scholarly journals Process-Oriented Diagnosis of Tropical Cyclones in High-Resolution GCMs

2018 ◽  
Vol 31 (5) ◽  
pp. 1685-1702 ◽  
Author(s):  
Daehyun Kim ◽  
Yumin Moon ◽  
Suzana J. Camargo ◽  
Allison A. Wing ◽  
Adam H. Sobel ◽  
...  
Keyword(s):  
Heat Flux ◽  
High Resolution ◽  
Tropical Cyclones ◽  
Surface Heat Flux ◽  
Surface Wind ◽  
Atmospheric Model ◽  
Surface Heat ◽  
The Other ◽  
Near Surface ◽  
Surface Latent Heat Flux

This study proposes a set of process-oriented diagnostics with the aim of understanding how model physics and numerics control the representation of tropical cyclones (TCs), especially their intensity distribution, in GCMs. Three simulations are made using two 50-km GCMs developed at NOAA’s Geophysical Fluid Dynamics Laboratory. The two models are forced with the observed sea surface temperature [Atmospheric Model version 2.5 (AM2.5) and High Resolution Atmospheric Model (HiRAM)], and in the third simulation, the AM2.5 model is coupled to an ocean GCM [Forecast-Oriented Low Ocean Resolution (FLOR)]. The frequency distributions of maximum near-surface wind near TC centers show that HiRAM tends to develop stronger TCs than the other models do. Large-scale environmental parameters, such as potential intensity, do not explain the differences between HiRAM and the other models. It is found that HiRAM produces a greater amount of precipitation near the TC center, suggesting that associated greater diabatic heating enables TCs to become stronger in HiRAM. HiRAM also shows a greater contrast in relative humidity and surface latent heat flux between the inner and outer regions of TCs. Various fields are composited on precipitation percentiles to reveal the essential character of the interaction among convection, moisture, and surface heat flux. Results show that the moisture sensitivity of convection is higher in HiRAM than in the other model simulations. HiRAM also exhibits a stronger feedback from surface latent heat flux to convection via near-surface wind speed in heavy rain-rate regimes. The results emphasize that the moisture–convection coupling and the surface heat flux feedback are critical processes that affect the intensity of TCs in GCMs.

How surface latent heat flux is related to lower-tropospheric stability in southern subtropica marine stratus and stratocumulus regions

2009 ◽  
Vol 1 (3) ◽  
Author(s):  
Yanping He
Keyword(s):  
Heat Flux ◽  
Latent Heat ◽  
Latent Heat Flux ◽  
Radiation Flux ◽  
Surface Wind ◽  
Surface Radiation ◽  
Near Surface ◽  
Marine Stratus ◽  
Surface Latent Heat Flux ◽  
Lower Tropospheric Stability

AbstractThe relationship between surface latent heat flux and the lower-tropospheric stability (LTS) is examined using ERA-40 reanalysis, NCEP reanalysis and COADS (Comprehensive Ocean-Atmosphere Data Set) ship data in two southern subtropical marine stratus and stratocumulus regions. The change of surface latent heat flux with LTS is determined by a comparison of the correlation of LTS with surface wind speed and with near surface humidity difference. At intermediate LTS (10 K-15 K), both surface evaporation and downward surface radiation flux amplify small LTS perturbations due to the surface wind-LTS relationship and cloud-radiation feedback. At high LTS, surface latent heat flux exceeds its peak value and becomes a regulating mechanism to keep LTS at its commonly observed equilibrium value. Surface radiation flux is seen to decrease at a smaller rate with LTS than surface latent heat flux. By applying the regulating effect of LTS on near surface humidity differences, monthly surface latent heat flux can be better represented.

