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Surface controls on the Planetary Boundary Layer height during different monsoon scenarios over a rain shadow region

Authors:

Abstract

In our study, PBL heights are estimated using air temperature and humidity from radiosonde and microwave radiometer. The micrometeorological observations on a 50 meter tower are used to study the surface controls on PBL height. The observations are taken from the Cloud Aerosol Interaction and Precipitation Enhancement Experiment (CAIPEEX) ground based observations conducted at Solapur, a rain shadow location in Maharashtra, by the Indian Institute of Tropical Meteorology, Ministry of Earth Sciences.
Introduction
Objectives
To estimate the PBL heights from continuous Microwave
Radiometer (MWR) observations and study their temporal
characteristics during a one year period over a rain shadow
region.
To study the relationship between PBLH and surface turbulent
fluxes.
Methodology & Study Area
Methods for boundary layer height calculation
Results
Acknowledgements
Department of atmospheric and space sciences , SPPU, Pune.
Indian Institute of Tropical Meteorology, Pune.
References
Ruijun Dang; Yang Y, Xiao-Ming Hu, Zhiting Wang,Shuwen Zhang. A Review of Techniques
for Diagnosing the Atmospheric Boundary Layer Height (ABLH) Using Aerosol Lidar Data.
Remote Sens.!2019, 11, 1590
Seibert, P.; Beyrich, F.; Gryning, S.-E.; Jo!re, S.; Rasmussen, A.; Tercier, P. Review and
intercomparison of operational methods for the determination of the mixing height.
Atmos.Environ.!2000, 34, 1001–1027.
Sathyanadh; Anusha; Thara Prabhakaran; Chetana Patil; Anandakumar Karipot. Planetary!
Boundary Layer Height over the Indian Subcontinent: Variability and Controls with Respect
to Monsoon.Atmospheric Research.!2017, 195 , 44–61.
Cumulative! Momentum flux vs PBLH!
Cumulative Sensible Heat Flux vs PBLH
The relationship between cumulative! momentum flux vs. PBLH indicate!
large scatter compared! to the cumulative sensible heat! vs. PBLH during all
seasons.!
The PBLH increase with cumulative momentum flux depict large seasonal
variations.!
!In pre-monsoon, PBLHs keep increasing with the increasing momentum
fluxes, whereas in the other seasons the surface flux dependence of the PBLH
decreases beyond certain cumulative values of momentum flux.
Acknowledgements & References
Comparison of PBLH calculated from radiosonde and
MWR
The results presented in Fig. shows! good agreement
between the values calculated from radiosonde and MWR
profiles. (source: Charuta M.,2019)
Gregori et al.(2018) Validated PBLH from MWR against
radiosonde using parcel method! and found that! PBLH
calculated from MWR very well agree with radiosonde
PBLH in convective situations, with high level of
correlation! ~ 0.96.!
Monthly Averaged Diurnal Variation of PBLH
Winter season(DJF)- Max CBLH in February (2700m), CBL
development starts at 0900 LST, reaches maximum at 1500 LST;
SBL development starts at 1900 LST and reaches maximum at
0600 LST.
Pre-Monsoon(MAM)- Max CBLH in April (upto 4900m), CBL
growth starts at 0800 LST, reaches maximum at 1500 LST; SBL
growth starts at 1800 LST and reaches maximum at! 0600 LST.
Monsoon(JJAS)- Max CBLH in June (2500m). CBL growth
starts at 0700 LST and reaches maximum at 1300 LST; SBL
growth starts at 2000 LST and reaches maximum at 0500 LST.
Post-Monsoon(ON)- Max CBL in October(2100m). CBL growth
starts at 0800 LST and reaches maximum at 1300 LST; SBL
development starts at 1900 LST and reaches maximum at 0600
LST.
Monthly averaged maximum CBLH and SBL
Maximum CBL growth rate
Abstract ID- IMA19-Th1-P009
Annual Monsoon E Workshop ( AMW 2019 2020)
&
National E Symposium on “Cloud and Precipitation
Processes”
January 18-21, 2021, Pune, Maharashtra, INDIA
Influence of Boundary Layer Mixing on Monsoon Clouds and PBL
height characteristics over a rain shadow region.
