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 Carbon and hydrogen isotopic ratios of atmospheric methane in the upper troposphere over the Western Pacific

2012 ◽  
Vol 12 (4) ◽  
pp. 9035-9077 ◽  
Author(s):  
T. Umezawa ◽  
T. Machida ◽  
K. Ishijima ◽  
H. Matsueda ◽  
Y. Sawa ◽  
...  
Keyword(s):  
Atmospheric Chemistry ◽  
Isotopic Ratio ◽  
Lower Troposphere ◽  
Western Pacific ◽  
Boreal Summer ◽  
Additional Contribution ◽  
Mixing Ratio ◽  
Upper Troposphere ◽  
The Tropics ◽  
The Western Pacific

Abstract. We present the mixing ratio, δ13C and δD of atmospheric CH4 using commercial aircraft in the upper troposphere (UT) over the Western Pacific for the period December 2005–September 2010. The observed results were compared with those obtained using commercial container ships in the lower troposphere (LT) over the same region. In the Northern Hemisphere (NH), the UT CH4 mixing ratio shows high values in the boreal summer–autumn, when the LT CH4 mixing ratio reaches a seasonal minimum. From tagged tracer experiments made using an atmospheric chemistry transport model, we found that such high CH4 values are due to rapid transport of air masses influenced by CH4 sources in South Asia and East Asia. The observed isotopic ratio data suggest that CH4 sources in these areas have relatively low δ13C and δD signatures, implying biogenic sources. Latitudinal distributions of the annual average UT and LT CH4 mixing ratio intersect each other in the tropics; the mixing ratio value is lower in the UT than in the LT in the NH and the situation is reversed in the Southern Hemisphere (SH), due mainly to the NH air intrusion into the SH through the UT. Such intersection of the latitudinal distributions is observable in δD but not in δ13C, implying additional contribution of a reaction of CH4 with active chlorine in the marine boundary layer. δ13C and δD show low values in the NH and high values in the SH both in the UT and in the LT. We also observed an increase in the CH4 mixing ratio and decreases in δ13C and δD during 2007–2008 in the UT and LT over the Western Pacific, possibly due to enhanced biogenic emissions in the tropics and NH.

scholarly journals Interdecadal weakening of the cross-equatorial flows over the Maritime Continent during the boreal summer in the mid-1990s: drivers and physical processes

2021 ◽  
Author(s):  
Xiaoxuan Zhao ◽  
Buwen Dong ◽  
Riyu Lu
Keyword(s):  
Dominant Role ◽  
Lower Troposphere ◽  
Hadley Circulation ◽  
Western Pacific ◽  
Boreal Summer ◽  
Maritime Continent ◽  
Coupled Models ◽  
The Cross ◽  
The Western Pacific ◽  
Sst Anomalies

AbstractIn this study, the cross-equatorial flows (CEF) on both high and low level (HCEF/LCEF) troposphere over the Maritime Continent (MC) in boreal summer are found to have experienced an interdecadal weakening in the mid-1990s based on both JRA55 and NCEP reanalyses. The outputs of 8 coupled models in CMIP6 are used to investigate drivers and the corresponding mechanisms. Model results show that the role of external forcing is weak in the interdecadal weakening of CEF. By contrast, the observed interdecadal weakening of both HCEF and LCEF can be largely explained by internal variability associated with a negative phase of the interdecadal Pacific Oscillation (IPO). Associated with negative IPO are anomalous divergence (convergence), enhanced precipitation over MC and anomalous cyclonic (anticyclonic) circulations, reduced precipitation over western North Pacific (WNP) in the upper (lower) troposphere. Sensitivity experiments based on MetUM-GA6 further manifest that this IPO phase transition can lead to the interdecadal weakening of CEF, in which the central tropical Pacific (CTP) sea surface temperature (SST) anomalies play a dominant role. The cold SST anomalies in CTP lead to reduced local convection and trigger enhanced convection over MC through changes in the Walker circulation. The enhanced convection over MC leads to a change in local Hadley circulation over the western Pacific sector. This change is characterized by anomalous ascents over MC, southerlies in the upper troposphere, descents and reduced precipitation over WNP and northerlies in the lower troposphere, leading to the weakening of CEF. Meanwhile, positive SST anomalies over MC associated with negative IPO also make a contribution to the weakening of CEF by inducing a change in the Hadley circulation in the western Pacific sector through similar processes.

