scholarly journals 2016 Monsoon Convection and its place in the Large-Scale Circulation using Doppler Radars

2021 ◽  
Author(s):  
Alex Doyle ◽  
Andrew Turner ◽  
Thorwald Stein
Keyword(s):  
Diurnal Cycle ◽  
Large Scale ◽  
Indian Monsoon ◽  
Monsoon Season ◽  
Model Development ◽  
India Meteorological Department ◽  
Convective Cloud ◽  
Atmospheric Environment ◽  
Annual Rainfall ◽  
Near Surface

<p>Convective cloud development during the Indian monsoon helps moisten the atmospheric environment and drive the monsoon trough northwards each year, bringing a large amount of India’s annual rainfall. Therefore, an increased understanding of how monsoon convection develops in observations will help inform model development. In this study, 139 days of India Meteorological Department Doppler weather radar data is analysed for 7 sites across India during the 2016 monsoon season. Convective cell-top heights (CTH) are objectively identified through the season, and compared with near-surface (at 2 km height) reflectivity. These variables are analysed over three time scales of variability during the monsoon: monsoon progression, active-break periods and the diurnal cycle. We find a modal maximum in CTH around 6–8 km for all sites. Reflectivity increases with CTH, at first sharply, then less sharply above the freezing level. Bhopal and Mumbai exhibit lower CTH for monsoon break periods compared to active periods. A clear diurnal cycle in CTH is seen at all sites except Mumbai. The phase of the diurnal cycle depends on the surface type being land or ocean for south-eastern India, with the frequency of oceanic cells typically exhibiting an early morning peak compared to those over land, consistent with the observed diurnal cycle of precipitation. The cell characteristics discovered are discussed in light of the differences in large-scale synoptic and mesoscale mechanisms responsible for different cell regimes. Our findings confirm that Indian monsoon convective regimes are partly regulated by the large-scale synoptic environment within which they are embedded.</p>

scholarly journals Interannual variability of isotopic composition in water vapor over western Africa and its relationship to ENSO

2015 ◽  
Vol 15 (6) ◽  
pp. 3193-3204 ◽  
Author(s):  
A. Okazaki ◽  
Y. Satoh ◽  
G. Tremoy ◽  
F. Vimeux ◽  
R. Scheepmaker ◽  
...  
Keyword(s):  
Isotopic Composition ◽  
Southern Oscillation ◽  
Monsoon Season ◽  
Precipitation Amount ◽  
Isotopic Signature ◽  
Atmospheric Environment ◽  
Global Spectral Model ◽  
Near Surface ◽  
Western Africa ◽  
The Relationship

Abstract. This study was performed to examine the relationship between isotopic composition in near-surface vapor (δ18Ov) over western Africa during the monsoon season and El Niño–Southern Oscillation (ENSO) activity using the Isotope-incorporated Global Spectral Model. The model was evaluated using a satellite and in situ observations at daily to interannual timescales. The model provided an accurate simulation of the spatial pattern and seasonal and interannual variations of isotopic composition in column and surface vapor and precipitation over western Africa. Encouraged by this result, we conducted a simulation stretching 34 years (1979–2012) to investigate the relationship between atmospheric environment and isotopic signature on an interannual timescale. The simulation indicated that the depletion in the monsoon season does not appear every year at Niamey. The major difference between the composite fields with and without depletion was in the amount of precipitation in the upstream area of Niamey. As the interannual variation of the precipitation amount is influenced by the ENSO, we regressed the monsoon season averaged δ18Ov from the model and annually averaged NINO3 index and found a statistically significant correlation (R = 0.56, P < 0.01) at Niamey. This relationship suggests that there is a possibility of reconstructing past western African monsoon activity and ENSO using climate proxies.

scholarly journals How Well Can We Represent the Spectrum of Convective Clouds in a Climate Model? Comparisons between Internal Parameterization Variables and Radar Observations

