scholarly journals Synoptic-Scale Controls of Persistent Low Temperature and Icy Weather over Southern China in January 2008

2009 ◽  
Vol 137 (11) ◽  
pp. 3978-3991 ◽  
Author(s):  
Wen Zhou ◽  
Johnny C. L. Chan ◽  
Wen Chen ◽  
Jian Ling ◽  
Joaquim G. Pinto ◽  
...  
Keyword(s):  
Large Scale ◽  
Southern China ◽  
Inversion Layer ◽  
Lower Troposphere ◽  
Western Pacific Subtropical High ◽  
Synoptic Scale ◽  
Blocking High ◽  
Moisture Advection ◽  
Main Factors ◽  
The Western Pacific

Abstract In January 2008, central and southern China experienced persistent low temperatures, freezing rain, and snow. The large-scale conditions associated with the occurrence and development of these snowstorms are examined in order to identify the key synoptic controls leading to this event. Three main factors are identified: 1) the persistent blocking high over Siberia, which remained quasi-stationary around 65°E for 3 weeks, led to advection of dry and cold Siberian air down to central and southern China; 2) a strong persistent southwesterly flow associated with the western Pacific subtropical high led to enhanced moisture advection from the Bay of Bengal into central and southern China; and 3) the deep inversion layer in the lower troposphere associated with the extended snow cover over most of central and southern China. The combination of these three factors is likely responsible for the unusual severity of the event, and hence a long return period.

scholarly journals Large-Scale Atmospheric and Oceanic Conditions for Extensive and Persistent Icing Events in China

2014 ◽  
Vol 53 (12) ◽  
pp. 2698-2709 ◽  
Author(s):  
Zunya Wang ◽  
Song Yang ◽  
Zongjian Ke ◽  
Xingwen Jiang
Keyword(s):  
Large Scale ◽  
Southern China ◽  
Dominant Role ◽  
Inversion Layer ◽  
La Niña ◽  
Northwestern Pacific ◽  
Cold Air ◽  
Blocking High ◽  
La Nina ◽  
Equal Chance

AbstractBased on the observational datasets of rime and glaze from 743 stations in China and the atmospheric circulation data from the NCEP–NCAR reanalysis during 1954–2009, large-scale atmospheric and oceanic conditions for extensive and persistent rime and glaze events were examined with a composite analysis. Results show that rime events mostly occur in northern China while glaze events are mainly observed in southern China. The icing events are accompanied by low temperature and high humidity but not necessarily by above-normal precipitation. The Asian low, blocking highs, strong moisture transport, and an inversion layer related to major abnormal circulation systems contribute to the occurrence and persistence of icing events in China. The Ural blocking high plays a major role in the glaze events, and the Okhotsk blocking high is closely related to the rime events. For glaze events, extratropical circulation anomalies and the southward outbreak of cold air play a dominant role. In contrast, the strong northward transport of warm and moist airflows plays a leading role and the blocking high and the southward outbreak of extratropical cold air take a supporting role for rime events. There is nearly an equal chance for occurrences of rime events under La Niña and El Niño backgrounds. However, glaze events more likely occur under the background of La Niña. Additionally, the sea surface temperatures from the tropical Indian Ocean to the tropical northwestern Pacific Ocean also contribute to the occurrence and maintenance of icing events in China.

scholarly journals The Role of Land–Sea Topography in Blocking Formation in a Block–Eddy Interaction Model

2006 ◽  
Vol 63 (11) ◽  
pp. 3056-3065 ◽  
Author(s):  
Dehai Luo ◽  
Zhe Chen
Keyword(s):  
Large Scale ◽  
Theoretical Study ◽  
Interaction Model ◽  
Synoptic Scale ◽  
Westerly Jet ◽  
Blocking High ◽  
Dipole Component ◽  
Large Scale Land ◽  
Northern And Southern Hemispheres

Abstract This paper is an extension of a theoretical study by Luo on the effect of large-scale land–sea contrast (LSC) topography on the formation of an eddy-driven blocking. It is found that the topography term can be included explicitly in the blocking evolution equation because of the inclusion of the higher-order wave–topography interaction. Although the blocking flow cannot be excited purely by the LSC topography, the LSC topography is found to be capable of enhancing the amplification of the dipole component in a blocking flow associated with upstream synoptic-scale eddies. In this case, a strong omega-type blocking high can be driven by the joint action of synoptic-scale eddies and LSC topography. This seems to provide an explanation of a difference in blocking intensity between the Northern and Southern Hemispheres. The most important finding of this paper is that in the presence of LSC topography the double jets that appear during the onset of an eddy-driven dipole block collapse into a strong single westerly jet that is within the south side of an omega-type blocking high, which is different from the result predicted by the theoretical model proposed in Luo’s previous work.