scholarly journals Tropical–Extratropical Interactions Associated with East Asian Cold Air Outbreaks. Part II: Intraseasonal Variation

2018 ◽  
Vol 31 (2) ◽  
pp. 473-490 ◽  
Author(s):  
Muhammad Rais Abdillah ◽  
Yuki Kanno ◽  
Toshiki Iwasaki
Keyword(s):  
Large Scale ◽  
East Asian ◽  
Atmospheric Model ◽  
Western Pacific ◽  
Maritime Continent ◽  
Intraseasonal Variation ◽  
Cold Air ◽  
Wave Trains ◽  
The Western Pacific ◽  
Cold Air Outbreaks

Intraseasonal variations of East Asian cold air outbreaks (CAOs) in relation to the tropical atmosphere during 34 winters (DJF) are investigated. This study is a continuation of Part I, which discussed the interannual variability of East Asian CAOs. Two types of quantitative East Asian CAOs, western and eastern CAOs, are examined. Their variations are identified by the zonal integration of equatorward flux of cold air mass (CAM) below 280 K at 45°N over 90°–135°E and 135°E–180°. A day-lagged regression analysis reveals that peaks of intraseasonal western and eastern CAO events are preconditioned by large-scale tropical convection anomalies resembling particular phases of the Madden–Julian oscillation (MJO). Western CAO events tend to occur when the convective phase of the MJO crosses over the Maritime Continent. In contrast, eastern CAO events are triggered by the MJO over the western Pacific. Observations of MJO-related atmospheric anomalies indicate the important roles of poleward Rossby wave trains in affecting extratropical East Asian CAOs. The barotropic Rossby waves develop negative geopotential height anomalies in midlatitude East Asia, which then induce a low-level equatorward cold airflow. Several experiments in an atmospheric model using prescribed MJO-like heating anomalies demonstrate that the Maritime Continent MJO and the western Pacific MJO clearly affect the equatorward CAM flux over the western and eastern CAO regions, respectively. Compared with the western CAO, the eastern CAO shows a more robust response to the MJO because of stronger wave activity during the western Pacific MJO.

scholarly journals Two case studies on the interaction of large-scale transport, mesoscale photochemistry, and boundary-layer processes on the lower tropospheric ozone dynamics in early spring

2001 ◽  
Vol 19 (4) ◽  
pp. 469-486 ◽  
Author(s):  
S. Brönnimann ◽  
F. C. Siegrist ◽  
W. Eugster ◽  
R. Cattin ◽  
C. Sidle ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Large Scale ◽  
Lower Troposphere ◽  
Early Spring ◽  
Atmospheric Composition ◽  
Late Winter ◽  
Chemical Production ◽  
Ozone Concentrations ◽  
Boundary Layer Ozone

Abstract. The vertical distribution of ozone in the lower troposphere over the Swiss Plateau is investigated in detail for two episodes in early spring (February 1998 and March 1999). Profile measurements of boundary-layer ozone performed during two field campaigns with a tethered balloon sounding system and a kite are investigated using regular aerological and ozone soundings from a nearby site, measurements from monitoring stations at various altitudes, backward trajectories, and synoptic analyses of meteorological fields. Additionally, the effect of in situ photochemistry was estimated for one of the episodes employing the Metphomod Eulerian photochemical model. Although the meteorological situations were completely different, both cases had elevated layers with high ozone concentrations, which is not untypical for late winter and early spring. In the February episode, the highest ozone concentrations of 55 to 60 ppb, which were found at around 1100 m asl, were partly advected from Southern France, but a considerable contribution of in situ photochemistry is also predicted by the model. Below that elevation, the local chemical sinks and surface deposition probably overcompensated chemical production, and the vertical ozone distribution was governed by boundary-layer dynamics. In the March episode, the results suggest that ozone-rich air parcels, probably of stratospheric or upper tropospheric origin, were advected aloft the boundary layer on the Swiss Plateau.Key words. Atmospheric composition and structure (pollution – urban and regional; troposphere – composition and  chemistry) – Meteorology and atmospheric dynamics (mesoscale meteorology)

scholarly journals Carbon and hydrogen isotopic ratios of atmospheric methane in the upper troposphere over the Western Pacific

