Observations of Marine Atmospheric Boundary Layer Transitions across the Summer Kuroshio Extension*

2009 ◽  
Vol 22 (6) ◽  
pp. 1360-1374 ◽  
Author(s):  
Youichi Tanimoto ◽  
Shang-Ping Xie ◽  
Kohei Kai ◽  
Hideki Okajima ◽  
Hiroki Tokinaga ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Atmospheric Boundary Layer ◽  
Kuroshio Extension ◽  
Cloud Base ◽  
Northwest Pacific ◽  
Turbulent Heat ◽  
Marine Atmospheric Boundary Layer ◽  
Near Surface ◽  
Low Cloud ◽  
Baiu Front

Abstract The baiu and Kuroshio Extension (KE) fronts, both zonally oriented and nearly collocated east of Japan, are the dominant summertime features of the atmosphere and ocean, respectively, over the midlatitude northwest Pacific. An atmospheric sounding campaign was conducted on board the R/V Roger Revelle during the 2005 summer. Transects of soundings across the KE front are analyzed to study its effects on the atmosphere, along with continuous surface meteorological and ceilometer cloud-base observations. While the KE front remained nearly stationary during the cruise, the baiu front displayed large meridional displacements that changed wind direction across the KE front. The presence of sharp sea surface temperature (SST) gradients anchored by the KE enhanced the thermal and moisture advection, causing substantial changes in the marine atmospheric boundary layer (MABL) structure. When the baiu front was displaced north of the KE front, southwesterly winds advected warm, humid air from the subtropics over the cold water, producing a surface inversion favorable to fog formation. When the baiu front was to the south, on the other hand, northerly winds across the KE front destabilized the MABL, leading to the formation of a solid low-cloud deck beneath a strong capping inversion. The wind changes with the meridional displacement of the baiu front thus caused large variations in near-surface atmospheric stability and surface turbulent heat fluxes, with potential feedback on deep convection and fog/low-cloud formation around the front.

scholarly journals Separation of Climatological Imprints of the Kuroshio Extension and Oyashio Fronts on the Wintertime Atmospheric Boundary Layer: Their Sensitivity to SST Resolution Prescribed for Atmospheric Reanalysis

2015 ◽  
Vol 28 (5) ◽  
pp. 1764-1787 ◽  
Author(s):  
Ryusuke Masunaga ◽  
Hisashi Nakamura ◽  
Takafumi Miyasaka ◽  
Kazuaki Nishii ◽  
Youichi Tanimoto
Keyword(s):  
Boundary Layer ◽  
High Resolution ◽  
Atmospheric Boundary Layer ◽  
Kuroshio Extension ◽  
Heat Fluxes ◽  
Turbulent Heat ◽  
Near Surface ◽  
The Kuroshio ◽  
Baroclinic Zone ◽  
Sst Fronts

Abstract Mesoscale structures of the wintertime marine atmospheric boundary layer (MABL) as climatological imprints of oceanic fronts within the Kuroshio–Oyashio Extension (KOE) region east of Japan are investigated by taking advantage of high horizontal resolution of the ERA-Interim global atmospheric reanalysis data, for which the resolution of sea surface temperature (SST) data has been improved. These imprints, including locally enhanced sensible and latent heat fluxes and local maxima in cloudiness and precipitation in association with locally strengthened surface-wind convergence in the vicinities of SST fronts along the warm Kuroshio Extension and cool Oyashio to its north, are also identified in high-resolution satellite data. In addition to these mesoscale MABL features, meridionally confined near-surface baroclinic zones and zonally oriented sea level pressure (SLP) minima associated with the dual SST fronts are represented in ERA-Interim only in the period of high-resolution SST, but those imprints of the Oyashio front are missing in the low-resolution SST period. In the presence of the prevailing monsoonal northerlies, latitudinal displacements of the SLP trough, baroclinic zone, and the peak meridional gradient of the turbulent heat fluxes from each of the corresponding SST fronts are also found to be sensitive to the frontal width that depends on the SST resolution. The analysis herein suggests that the converging surface northerlies into the SLP minima can contribute positively to the formation of a surface baroclinic zone along the Kuroshio Extension, while a stronger baroclinic zone along the Oyashio front is maintained primarily through the pronounced cross-frontal contrast in sensible heat release from the ocean.

