scholarly journals Attribution of the seasonality of atmospheric heating changes over the western tropical Pacific with a focus on the spring season

2021 ◽  
Author(s):  
Shuheng Lin ◽  
Song Yang ◽  
Shan He ◽  
Zhenning Li ◽  
Jiaxin Chen ◽  
...  
Keyword(s):  
Diabatic Heating ◽  
Global Climate ◽  
Deep Convection ◽  
Tropical Indian Ocean ◽  
Reanalysis Data ◽  
The Other ◽  
Convective Heating ◽  
Easterly Wind ◽  
Boreal Spring ◽  
The Tropics

AbstractAtmospheric diabatic heating, a major driving force of atmospheric circulation over the tropics, is strongly confined to the tropical western North Pacific (TWNP) region, with the global warmest sea surface temperature (SST). The changes in diabatic heating over the TWNP, which exert great impacts on the global climate system, have recently exhibited a noticeable seasonal dependence with a remarkable increase in boreal spring. In this study, we applied observations, reanalysis data, and numerical experiments to investigate the causes of the seasonality in heating changes. Results show that in boreal spring convection is more sensitive to the TWNP SST, leading to a more significant enhancement of deep convection, although the increase in the SST is nearly the same as that in the other seasons. In the non-spring seasons, the enhanced convection due to increased local SST is suppressed by the anomalous anticyclonic wind shear over the TWNP, generated by the easterly wind anomalies induced by the tropical Indian Ocean (TIO) warming via the Kevin waves. However, the TIO warming does not show any suppressing effect in spring because it is much weaker than that in the other seasons and thus the warming itself cannot induce sufficient convective heating anomalies to excite the Kelvin waves.

scholarly journals An Episodic Weakening in the Boreal Spring SST–Precipitation Relationship in the Western Tropical Pacific since the Late 1990s

2019 ◽  
Vol 32 (13) ◽  
pp. 3837-3845 ◽  
Author(s):  
Hyun-Su Jo ◽  
Sang-Wook Yeh ◽  
Wenju Cai
Keyword(s):  
Solar Radiation ◽  
Surface Air Temperature ◽  
Tropical Pacific ◽  
Convective Heating ◽  
Easterly Wind ◽  
Atmospheric Teleconnection ◽  
Boreal Spring ◽  
Western Tropical Pacific ◽  
Sst Cooling ◽  
Incoming Solar Radiation

Abstract We found that a positive sea surface temperature (SST)–precipitation relationship in the western tropical Pacific (WTP) during boreal spring, in which higher SSTs are associated with higher precipitation, episodically weakens from the late 1990s to the early 2010s. During 1980–98, warm SSTs induce positive precipitation and low pressure in the WTP. The associated enhanced convection dampens the initial warm SSTs by reflecting incoming solar radiation. The reduced incoming solar radiation into the ocean leads to a SST cooling tendency. In contrast, the associated southwesterly wind anomalies reduce oceanic mixing by decreasing the mean wind, contributing to an SST warming tendency, though relatively small. Therefore, the cloud–radiation effect is a dominant process of the negative SST tendency. By contrast, during 1999–2014, although an SST cooling tendency is similarly induced by warm SST anomalies, the cooling tendency is enhanced by anomalous ocean advection, as a result of enhanced easterly wind anomalies in the southern part of the WTP. This results in a weakening of a positive relationship of the SST and precipitation during 1999–2014. As such, the associated anomalous convective heating in the WTP during 1999–2014 is weak, changing the atmospheric teleconnection patterns in the midlatitude and surface air temperature anomalies in western North America and northeastern Eurasia.

