Differences in Atmospheric Boundary-Layer Characteristics Between Wet and Dry Episodes of the Indian Summer Monsoon

Sandeep, A.; Rao, T. Narayana; Ramkiran, C. N.; Rao, S. Vijaya Bhaskara

doi:10.1007/s10546-014-9945-z

Cited by 60 publications

(32 citation statements)

References 36 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…The soil moisture levels, therefore, remain high in this season. It is known from earlier studies that the abundance of soil moisture not only produces shallow ABL, but also delays the growth of the ABL (Sandeep et al, 2014). It appears from present observations that not only the growth but also the descent (or transition) is getting delayed due to the excess soil moisture.…”

Section: Discussionmentioning

confidence: 99%

A comprehensive investigation on afternoon transition of the atmospheric boundary layer over a tropical rural site

Sandeep

Rao

2015

Atmos. Chem. Phys.

Self Cite

View full text Add to dashboard Cite

Abstract. The transitory nature of the atmospheric boundary layer (ABL) a few hours before and after the time of sunset has been studied comprehensively over a tropical station, Gadanki (13.45 • N, 79.18 • E), using a suite of in situ and remote sensing devices. This study addresses the following fundamental and important issues related to the afternoon transition (AT): which state variable first identifies the AT? Which variable best identifies the AT? Does the start time of the AT vary with season and height? If so, which physical mechanism is responsible for the observed height variation in the start time of the transition?At the surface, the transition is first seen in temperature (T ) and wind variance (σ 2 WS ), ∼ 100 min prior to the time of local sunset, then in the vertical temperature gradient and finally in water vapor mixing ratio variations. Aloft, both signal-to-noise ratio (SNR) and spectral width (σ ) show the AT nearly at the same time. The T at the surface and SNR aloft are found to be the best indicators of transition. Their distributions for the start time of the AT with reference to time of sunset are narrow and consistent in both total and seasonal plots. The start time of the transition shows some seasonal variation, with delayed transitions occurring mostly in the rainy and humid season of the northeast monsoon. Interestingly, in contrast to the general perception, the signature of the transition is first seen in the profiler data, then in the sodar data, and finally in the surface data. This suggests that the transition follows a top-to-bottom evolution. It indicates that other processes, like entrainment, could also play a role in altering the structure of the ABL during the AT, when the sensible heat flux decreases progressively. These mechanisms are quantified using a unique high-resolution data set to understand their variation in light of the intriguing height dependency of the start time of the AT.

show abstract

Section: Discussionmentioning

confidence: 99%

A comprehensive investigation on afternoon transition of the atmospheric boundary layer over a tropical rural site

Sandeep

Rao

2015

Atmos. Chem. Phys.

Self Cite

View full text Add to dashboard Cite

show abstract

“…Considering the differences after classification and the amount of data, the net radiation is divided into four levels, <150, 150-300, 300-500, and >500 W m −2 and the VPD is divided into four levels, <6, 6-12, 12-20, and >20 hPa. Mohan and Rao [38] and Sandeep et al [39] described a methodology to identify wet and dry episodes using rainfall data. The present study uses a similar classification method but for soil moisture.…”

Section: Methods Of Analysismentioning

confidence: 99%

Understanding the Partitioning of the Available Energy over the Semi-Arid Areas of the Loess Plateau, China

et al. 2017

View full text Add to dashboard Cite

Abstract:To investigate the mechanism of available energy partitioning to sensible and latent heat fluxes over semi-arid regions, data from the Semi-Arid Climate and Environment Observatory of Lanzhou University (SACOL) were analyzed to assess the effects of soil moisture, net radiation, and vapor pressure deficit (VPD) on available energy partitioning, as quantified by Bowen ratio. It was found that the Bowen ratio decreased rapidly with increasing soil moisture when soil was dry but was insensitive to the change in soil moisture when soil became wet. Net radiation and VPD affected the sensitivity of the Bowen ratio to soil moisture under dry conditions and the soil moisture threshold above which the Bowen ratio became insensitive to soil moisture. The Bowen ratio increases with net radiation at a high level of VPD, while the Bowen ratio first increases and then decreases with net radiation at a low level of VPD. Reduced soil moisture enhanced the effects of the net radiation and VPD on available energy partitioning. The effects of the VPD on Bowen ratio depended on the relative strength of the positive and negative impacts of VPD on the latent heat flux under different soil and net radiation conditions.

