scholarly journals Roles of vertical distributions of atmospheric transient eddy dynamical forcing and diabatic heating in midlatitude unstable air-sea interaction

2021 ◽  
Author(s):  
Jiabei Fang ◽  
Lilan Chen ◽  
Xiu-Qun Yang
Keyword(s):  
Positive Feedback ◽  
Diabatic Heating ◽  
Spatial Configuration ◽  
Lower Layer ◽  
Theoretical Work ◽  
Atmospheric Model ◽  
Transient Eddy ◽  
Coupled Mode ◽  
Vertical Distributions ◽  
Oceanic Model

Abstract Atmospheric transient eddy dynamical forcing (TEDF)-driven midlatitude unstable air-sea interaction has recently been recognized as a crucial positive feedback for the maintenance of the extratropical decadal variabilities. Our previous theoretical work by Chen et al. (2020) characterizes such an interaction with building an analytical midlatitude barotropic atmospheric model coupled to a simplified upper oceanic model. This study firstly extends the analytical model to a two-layer quasi-geostrophic baroclinic atmospheric model coupled to a simplified upper oceanic model and then identifies the roles of vertical distributions of atmospheric TEDF and diabatic heating in midlatitude unstable air-sea interaction. It is found that the midlatitude air-sea coupling through atmospheric TEDF and diabatic heating with more realistic vertical profile destabilizes the oceanic Rossby wave mode over the entire range of zonal wavelengths, and the most unstable mode exhibits an equivalent barotropic structure with geopotential lows (highs) over cold (warm) water. The spatial configuration structure and period of the most unstable coupled mode are more consistent with the observation than those from the previous model. Although either TEDF or diabatic heating alone can lead to unstable air-sea interaction, the former is dominant to the instability. TEDF in both higher and lower layers can cause unstable coupled mode individually, while the lower-layer forcing stimulates instability more effectively. Surface diabatic heating always destabilizes the coupled mode, while the mid-level heating always decays the coupled mode. Moreover, the influences of oceanic adjustment processes, air-sea coupling strength and background zonal wind on the unstable coupled mode are also discussed. The results of this study further prove the TEDF-driven positive feedback mechanism in midlatitude air-sea interaction proposed by recent observational and numerical experiment studies.

scholarly journals Roles of vertical distributions of atmospheric transient eddy dynamical forcing and diabatic heating in midlatitude unstable air–sea interaction

2021 ◽  
Author(s):  
Jiabei Fang ◽  
Lilan Chen ◽  
Xiu-Qun Yang
Keyword(s):  
Positive Feedback ◽  
Diabatic Heating ◽  
Lower Layer ◽  
Theoretical Work ◽  
Atmospheric Model ◽  
Feedback Mechanism ◽  
Transient Eddy ◽  
Coupled Mode ◽  
Vertical Distributions ◽  
Positive Feedback Mechanism

AbstractAtmospheric transient eddy dynamical forcing (TEDF)-driven midlatitude unstable air–sea interaction has recently been recognized as a crucial positive feedback for the maintenance of the extratropical decadal variabilities. Our recent theoretical work (Chen et al., Clim Dyn 10.1007/s00382-020-05405-0, 2020) has characterized such an interaction through building an analytical midlatitude barotropic atmospheric model coupled to a simplified upper oceanic model. This study extends the analytical model to including a two-layer quasi-geostrophic baroclinic atmospheric model and then identifies the roles of vertical distributions of atmospheric TEDF and diabatic heating in midlatitude unstable air–sea interaction. It is found that midlatitude air–sea coupling with more realistic vertical profiles of atmospheric TEDF and diabatic heating destabilizes oceanic Rossby wave modes over the entire range of zonal wavelengths, in which the most unstable coupled mode features an equivalent barotropic atmospheric low (high) pressure over a cold (warm) oceanic surface. Spatial structure and period of the most unstable mode are more consistent with the observation than those from in previous model. Although either TEDF or diabatic heating alone can lead to a destabilized coupled mode, the former makes a dominant contribution to the instability. The increase of low-layer TEDF stimulates the instability more effectively if the TEDF in upper layer is larger than in lower layer, while the TEDF in either high or low layers can individually cause the instability. The surface heating always destabilizes the air–sea interaction, while the mid-level heating always decays the coupled mode. The results of this study further confirm the TEDF-driven positive feedback mechanism in midlatitude air–sea interaction proposed by recent observational and numerical experiment studies.