A Moist Static Energy Budget Analysis of Quasi-2-Day Waves Using Satellite and Reanalysis Data

2016 ◽  
Vol 73 (2) ◽  
pp. 743-759 ◽  
Author(s):  
Yukari Sumi ◽  
Hirohiko Masunaga
Keyword(s):  
Large Scale ◽  
Deep Convection ◽  
Reanalysis Data ◽  
Convective Heating ◽  
Moist Static Energy ◽  
Wave Dynamics ◽  
Vertical Advection ◽  
Budget Analysis ◽  
Static Energy ◽  
Thermodynamic Processes

Abstract A moist static energy (MSE) budget analysis is applied to quasi-2-day waves to examine the effects of thermodynamic processes on the wave propagation mechanism. The 2-day waves are defined as westward inertia–gravity (WIG) modes identified with filtered geostationary infrared measurements, and the thermodynamic parameters and MSE budget variables computed from reanalysis data are composited with respect to the WIG peaks. The composite horizontal and vertical MSE structures are overall as theoretically expected from WIG wave dynamics. A prominent horizontal MSE advection is found to exist, although the wave dynamics is mainly regulated by vertical advection. The vertical advection decreases MSE around the times of the convective peak, plausibly resulting from the first baroclinic mode associated with deep convection. Normalized gross moist stability (NGMS) is used to examine the thermodynamic processes involving the large-scale dynamics and convective heating. NGMS gradually decreases to zero before deep convection and reaches a maximum after the convection peak, where low (high) NGMS leads (lags) deep convection. The decrease in NGMS toward zero before the occurrence of active convection suggests an increasingly efficient conversion from convective heating to large-scale dynamics as the wave comes in, while the increase afterward signifies that this linkage swiftly dies out after the peak.

scholarly journals Structure and Origin of the Quasi-Biweekly Oscillation over the Tropical Indian Ocean in Boreal Spring

2010 ◽  
Vol 67 (6) ◽  
pp. 1965-1982 ◽  
Author(s):  
Min Wen ◽  
Tim Li ◽  
Renhe Zhang ◽  
Yanjun Qi
Keyword(s):  
Boundary Layer ◽  
Indian Ocean ◽  
Vertical Motion ◽  
Longwave Radiation ◽  
Tropical Indian Ocean ◽  
Momentum Equation ◽  
Reanalysis Data ◽  
Triggering Mechanism ◽  
Boreal Spring ◽  
Zonal Momentum

Abstract The structure and evolution features of the quasi-biweekly (10–20 day) oscillation (QBWO) in boreal spring over the tropical Indian Ocean (IO) are investigated using 27-yr daily outgoing longwave radiation (OLR) and the National Centers for Environment Prediction–National Center for Atmospheric Research (NCEP–NCAR) reanalysis data. It is found that a convective disturbance is initiated over the western IO and moves slowly eastward. After passing the central IO, it abruptly jumps into the eastern IO. Meanwhile, the preexisting suppressed convective anomaly in the eastern IO moves poleward in the form of double-cell Rossby gyres. The analysis of vertical circulation shows that a few days prior to the onset of local convection in the eastern equatorial IO an ascending motion appears in the boundary layer. Based on the diagnosis of the zonal momentum equation, a possible boundary layer–triggering mechanism over the eastern equatorial IO is proposed. The cause of the boundary layer convergence and vertical motion is attributed to the free-atmospheric divergence in association with the development of the barotropic wind. It is the downward transport of the background mean easterly momentum by perturbation vertical motion during the suppressed convective phase of the QBWO that leads to the generation of a barotropic easterly—the latter of which further causes the free-atmospheric divergence and, thus, the boundary layer convergence. The result suggests that the local process, rather than the eastward propagation of the disturbance from the western IO, is essential for the phase transition of the QBWO convection over the eastern equatorial IO.