2018 ◽  
Vol 75 (5) ◽  
pp. 1509-1524 ◽  
Author(s):  
Laurent Labbouz ◽  
Zak Kipling ◽  
Philip Stier ◽  
Alain Protat
Keyword(s):  
Large Scale ◽  
Climate Models ◽  
Climate Model ◽  
Aerodynamic Drag ◽  
Model Development ◽  
Convective Cloud ◽  
Height Distribution ◽  
Radar Observations ◽  
Convective Parameterization ◽  
Convective Clouds

Current climate models cannot resolve individual convective clouds, and hence parameterizations are needed. The primary goal of convective parameterization is to represent the bulk impact of convection on the gridbox-scale variables. Spectral convective parameterizations also aim to represent the key features of the subgrid-scale convective cloud field such as cloud-top-height distribution and in-cloud vertical velocities in addition to precipitation rates. Ground-based radar retrievals of these quantities have been made available at Darwin, Australia, permitting direct comparisons of internal parameterization variables and providing new observational references for further model development. A spectral convective parameterization [the convective cloud field model (CCFM)] is discussed, and its internal equation of motion is improved. Results from the ECHAM–HAM model in single-column mode using the CCFM and the bulk mass flux Tiedtke–Nordeng scheme are compared with the radar retrievals at Darwin. The CCFM is found to outperform the Tiedtke–Nordeng scheme for cloud-top-height and precipitation-rate distributions. Radar observations are further used to propose a modified CCFM configuration with an aerodynamic drag and reduced entrainment parameter, further improving both the convective cloud-top-height distribution (important for large-scale impact of convection) and the in-cloud vertical velocities (important for aerosol activation). This study provides a new development in the CCFM, improving the representation of convective cloud spectrum characteristics observed in Darwin. This is a step toward an improved representation of convection and ultimately of aerosol effects on convection. It also shows how long-term radar observations of convective cloud properties can help constrain parameters of convective parameterization schemes.

scholarly journals Physical processes controlling the diurnal cycle of convective storms in the Western Ghats

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
U. V. Murali Krishna ◽  
Subrata Kumar Das ◽  
Sachin M. Deshpande ◽  
G. Pandithurai
Keyword(s):  
Diurnal Variation ◽  
Diurnal Cycle ◽  
Western Ghats ◽  
Large Scale ◽  
Monsoon Season ◽  
Surface Wind ◽  
Bimodal Distribution ◽  
Early Morning ◽  
Coastal Areas ◽  
Convective Storms

AbstractDiurnal variation of convective storms (CSs) during monsoon season and associated physical mechanisms are significantly important for accurate forecast of short-time and extreme precipitation. The diurnal cycle of CSs is investigated using ground-based X-band radar, Tropical Rainfall Measuring Mission Precipitation Radar, and reanalysis data during the summer monsoon (June–September of 2014) over complex mountain terrain of Western Ghats, India. Diurnally, CSs show a bimodal distribution in the coastal areas, but this bimodality became weak along the upslope regions and on the mountain top. The first occurrence mode of CSs is in the afternoon–evening hours, while the second peak is in the early-morning hours. The diurnal cycle’s intensity varies with location, such that it reaches maximum in the afternoon–evening hours and early morning on the mountain top and coastal areas, respectively. Two possible mechanisms are proposed for the observed diurnal variation in CSs (a) the radiative cooling effect and (b) the surface wind convergence induced by the interaction between land-sea breeze, local topography and large-scale monsoon winds. It is also observed that the CSs developed on the mountain top during afternoon–evening hours are deeper than those along the coast. The higher moisture in the lower- and mid-troposphere, higher instability and strong upward motion facilitate deeper CSs during afternoon–evening hours.

scholarly journals Diurnal cycle of precipitation and near-surface atmospheric conditions over the maritime continent: land–sea contrast and impacts of ambient winds in cloud-permitting simulations

2021 ◽  
Author(s):  
Yuntao Wei ◽  
Zhaoxia Pu
Keyword(s):  
Diurnal Cycle ◽  
Large Scale ◽  
Deep Convection ◽  
Vertical Motion ◽  
Sea Breeze ◽  
Return Flow ◽  
Atmospheric Conditions ◽  
Maritime Continent ◽  
Regional Variability ◽  
Near Surface

