Role of the Kuroshio Current on the Diurnal Variation of the Early-Summer Meiyu-Baiu Rainband

Diurnal Cycle Of Precipitation ◽

The Kuroshio ◽

Baiu Front

Abstract Mechanism of the strong diurnal cycle of precipitation over the Kuroshio Current (KC) during mid-June is investigated, when the climatological location of the Meiyu-Baiu front overlaps the KC. Heating from the KC intensifies in the morning when the temperature difference between the sea surface and the surface air (TDF) maximizes. The diurnal cycle of precipitation, on the other hand, peaks in the afternoon, consistent with previous studies. It is revealed that convective precipitation (CP) due to convective instability is in phase with TDF, whereas large-scale precipitation (LSP) caused by the cross-frontal circulation matures later. Intensified convective instability via enhanced heating from the KC in the morning hours (03–12 LST) increases the mean amount of CP as well as the probability of stronger CP. Surface wind convergence is also strengthened during the morning hours and helps sustain the convection. The diurnal cycle of LSP, which peaks in the afternoon hours (12–15 LST), covaries with the intensity of the Meiyu-Baiu front and the assocaited cross-frontal circulation. The wind convergence and deformation anomalies associated with the intensified thermal heating over the KC during the morning hours intensifies the frontogenesis function, which leads to the maximization of the frontal intensity in the afternoon. The direct contribution of diabatic heating to the frontogenesis is relatively weak.

Deep Atmospheric Response to the Spring Kuroshio over the East China Sea*

Journal of Climate ◽

10.1175/jcli-d-10-05034.1 ◽

2011 ◽

Vol 24 (18) ◽

pp. 4959-4972 ◽

Cited By ~ 68

Author(s):

Haiming Xu ◽

Mimi Xu ◽

Shang-Ping Xie ◽

Yuqing Wang

Keyword(s):

Wind Speed ◽

East China Sea ◽

Surface Wind ◽

East China ◽

Atmospheric Response ◽

The East China Sea ◽

Sst Front ◽

China Sea ◽

Abstract The atmospheric response to the spring Kuroshio Front over the East China Sea is investigated using a suite of high-resolution satellite data and a regional atmospheric model. The atmospheric response appears to extend beyond the marine atmospheric boundary layer, with frequent occurrence of cumulus convection. In spring, Quick Scatterometer (QuikSCAT) wind speed shows a clear effect of sea surface temperature (SST), with high (low) wind speed observed over the warm (cold) tongue. This in-phase relationship between SST and surface wind speed is indicative of SST influence on the atmosphere. Wind convergence is found on the warmer flank of the Kuroshio Front, accompanied by a narrow rainband. The analysis of satellite-borne radar measurements indicates that deep convection appears over the Kuroshio warm tongue in the spring season, with enhanced convective precipitation, frequent occurrence of cumulus convection, and increased precipitation (cloud) tops in altitude. These deep convective activities along the Kuroshio warm tongue are further supported by enhanced lightning flash rate observed by satellite and atmospheric heating estimated by a Japanese reanalysis. The Weather Research and Forecasting (WRF) model is used to investigate the precipitation response to the spring Kuroshio SST front over the East China Sea. Forced by observed SST [control (CTL)], the model well simulates a narrow band of precipitation, high wind speed, and surface wind convergence that closely follows the Kuroshio warm current, consistent with satellite observations. This narrow rainband completely disappears in the model when the SST front is removed by horizontally smoothed SST (SmSST). The results show that it is convective precipitation that is sensitive to the Kuroshio SST front. A case study for an eastward-moving extratropical cyclone indicates that convective precipitation increases its intensity and duration in the CTL run compared to the SmSST run. Local enhancement of upward sensible and latent heat fluxes and convective instability in the lower atmosphere are the key to anchoring the narrow band of convective precipitation that closely follows the Kuroshio.