Thermocline warming induced extreme Indian Ocean Dipole in 2019

2021 ◽  
Author(s):  
Yan Du ◽  
Yuhong Zhang ◽  
Lian-Yi Zhang ◽  
Tomoki Tozuka ◽  
Wenju Cai
Keyword(s):  
Indian Ocean ◽  
Indian Ocean Dipole ◽  
Rossby Waves ◽  
Deep Convection ◽  
Tropical Indian Ocean ◽  
Triggering Mechanism ◽  
Bjerknes Feedback ◽  
Easterly Wind ◽  
Positive Indian Ocean Dipole ◽  
The 1960S

<p>The 2019 positive Indian Ocean Dipole (IOD) was the strongest event since the 1960s which developed independently without coinciding El Niño. The dynamics is not fully understood. Here we show that in March-May, westward propagating oceanic Rossby waves, a remnant consequence of the weak 2018 Pacific warm condition, led to anomalous sea surface temperature warming in the southwest tropical Indian Ocean (TIO), inducing deep convection and anomalous easterly winds along the equator, which triggered the initial cooling in the east. In June-August, the easterly wind anomalies continued to evolve through ocean-atmosphere coupling involving Bjerknes feedback and equatorial nonlinear ocean advection, until its maturity in September-November. This study clarifies the contribution of oceanic Rossby waves in the south TIO in different dynamic settings and reveals a new triggering mechanism for extreme IOD events that will help to understand IOD diversity.</p>

scholarly journals Sensitivities of the MJO Forecasts on Configurations of Physics in the ECMWF Global Model

2020 ◽  
Author(s):  
Jun-Ichi Yano ◽  
Nils P. Wedi
Keyword(s):  
Diabatic Heating ◽  
Rossby Waves ◽  
Deep Convection ◽  
Global Model ◽  
Rapid Decay ◽  
Free Wave ◽  
Eddy Diffusivities ◽  
The Tropics

Abstract. Sensitivities of MJO forecasts to various different configurations of physics are examined with the ECMWF global model, IFS. A motivation behind this study is to explore a possibility of interpreting the MJO as a nonlinear free wave under active interactions with Rossby waves from and to higher latitudes. With this motivation in mind, various momentum dissipation terms as well as diabatic heating are selectively turned off over the tropics for the range of the latitudes 20° S–20° N, and it is examined how physical tendencies control the MJO dynamics. The former include eddy diffusivities as well as dissipations by both shallow and deep convection. The reduction of momentum dissipations tends to improve the MJO forecasts, but the effects are hardly additive, and their total removals rather lead to a rapid decay of the MJO, illustrating the complexity of interactions between the physics.

scholarly journals Transport pathways from the Asian monsoon anticyclone to the stratosphere

2015 ◽  
Vol 15 (18) ◽  
pp. 25981-26023 ◽  
Author(s):  
H. Garny ◽  
W. J. Randel
Keyword(s):  
Large Scale ◽  
Asian Monsoon ◽  
Deep Convection ◽  
Three Dimensional ◽  
Reanalysis Data ◽  
Vertical Transport ◽  
Heating Rates ◽  
Transport Pathways ◽  
Northern Summer ◽  
The Tropics

Abstract. Transport pathways of air originating in the upper tropospheric Asian monsoon anticyclone are investigated based on three-dimensional trajectories. The Asian monsoon anticyclone emerges in response to persistent deep convection over India and southeast Asia in northern summer, and this convection is associated with rapid transport from the surface to the upper troposphere, and possibly into the stratosphere. Here, we investigate the fate of air that originates within the upper tropospheric anticyclone from the outflow of deep convection, using trajectories driven by ERA-interim reanalysis data. Calculations include isentropic estimates, plus fully three-dimensional results based on kinematic and diabatic transport calculations. Isentropic calculations show that air parcels are typically confined within the anticyclone for 10–20 days, and spread over the tropical belt within a month of their initialization. However, only few parcels (3 % at 360 K, 8 % at 380 K) reach the extratropical stratosphere by isentropic mixing. When considering vertical transport we find that 31 % (48%) of the trajectories reach the stratosphere within 60 days when using vertical velocities or diabatic heating rates to calculate vertical transport, respectively. In both cases, most parcels that reach the stratosphere are transported upward within the anticyclone and enter the stratosphere in the tropics, typically 10–20 days after their initialization at 360 K. This suggests that trace gases, including pollutants, that are transported into the stratosphere via the Asian monsoon system are in a position to enter the tropical pipe and thus be transported into the deep stratosphere. Sensitivity calculations with respect to the initial altitude of the trajectories showed that air needs to be transported to levels of 360 K or above by deep convection to likely (≧50 %) reach the stratosphere through transport by the large-scale circulation.

