014-2018 seasons.  Results show a 6-20% SST cooling error induced using wind radii from the Joint Typhoon Warning Center official forecast and a 35-40% SST cooling error using wind radii from the operational runs of the Hurricane Weather Research and Forecasting (HWRF) model.  Our results indicate that SST cooling is most sensitive to the radius of 64 kt winds.  The correlation between SST cooling induced by the TC and its size is 0.49, which is highest among all the parameters tested.  This suggests that it is extremely important to get TC size correct in order to predict the SST cooling response, which then impacts TC evolution in numerical weather prediction models.</p>

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