4-5-Day-Period Variation and Low-Level Dry Air Observed in the Equatorial Western Pacific during the TOGA-COARE IOP

Numaguti, Atusi; Oki, Riko; Nakamura, Kozo; Tsuboki, Kazuhisa; Misawa, Nobuhiko; Asai, Tomio; Kodama, Y.

doi:10.2151/jmsj1965.73.2b_267

Cited by 68 publications

(81 citation statements)

References 9 publications

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“…In order to investigate the origin of the dry air masses, we calculated Lagrangian backward air parcel trajectories for all very dry sounding cases listed in Table 4 using NCEP/ NCAR reanalysis data sets, and following the previous works of Numaguti et al (1995) and Yoneyama and Parsons (1999). Calculations were started from 700 hPa and linear interpolation was used for both time and space.…”

Section: Air Parcel Trajectoriesmentioning

confidence: 99%

“…They concluded that this bimodality resulted from the frequent occurrence of extremely dry air intrusions from higher latitudes into the basically moist tropical environment. Since the warm pool had been considered to be perpetually in the moist conditions with the knowledge before TOGA COARE, the dry intrusion event has attracted many researchers in studying the mechanism, and its impact on moisture variability (e.g., Parsons et al 1994;Numaguti et al 1995;Yoneyama and Fujitani 1995;Sheu and Liu 1995;Mapes and Zuidema 1996;DeMott and Rutledge 1998;Yoneyama and Parsons 1999;Parsons et al 2000;Redelsperger et al 2002). Yoneyama and Parsons (1999) showed that these lateral intrusions were associated with mid-latitudes breaking Rossby waves.…”

Section: Introductionmentioning

confidence: 99%

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Moisture Variability over the Tropical Western Pacific Ocean

Yoneyama

2003

Journal of the Meteorological Society of Japan

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In this paper, we study the characteristics of moisture variability over the tropical western Pacific warm pool region using sounding data obtained through the use of research vessels. Data used here were collected in both boreal summer and winter seasons over a nine-year period from 1993 through 2001. Sounding data are categorized into five zonal wind vertical shear modes, and then examined for common and singular features of moisture variability.The results show frequent occurrences of high relative humidity centered around 945 hPa, and 560 hPa, for any wind shear conditions, as previously found in the Tropical Ocean and Global Atmosphere/Coupled Ocean-Atmosphere Response Experiment (TOGA COARE) studies. We also found another small peak at 845 hPa in low-level easterly conditions. The degree of these features is modulated by wind shear mode differences. An interesting feature is that the variation of total precipitable water is well represented by the synoptic scale mid-tropospheric moisture variation. However, a close relation between the total moisture budget and the moisture variation in the boundary layer is also obtained for a time scale of less than a few days (especially the diurnal cycle).We investigated extremely dry air conditions as one factor modulating mid-tropospheric moisture. Backward air parcel trajectories show that there are two major routes for the intrusion of dry air over the warm pool. In the first, the air parcel could be traced back to higher latitudes and the upper troposphere. For this type, anticyclonic equatorward flow associated with developing mid-latitude baroclinic waves, such as Rossby wave breaking, is responsible for injecting subtropical dry air into the Tropics-as proposed by Yoneyama and Parsons for TOGA COARE dry events. In the second type, the air parcel could be traced back to the upper troposphere, but within lower latitudes in the central-eastern Pacific. For this case, the air parcel originates from the trade winds that passed over the region where dry air was injected by the anticyclonic equatorward flow associated with the baroclinic wave development in the subtropical region.The relationship between dry air conditions and large-scale features is also discussed.

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Section: Air Parcel Trajectoriesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Moisture Variability over the Tropical Western Pacific Ocean

Yoneyama

2003

Journal of the Meteorological Society of Japan

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“…4 resembles the case analyzed by Numaguti et al (1995), in that the dry air appeared associated with the @5-dayperiod meridional wind variation. To investigate the large-scale structure responsible for the 5-dayperiod variation in the wind and humidity, the NCEP/NCAR global objective analysis data in the observation period was examined.…”

Section: Equatorial Rossby Wavementioning

confidence: 61%

“…Frequent appearances of extremely dry air in the lower and mid troposphere over the tropical western Pacific Ocean, first recognized in the TOGA COARE IOP data sets, has received a great deal of attention (e.g., Parsons et al 1994;Numaguti et al 1995;Yoneyama and Fujitani 1995;Mapes and Zuidema 1996; Johnson et al 1996;Sheu and Liu 1995;DeMott and Rutledge 1998;Yoneyama and Parsons 1999;Parsons et al 2000). The formation of the dry layer cannot be explained by vertical adiabatic displacements near the trailing edge of mesoscale convective systems.…”