AbstractA set of cloud-permitting-scale numerical simulations during January–February 2018 is used to examine the diurnal cycle (DC) of precipitation and near-surface variables (e.g., 2 m temperature, 10 m wind and convergence) over the Indo-Pacific Maritime Continent under the impacts of shore-orthogonal ambient winds (SOAWs). It is found that the DC of these variables and their variabilities of daily maxima, minima, and diurnal amplitudes vary over land, sea, and coastal regions. Among all variables, the DC of precipitation has the highest linear correlation with near-surface convergence (near-surface temperature) over coastal (noncoastal) regions. The correlations among the DCs of precipitation, wind, and heating are greater over the ocean than over land. Sine curves can model accurately the DCs of most variables over the ocean, but not over land. SOAWs act to influence the DC mainly by affecting the diurnal amplitude of the considered variables, with DC being stronger under more strengthened offshore SOAWs, though variable dependence and regional variability exist. Composite analysis over Sumatra reveals that under weak SOAWs, shallow clouds are dominant and cause a pre-moistening effect, supporting shallow-to-deep convection transition. A sea breeze circulation (SBC) with return flow aloft can develop rapidly. Cold pools are better able to trigger new updrafts and contribute to the upscale growth and inland migration of deep convection. In addition, warm gravity waves can propagate upward throughout the troposphere, thereby supporting a strong DC. In contrast, under strong SOAWs, both shallow and middle-high clouds prevail and persist throughout the day. The evolution of moistening and SBC is reduced, leading to weak variation in vertical motion and rainwater confined to the boundary layer. Large-scale winds, moisture, and convection are discussed to interpret how strong SOAWs affect the DC of Sumatra.

scholarly journals Distribution of precipitable water contents over Indian monsoon region

MAUSAM ◽  
2021 ◽  
Vol 58 (2) ◽  
pp. 241-250
Author(s):  
V. R. DURAI ◽  
S. K. ROY BHOWMIK ◽  
H. R. HATWAR
Keyword(s):  
Large Scale ◽  
Indian Monsoon ◽  
Weather Prediction ◽  
India Meteorological Department ◽  
Precipitable Water ◽  
Southwest Monsoon ◽  
Rainfall Events ◽  
Time Availability ◽  
Heavy Rainfall Events ◽  
Water Contents

This paper investigates the spatial distribution of precipitable water contents over Indian region for the southwest monsoon 2005. The precipitable water contents are derived from the objective analysis field of operational Numerical Weather Prediction system of India Meteorological Department. The study shows that the distribution of PWC is capable to capture large scale features of monsoon precipitation system. Real-time availability of this product is expected to be useful in monitoring and prediction of heavy rainfall events.

scholarly journals Scale Interactions between the MJO and the Western Maritime Continent

2016 ◽  
Vol 29 (7) ◽  
pp. 2471-2492 ◽  
Author(s):  
C. E. Birch ◽  
S. Webster ◽  
S. C. Peatman ◽  
D. J. Parker ◽  
A. J. Matthews ◽  
...  
Keyword(s):  
Diurnal Cycle ◽  
Large Scale ◽  
Atmospheric Stability ◽  
Sea Breeze ◽  
Maritime Continent ◽  
Convective Envelope ◽  
Mesoscale Circulations ◽  
Near Surface ◽  
Model Simulations ◽  
Scale Interactions

Abstract State-of-the-art regional climate model simulations that are able to resolve key mesoscale circulations are used, for the first time, to understand the interaction between the large-scale convective environment of the MJO and processes governing the strong diurnal cycle over the islands of the Maritime Continent (MC). Convection is sustained in the late afternoon just inland of the coasts because of sea breeze convergence. Previous work has shown that the variability in MC rainfall associated with the MJO is manifested in changes to this diurnal cycle; land-based rainfall peaks before the active convective envelope of the MJO reaches the MC, whereas oceanic rainfall rates peak while the active envelope resides over the region. The model simulations show that the main controls on oceanic MC rainfall in the early active MJO phases are the large-scale environment and atmospheric stability, followed by high oceanic latent heat flux forced by high near-surface winds in the later active MJO phases. Over land, rainfall peaks before the main convective envelope arrives (in agreement with observations), even though the large-scale convective environment is only moderately favorable for convection. The causes of this early rainfall peak are strong convective triggers from land–sea breeze circulations that result from high surface insolation and surface heating. During the peak MJO phases cloud cover increases and surface insolation decreases, which weakens the strength of the mesoscale circulations and reduces land-based rainfall, even though the large-scale environment remains favorable for convection at this time. Hence, scale interactions are an essential part of the MJO transition across the MC.