Processes Shaping the Frontal-Scale Time-Mean Surface Wind Convergence Patterns around the Kuroshio Extension in Winter

Journal of Climate ◽

10.1175/jcli-d-19-0097.1 ◽

2020 ◽

Vol 33 (1) ◽

pp. 3-25

Author(s):

Ryusuke Masunaga ◽

Hisashi Nakamura ◽

Bunmei Taguchi ◽

Takafumi Miyasaka

Keyword(s):

Kuroshio Extension ◽

Surface Wind ◽

Western Boundary ◽

Boundary Currents ◽

Sst Front ◽

Atmospheric Structure ◽

Mean Convergence ◽

Daily Scale ◽

AbstractHigh-resolution satellite observations and numerical simulations have revealed that climatological-mean surface wind convergence and precipitation are enhanced locally around the midlatitude warm western boundary currents (WBCs) with divergence slightly to their poleward side. While steep sea surface temperature (SST) fronts along the WBCs have been believed to play an important role in shaping those frontal-scale atmospheric structures, the mechanisms and processes involved are still under debate. The present study explores specific daily scale atmospheric processes that are essential for shaping the frontal-scale atmospheric structure around the Kuroshio Extension (KE) in winter, taking advantage of a new product of global atmospheric reanalysis. Cluster analysis and case studies reveal that a zonally extending narrow band of surface wind convergence frequently emerges along the KE, which is typically observed under the surface northerlies after the passage of a developed synoptic-scale cyclone. Unlike its counterpart around the cyclone center and associated cold front, the surface convergence tends to be in moderate strength and more persistent, contributing dominantly to the distinct time-mean convergence/divergence contrast across the SST front. Accompanying ascent and convective precipitation, the band of convergence is a manifestation of a weak stationary atmospheric front anchored along the SST front or generation of a weak meso-α-scale cyclone. By reinforcing the ascent and convergence, latent heating through convective processes induced by surface convergence plays an important role in shaping the frontal-scale atmospheric structure around the KE.

Simulation of the Diurnal Cycle in Tropical Rainfall and Circulation during Boreal Summer with a High-Resolution GCM

Monthly Weather Review ◽

10.1175/2010mwr3291.1 ◽

2010 ◽

Vol 138 (9) ◽

pp. 3434-3453 ◽

Cited By ~ 26

Author(s):

Jeffrey J. Ploshay ◽

Ngar-Cheung Lau

Keyword(s):

Diurnal Cycle ◽

General Circulation ◽

Large Scale ◽

Surface Wind ◽

Circulation Model ◽

Horizontal Resolution ◽

Boreal Summer ◽

Tropical Rainfall ◽

Early Afternoon ◽

Seaward Migration

Abstract The simulation of the diurnal cycle (DC) of precipitation and surface wind pattern by a general circulation model (GCM) with a uniform horizontal resolution of 50 km over the global domain is evaluated. The model output is compared with observational counterparts based on datasets provided by the Tropical Rainfall Measuring Mission and reanalysis products of the European Centre for Medium-Range Weather Forecasts. The summertime diurnal characteristics over tropical regions in Asia, the Americas, and Africa are portrayed using the amplitude and phase of the first harmonic of the 24-h cycle, departures of data fields during selected hours from the daily mean, and differences between extreme phases of the DC. There is general agreement between the model and observations with respect to the large-scale land–sea contrasts in the DC. Maximum land precipitation, onshore flows, and landward migration of rainfall signals from the coasts occur in the afternoon, whereas peak maritime rainfall and offshore flows prevail in the morning. Seaward migration of precipitation is discernible over the western Bay of Bengal and South China Sea during nocturnal and morning hours. The evolution from low-intensity rainfall in the morning/early afternoon to heavier precipitation several hours later is also evident over selected continental sites. However, the observed incidence of rainfall with very high intensity in midafternoon is not reproduced in the model atmosphere. Although the model provides an adequate simulation of the daytime upslope and nighttime downslope winds in the vicinity of mountain ranges, valleys, and basins, there are notable discrepancies between model and observations in the DC of precipitation near some of these orographic features. The model does not reproduce the observed seaward migration of precipitation from the western coasts of Myanmar (Burma) and India, and from individual islands of the Indonesian Archipelago at nighttime.