Estimation of the Surface Heat Flux Response to Sea Surface Temperature Anomalies over the Global Oceans

2005 ◽  
Vol 18 (21) ◽  
pp. 4582-4599 ◽  
Author(s):  
Sungsu Park ◽  
Clara Deser ◽  
Michael A. Alexander
Keyword(s):  
Heat Flux ◽  
North Atlantic ◽  
Surface Heat Flux ◽  
Surface Wind ◽  
Surface Heat ◽  
Radiative Flux ◽  
Turbulent Heat ◽  
Global Oceans ◽  
Sst Anomalies ◽  
Heat Flux Feedback

Abstract The surface heat flux response to underlying sea surface temperature (SST) anomalies (the surface heat flux feedback) is estimated using 42 yr (1956–97) of ship-derived monthly turbulent heat fluxes and 17 yr (1984–2000) of satellite-derived monthly radiative fluxes over the global oceans for individual seasons. Net surface heat flux feedback is generally negative (i.e., a damping of the underlying SST anomalies) over the global oceans, although there is considerable geographical and seasonal variation. Over the North Pacific Ocean, net surface heat flux feedback is dominated by the turbulent flux component, with maximum values (28 W m−2 K−1) in December–February and minimum values (5 W m−2 K−1) in May–July. These seasonal variations are due to changes in the strength of the climatological mean surface wind speed and the degree to which the near-surface air temperature and humidity adjust to the underlying SST anomalies. Similar features are observed over the extratropical North Atlantic Ocean with maximum (minimum) feedback values of approximately 33 W m−2 K−1 (9 W m−2 K−1) in December–February (June–August). Although the net surface heat flux feedback may be negative, individual components of the feedback can be positive depending on season and location. For example, over the midlatitude North Pacific Ocean during late spring to midsummer, the radiative flux feedback associated with marine boundary layer clouds and fog is positive, and results in a significant enhancement of the month-to-month persistence of SST anomalies, nearly doubling the SST anomaly decay time from 2.8 to 5.3 months in May–July. Several regions are identified with net positive heat flux feedback: the tropical western North Atlantic Ocean during boreal winter, the Namibian stratocumulus deck off West Africa during boreal fall, and the Indian Ocean during boreal summer and fall. These positive feedbacks are mainly associated with the following atmospheric responses to positive SST anomalies: 1) reduced surface wind speed (positive turbulent heat flux feedback) over the tropical western North Atlantic and Indian Oceans, 2) reduced marine boundary layer stratocumulus cloud fraction (positive shortwave radiative flux feedback) over the Namibian stratocumulus deck, and 3) enhanced atmospheric water vapor (positive longwave radiative flux feedback) in the vicinity of the tropical deep convection region over the Indian Ocean that exceeds the negative shortwave radiative flux feedback associated with enhanced cloudiness.

scholarly journals An empirical model for the statistics of sea surface diurnal warming

Ocean Science ◽  
2012 ◽  
Vol 8 (2) ◽  
pp. 197-209 ◽  
Author(s):  
M. J. Filipiak ◽  
C. J. Merchant ◽  
H. Kettle ◽  
P. Le Borgne
Keyword(s):  
Heat Flux ◽  
Wind Speed ◽  
Statistical Model ◽  
Surface Heat Flux ◽  
Surface Wind ◽  
Surface Wind Speed ◽  
Surface Heat ◽  
Sea Surface ◽  
Diurnal Warming ◽  
Nwp Model

Abstract. A statistical model is derived relating the diurnal variation of sea surface temperature (SST) to the net surface heat flux and surface wind speed from a numerical weather prediction (NWP) model. The model is derived using fluxes and winds from the European Centre for Medium-Range Weather Forecasting (ECMWF) NWP model and SSTs from the Spinning Enhanced Visible and Infrared Imager (SEVIRI). In the model, diurnal warming has a linear dependence on the net surface heat flux integrated since (approximately) dawn and an inverse quadratic dependence on the maximum of the surface wind speed in the same period. The model coefficients are found by matching, for a given integrated heat flux, the frequency distributions of the maximum wind speed and the observed warming. Diurnal cooling, where it occurs, is modelled as proportional to the integrated heat flux divided by the heat capacity of the seasonal mixed layer. The model reproduces the statistics (mean, standard deviation, and 95-percentile) of the diurnal variation of SST seen by SEVIRI and reproduces the geographical pattern of mean warming seen by the Advanced Microwave Scanning Radiometer (AMSR-E). We use the functional dependencies in the statistical model to test the behaviour of two physical model of diurnal warming that display contrasting systematic errors.