2012 ◽  
Vol 12 (17) ◽  
pp. 8095-8113 ◽  
Author(s):  
T. Umezawa ◽  
T. Machida ◽  
K. Ishijima ◽  
H. Matsueda ◽  
Y. Sawa ◽  
...  
Keyword(s):  
Atmospheric Chemistry ◽  
Transport Model ◽  
Isotopic Ratio ◽  
Lower Troposphere ◽  
Western Pacific ◽  
Boreal Summer ◽  
Additional Contribution ◽  
Mixing Ratio ◽  
Upper Troposphere ◽  
The Western Pacific

Abstract. We present the mixing ratio, δ13C and δD of atmospheric CH4 using commercial aircraft in the upper troposphere (UT) over the Western Pacific for the period December 2005–September 2010. The observed results were compared with those obtained using commercial container ships in the lower troposphere (LT) over the same region. In the Northern Hemisphere (NH), the UT CH4 mixing ratio shows high values in the boreal summer–autumn, when the LT CH4 mixing ratio reaches a seasonal minimum. From tagged tracer experiments made using an atmospheric chemistry transport model, we found that such high CH4 values are due to rapid transport of air masses influenced by CH4 sources in South Asia and East Asia. The observed isotopic ratio data imply that these areas have CH4 sources with relatively low δ13C and δD signatures such as biogenic sources. Latitudinal distributions of the annual average UT and LT CH4 mixing ratio intersect each other in the tropics; the mixing ratio value is lower in the UT than in the LT in the NH and the situation is reversed in the Southern Hemisphere (SH), due mainly to the NH air intrusion into the SH through the UT. Such intersection of the latitudinal distributions is observable in δD but not in δ13C, implying an additional contribution from reaction of CH4 with active chlorine in the marine boundary layer. δ13C and δD show low values in the NH and high values in the SH both in the UT and in the LT. We also observed an increase in the CH4 mixing ratio and decreases in δ13C and δ

scholarly journals Contributions of ENSO and East Indian Ocean SSTA to the Interannual Variability of Northwest Pacific Tropical Cyclone Frequency*

2011 ◽  
Vol 24 (2) ◽  
pp. 509-521 ◽  
Author(s):  
Ruifen Zhan ◽  
Yuqing Wang ◽  
Xiaotu Lei
Keyword(s):  
Tropical Cyclone ◽  
Indian Ocean ◽  
Interannual Variability ◽  
Large Scale ◽  
Western Pacific ◽  
Boreal Summer ◽  
Northwest Pacific ◽  
East Indian ◽  
East Indian Ocean ◽  
The Western Pacific

Abstract This study attempts to understand contributions of ENSO and the boreal summer sea surface temperature anomaly (SSTA) in the East Indian Ocean (EIO) to the interannual variability of tropical cyclone (TC) frequency over the western North Pacific (WNP) and the involved physical mechanisms. The results show that both ENSO and EIO SSTA have a large control on the WNP TC genesis frequency, but their effects are significantly different. ENSO remarkably affects the east–west shift of the mean genesis location and accordingly contributes to the intense TC activity. The EIO SSTA affects the TC genesis in the entire genesis region over the WNP and largely determines the numbers of both the total and weak TCs. ENSO modulates the large-scale atmospheric circulation and barotropic energy conversion over the WNP, contributing to changes in both the TC genesis location and the frequency of intense TCs. The EIO SSTA significantly affects both the western Pacific summer monsoon and the equatorial Kelvin wave activity over the western Pacific, two major large-scale dynamical controls of TC genesis over the WNP. In general the warm (cold) EIO SSTA suppresses (promotes) the TC genesis over the WNP. Therefore, a better understanding of the combined contributions of ENSO and EIO SSTA could help improve the seasonal prediction of the WNP TC activity.

scholarly journals Surface fluxes of bromoform and dibromomethane over the tropical western Pacific inferred from airborne in situ measurements