scholarly journals The co-influence of the sea breeze and the coastal upwelling at Cabo Frio: a numerical investigation using coupled models

2011 ◽  
Vol 59 (2) ◽  
pp. 131-144 ◽  
Author(s):  
Flávia Noronha Dutra Ribeiro ◽  
Jacyra Soares ◽  
Amauri Pereira de Oliveira
Keyword(s):  
Positive Feedback ◽  
Coastal Upwelling ◽  
Coupled Model ◽  
Sea Breeze ◽  
Atmospheric Model ◽  
Breeze Circulation ◽  
Coupled Models ◽  
Initial Field ◽  
Oceanic Model ◽  
Cabo Frio

A coupled atmospheric-oceanic model was used to investigate whether there is a positive feedback between the coastal upwelling and the sea breeze at Cabo Frio - RJ (Brazil). Two experiments were performed to ascertain the influence of the sea breeze on the coastal upwelling: the first one used the coupled model forced with synoptic NE winds of 8 m s-1 and the sign of the sea breeze circulation was set by the atmospheric model; the second experiment used only the oceanic model with constant 8 m s-1 NE winds. Then, to study the influence of the coastal upwelling on the sea breeze, two more experiments were performed: one using a coastal upwelling representative SST initial field and the other one using a constant and homogeneous SST field of 26°C. Finally, two more experiments were conducted to verify the influence of the topography and the spatial distribution of the sea surface temperature on the previous results. The results showed that the sea breeze can intensify the coastal upwelling, but the coastal upwelling does not intensify the sea breeze circulation, suggesting that there is no positive feedback between these two phenomena at Cabo Frio.

scholarly journals Diabatic Damping of Zonal Index Variations

2014 ◽  
Vol 71 (8) ◽  
pp. 3090-3105 ◽  
Author(s):  
Xiaoming Xia ◽  
Edmund K. M. Chang
Keyword(s):  
Positive Feedback ◽  
Momentum Flux ◽  
Diabatic Heating ◽  
Mechanistic Model ◽  
Low Frequency ◽  
Dominant Mode ◽  
Precipitation Anomaly ◽  
Model Experiments ◽  
Zonal Index ◽  
The Impact

Abstract Zonal index variations, or north–south shifts of the midlatitude jet, are the dominant mode of zonal wind variability in the Southern Hemisphere. Previous studies have shown that synoptic-time-scale eddy momentum flux provides a positive feedback and acts to increase the persistence and low-frequency variance of the zonal index. However, the impact of diabatic heating due to the precipitation associated with these eddies has not been investigated. In this study, regression analyses have been conducted to demonstrate that a robust precipitation anomaly can be found to accompany the jet and eddy momentum flux anomalies associated with a poleward shift of the jet, with enhanced precipitation on the poleward flank of the jet and reduced precipitation on the equatorward flank. Diabatic heating associated with such a precipitation anomaly is expected to reduce the temperature gradient across the jet anomaly, thus decreasing eddy generation and damping the anomaly. This expectation is confirmed by three sets of mechanistic model experiments, using three different ways to mimic the impact of moist heating in a dry model. Results of this study suggest that diabatic heating provides a negative feedback to zonal index variations, partially offsetting the positive feedback provided by eddy momentum flux. These results could partially explain why zonal index variations have been found to be very persistent in dry mechanistic model experiments since this negative diabatic feedback is absent in dry models. These results suggest that these models may be overly sensitive to climate forcings that produce a jet shift response.

scholarly journals A diagnostic analysis of MONEX-1979 onset vortex over the Arabian Sea

MAUSAM ◽  
2022 ◽  
Vol 44 (4) ◽  
pp. 321-328
Author(s):  
KSHUDIRAM SAHA ◽  
R SURANJANA SAHA
Keyword(s):  
Arabian Sea ◽  
Diabatic Heating ◽  
Heat Budget ◽  
The Other ◽  
Diagnostic Analysis ◽  
Structure Development ◽  
Cyclonic Storm ◽  
Vertical Distributions ◽  
Differential Behaviour ◽  
Temperature Tendency

