Influence of the Upper-Tropospheric Wind Shear upon Cloud Radiative Forcing in the Asian Monsoon Region

Sathiyamoorthy, V.; Pal, P. K.; Joshi, P. C.

doi:10.1175/1520-0442(2004)017<2725:iotuws>2.0.co;2

Cited by 61 publications

(41 citation statements)

References 17 publications

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“…The spatial distribution of Sc clouds is also very crucial as it plays an important role in shortwave radiative forcing resulting in cooling of the surface. The confinement of Sc clouds over the Arabian Sea can be attributed to the descending motion from monsoon convection apart from lower tropospheric thermal inversion that occurs during the ISM period over this region (Sathiyamoorthy et al, 2011). The weak descending motions over the Arabian Sea during the ISM period can suppress the vertical development of clouds.…”

Section: Resultsmentioning

confidence: 99%

CloudSat observations of cloud-type distribution over the Indian summer monsoon region

Subrahmanyam

Kumar

2013

Ann. Geophys.

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The three-dimensional distribution of various cloud types over the Indian summer monsoon (ISM) region using five years (2006–2010) of CloudSat observations during June-July-August-September months is discussed for the first time. As the radiative properties, latent heat released and microphysical properties of clouds differ largely depending on the cloud type, it becomes important to know what types of clouds occur over which region. In this regard, the present analysis establishes the three-dimensional distribution of frequency of occurrence of stratus (St), stratocumulus (Sc), nimbostratus (Ns), cumulus (Cu), altocumulus (Ac), altostratus (As), cirrus (Ci) and deep convective (DC) clouds over the ISM region. The results show that the various cloud types preferentially occur over some regions of the ISM, which are consistent during all the years of observations. It is found that the DC clouds frequently occur over northeast of Bay of Bengal (BoB), Ci clouds over a wide region of south BoB–Indian peninsula–equatorial Indian Ocean, and Sc clouds over the north Arabian Sea. Ac clouds preferentially occur over land, and a large amount of As clouds are found over BoB. The occurrence of both St and Ns clouds over the study region is much lower than all other cloud types.The interannual variability of all these clouds including their vertical distribution is discussed. It is envisaged that the present study opens up possibilities to quantify the feedback of individual cloud type in the maintenance of the ISM through radiative forcing and latent heat release

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Section: Resultsmentioning

confidence: 99%

CloudSat observations of cloud-type distribution over the Indian summer monsoon region

Subrahmanyam

Kumar

2013

Ann. Geophys.

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“…Similar to F c , the considerably less value of F ALT observed below ∼7 km in the "pool" is most prominent in July-August. Most of the high-altitude clouds observed over the "pool" region might be cirrus clouds generated by westward spreading of outflows from the deep convective systems situated at the eastern BoB by the strong upper tropospheric easterly winds, which is a characteristic feature of ASM (e.g., Sathiyamoorthy et al, 2004).…”

Section: Resultsmentioning

confidence: 99%

Characteristics of a persistent "pool of inhibited cloudiness" and its genesis over the Bay of Bengal associated with the Asian summer monsoon

et al. 2011

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Abstract. Using spatial and vertical distributions of clouds derived from multi-year spaceborne observations, this paper presents the characteristics of a significant "pool of inhibited cloudiness" covering an area of >10 6 km 2 between 3-13 • N and 77-90 • E over the Bay of Bengal (BoB), persisting throughout the Asian summer monsoon season (ASM). Seasonal mean precipitation rate over the "pool" is <3 mm day −1 while that over the surrounding regions is mostly in the range of 6-14 mm day −1 . Frequency of occurrence of clouds in this "pool" is ∼20-40 % less than that over the surrounding deep convective regions. Zonal and meridional cross sections of the altitude distribution of clouds derived from CloudSat data reveal a vault-like structure at the "pool" with little cloudiness below ∼7 km, indicating that this "pool" is almost fully contributed by the substantially reduced or near-absence of low-and middle-level clouds. This suggest the absence of convection in the "pool" region. Spaceborne scatterometer observations show divergence of surface wind at the "pool" and convergence at its surroundings, suggesting the existence of a mini-circulation embedded in the large-scale monsoon circulation. Reanalysis data shows a mini-circulation extending between the surface and ∼3 km altitude, but its spatial structure does not match well with that inferred from the above observations. Sea surface at the south BoB during ASM is sufficiently warm to trigger convection, but is inhibited by the subsidence associated with the mini-circulation, resulting in the "pool". This minicirculation might be a dynamical response of the atmosphere to the substantial spatial gradient of latent heating by largescale cloudiness and precipitation at the vast and geographically fixed convective zones surrounding the "pool". Subsidence at the "pool" might contribute to the maintenance of convection at the above zones and be an important component of ASM that is overlooked hitherto.Correspondence to: K. Rajeev (k rajeev@vssc.gov.in)