2017 ◽  
Author(s):  
Liang Feng ◽  
Paul I. Palmer ◽  
Robyn Butler ◽  
Stephen J. Andrews ◽  
Elliot L. Atlas ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Atmospheric Chemistry ◽  
Marine Boundary Layer ◽  
Current Knowledge ◽  
A Priori ◽  
Surface Fluxes ◽  
Western Pacific ◽  
Study Region ◽  
The Western Pacific ◽  
Aircraft Data

Abstract. We infer surface fluxes of bromoform (CHBr3) and dibromoform (CH2Br2) from aircraft observations over the western Pacific using a tagged version of the GEOS-Chem global 3-D atmospheric chemistry model and a Maximum A Posteriori inverse model. The distribution of a priori ocean emissions of these gases are reasonably consistent with observed atmospheric mole fractions of CHBr3 (r = 0.62) and CH2Br2 (r = 0.38). These a priori emissions result in a positive model bias in CHBr3 peaking in the marine boundary layer, but capture observed values of CH2Br2 with no significant bias by virtue of its longer atmospheric lifetime. Using GEOS-Chem, we find that observed variations in atmospheric CHBr3 are determined equally by sources over the western Pacific and those outside the study region, but observed variations in CH2Br2 are determined mainly by sources outside the western Pacific. Numerical closed-loop experiments show that the spatial and temporal distribution of boundary layer aircraft data have the potential to substantially improve current knowledge of these fluxes, with improvements related to data density. Using the aircraft data, we estimate aggregated regional fluxes of 3.6 ± 0.3 × 108 g/month and 0.7 ± 0.1 × 108 g/month for CHBr3 and CH2Br2 over 130°–155° E and 0°–12° N, respectively, which represent reductions of 20–40 % and substantial spatial deviations from the a priori inventory. We find no evidence to support a robust linear relationship between CHBr3 and CH2Br2 oceanic emissions, as used by previous studies.

scholarly journals Vertical Structure and Energetics of the Western Pacific Teleconnection Pattern

2016 ◽  
Vol 29 (18) ◽  
pp. 6597-6616 ◽  
Author(s):  
Sho Tanaka ◽  
Kazuaki Nishii ◽  
Hisashi Nakamura
Keyword(s):  
Heat Flux ◽  
North Pacific ◽  
Thermal Gradient ◽  
Far East ◽  
Storm Track ◽  
Lower Troposphere ◽  
Western Pacific ◽  
Mean Flow ◽  
Eddy Heat Flux ◽  
The Western Pacific

Abstract The western Pacific (WP) pattern, characterized by north–south dipolar anomalies in pressure over the Far East and western North Pacific, is known as one of the dominant teleconnection patterns in the wintertime Northern Hemisphere. Composite analysis reveals that monthly height anomalies exhibit baroclinic structure with their phase lines tilting southwestward with height in the lower troposphere. The anomalies can thus yield not only a poleward heat flux across the climatological thermal gradient across the strong Pacific jet but also a westward heat flux across the climatological thermal gradient between the North Pacific and the cooler Asian continent. The resultant baroclinic conversion of available potential energy (APE) from the climatological-mean flow contributes most efficiently to the APE maintenance of the monthly WP pattern, acting against strong thermal damping effects by anomalous heat exchanges with the underlying ocean and anomalous precipitation in the subtropics and by the effect of anomalous eddy heat flux under modulated storm-track activity. Kinetic energy (KE) of the pattern is maintained through barotropic feedback forcing associated with modulated activity of transient eddies and the conversion from the climatological-mean westerlies, both of which act against frictional damping. The net feedback forcing by transient eddies is therefore not particularly efficient. The present study suggests that the WP pattern has a characteristic of a dynamical mode that can maintain itself through efficient energy conversion from the climatological-mean fields even without external forcing, including remote influence from the tropics.

scholarly journals Tropospheric ozone over Equatorial Africa: regional aspects from the MOZAIC data

2004 ◽  
Vol 4 (3) ◽  
pp. 3285-3332 ◽  
Author(s):  
B. Sauvage ◽  
V. Thouret ◽  
J.-P. Cammas ◽  
F. Gheusi ◽  
G. Athier ◽  
...  
Keyword(s):  
Biomass Burning ◽  
Tropospheric Ozone ◽  
Central Africa ◽  
Lower Troposphere ◽  
Boreal Summer ◽  
Boreal Winter ◽  
Vertical Profiles ◽  
Middle Troposphere ◽  
Ozone Distribution ◽  
Equatorial Africa