scholarly journals Inference of Marine Atmospheric Boundary Layer Moisture and Temperature Structure Using Airborne Lidar and Infrared Radiometer Data

1998 ◽  
Vol 37 (3) ◽  
pp. 308-324 ◽  
Author(s):  
Stephen P. Palm ◽  
Denise Hagan ◽  
Geary Schwemmer ◽  
S. H. Melfi
Keyword(s):  
Boundary Layer ◽  
Atmospheric Boundary Layer ◽  
Potential Temperature ◽  
Airborne Lidar ◽  
Temperature Structure ◽  
Marine Atmospheric Boundary Layer ◽  
Space Technology ◽  
Near Surface ◽  
Surface Moisture ◽  
Infrared Radiometer

Abstract A new technique for retrieving near-surface moisture and profiles of mixing ratio and potential temperature through the depth of the marine atmospheric boundary layer (MABL) using airborne lidar and multichannel infrared radiometer data is presented. Data gathered during an extended field campaign over the Atlantic Ocean in support of the Lidar In-space Technology Experiment are used to generate 16 moisture and temperature retrievals that are then compared with dropsonde measurements. The technique utilizes lidar-derived statistics on the height of cumulus clouds that frequently cap the MABL to estimate the lifting condensation level. Combining this information with radiometer-derived sea surface temperature measurements, an estimate of the near-surface moisture can be obtained to an accuracy of about 0.8 g kg−1. Lidar-derived statistics on convective plume height and coverage within the MABL are then used to infer the profiles of potential temperature and moisture with a vertical resolution of 20 m. The rms accuracy of derived MABL average moisture and potential temperature is better than 1 g kg−1 and 1°C, respectively. The method relies on the presence of a cumulus-capped MABL, and it was found that the conditions necessary for use of the technique occurred roughly 75% of the time. The synergy of simple aerosol backscatter lidar and infrared radiometer data also shows promise for the retrieval of MABL moisture and temperature from space.

scholarly journals Observed Variations of the Atmospheric Boundary Layer and Stratocumulus over a Warm Eddy in the Kuroshio Extension

2019 ◽  
Vol 147 (5) ◽  
pp. 1581-1591 ◽  
Author(s):  
Qian Wang ◽  
Su-Ping Zhang ◽  
Shang-Ping Xie ◽  
Joel R. Norris ◽  
Jian-Xiang Sun ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Heat Flux ◽  
Atmospheric Boundary Layer ◽  
Kuroshio Extension ◽  
Atmospheric Model ◽  
Low Pressure ◽  
Marine Atmospheric Boundary Layer ◽  
Warm Eddy ◽  
Lifting Condensation Level ◽  
The Kuroshio

Abstract A research vessel sailing across a warm eddy in the Kuroshio Extension on 13 April 2016 captured an abrupt development of stratocumulus under synoptic high pressure. Shipboard observations and results from regional atmospheric model simulations indicate that increased surface heat flux over the ocean eddy lowered surface pressure and thereby accelerated southeasterly winds. The southeasterly winds transported moisture toward the low pressure and enhanced the air–sea interface heat flux, which in turn deepened the low pressure and promoted low-level convergence and rising motion over the warm eddy. The lifting condensation level lowered and the top of the marine atmospheric boundary layer (MABL) rose, thereby aiding the development of the stratocumulus. Further experiments showed that 6°C sea surface temperature anomalies associated with the 400-km-diameter warm eddy accounted for 80% of the total ascending motion and 95% of total cloud water mixing ratio in the marine atmospheric boundary layer during the development of stratocumulus. The synthesis of in situ soundings and modeling contributes to understanding of the mechanism by which the MABL and marine stratocumulus respond to ocean eddies.

scholarly journals Continuous Daily Observation of the Marine Atmospheric Boundary Layer over the Kuroshio by a Helicopter Shuttle Service

2015 ◽  
Vol 32 (1) ◽  
pp. 3-21 ◽  
Author(s):  
Youichi Tanimoto ◽  
Kou Shimoyama ◽  
Shoichi Mori
Keyword(s):  
Boundary Layer ◽  
Atmospheric Boundary Layer ◽  
Dynamic Pressure ◽  
Japan Meteorological Agency ◽  
Observation System ◽  
Vertical Profiles ◽  
Marine Atmospheric Boundary Layer ◽  
Near Surface ◽  
Ocean Front ◽  
Observation Method