scholarly journals Observed Evolution of Northward-Propagating Intraseasonal Variation over the Western Pacific: A Case Study in Boreal Early Summer

2013 ◽  
Vol 141 (2) ◽  
pp. 690-706 ◽  
Author(s):  
Masaki Katsumata ◽  
Hiroyuki Yamada ◽  
Hisayuki Kubota ◽  
Qoosaku Moteki ◽  
Ryuichi Shirooka
Keyword(s):  
Boundary Layer ◽  
Large Scale ◽  
Lower Troposphere ◽  
Western Pacific ◽  
Boreal Summer ◽  
Intraseasonal Variation ◽  
Middle Troposphere ◽  
Inactive Period ◽  
The Western Pacific

Abstract This report describes the in situ observed evolution of the atmospheric profile during an event of the boreal summer intraseasonal variation (BSISV) in the tropical western Pacific Ocean. The convectively active region of the BSISV proceeded northward over the sounding and radar network. Over the array, the situation changed from a convectively inactive period to an active period. Inspection of the sounding data revealed the gradual moistening of the lower troposphere during the convectively inactive period. The sounding-derived heat and moisture budget analyses indicated that both the convective- and large-scale processes caused moistening of the lower and middle troposphere where the radar echo tops were observed most frequently. This study is the first to identify such a “preconditioning” process for the BSISV in the western Pacific using detailed in situ observational data. During the preconditioning, an increase in CAPE was observed, as in previous studies of the MJO. An increase of moisture in the boundary layer was responsible for the increase of CAPE. The large-scale horizontal convergence in the boundary layer may be a key factor to moisten the boundary layer through the convective-scale processes, as well as through the large-scale processes to moisten the lower and middle troposphere.

scholarly journals Methodology for determining multilayered temperature inversions

2015 ◽  
Vol 8 (5) ◽  
pp. 2051-2060 ◽  
Author(s):  
G. J. Fochesatto
Keyword(s):  
Temperature Profile ◽  
Large Scale ◽  
Error Function ◽  
Inversion Layer ◽  
Lower Troposphere ◽  
Temperature Inversion ◽  
Linear Interpolation ◽  
Pollution Dispersion ◽  
Thermal Inversion ◽  
Temperature Inversions

Abstract. Temperature sounding of the atmospheric boundary layer (ABL) and lower troposphere exhibits multilayered temperature inversions specially in high latitudes during extreme winters. These temperature inversion layers are originated based on the combined forcing of local- and large-scale synoptic meteorology. At the local scale, the thermal inversion layer forms near the surface and plays a central role in controlling the surface radiative cooling and air pollution dispersion; however, depending upon the large-scale synoptic meteorological forcing, an upper level thermal inversion can also exist topping the local ABL. In this article a numerical methodology is reported to determine thermal inversion layers present in a given temperature profile and deduce some of their thermodynamic properties. The algorithm extracts from the temperature profile the most important temperature variations defining thermal inversion layers. This is accomplished by a linear interpolation function of variable length that minimizes an error function. The algorithm functionality is demonstrated on actual radiosonde profiles to deduce the multilayered temperature inversion structure with an error fraction set independently.

Diurnal Variations of Low-Level Winds and Precipitation Response to Large-Scale Circulations during a Heavy Rainfall Event

2019 ◽  
Vol 147 (11) ◽  
pp. 3981-4004 ◽  
Author(s):  
Wenxin Zeng ◽  
Guixing Chen ◽  
Yu Du ◽  
Zhiping Wen
Keyword(s):  
Heavy Rainfall ◽  
Large Scale ◽  
Southern China ◽  
Western Pacific Subtropical High ◽  
Central China ◽  
Subtropical High ◽  
Heavy Rainfall Event ◽  
Inertial Oscillation ◽  
Atmospheric Conditions ◽  
Low Level