Reduced Near-Surface Thermal Inversions in 2005–06 in the Southeastern Arabian Sea (Lakshadweep Sea)*

2009 ◽  
Vol 39 (5) ◽  
pp. 1184-1199 ◽  
Author(s):  
K. Nisha ◽  
Suryachandra A. Rao ◽  
V. V. Gopalakrishna ◽  
R. R. Rao ◽  
M. S. Girishkumar ◽  
...  
Keyword(s):  
Bay Of Bengal ◽  
Arabian Sea ◽  
Surface Wind ◽  
Surface Heat ◽  
The Other ◽  
Near Surface ◽  
Low Salinity ◽  
Southeastern Arabian Sea ◽  
Surface Wind Field ◽  
Lakshadweep Sea

Abstract Repeat XBT transects made at near-fortnightly intervals in the Lakshadweep Sea (southeastern Arabian Sea) and ocean data assimilation products are examined to describe the year-to-year variability in the observed near-surface thermal inversions during the winter seasons of 2002–06. Despite the existence of a large low-salinity water intrusion into the Lakshadweep Sea, there was an unusually lower number of near-surface thermal inversions during the winter 2005/06 compared to the other winters. The possible causative mechanisms are examined. During the summer monsoon of 2005 and the following winter season, unusually heavy rainfall occurred over the southwestern Bay of Bengal and the Lakshadweep Sea compared to other years in the study. Furthermore, during the winter of 2005, both the East India Coastal Current and the Winter Monsoon Current were stronger compared to the other years, transporting larger quantities of low salinity waters from the Bay of Bengal into the Lakshadweep Sea where a relatively cooler near-surface thermal regime persisted owing to prolonged upwelling until November 2005. In addition, the observed local surface wind field was relatively stronger, and the net surface heat gain to the ocean was weaker over the Lakshadweep Sea during the postmonsoon season of 2005. Thus, in winter 2005/06, the combination of prolonged upwelling and stronger surface wind field resulting in anomalous net surface heat loss caused weaker secondary warming of the near-surface waters in the Lakshadweep Sea. This led to a weaker horizontal sea surface temperature (SST) gradient between the Lakshadweep Sea and the intruding Bay of Bengal waters and, hence, a reduced number of thermal inversions compared to other winters despite the presence of stronger vertical haline stratification.

scholarly journals Topographic and Mixed Layer Submesoscale Currents in the Near-Surface Southwestern Tropical Pacific

2017 ◽  
Vol 47 (6) ◽  
pp. 1221-1242 ◽  
Author(s):  
Kaushik Srinivasan ◽  
James C. McWilliams ◽  
Lionel Renault ◽  
Hristina G. Hristova ◽  
Jeroen Molemaker ◽  
...  
Keyword(s):  
Heat Flux ◽  
Surface Layer ◽  
Kinetic Energy ◽  
Wind Stress ◽  
Mixed Layer ◽  
Surface Heat Flux ◽  
Seasonal Cycle ◽  
Surface Heat ◽  
Near Surface ◽  
Coral Sea

AbstractThe distribution and strength of submesoscale (SM) surface layer fronts and filaments generated through mixed layer baroclinic energy conversion and submesoscale coherent vortices (SCVs) generated by topographic drag are analyzed in numerical simulations of the near-surface southwestern Pacific, north of 16°S. In the Coral Sea a strong seasonal cycle in the surface heat flux leads to a winter SM “soup” consisting of baroclinic mixed layer eddies (MLEs), fronts, and filaments similar to those seen in other regions farther away from the equator. However, a strong wind stress seasonal cycle, largely in sync with the surface heat flux cycle, is also a source of SM processes. SM restratification fluxes show distinctive signatures corresponding to both surface cooling and wind stress. The winter peak in SM activity in the Coral Sea is not in phase with the summer dominance of the mesoscale eddy kinetic energy in the region, implying that local surface layer forcing effects are more important for SM generation than the nonlocal eddy deformation field. In the topographically complex Solomon and Bismarck Seas, a combination of equatorial proximity and boundary drag generates SCVs with large-vorticity Rossby numbers (Ro ~ 10). River outflows in the Bismarck and Solomon Seas make a contribution to SM generation, although they are considerably weaker than the topographic effects. Mean to eddy kinetic energy conversions implicate barotropic instability in SM topographic wakes, with the strongest values seen north of the Vitiaz Strait along the coast of Papua New Guinea.