AbstractThis paper describes a new initiative in which in situ observations of the marine atmospheric boundary layer (MABL) are made by a helicopter shuttle connecting six islands south of Tokyo. This observation method aims to make frequent measurements of temperature and moisture in the MABL across an ocean front, where direct measurements of the MABL have been limited. An onboard observation system to meet flight regulations was developed. Observed temperature and moisture as a function of pressure at 1-s intervals provided vertical profiles up to the 900-hPa level above each of the islands, from 24 December 2010 to 6 April 2011, with the exception of an accidental power down in mid-February 2011. The observed values are validated by intercomparison with surface measurements from weather stations, atmospheric soundings, and mesoscale weather analysis provided by the Japan Meteorological Agency. Temperature and moisture values obtained using the system described here at the surface are significantly correlated with those from the weather station. The meridional changes revealed by the observed vertical profiles depict rich MABL structures, such as a cold-air intrusion and a strong near-surface inversion, that are not captured by the mesoscale weather analysis. However, this discrepancy is probably due to insufficient treatment in the mesoscale numerical model rather than observational errors. Additional intercomparisons indicate no influence from either artificial mixing by the helicopter rotor or by dynamic pressure caused by the fast-moving helicopter when obtaining the vertical profiles. Following these validations, the continuation of the initiative will allow for examining the influence of the ocean front on the overlying MABL on a synoptic time scale.

scholarly journals An overview of the diurnal cycle of the atmospheric boundary layer during the West African monsoon season: results from the 2016 observational campaign

2018 ◽  
Vol 18 (4) ◽  
pp. 2913-2928 ◽  
Author(s):  
Norbert Kalthoff ◽  
Fabienne Lohou ◽  
Barbara Brooks ◽  
Gbenga Jegede ◽  
Bianca Adler ◽  
...  
Keyword(s):  
Boundary Layer ◽  
West Africa ◽  
Atmospheric Boundary Layer ◽  
Radiation Budget ◽  
Cloud Base ◽  
Data Set ◽  
Near Surface ◽  
Low Level ◽  
Synoptic Conditions ◽  
Low Level Jet

Abstract. A ground-based field campaign was conducted in southern West Africa from mid-June to the end of July 2016 within the framework of the Dynamics–Aerosol–Chemistry–Cloud Interactions in West Africa (DACCIWA) project. It aimed to provide a high-quality comprehensive data set for process studies, in particular of interactions between low-level clouds (LLCs) and boundary-layer conditions. In this region missing observations are still a major issue. During the campaign, extensive remote sensing and in situ measurements were conducted at three supersites: Kumasi (Ghana), Savè (Benin) and Ile-Ife (Nigeria). Daily radiosoundings were performed at 06:00 UTC, and 15 intensive observation periods (IOPs) were performed during which additional radiosondes were launched, and remotely piloted aerial systems were operated. Extended stratiform LLCs form frequently in southern West Africa during the nighttime and persist long into the following day. They affect the radiation budget and hence the evolution of the atmospheric boundary layer and regional climate. The relevant parameters and processes governing the formation and dissolution of the LLCs are still not fully understood. This paper gives an overview of the diurnal cycles of the energy-balance components, near-surface temperature, humidity, wind speed and direction as well as of the conditions (LLCs, low-level jet) in the boundary layer at the supersites and relates them to synoptic-scale conditions (monsoon layer, harmattan layer, African easterly jet, tropospheric stratification) in the DACCIWA operational area. The characteristics of LLCs vary considerably from day to day, including a few almost cloud-free nights. During cloudy nights we found large differences in the LLCs' formation and dissolution times as well as in the cloud-base height. The differences exist at individual sites and also between the sites. The synoptic conditions are characterized by a monsoon layer with south-westerly winds, on average about 1.9 km deep, and easterly winds above; the depth and strength of the monsoon flow show great day-to-day variability. Within the monsoon layer, a nocturnal low-level jet forms in approximately the same layer as the LLC. Its strength and duration is highly variable from night to night. This unique data set will allow us to test some new hypotheses about the processes involved in the development of LLCs and their interaction with the boundary layer and can also be used for model evaluation.

scholarly journals An overview of the diurnal cycle of the atmospheric boundary layer during the West African monsoon season: Results from the 2016 observational campaign