Distribution of late-stage phyllosoma larvae of Panulirus japonicus in the Kuroshio Subgyre

Marine and Freshwater Research ◽

10.1071/mf01184 ◽

2001 ◽

Vol 52 (8) ◽

pp. 1201 ◽

Cited By ~ 12

Author(s):

Nariaki Inoue ◽

Hideo Sekiguchi

Keyword(s):

Late Stage ◽

Final Stage ◽

Kuroshio Current ◽

Early Summer ◽

Ryukyu Archipelago ◽

Larval Recruitment ◽

Panulirus Japonicus ◽

Japanese Waters ◽

Phyllosoma Larvae ◽

The present study was undertaken in waters south of the Kuroshio Subgyre to examine and/or test Sekiguchi’s (1985, 1997) hypothesis about the larval recruitment processes of Panulirus japonicus by which the benthic populations of the species are maintained in Japanese waters. A total of 61 Panulirus phyllosoma larvae were collected in early summer; 56 belonged to P. japonicus, of which 30 were in the final stage, 24 in the subfinal stage, and 2 were too heavily damaged to permit identification of the stage. Most of the final-stage phyllosoma larvae were found in the northern part of the waters east of the Ryukyu Archipelago, whereas the larvae in the subfinal stage were found in the southern part. The present study supports Sekiguchi’s hypothesis that late-stage P. japonicus phyllosoma larvae are transported by the Kuroshio Countercurrent into waters east of the archipelago and then again enter the Kuroshio Current.

Influence of the Kuroshio in the East China Sea on the Early Summer (Baiu) Rain

Journal of Climate ◽

10.1175/jcli-d-11-00727.1 ◽

2012 ◽

Vol 25 (19) ◽

pp. 6627-6645 ◽

Cited By ~ 55

Author(s):

Yoshi N. Sasaki ◽

S. Minobe ◽

T. Asai ◽

M. Inatsu

Keyword(s):

East China Sea ◽

Large Scale ◽

Atmospheric Model ◽

Early Summer ◽

Satellite Observations ◽

East China ◽

The East China Sea ◽

China Sea ◽

Regional Atmospheric Model ◽

Abstract Influence of the Kuroshio in the East China Sea on the baiu rainband is examined using satellite observations, a reanalysis dataset, and a regional atmospheric model from 2003 to 2008. Satellite observations and reanalysis data reveal that precipitation over the Kuroshio is the highest in early summer (June), when the baiu rainband covers the East China Sea. The high rainfall is collocated with the warm sea surface temperature (SST) tongue of the Kuroshio. This locally enhanced precipitation is embedded in the large-scale baiu rainband, so that the amplitude of precipitation over the Kuroshio is twice as large as that in its surrounding area. The Kuroshio is also accompanied by high surface wind speed, energetic evaporation, and wind convergence. This wind convergence likely results from the SST influence on atmospheric pressure through not only temperature changes, but also humidity changes. Furthermore, the Kuroshio anchors the ascent motion and large diabatic heating with a peak in the midtroposphere, suggesting that the influence of the Kuroshio extends to the upper troposphere. It is also found that the East China Sea in June is the region of the strongest deep atmospheric response to western boundary currents along with the Gulf Stream region in summer. The observational results are well reproduced by the regional atmospheric model. The model indicates that when the SST tongue of the Kuroshio is smoothed, the enhanced precipitation, the energetic evaporation, and the wind convergence over the Kuroshio disappear, although the large-scale structure of the baiu rainband is not essentially changed.

Precipitation Characteristics over East Asia in Early Summer: Effects of the Subtropical Jet and Lower-Tropospheric Convective Instability

Journal of Climate ◽

10.1175/jcli-d-16-0724.1 ◽

2017 ◽

Vol 30 (20) ◽

pp. 8127-8147 ◽

Cited By ~ 10

Author(s):

Chie Yokoyama ◽

Yukari N. Takayabu ◽

Takeshi Horinouchi

Keyword(s):

East Asia ◽

Convective Instability ◽

Large Scale ◽

Early Summer ◽

Shallow Convection ◽

The South ◽

Subtropical Jet ◽

High Dependency ◽

Precipitation Characteristics ◽

Stratiform Precipitation

Abstract A quasi-stationary front, called the baiu front, often appears during the early-summer rainy season in East Asia (baiu in Japan). The present study examines how precipitation characteristics during the baiu season are determined by the large-scale environment, using satellite observation three-dimensional precipitation data. Emphasis is placed on the effect of subtropical jet (STJ) and lower-tropospheric convective instability (LCI). A rainband appears together with a deep moisture convergence to the south of the STJ. Two types of mesoscale rainfall events (REs; contiguous rainfall areas), which are grouped by the stratiform precipitation ratio (SPR; stratiform precipitation over total precipitation), are identified: moderately stratiform REs (SPR of 0%–80%) representing tropical organized precipitation systems and highly stratiform REs (SPR of 80%–100%) representing midlatitude precipitation systems associated with extratropical cyclones. As the STJ becomes strong, rainfall from both types of mesoscale precipitation systems increases, with a distinct eastward extension of a midtropospheric moist region. In contrast, small systems appear regardless of the STJ, with high dependency on the LCI. The results indicate that the STJ plays a role in moistening the midtroposphere owing to ascent associated with secondary circulation to the south of the STJ, producing environments favorable for organized precipitation systems in the southern part of the rainband. The horizontal moisture flux convergence may also contribute to precipitation just along the STJ. On the other hand, the LCI plays a role in generating shallow convection. In high-LCI conditions, deep convection can occur without the aid of mesoscale organization.