Abstract A succession of MCSs developed during the last week of October 2016 and produced extreme heavy rainfall in central China. The event underwent an evident shift from a mei-yu-like warm scenario to an autumn cold scenario. Diurnal cycles of rainfall and low-level winds may be modulated by the shifting of large-scale atmospheric conditions. We conducted observational analyses and numerical experiments to examine how large-scale circulations influenced rainfall systems through diurnally varying processes. The results show that, in the first half (warm) period of the event, intense rainfall mostly occurred in eastern-central China with an early morning peak. It was closely related to a nocturnal southwesterly low-level jet (NLLJ) on the flank of the western Pacific subtropical high. The NLLJ formed near midnight in southern China where ageostrophic wind rotated clockwise due to Blackadar’s inertial oscillation. The NLLJ extended downstream to central China during the predawn hours due to the horizontal advection of momentum. Both the formation and extension of the NLLJ were supported by an enhanced subtropical high that provided relatively warm conditions with surface heating for boundary layer inertial oscillation and strong background southwesterly winds for momentum transport. The NLLJ induced MCSs at its northern terminus where the low-level ascent, moisture flux convergence, and convective instability were enhanced during the predawn hours. In the second half period with an intrusion of cold air, the diurnal amplitude of low-level winds became small under relatively cold and cloudy conditions. Moderate rainfall tended to occur in western-central China with a peak after midnight, most likely due to frontogenetic processes, upslope lifting, and nighttime cloud-top cooling.

scholarly journals Multiscale Interactions in an Idealized Walker Cell: Analysis with Isentropic Streamfunctions

2016 ◽  
Vol 73 (3) ◽  
pp. 1187-1203 ◽  
Author(s):  
Joanna Slawinska ◽  
Olivier Pauluis ◽  
Andrew J. Majda ◽  
Wojciech W. Grabowski
Keyword(s):  
Large Scale ◽  
Strong Dependence ◽  
Low Frequency ◽  
Lower Troposphere ◽  
Walker Circulation ◽  
Synoptic Scale ◽  
Overturning Circulation ◽  
Planetary Scale ◽  
Walker Cell ◽  
Convective Scale

Abstract A new approach for analyzing multiscale properties of the atmospheric flow is proposed in this study. For that, the recently introduced isentropic streamfunctions are employed here for scale decomposition with Haar wavelets. This method is applied subsequently to a cloud-resolving simulation of a planetary Walker cell characterized by pronounced multiscale flow. The resulting set of isentropic streamfunctions—obtained at the convective, meso-, synoptic, and planetary scales—capture many important features of the across-scale interactions within an idealized Walker circulation. The convective scale is associated with the shallow, congestus, and deep clouds, which jointly dominate the upward mass flux in the lower troposphere. The synoptic and planetary scales play important roles in extending mass transport to the upper troposphere, where the corresponding streamfunctions mainly capture the first baroclinic mode associated with large-scale overturning circulation. The intermediate-scale features of the flow, such as anvil clouds associated with organized convective systems, are extracted with the mesoscale and synoptic-scale isentropic streamfunctions. Multiscale isentropic streamfunctions are also used to extract salient mechanisms that underlie the low-frequency variability of the Walker cell. In particular, the lag of a few days of the planetary scale behind the convective scale indicates the importance of the convective scale in moistening the atmosphere and strengthening the planetary-scale overturning circulation. Furthermore, the mesoscale and synoptic scale lags behind the planetary scale reflect the strong dependence of convective organization on the background shear.

scholarly journals Sensitivity of Tropical Cyclone Track Simulation over the Western North Pacific to Different Heating/Drying Rates in the Betts–Miller–Janjić Scheme

2015 ◽  
Vol 143 (9) ◽  
pp. 3478-3494 ◽  
Author(s):  
Yuan Sun ◽  
Zhong Zhong ◽  
Hong Dong ◽  
Jian Shi ◽  
Yijia Hu
Keyword(s):  
Tropical Cyclone ◽  
Large Scale ◽  
Lower Troposphere ◽  
Western Pacific Subtropical High ◽  
Cumulus Parameterization ◽  
Weather Research And Forecasting ◽  
Upper Troposphere ◽  
Steering Flow ◽  
Correct Representation ◽  
Drying Rates

Abstract The Weather Research and Forecasting Model is employed to examine the sensitivity of simulated tropical cyclone (TC) motion and associated intensity of the western Pacific subtropical high (WSPH) to different heating and drying rates in the Betts–Miller–Janjić (BMJ) cumulus parameterization (CP) scheme. A case study of Tropical Cyclone Megi (2010) is performed. Results indicate that the simulated WPSH strengthens as the heating/drying effects of the BMJ decrease. A strong WPSH subsequently leads to changes in the large-scale steering flow in its southern edge and delays the northward turning of the simulated storm. The associated physical mechanism is revealed. As the heating/drying is overestimated in the BMJ, the model produces unrealistic drying below 500 hPa whereas the atmosphere becomes moist above 500 hPa. Drying in the lower troposphere hinders the activation of the microphysics while moistening in the upper troposphere facilitates the microphysics. As a result, the model generates extensive anvil clouds that extend far away from the TC center and reach the upper troposphere over the WPSH. This leads to a warming in the upper troposphere due to condensation in the anvil clouds, and a cooling in the lower troposphere due to precipitation evaporation below the anvil clouds. Subsequently, the WPSH weakens and the large-scale steering flow becomes anomalously northward, leading to an early recurvature of TC Megi. Results of this study emphasize the importance of a correct representation of anvil clouds in simulating the WPSH and TC track. This study also implies that correcting the heating/drying can be an effective way to reduce errors in simulating the WPSH and TC motion.