2017 ◽  
Author(s):  
Norbert Kalthoff ◽  
Fabienne Lohou ◽  
Barbara Brooks ◽  
Gbenga Jegede ◽  
Bianca Adler ◽  
...  
Keyword(s):  
Boundary Layer ◽  
West Africa ◽  
Atmospheric Boundary Layer ◽  
Cloud Base ◽  
Data Set ◽  
Near Surface ◽  
Easterly Wind ◽  
Low Level ◽  
Synoptic Conditions ◽  
Low Level Jet

Abstract. A ground-based field campaign was conducted in southern West Africa from mid June to the end of July 2016 within the framework of the Dynamics–Aerosol–Chemistry–Cloud Interactions in West Africa (DACCIWA) project. It aimed to provide a high-quality comprehensive data set for process studies, in particular into interactions between low-level clouds (LLCs) and boundary-layer conditions. In this region missing observations are still a major issue. During the campaign, extensive remote sensing and in-situ measurements were conducted at three supersites: Kumasi (Ghana), Savè (Benin) and Ile-Ife (Nigeria). Daily radiosoundings were performed at 06:00 UTC and 15 intensive observation periods (IOPs) were performed during which additional radiosondes were launched every 1.5 to 3 h. Remotely piloted aerial systems were also operated during the IOPs. Extended stratiform LLCs form frequently in southern West Africa during the night time and persist long into the following day. They affect the radiation budget and hence the evolution of the atmospheric boundary layer and regional climate. The relevant parameters and processes governing the formation and dissolution of the LLCs are still not fully understood. This paper gives an overview of the diurnal cycles of the energy-balance components, near-surface temperature, humidity, wind speed and direction as well as the conditions (LLCs, low-level jet) in the boundary layer at the supersites and relates them to synoptic-scale conditions (monsoon layer, Harmattan layer, African easterly jet, tropospheric stratification) in the DACCIWA operational area. The characteristics of LLCs vary considerably from day to day, including a few almost cloud-free nights. During cloudy nights we found large differences in the LLC's formation and dissolution times as well as in the cloud-base height. The differences exist at individual sites and also between the sites. The synoptic conditions are characterised by a monsoon layer with south-westerly wind, on average about 1.9 km deep, and easterly wind above; the depth and strength of the monsoon flow show great day-to-day variability. Within the monsoon layer, a nocturnal low-level jet forms in approximately the same layer as the LLC. Its strength and duration is highly variable from night to night. This unique data set will allow us to test some new hypotheses about the processes involved in the development of LLCs and their interaction with the boundary layer and can also be used for model evaluation.

scholarly journals Meteorological responses in the atmospheric boundary layer over southern England to the deep partial eclipse of 20 March 2015

2016 ◽  
Vol 374 (2077) ◽  
pp. 20150214 ◽  
Author(s):  
Stephen Burt
Keyword(s):  
Boundary Layer ◽  
Atmospheric Boundary Layer ◽  
Meteorological Parameter ◽  
Atmospheric Stability ◽  
Cloud Base ◽  
Atmospheric Effects ◽  
Near Surface ◽  
Southern England ◽  
Wide Range ◽  
Instrumental Records

A wide range of surface and near-surface meteorological observations were made at the University of Reading’s Atmospheric Observatory in central southern England (latitude 51.441° N, longitude 0.938° W, altitude 66 m above mean sea level) during the deep partial eclipse on the morning of 20 March 2015. Observations of temperature, humidity, radiation, wind speed and direction, and atmospheric pressure were made by computerized logging equipment at 1 Hz, supplemented by an automated cloud base recorder sampling at 1 min intervals and a high-resolution (approx. 10 m vertical interval) atmospheric sounding by radiosonde launched from the same location during the eclipse. Sources and details of each instrumental measurement are described briefly, followed by a summary of observed and derived measurements by meteorological parameter. Atmospheric boundary layer responses to the solar eclipse were muted owing to the heavily overcast conditions which prevailed at the observing location, but instrumental records of the event documented a large (approx. 80%) reduction in global solar radiation, a fall in air temperature of around 0.6°C, a decrease in cloud base height, and a slight increase in atmospheric stability during the eclipse. Changes in surface atmospheric moisture content and barometric pressure were largely insignificant during the event. This article is part of the themed issue ‘Atmospheric effects of solar eclipses stimulated by the 2015 UK eclipse’.

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