Influence of Subseasonal Variability on the Diurnal Cycle of Precipitation on a Mountainous Island: The Case of New Caledonia

Monthly Weather Review ◽

10.1175/mwr-d-19-0177.1 ◽

2019 ◽

Vol 148 (1) ◽

pp. 333-351 ◽

Cited By ~ 2

Author(s):

Damien Specq ◽

Gilles Bellon ◽

Alexandre Peltier ◽

Jérôme Lefèvre ◽

Christophe Menkes

Keyword(s):

Diurnal Cycle ◽

Large Scale ◽

New Caledonia ◽

Austral Summer ◽

Mountain Range ◽

Wet Season ◽

Diurnal Variability ◽

Synoptic Wind ◽

Diurnal Cycle Of Precipitation ◽

Wind Regimes

Abstract The relationship between the large-scale intraseasonal variability, synoptic wind regimes, and the local daily variability of precipitation over the main island of New Caledonia (southwest tropical Pacific) is investigated with a focus on the austral summer wet season (November–April). The average diurnal cycle of precipitation over the island is characterized by a sharp afternoon maximum around 1600 local time, with significant differences between the windward east coast, the leeward west coast, and the mountain range. The afternoon peak is related to the afternoon sea-breeze circulation and to the diurnal cycle of convection over land. In general, its magnitude follows the same evolution as the daily mean. In agreement with past studies, a clear modulation of the Madden–Julian oscillation (MJO) on both the diurnal cycle of precipitation and the probability of occurrence of four robust wind regimes can be identified in the New Caledonia region during the wet season. From the evidence that there is a qualitative correspondence between the effects of both the MJO phases and the wind regimes on features in the diurnal cycle of precipitation, a simple model is proposed to inspect the MJO forcing mediated by wind regimes on the diurnal variability of rain. The complete decomposition of the MJO impact shows that the modulation of diurnal cycle by the MJO relies on complex interactions between the MJO and synoptic winds that involve both large-scale MJO convective anomalies and MJO-induced modification of wind patterns.

Changes of Early Summer Precipitation in the Korean Peninsula and Nearby Regions Based on RCP Simulations

Journal of Climate ◽

10.1175/jcli-d-14-00504.1 ◽

2015 ◽

Vol 28 (9) ◽

pp. 3557-3578 ◽

Cited By ~ 22

Author(s):

Ja-Young Hong ◽

Joong-Bae Ahn

Keyword(s):

Korean Peninsula ◽

Large Scale ◽

Climate Model ◽

Circulation Model ◽

Regional Model ◽

Horizontal Resolution ◽

Early Summer ◽

Lower Atmosphere ◽

Global Circulation Model

Abstract In this study, the projected regional precipitation changes over northeast Asia (NEA) during early summer [May–July (MJJ)] for the late twenty-first century (2071–2100) were investigated using a high-resolution regional climate model (WRF3.4) based on the representative concentration pathways (RCPs) induced by the global circulation model (HadGEM2-AO). The increased horizontal resolution of the regional model with a 12.5-km horizontal resolution enabled it to reproduce the terrain-following features reasonably well compared to low-resolution reanalysis and HadGEM2-AO model data. The results of a regionally downscaled historical (1981–2010) experiment (D_Historical) demonstrated the model’s ability to capture the spatial and temporal variations of rainband migrating meridionally during MJJ over NEA. According to the regional model projection, intensive precipitation will increase and the rainband will affect the Korean Peninsula approximately 10 days earlier than in the D_Historical cases in both RCP4.5 and RCP8.5 (2071–2100). The precipitation will also increase in most of the domain, particularly in the southern Korean Peninsula and Kyushu, Japan. These increases in precipitation are attributed to increases in the northward moist transport coming from the lower latitudes and moist static instability in the lower atmosphere. According to this study, the convective precipitation contributes mainly to the increase in total precipitation. On the other hand, the large-scale nonconvective precipitation related to the stationary front will not change significantly but even tends to decrease approximately from the middle of July. The extreme precipitation intensity is also projected to increase by at least 22% (38%) in RCP4.5 (RCP8.5).