Development of a Monsoon Depression and Its Interaction with the Large-Scale Background: A Case Study

2021 ◽  
Vol 149 (11) ◽  
pp. 3627-3646
Author(s):  
S. K. Mishra
Keyword(s):  
Large Scale ◽  
Baroclinic Instability ◽  
Lower Troposphere ◽  
Monsoon Depression ◽  
Necessary Condition ◽  
Synoptic Scale ◽  
Warm Core ◽  
Barotropic Energy Conversion ◽  
Cold Core

Abstract Structure and time evolution of the large-scale background and an embedded synoptic-scale monsoon depression and their interactions are studied. The depression formation is preceded by a cyclonic circulation around 400 hPa. The Fourier-based scale separation technique is used to isolate large (wavenumbers 0–8) and synoptic-scale (wavenumbers 12–60). The wavelength and depression center is determined objectively. The synoptic-scale depression has an average longitudinal wavelength of around 1900 km and a north–south size of 1100 km; it is most intense with a vorticity of 20.5 × 10 −5 s −1 at 900 hPa. The strongest cold core of −3.0°C below 850 hPa and the above warm core of around 2.0°C are evident. The depression is tilted southwestward in the midtroposphere with no significant vertical tilt in the lower troposphere. The mean maximum intensity and upward motion over the life cycle of depression are in close agreement with the composite values. A strong cyclonic shear zone is developed in the midtroposphere preceding the depression. The necessary condition for barotropic (baroclinic) instability is satisfied in the midtroposphere (boundary layer). Strong northward transport of momentum by the depression against the southward shear is found. The strong growth of the MD in the lower troposphere is due to downward transfer of excess energy gained in the midtroposphere from the barotropic energy conversion and east–west direct thermal circulation as the vertical energy flux. The baroclinic interaction contributes to the maintenance of the cold core in the lower troposphere. The diabatic heating rate is computed and its role in the genesis and growth of MD is investigated.

scholarly journals Tropical Cyclogenesis in the Western North Pacific as Revealed by the 2008–09 YOTC Data*

2013 ◽  
Vol 28 (4) ◽  
pp. 1038-1056 ◽  
Author(s):  
Yamei Xu ◽  
Tim Li ◽  
Melinda Peng
Keyword(s):  
Rossby Wave ◽  
Wave Energy ◽  
North Pacific ◽  
Western North Pacific ◽  
Large Scale ◽  
Lower Troposphere ◽  
Energy Dispersion ◽  
Reanalysis Dataset ◽  
Initial Development ◽  
Wave Trains

Abstract The Year of Tropical Convection (YOTC) high-resolution global reanalysis dataset was analyzed to reveal precursor synoptic-scale disturbances related to tropical cyclone (TC) genesis in the western North Pacific (WNP) during the 2008–09 typhoon seasons. A time filtering is applied to the data to isolate synoptic (3–10 day), quasi-biweekly (10–20 day), and intraseasonal (20–90 day) time-scale components. The results show that four types of precursor synoptic disturbances associated with TC genesis can be identified in the YOTC data. They are 1) Rossby wave trains associated with preexisting TC energy dispersion (TCED) (24%), 2) synoptic wave trains (SWTs) unrelated to TCED (32%), 3) easterly waves (EWs) (16%), and 4) a combination of either TCED-EW or SWT-EW (24%). The percentage of identifiable genesis events is higher than has been found in previous analyses. Most of the genesis events occurred when atmospheric quasi-biweekly and intraseasonal oscillations are in an active phase, suggesting a large-scale control of low-frequency oscillations on TC formation in the WNP. For genesis events associated with SWT and EW, maximum vorticity was confined in the lower troposphere. During the formation of Jangmi (2008), maximum Rossby wave energy dispersion appeared in the middle troposphere. This differs from other TCED cases in which energy dispersion is strongest at low level. As a result, the midlevel vortex from Rossby wave energy dispersion grew faster during the initial development stage of Jangmi.

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