Based on MONEX-,1979 data over the Arabian Sea, the paper analyses observationally the structure, development and movement of a vortex which formed during onset of the monsoon around mid-June near the coast of Kerala developed into a cyclonic storm at mid-sea and moved towards the coast of Oman to die out there Heat budget computations bring out the differential behaviour of the different quadrants of the disturbance and appear to highlight the contrasting features between the northwestern and the other quadrants in regard to vertical. distributions of diabatic heating, local temperature tendency thermal advection and adiabatic heating or cooling. The study reveals an interaction of the vortex with two eastward-propagating subtropical westerly troughs which might have contributed significantly to its explosive development (decay) through warm (cold) advection. Both barotropic and baroclinic energy conversions appear to supply energy to the storm; though there appears to be a dominance of one over the other at different stages of development and at different heights. It seems likely that condensation heating also contributed to development of the storm.

scholarly journals Multiple equilibria and oscillatory modes in a mid-latitude ocean-forced atmospheric model

2012 ◽  
Vol 19 (5) ◽  
pp. 479-499 ◽  
Author(s):  
B. Deremble ◽  
E. Simonnet ◽  
M. Ghil
Keyword(s):  
Multiple Equilibria ◽  
Low Frequency ◽  
Atmospheric Model ◽  
Sea Surface ◽  
Hopf Bifurcations ◽  
Barotropic Instability ◽  
Atmospheric Variability ◽  
Oceanic Forcing ◽  
Sst Fronts ◽  
Oceanic Model

Abstract. Atmospheric response to a mid-latitude sea surface temperature (SST) front is studied, while emphasizing low-frequency modes induced by the presence of such a front. An idealized atmospheric quasi-geostrophic (QG) model is forced by the SST field of an idealized oceanic QG model. First, the equilibria of the oceanic model and the associated SST fronts are computed. Next, these equilibria are used to force the atmospheric model and compute its equilibria when varying the strength of the oceanic forcing. Low-frequency modes of atmospheric variability are identified and associated with successive Hopf bifurcations. The origin of these Hopf bifurcations is studied in detail, and connected to barotropic instability. Finally, a link is established between the model's time integrations and the previously obtained equilibria.

scholarly journals Coupling of a regional atmospheric model (RegCM3) and a regional oceanic model (FVCOM) over the maritime continent

2013 ◽  
Vol 43 (5-6) ◽  
pp. 1575-1594 ◽  
Author(s):  
Jun Wei ◽  
Paola Malanotte-Rizzoli ◽  
Elfatih A. B. Eltahir ◽  
Pengfei Xue ◽  
Danya Xu
Keyword(s):  
Atmospheric Model ◽  
Maritime Continent ◽  
Regional Atmospheric Model ◽  
Oceanic Model

scholarly journals Indian Ocean Variability and Its Association with ENSO in a Global Coupled Model

2005 ◽  
Vol 18 (17) ◽  
pp. 3634-3649 ◽  
Author(s):  
Aihong Zhong ◽  
Harry H. Hendon ◽  
Oscar Alves
Keyword(s):  
Indian Ocean ◽  
Positive Feedback ◽  
El Niño ◽  
El Nino ◽  
Equatorial Indian Ocean ◽  
Boreal Summer ◽  
Enso Events ◽  
Coupled Mode ◽  
Eastern Equatorial Indian Ocean ◽  
The Indian Ocean

Abstract The evolution of the Indian Ocean during El Niño–Southern Oscillation is investigated in a 100-yr integration of an Australian Bureau of Meteorology coupled seasonal forecast model. During El Niño, easterly anomalies are induced across the eastern equatorial Indian Ocean. These act to suppress the equatorial thermocline to the west and elevate it to the east and initially cool (warm) the sea surface temperature (SST) in the east (west). Subsequently, the entire Indian Ocean basin warms, mainly in response to the reduced latent heat flux and enhanced shortwave radiation that is associated with suppressed rainfall. This evolution can be partially explained by the excitation of an intrinsic coupled mode that involves a feedback between anomalous equatorial easterlies and zonal gradients in SST and rainfall. This positive feedback develops in the boreal summer and autumn seasons when the mean thermocline is shallow in the eastern equatorial Indian Ocean in response to trade southeasterlies. This positive feedback diminishes once the climatological surface winds become westerly at the onset of the Australian summer monsoon. ENSO is the leading mechanism that excites this coupled mode, but not all ENSO events are efficient at exciting it. During the typical El Niño (La Niña) event, easterly (westerly) anomalies are not induced until after boreal autumn, which is too late in the annual cycle to instigate strong dynamical coupling. Only those ENSO events that develop early (i.e., before boreal summer) instigate a strong coupled response in the Indian Ocean. The coupled mode can also be initiated in early boreal summer by an equatorward shift of the subtropical ridge in the southern Indian Ocean, which stems from uncoupled extratropical variability.