Section: Equatorial Rossby Wavementioning

confidence: 99%

“…The formation of the dry layer cannot be explained by vertical adiabatic displacements near the trailing edge of mesoscale convective systems. Instead, the horizontal advection of air from the subtropics has been shown to explain the appearance of the dry air masses (Numaguti et al 1995;Yoneyama and Fujitani 1995;Mapes and Zuidema 1996;Johnson et al 1996). Numaguti et al (1995) showed that 4-5-dayperiod mixed Rossby-gravity (MRG) waves played an important role in the advection of dry air in the two cases of dry events observed during TOGA COARE.…”

Section: Equatorial Rossby Wavementioning

confidence: 99%

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Case Study of an Intense Wind Event Associated with a Mesoscale Convective System in West Sumatera during the HARIMAU2006 Campaign

Kawashima

Fujiyoshi

Ohi

et al. 2011

Journal of the Meteorological Society of Japan

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In this study, the processes responsible for an intense wind event that occurred in west Sumatera on November 19, 2006, during the first campaign of the Hydrometeorological ARay for Isv-Monsoon AUtomonitoring (HAR-IMAU) were investigated.Strong winds of 17 m s À1 and a sudden temperature drop of 5 K were observed at an X-band Doppler radar site associated with the passage of a convective system, and some houses were severely damaged. The convective system developed under an environment of strong low-level easterly vertical shear associated with the easterly region of an equatorial Rossby wave. The northern part of the convective system possessed qualitatively similar structures to midlatitude bow echoes, including the convex shape of the convective line, a descending rear-inflow jet positioned at its apex, and mesoscale vortices on both sides of the rear-inflow jet. The low-level wind behind the convective system formed a channel of strong easterly wind as it passed through an area of relatively low topography in the mountain range. The enhanced easterly wind was thought to contribute to the formation of the bow echo-like structure in the northern part of the convective system. This easterly rear-inflow jet was further accelerated in the convective system and descended near the leading edge, forming divergent strong winds at the surface.The sounding data that were taken after the passage of the convective system indicated that dry air appeared in the lower troposphere associated with an enhancement of the southerly component of the wind. An analysis of objective reanalysis data suggests that the southerly was probably associated with westward-propagating mixed Rossby-gravity waves with a period of approximately 5 days. It is suggested that the dry air intruded into the convective system across the back edge of the precipitation area and caused enhanced evaporative cooling, which resulted in the e¤ective downward transport of the enhanced easterly momentum.

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Influence of topography on temperature variations in the tropical tropopause layer

et al. 2016

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Temperature variations in the tropical tropopause layer (TTL) play an important role in dehydration in the upper troposphere and lower stratosphere. Equatorial Kelvin waves associated with the Madden‐Julian Oscillation (MJO) are known to induce remarkable temperature variations in the TTL. In this study, the influence of topography on temperature variations in the TTL is investigated by using radiosonde data, satellite data, reanalysis data, and numerically simulated data. When MJO convection passes over the radiosonde sites, temperature variations near mountainous regions are larger than those measured in regions of lower elevation. The difference in temperature amplitude reaches ~1–2 K. Large temperature variations over mountainous regions were also found in other data sets. Numerically simulated data from the Nonhydrostatic Icosahedral Atmospheric Model (NICAM) are also used to investigate the temperature variations in the TTL. The results show that the temperature variations associated with Kelvin waves become large over mountainous regions. A sensitivity test using the stretched version of NICAM gave two important results: (i) the height of mountains affects the magnitude of the temperature variations in the TTL, and (ii) the terrain‐following coordinate system used in the model produces the artificially high‐temperature variation in the TTL. When Kelvin waves pass over mountainous regions, topographic gravity waves are excited and superimposed on the Kelvin waves, thereby producing large temperature variations over these regions. The mountainous region of the Indonesian Maritime Continent is a favorable location for large temperature variations in the TTL.

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4-5-Day-Period Variation and Low-Level Dry Air Observed in the Equatorial Western Pacific during the TOGA-COARE IOP

Cited by 68 publications

References 9 publications

Moisture Variability over the Tropical Western Pacific Ocean

Moisture Variability over the Tropical Western Pacific Ocean

Case Study of an Intense Wind Event Associated with a Mesoscale Convective System in West Sumatera during the HARIMAU2006 Campaign

Influence of topography on temperature variations in the tropical tropopause layer

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