scholarly journals Climatology of Borneo Vortices in the HadGEM3-GC31 General Circulation Model

2021 ◽  
pp. 1-61
Author(s):  
Ju Liang ◽  
Jennifer L. Catto ◽  
Matthew Hawcroft ◽  
Kevin I. Hodges ◽  
Mouleong Tan ◽  
...  
Keyword(s):  
General Circulation ◽  
Climate Model ◽  
Global Climate ◽  
Global Climate Model ◽  
Deep Convection ◽  
Circulation Model ◽  
Winter Precipitation ◽  
Reanalysis Data ◽  
Horizontal Resolution ◽  
Hadley Centre

AbstractBorneo Vortices (BVs) are intense precipitating winter storms that develop over the equatorial South China Sea and strongly affect the weather and climate over the western Maritime Continent due to their association with deep convection and heavy rainfall. In this study, the ability of the HadGEM3-GC31 (Hadley Centre Global Environment Model 3 - Global Coupled vn. 3.1) global climate model to simulate the climatology of BVs at different horizontal resolutions are examined using an objective feature tracking algorithm. The HadGEM3-GC31 at the N512 ( 25 km) horizontal resolution simulates BVs with well-represented characteristics, including their frequency, spatial distribution and their lower-tropospheric structures when compared with BVs identified in a climate reanalysis, whereas the BVs in the N96 (∼135 km) and N216 (∼65 km) simulations are much weaker and less frequent. Also, the N512 simulation better captures the contribution of BVs to the winter precipitation in Borneo and Malay Peninsula compared with precipitation from a reanalysis data and from observations, while the N96 and N216 simulations underestimate this contribution due to the overly weak low-level convergence of the simulated BVs. The N512 simulation also exhibits an improved ability to reproduce the modulation of BV activity by the occurrence of northeasterly cold surges and active phases of Madden-Julian Oscillation in the region, including increased BV track densities, intensities and lifetimes. A sufficiently high model resolution is thus found to be important to realistically simulate the present-climate precipitation extremes associated with BVs and to study their possible changes in a warmer climate.

scholarly journals Baroclinicity Influences on Storm Divergence and Stratiform Rain: Subtropical Upper-Level Disturbances

2009 ◽  
Vol 137 (4) ◽  
pp. 1338-1357 ◽  
Author(s):  
Larry J. Hopper ◽  
Courtney Schumacher
Keyword(s):  
Diabatic Heating ◽  
Doppler Radar ◽  
Mesoscale Model ◽  
Deep Convection ◽  
Separation Algorithm ◽  
Rain Area ◽  
Stratiform Rain ◽  
Wide Range ◽  
Upper Level ◽  
The Tropics

Abstract Divergence structures associated with the spectrum of precipitating systems in the subtropics and midlatitudes are not well documented. A mesoscale model is used to quantify the relative importance different baroclinic environments have on divergence profiles for storms primarily caused by upper-level disturbances in southeastern Texas, a subtropical region. The divergence profiles simulated for a subset of the modeled storms are consistent with those calculated from an S-band Doppler radar. Realistic convective and stratiform divergence signals are also generated when applying a two-dimensional convective–stratiform separation algorithm to reflectivities derived from the mesoscale model, although the model appears to underestimate stratiform rain area. Divergence profiles from the modeled precipitating systems vary in magnitude and structure across the wide range of baroclinicities common in southeastern Texas. Barotropic storms more characteristic of the tropics generate the most elevated divergence (and thus diabatic heating) structures with the largest magnitudes. In addition, stratiform rain regions in barotropic storms contain thicker, more elevated midlevel convergence signatures than more baroclinic storms. As the degree of baroclinicity increases, stratiform area fractions generally increase while the levels of nondivergence (LNDs) decrease. However, some weakly baroclinic storms contain stratiform area fractions and/or divergence profiles with magnitudes and LNDs that are similar to barotropic storms, despite having lower tropopause heights and less deep convection. Additional convection forms after the passage of barotropic and weakly baroclinic storms that contain elevated divergence signatures, circumstantially suggesting that heating at upper levels may cause diabatic feedbacks that help to drive regions of persistent convection in the subtropics.