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“…For example, Rajeevan and Srinivasan (2000) showed that the widespread coverage of a large amount of high clouds with large optical depths over the Asian summer monsoon region gives rise to a large negative net cloud-radiative forcing (NETCRF) during the June-September months. In a more recent study, Sathiyamoorthy et al (2004) pointed out that the spreading of cloud tops by the strong easterly winds in the upper troposphere can increase the high-cloud amount over the Asian monsoon region during the northern summer.…”

Section: Introductionmentioning

confidence: 99%

Cloud‐radiative impacts on the tropical Indian Ocean associated with the evolution of ‘monsoon breaks’

Samala¹,

Krishnan²

2007

Intl Journal of Climatology

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ABSTRACT:A detailed diagnostic analysis of a suite of observed datasets was carried out with a view to understand the importance of cloud-radiative effects on the evolution of prolonged 'monsoon breaks' over the Indian region. The study particularly focuses on the role of clouds in affecting the sub-seasonal/intra-seasonal variability of sea surface temperature (SST) and atmospheric convection in the equatorial and south-eastern tropical Indian Ocean (SETIO) during monsoonbreak transitions. A characteristic feature of the monsoon-break evolution is the appearance of suppressed convection over the SETIO region nearly 7-10 days prior to the commencement of a break spell over India. It is seen from the present analysis that the lack of cloud cover over the SETIO during the 'pre-break' phase leads to significant warming of the tropical Indian Ocean due to strong solar insolation at the surface. During the 'pre-break' phase, the net cloud-radiative forcing (NETCRF) at the surface is found to be typically around −30 Wm −2 and the mean SST in the SETIO is about 29.3°C. Following the transition to a monsoon-break phase, the cloud amount increases by about 25% over the SETIO region in association with intensified convection. The NETCRF at the surface over the SETIO averaged during the 'break' phase is found to be about −60 Wm −2 (i.e. a change of about −30 Wm −2 from the 'pre-break' phase). Consistent with the above change in the NETCRF, the SST in the SETIO shows a cooling of about 0.7°C, although the mean SSTs during the 'break' phase remain as high as 28.6°C. On the basis of the findings from this study, it is suggested that the SST warming during the 'pre-break' phase plays a key role in maintaining high SST and allows sustained convection to occur over the SETIO during prolonged monsoon breaks.

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Influence of the Upper-Tropospheric Wind Shear upon Cloud Radiative Forcing in the Asian Monsoon Region

Cited by 61 publications

References 17 publications

CloudSat observations of cloud-type distribution over the Indian summer monsoon region

CloudSat observations of cloud-type distribution over the Indian summer monsoon region

Characteristics of a persistent "pool of inhibited cloudiness" and its genesis over the Bay of Bengal associated with the Asian summer monsoon

Cloud‐radiative impacts on the tropical Indian Ocean associated with the evolution of ‘monsoon breaks’

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Influence of the Upper-Tropospheric Wind Shear upon Cloud Radiative Forcing in the Asian Monsoon Region

Cited by 61 publications

References 17 publications

CloudSat observations of cloud-type distribution over the Indian summer monsoon region

CloudSat observations of cloud-type distribution over the Indian summer monsoon region

Characteristics of a persistent &quot;pool of inhibited cloudiness&quot; and its genesis over the Bay of Bengal associated with the Asian summer monsoon

Cloud‐radiative impacts on the tropical Indian Ocean associated with the evolution of ‘monsoon breaks’

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Characteristics of a persistent "pool of inhibited cloudiness" and its genesis over the Bay of Bengal associated with the Asian summer monsoon