Punde Pravin1, Charuta Murkute2, S. A. Dixit2, Y. Jaya Rao2, Thara Prabhakaran2, Kishore Kumar
Grandhi1, Anandakumar Karipot1
1Department of Atmospheric and Space Sciences, Savitribai Phule Pune University, Pune
2Indian Institute of Tropical Meteorology, Pune
The vertical transport of momentum, heat and moisture are affected by
turbulent mixing in the atmospheric boundary layer effects and play an
important role in the low-level cloud development. Planetary Boundary Layer
(PBL) is the lowest part of the troposphere, interacts with the earth’s surface
and influences the weather and! climate. According to geographical location
The PBL shows large differences at diurnal and seasonal scales. Surface
conditions and forcing mechanisms over the Indian sub-continent changes
during Monsoon circulations and rainfall, which affects PBL characteristics.
For numerical modelling, air pollution and agro-meteorological applications
PBL height evolution from observations and understanding their controls is
important..
Structure of Boundary Layer
Day time:
Surface Layer
Mixed layer
Entrainment Zone (EZ)
Night time:
Surface layer
Stable boundary layer
Residual layer
Capping inversion
Parcel method: (used for CBL)
As depicted, the PBL height is set to the altitude z where the T
profile crosses the dry adiabatic or where the potential
temperature is equal to the surface potential temperature.
Brunt Vaisala Frequency Method : (used for SBL)
Method based on the frequency of oscillation of the parcel in a
stably stratified atmosphere. The critical frequency 0.02 rad/sec
for locating SBLH(Hyun et al.,2005).
From December to May CBL
maximum heights show an
increasing trend while SBL
maximum heights show the
opposite trend. SBL maximum
observed in Jan and minimum in
May.!
CBL maximum growth rates are
observed during the pre-monsoon
season ~600 m/hr and lowest
during January ~50m/hr
The relationship between cumulative! momentum flux vs. PBLH
indicate! large scatter compared! to the cumulative sensible heat!
vs. PBLH during all seasons.!
The PBLH increase with cumulative momentum flux depict large
seasonal variations.!
!In pre-monsoon, PBLHs keep increasing with the increasing
momentum fluxes, whereas in the other seasons the surface flux
dependence of the PBLH decreases beyond certain cumulative
values of momentum flux.
The MWR provides continuous and reliable observations for
observing the PBL evaluation and to study the diurnal and seasonal
variation of PBL.
The Parcel Method is a reliable method for the estimation of CBLH
and the Brunt-Vaisala frequency method for SBLH.
Pre-monsoon months have deeper CBLs, with heights reaching up
to 5000 m. Shallowest PBLs are noted during peak monsoon period,
July and August.
Higher SBL are observed during post monsoon and winter months.!
The CBL growth rate is large during pre-monsoon 400 600 m/hr
and in the range 100 - 300 m/hr! during other periods.
CBL growth is well correlated to cumulative sensible and
momentum fluxes during winter compared to other seasons.
The results suggest that the surface control on the PBL growth
diminishes beyond certain heights in all seasons, except in pre-
monsoon.
The PBLH height can be calculated from vertical profiles of
temperature, wind, relative humidity, pressure and dew point
temperature. Radiosonde and Microwave Radiometer
observations are used in the present study. The data from the
Cloud Aerosol Interaction and Precipitation Enhancement
Experiment (CAIPEEX) Phase 4 ground based observations at
Solapur, Maharashtra during 2018-19 are used for the present
study.
Radiosonde, MWR and micrometeorological tower
observations are used.
The PBLH heights are calculated from vertical profiles of
temperature using Parcel method (Convective Boundary
Layer) and Brunt Vaisala Frequency (Stable Boundary
Layer) methods.
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