scholarly journals Transport pathways from the Asian monsoon anticyclone to the stratosphere

2016 ◽  
Vol 16 (4) ◽  
pp. 2703-2718 ◽  
Author(s):  
Hella Garny ◽  
William J. Randel
Keyword(s):  
Large Scale ◽  
Asian Monsoon ◽  
Deep Convection ◽  
Three Dimensional ◽  
Reanalysis Data ◽  
Vertical Transport ◽  
Heating Rates ◽  
Transport Pathways ◽  
Northern Summer ◽  
The Tropics

Abstract. Transport pathways of air originating in the upper-tropospheric Asian monsoon anticyclone are investigated based on three-dimensional trajectories. The Asian monsoon anticyclone emerges in response to persistent deep convection over India and southeast Asia in northern summer, and this convection is associated with rapid transport from the surface to the upper troposphere and possibly into the stratosphere. Here, we investigate the fate of air that originates within the upper-tropospheric anticyclone from the outflow of deep convection, using trajectories driven by ERA-interim reanalysis data. Calculations include isentropic estimates, plus fully three-dimensional results based on kinematic and diabatic transport calculations. Isentropic calculations show that air parcels are typically confined within the anticyclone for 10–20 days and spread over the tropical belt within a month of their initialization. However, only few parcels (3 % at 360 K, 8 % at 380 K) reach the extratropical stratosphere by isentropic transport. When considering vertical transport we find that 31 %  or 48 % of the trajectories reach the stratosphere within 60 days when using vertical velocities or diabatic heating rates to calculate vertical transport, respectively. In both cases, most parcels that reach the stratosphere are transported upward within the anticyclone and enter the stratosphere in the tropics, typically 10–20 days after their initialization at 360 K. This suggests that trace gases, including pollutants, that are transported into the stratosphere via the Asian monsoon system are in a position to enter the tropical pipe and thus be transported into the deep stratosphere. Sensitivity calculations with respect to the initial altitude of the trajectories showed that air needs to be transported to levels of 360 K or above by deep convection to likely (≧ 50 %) reach the stratosphere through transport by the large-scale circulation.

scholarly journals Global climatology and trends in convective environments from ERA5 and rawinsonde data

2021 ◽  
Vol 4 (1) ◽  
Author(s):  
Mateusz Taszarek ◽  
John T. Allen ◽  
Mattia Marchio ◽  
Harold E. Brooks
Keyword(s):  
Large Scale ◽  
Climate Models ◽  
Global Climate ◽  
Convective Available Potential Energy ◽  
Global Climate Models ◽  
Convective Precipitation ◽  
The Past ◽  
The Tropics ◽  
Rawinsonde Data

AbstractGlobally, thunderstorms are responsible for a significant fraction of rainfall, and in the mid-latitudes often produce extreme weather, including large hail, tornadoes and damaging winds. Despite this importance, how the global frequency of thunderstorms and their accompanying hazards has changed over the past 4 decades remains unclear. Large-scale diagnostics applied to global climate models have suggested that the frequency of thunderstorms and their intensity is likely to increase in the future. Here, we show that according to ERA5 convective available potential energy (CAPE) and convective precipitation (CP) have decreased over the tropics and subtropics with simultaneous increases in 0–6 km wind shear (BS06). Conversely, rawinsonde observations paint a different picture across the mid-latitudes with increasing CAPE and significant decreases to BS06. Differing trends and disagreement between ERA5 and rawinsondes observed over some regions suggest that results should be interpreted with caution, especially for CAPE and CP across tropics where uncertainty is the highest and reliable long-term rawinsonde observations are missing.

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