show abstract

“…In general, the CBL is shallower during the active monsoon conditions when compared to break monsoon conditions (Satyanarayana Mohan and Narayana Rao, 2012;Sandeep et al, 2014). In the active monsoon situations, the evolution of the CBL is delayed by ∼ 1-4 h when compared to weak episodes (Sandeep et al, 2014). The diurnal variation in the ABL is weak during the summer monsoon season when compared to the winter season (Mehta et al, 2017).…”

mentioning

confidence: 95%

“…The diurnal variation in the ABL is weak during the summer monsoon season when compared to the winter season (Mehta et al, 2017). There is a close association between the diurnal evolution of the low-level jet (LLJ) streams and the CBL (Sandeep et al, 2014). It was observed that both the LLJ and CBL were elevated during afternoon hours on the non-rainy (dry episode) days over Gadanki (13.45 • N, 79.2 • E).…”

mentioning

confidence: 98%

“…The Indian summer monsoon is dominated by synoptic-scale cloudiness and precipitations associated with a cycle of active and break spells (Webster et al, 1998;Goswami, 2005). There have been several studies on the ABL characteristics over the Indian region during summer monsoon season (Holt and Raman, 1987;Parasnis and Goyal, 1990;Raman et al, 1990;Kusuma et al, 1991;Joseph and Sijikumar, 2004;Roja Raman et al, 2011;Satyanarayana Mohan and Narayana Rao, 2012;Sandeep et al, 2014Sandeep et al, , 2015Mehta et al, 2017). In general, the CBL is shallower during the active monsoon conditions when compared to break monsoon conditions (Satyanarayana Mohan and Narayana Rao, 2012;Sandeep et al, 2014).…”

mentioning

confidence: 99%

See 1 more Smart Citation

Thermodynamic structure of the convective boundary layer (CBL) over the Indian monsoon region during CAIPEEX campaigns

et al. 2017

View full text Add to dashboard Cite

Abstract. Spatial and temporal variability in the convective boundary layer (CBL) height for the Cloud Aerosol Interaction and Precipitation Enhancement Experiment (CAIPEEX) study period are examined using the data collected from high-resolution radiosondes during May-September 2009 over the Indian monsoon region. In total, 57 radiosonde launchings were carried out at ∼ 11:00-17:00 IST over six different stations covering a large geographical region, ranging from latitude ∼ 13 to 32 • N and longitude 73 to 92 • E. Of the total 57 launchings, 17 were made during cloudy conditions during which relative humidity (RH) was found to be greater than 83 % for an ∼ 1.0 km layer at various altitudes below 6 km. Within the layer the difference between saturated equivalent potential temperature and equivalent potential temperature is small, and it satisfies the condition that RH > 83 % for about 1 km is considered as the cloudy layer. There are eight cases when the cloud-topped boundary layer (CTBL) and 19 cases when fair-weather boundary layer (FWBL) is observed. The CBL heights are obtained using thermodynamic profiles, which vary from ∼ 0.4 to 2.5 km a.g.l. The formation of the cloud layers above the boundary layer generally lowers the CBL height and is responsible for its day-to-day variability. The development of the cloud beneath the boundary layer generally elevates the CBL, which is also responsible for the large day-to-day variability in the CBL. The FWBL identified using relative invariance of the thermodynamic profiles varies from ∼ 2.0 to 5.5 km, which is clearly marked by a local minimum in the refractivity gradient. During cloudy days, the CBL is found to be shallow and the surface temperature lower when compared to clear-sky days. The CBL and the lifting condensation level (LCL) heights are randomly related and are found to be at a lower height during cloudy days when compared to clear-sky days. Finally, the typical comparison between the CBL height obtained using thermodynamic profiles and backscattering profiles using Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) is examined.

show abstract

Differences in Atmospheric Boundary-Layer Characteristics Between Wet and Dry Episodes of the Indian Summer Monsoon

Cited by 60 publications

References 36 publications

A comprehensive investigation on afternoon transition of the atmospheric boundary layer over a tropical rural site

A comprehensive investigation on afternoon transition of the atmospheric boundary layer over a tropical rural site

Understanding the Partitioning of the Available Energy over the Semi-Arid Areas of the Loess Plateau, China

Thermodynamic structure of the convective boundary layer (CBL) over the Indian monsoon region during CAIPEEX campaigns

Contact Info

Product

Resources

About