scholarly journals Multi-scale forcing and the formation of subtropical desert and monsoon

2009 ◽  
Vol 27 (9) ◽  
pp. 3631-3644 ◽  
Author(s):  
G. X. Wu ◽  
Y. Liu ◽  
X. Zhu ◽  
W. Li ◽  
R. Ren ◽  
...  
Keyword(s):  
Positive Feedback ◽  
Diabatic Heating ◽  
Radiative Cooling ◽  
Forced Circulation ◽  
Multi Scale ◽  
Continental Scale ◽  
Eurasian Continent ◽  
Vorticity Advection ◽  
Vorticity Generation ◽  
Heating Pattern

Abstract. This study investigates three types of atmospheric forcing across the summertime subtropics that are shown to contribute in various ways to the occurrence of dry and wet climates in the subtropics. To explain the formation of desert over the western parts of continents and monsoon over the eastern parts, we propose a new mechanism of positive feedback between diabatic heating and vorticity generation that occurs via meridional advection of planetary vorticity and temperature. Monsoon and desert are demonstrated to coexist as twin features of multi-scale forcing, as follows. First, continent-scale heating over land and cooling over ocean induce the ascent of air over the eastern parts of continents and western parts of oceans, and descent over eastern parts of oceans and western parts of continents. Second, local-scale sea-breeze forcing along coastal regions enhances air descent over eastern parts of oceans and ascent over eastern parts of continents. This leads to the formation of the well-defined summertime subtropical LOSECOD quadruplet-heating pattern across each continent and adjacent oceans, with long-wave radiative cooling (LO) over eastern parts of oceans, sensible heating (SE) over western parts of continents, condensation heating (CO) over eastern parts of continents, and double dominant heating (D: LO+CO) over western parts of oceans. Such a quadruplet heating pattern corresponds to a dry climate over the western parts of continents and a wet climate over eastern parts. Third, regional-scale orographic-uplift-heating generates poleward ascending flow to the east of orography and equatorward descending flow to the west. The Tibetan Plateau (TP) is located over the eastern Eurasian continent. The TP-forced circulation pattern is in phase with that produced by continental-scale forcing, and the strongest monsoon and largest deserts are formed over the Afro-Eurasian Continent. In contrast, the Rockies and the Andes are located over the western parts of their respective continents, and orography-induced ascent is separated from ascent due to continental-scale forcing. Accordingly, the deserts and monsoon climate over these continents are not as strongly developed as those over the Eurasian Continent. A new mechanism of positive feedback between diabatic heating and vorticity generation, which occurs via meridional transfer of heat and planetary vorticity, is proposed as a means of explaining the formation of subtropical desert and monsoon. Strong low-level longwave radiative cooling over eastern parts of oceans and strong surface sensible heating on western parts of continents generate negative vorticity that is balanced by positive planetary vorticity advection from high latitudes. The equatorward flow generated over eastern parts of oceans produces cold sea-surface temperature and stable stratification, leading in turn to the formation of low stratus clouds and the maintenance of strong in situ longwave radiative cooling. The equatorward flow over western parts of continents carries cold, dry air, thereby enhancing local sensible heating as well as moisture release from the underlying soil. These factors result in a dry desert climate. Over the eastern parts of continents, condensation heating generates positive vorticity in the lower troposphere, which is balanced by negative planetary vorticity advection of the meridional flow from low latitudes. The flow brings warm and moist air, thereby enhancing local convective instability and condensation heating associated with rainfall. These factors produce a wet monsoonal climate. Overall, our results demonstrate that subtropical desert and monsoon coexist as a consequence of multi-scale forcing along the subtropics.