scholarly journals Role of Wind Shear in the Decay of Convective Boundary Layers

Atmosphere ◽  
2020 ◽  
Vol 11 (6) ◽  
pp. 622 ◽  
Author(s):  
Seung-Bu Park ◽  
Jong-Jin Baik ◽  
Beom-Soon Han
Keyword(s):  
Boundary Layer ◽  
Heat Flux ◽  
Boundary Layers ◽  
Vertical Velocity ◽  
Surface Heat Flux ◽  
Wind Shear ◽  
Surface Heat ◽  
The Other ◽  
Convective Boundary

The role of wind shear in the decay of the convective boundary layer (CBL) is systematically investigated using a series of large-eddy simulations. Nine CBLs with weak, intermediate, and strong wind shear are simulated, and their decays after stopping surface heat flux are investigated. After the surface heat flux is stopped, the boundary-layer-averaged turbulent kinetic energy (TKE) stays constant for almost one convective time scale and then decreases following a power law. While the decrease persists until the end of the simulation in the buoyancy-dominated (weak-shear) cases, the TKE in the other cases decreases slowly or even increases to a level which can be maintained by wind shear. In the buoyancy-dominated cases, convective cells occur, and they decay and oscillate over time. The oscillation of vertical velocity is not distinct in the other cases, possibly because wind shear disturbs the reversal of vertical circulations. The oscillations are detected again in the profiles of vertical turbulent heat flux in the buoyancy-dominated cases. In the strong-shear cases, mechanical turbulent eddies are generated, which transport heat downward in the lower boundary layers when convective turbulence decays significantly. The time series of vertical velocity skewness demonstrates the shear-dependent flow characteristics of decaying CBLs.

scholarly journals Intensification Variability of Tropical Cyclones in Directional Shear Flows: Vortex Tilt–Convection Coupling

2019 ◽  
Vol 76 (6) ◽  
pp. 1827-1844 ◽  
Author(s):  
Jian-Feng Gu ◽  
Zhe-Min Tan ◽  
Xin Qiu
Keyword(s):  
Heat Flux ◽  
Tropical Cyclones ◽  
Surface Heat Flux ◽  
Shear Flows ◽  
Deep Layer ◽  
Surface Heat ◽  
Moist Convection ◽  
Low Level ◽  
Stage Of Development ◽  
The Right

Abstract The coupling of vortex tilt and convection, and their effects on the intensification variability of tropical cyclones (TCs) in directional shear flows, is investigated in this study. The height-dependent vortex tilt controls TC structural differences in clockwise (CW) and counterclockwise (CC) hodographs during their initial stage of development. Moist convection may enhance the coupling between displaced vortices at different levels and thus reduce the vortex tilt amplitude and enhance precession of the overall vortex tilt during the early stage of development. However, differences in the overall vortex tilt between CW and CC hodographs are further amplified by a feedback from convective heating and therefore result in much higher intensification rates for TCs in CW hodographs than those in CC hodographs. In CW hodographs, convection organization in the left-of-shear region is favored because the low-level vortex tilt is ahead of the overall vortex tilt and the TC moves to the left side of the deep-layer shear. This results in a more humid midtroposphere and stronger surface heat flux on the left side (azimuthally downwind) of the overall vortex tilt, thus providing a positive feedback and supporting continuous precession of the vortex tilt into the upshear-left region. In CC hodographs, convection tends to organize on the right side (azimuthally upwind) of the overall vortex tilt because the low-level vortex tilt is behind the overall vortex tilt and the TC moves to the right side of the deep-layer shear. In addition, convection organizes radially outward near the downshear-right region, which weakens convection within the inner region. These configurations lead to a drier midtroposphere and weaker surface heat flux in the downwind region of the overall vortex tilt and also a broader potential vorticity skirt. As a result, a negative feedback is established that prevents continuous precession of the overall vortex tilt.

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