Physical processes controlling the diurnal cycle of convective storms in the Western Ghats

Scientific Reports ◽

10.1038/s41598-021-93173-0 ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

U. V. Murali Krishna ◽

Subrata Kumar Das ◽

Sachin M. Deshpande ◽

G. Pandithurai

Keyword(s):

Diurnal Variation ◽

Diurnal Cycle ◽

Western Ghats ◽

Large Scale ◽

Monsoon Season ◽

Surface Wind ◽

Bimodal Distribution ◽

Early Morning ◽

Coastal Areas ◽

Convective Storms

AbstractDiurnal variation of convective storms (CSs) during monsoon season and associated physical mechanisms are significantly important for accurate forecast of short-time and extreme precipitation. The diurnal cycle of CSs is investigated using ground-based X-band radar, Tropical Rainfall Measuring Mission Precipitation Radar, and reanalysis data during the summer monsoon (June–September of 2014) over complex mountain terrain of Western Ghats, India. Diurnally, CSs show a bimodal distribution in the coastal areas, but this bimodality became weak along the upslope regions and on the mountain top. The first occurrence mode of CSs is in the afternoon–evening hours, while the second peak is in the early-morning hours. The diurnal cycle’s intensity varies with location, such that it reaches maximum in the afternoon–evening hours and early morning on the mountain top and coastal areas, respectively. Two possible mechanisms are proposed for the observed diurnal variation in CSs (a) the radiative cooling effect and (b) the surface wind convergence induced by the interaction between land-sea breeze, local topography and large-scale monsoon winds. It is also observed that the CSs developed on the mountain top during afternoon–evening hours are deeper than those along the coast. The higher moisture in the lower- and mid-troposphere, higher instability and strong upward motion facilitate deeper CSs during afternoon–evening hours.

Diurnal Cycle of Summer Precipitation over Subtropical East Asia in CAM5

Journal of Climate ◽

10.1175/jcli-d-12-00119.1 ◽

2013 ◽

Vol 26 (10) ◽

pp. 3159-3172 ◽

Cited By ~ 36

Author(s):

Weihua Yuan ◽

Rucong Yu ◽

Minghua Zhang ◽

Wuyin Lin ◽

Jian Li ◽

...

Keyword(s):

East Asia ◽

Diurnal Cycle ◽

Large Scale ◽

Early Morning ◽

Total Rainfall ◽

Low Level ◽

Resolution Model ◽

Diurnal Rainfall ◽

Stratiform Rainfall

Abstract The simulations of summertime diurnal cycle of precipitation and low-level winds by the Community Atmosphere Model, version 5, are evaluated over subtropical East Asia. The evaluation reveals the physical cause of the observed diurnal rainfall variation in East Asia and points to the source of model strengths and weaknesses. Two model versions with horizontal resolutions of 2.8° and 0.5° are used. The models can reproduce the diurnal phase of large-scale winds over East Asia, with an enhanced low-level southwesterly in early morning. Correspondingly, models successfully simulated the diurnal variation of stratiform rainfall with a maximum in early morning. However, the simulated convective rainfall occurs at local noontime, earlier than observations and with larger amplitude (normalized by the daily mean). As a result, models simulated a weaker diurnal cycle in total rainfall over the western plain of China due to an out-of-phase cancellation between convective and stratiform rainfalls and a noontime maximum of total rainfall over the eastern plain of China. Over the East China Sea, models simulated the early-morning maximum of convective precipitation and, together with the correct phase of the stratiform rainfall, they captured the diurnal cycle of total precipitation. The superposition of the stratiform and convective rainfalls also explains the observed diurnal cycle in total rainfall in East Asia. Relative to the coarse-resolution model, the high-resolution model simulated slight improvement in diurnal rainfall amplitudes, due to the larger amplitude of stratiform rainfall. The two models, however, suffer from the same major biases in rainfall diurnal cycles due to the convection parameterization.