scholarly journals The characteristics and structure of extra-tropical cyclones in a warmer climate

2020 ◽  
Vol 1 (1) ◽  
pp. 1-25 ◽  
Author(s):  
Victoria A. Sinclair ◽  
Mika Rantanen ◽  
Päivi Haapanala ◽  
Jouni Räisänen ◽  
Heikki Järvinen
Keyword(s):  
Tropical Cyclones ◽  
Diabatic Heating ◽  
Vertical Motion ◽  
Atmospheric Model ◽  
Sea Surface ◽  
Intermediate Step ◽  
Thermal Advection ◽  
Vorticity Advection ◽  
Omega Equation ◽  
Total Column

Abstract. Little is known about how the structure of extra-tropical cyclones will change in the future. In this study aqua-planet simulations are performed with a full-complexity atmospheric model. These experiments can be considered an intermediate step towards increasing knowledge of how, and why, extra-tropical cyclones respond to warming. A control simulation and a warm simulation in which the sea surface temperatures are increased uniformly by 4 K are run for 11 years. Extra-tropical cyclones are tracked, cyclone composites created, and the omega equation applied to assess causes of changes in vertical motion. Warming leads to a 3.3 % decrease in the number of extra-tropical cyclones, with no change to the median intensity or lifetime of extra-tropical cyclones but to a broadening of the intensity distribution resulting in both more stronger and more weaker storms. Composites of the strongest extra-tropical cyclones show that total column water vapour increases everywhere relative to the cyclone centre and that precipitation increases by up to 50 % with the 4 K warming. The spatial structure of the composite cyclone changes with warming: the 900–700 hPa layer averaged potential vorticity, 700 hPa ascent, and precipitation maximums associated with the warm front all move polewards and downstream, and the area of ascent expands in the downstream direction. Increases in ascent forced by diabatic heating and thermal advection are responsible for the displacement, whereas increases in ascent due to vorticity advection lead to the downstream expansion. Finally, maximum values of ascent due to vorticity advection and thermal advection weaken slightly with warming, whereas those attributed to diabatic heating increase. Thus, cyclones in warmer climates are more diabatically driven.

scholarly journals Transient Tropical Diabatic Heating and the Seasonal-Mean Response to ENSO

2015 ◽  
Vol 72 (5) ◽  
pp. 1891-1907 ◽  
Author(s):  
Erik T. Swenson ◽  
David M. Straus
Keyword(s):  
Diabatic Heating ◽  
Grid Point ◽  
Low Frequency ◽  
Setup Time ◽  
Atmospheric Model ◽  
Frequency Component ◽  
Meridional Wind ◽  
Ensemble Member ◽  
Boreal Winter ◽  
Time Step

Abstract Boreal winter simulations of the Community Atmospheric Model, version 4.0, were carried out using observed sea surface temperature (SST) fields from the three El Niño events of 1982/83, 1991/92, and 1997/98 [control (CTL) runs] and from observed climatology (CLIM run). In each case, 50 ensemble members were run (1 November–31 March). The diabatic heating Q at every grid point, level, and day of the CTL runs in the Indo-Pacific region was stored and used in four additional suites of experiments, each of which parallels the appropriate CTL suite. In each suite, Q generated by the model is replaced by a specified subset of Q at every time step, grid point, and level spanning the Indo-Pacific. The Q subsets consist of the seasonal ensemble-CTL-mean Q for each ensemble member (suite FIX), the seasonal-mean Q from the appropriate ensemble member of the CTL (suite EFIX), the seasonal mean plus low-frequency component of Q (suite ESUBFIX), and the daily means of Q (suite DAYFIX). The midlatitude ENSO anomalies of the seasonal-mean upper-level height field and time-filtered meridional wind variance are enhanced in the FIX, EFIX, and ESUBFIX suites, with little change in patterns, compared to CTL anomalies. The enhancements have a smaller magnitude in ESUBFIX and especially in DAYFIX; qualitative differences are seen in DAYFIX. These differences are due to (i) the required setup time for midlatitude response, (ii) the altered relationship between vertical structure and vertically integrated heating, and (iii) the lack of midlatitude interactive influence on tropical heating in the experiments.

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