Abstract. We analyze MOZAIC ozone observations recorded over Equatorial Africa, from April 1997 to March 2003 to give the first ozone climatology of this region. The monthly mean vertical profiles have been systematically analyzed with monthly mean ECMWF data using a Lagrangian-model (LAGRANTO). We assess the roles played by the dynamical features of Equatorial Africa and the intense biomass burning sources within the region in defining the ozone distribution. The lower troposphere exhibits layers of enhanced ozone during the biomass burning season in each hemisphere (boreal winter in the northern tropics and boreal summer in the southern tropics). The monthly mean vertical profiles of ozone are clearly influenced by the local dynamical situation. Over the Gulf of Guinea during boreal winter, the ozone profile is characterized by systematically high ozone below 650 hPa. This is due to the high stability caused by the Harmattan winds in the lower troposphere and the blocking Saharan anticyclone in the middle troposphere that prevents any efficient vertical mixing. In contrast, Central African enhancements are not only found in the lower troposphere but throughout the troposphere. The boreal summer ozone maximum in the lower troposphere of Central Africa continues up to November in the middle troposphere due to the influx of air masses laden with biomass burning products from Brazil and Southern Africa. Despite its southern latitude, Central Africa during the boreal winter is also under the influence of the northern tropical fires. This phenomenon is known as the "ozone paradox". However, the tropospheric ozone columns calculated from the MOZAIC data give evidence that the Tropical Tropospheric Ozone Column (TTOC) maximum over Africa swings from West Africa in DJF to Central Africa in JJA. This contrasts with studies based on TOMS satellite data. A rough assessment of the regional ozone budget shows that the northern tropics fires in boreal winter might contribute up to 20% of the global photochemical ozone production. This study gives the first detailed picture of the ozone distribution over Equatorial Africa that should be used to validate both global models over this region and future satellite products.

scholarly journals Improved Physical Processes in a Regional Climate Model and Their Impact on the Simulated Summer Monsoon Circulations over East Asia

2008 ◽  
Vol 21 (5) ◽  
pp. 963-979 ◽  
Author(s):  
Yoo-Bin Yhang ◽  
Song-You Hong
Keyword(s):  
Boundary Layer ◽  
Summer Monsoon ◽  
Large Scale ◽  
Climate Model ◽  
Asian Summer Monsoon ◽  
Regional Climate ◽  
Analysis Data ◽  
Cumulus Parameterization ◽  
Intraseasonal Variation ◽  
Thermal Roughness Length

Abstract This paper documents the sensitivity of the modeled evolution of the East Asian summer monsoon (EASM) to physical parameterization using the National Centers for Environmental Prediction (NCEP) Regional Spectral Model (RSM). To this end, perfect boundary condition experiments driven by analysis data are designed for August 2003 to investigate the individual role of the surface processes, boundary layer, and convection parameterization on the simulated monsoon. Also, 10-yr June–August (JJA) simulations from 1996 to 2005 are performed to evaluate the overall impacts of these revisions on the simulated EASM climatology. The one-month simulation for August 2003 reveals that the experiment with a realistic distribution of land use conditions and vegetation and smaller thermal roughness length simulates higher temperature and geopotential height. On the other hand, in the experiment with an improved boundary layer scheme, the rainfall amount is slightly decreased due to reduced vertical mixing. The simulation with revised subgrid-scale processes in the cumulus parameterization scheme reproduces a rainband over the subtropics, which is weakly simulated by the default package. The overall large-scale distribution from the experiment, which includes all three revised physics processes, shows the same direction as that of the revised convection run in the middle and upper troposphere, but is improved further when other newly enhanced processes are combined. These improvements are also achieved in a 10-yr summer simulation. It is distinct that the revised physics package improves the large-scale patterns by strengthening the intensity of the North Pacific high and reducing the intensity of the lower-level jet, which are critical components in the EASM. The general patterns of the interannual and intraseasonal variation of precipitation are also improved, in particular, over land.

Sign in / Sign up

Export Citation Format

Share Document