Diurnally Modulated Cumulus Moistening in the Preonset Stage of the Madden–Julian Oscillation during DYNAMO*

2015 ◽  
Vol 72 (4) ◽  
pp. 1622-1647 ◽  
Author(s):  
James H. Ruppert ◽  
Richard H. Johnson
Keyword(s):  
Diurnal Cycle ◽  
Large Scale ◽  
Deep Convection ◽  
Tropical Indian Ocean ◽  
Convective Cloud ◽  
Madden Julian Oscillation ◽  
Cumulus Clouds ◽  
Large Scale Circulation ◽  
Areal Coverage ◽  
New Finding

Abstract Atmospheric soundings, radar, and air–sea flux measurements collected during Dynamics of the Madden–Julian Oscillation (DYNAMO) are employed to study MJO convective onset (i.e., the transition from shallow to deep convection) in the tropical Indian Ocean. The findings indicate that moistening of the low–midtroposphere during the preonset stage of the MJO is achieved by simultaneous changes in the convective cloud population and large-scale circulation. Namely, cumuliform clouds deepen and grow in areal coverage as the drying by large-scale subsidence and horizontal (westerly) advection wane. The reduction of large-scale subsidence is tied to the reduction of column radiative cooling during the preonset stage, which ultimately links back to the evolving cloud population. While net column moistening in the preonset stage is tied to large-scale circulation changes, a new finding of this study is the high degree to which the locally driven diurnal cycle invigorates convective clouds and cumulus moistening each day. This diurnal cycle is manifest in a daytime growth of cumulus clouds (in both depth and areal coverage) in response to oceanic diurnal warm layers, which drive a daytime increase of the air–sea fluxes of heat and moisture. This diurnally modulated convective cloud field exhibits prominent mesoscale organization in the form of open cells and horizontal convective rolls. It is hypothesized that the diurnal cycle and mesoscale cloud organization characteristic of the preonset stage of the MJO represent two manners in which local processes promote more vigorous daily-mean column moistening than would otherwise occur.

scholarly journals Principal Component Analysis of the Summertime Winds over the Gulf of California: A Gulf Surge Index

2006 ◽  
Vol 134 (11) ◽  
pp. 3395-3414 ◽  
Author(s):  
Simona Bordoni ◽  
Bjorn Stevens
Keyword(s):  
Principal Component Analysis ◽  
Time Series ◽  
Gulf Of California ◽  
Large Scale ◽  
Monsoon Season ◽  
Principal Component ◽  
Component Analysis ◽  
Near Surface ◽  
The North ◽  
Gulf Surges

Abstract A principal component analysis of the summertime near-surface Quick Scatterometer (QuikSCAT) winds is used to identify the leading mode of synoptic-scale variability of the low-level flow along the Gulf of California during the North American monsoon season. A gulf surge mode emerges from this analysis as the leading EOF, with the corresponding principal component time series interpretable as an objective index for gulf surge occurrence. This index is used as a reference time series for regression analysis and compositing meteorological fields of interest, to explore the relationship between gulf surges and precipitation over the core and marginal regions of the monsoon, as well as the manifestation of these transient events in the large-scale circulation. It is found that, although seemingly mesoscale features confined over the Gulf of California, gulf surges are intimately linked to patterns of large-scale variability of the eastern Pacific ITCZ and greatly contribute to the definition of the northward extent of the monsoonal rains.

Observations of Upper-Tropospheric Temperature Inversions in the Indian Monsoon and Their Links to Convectively Forced Quasi-Stationary Kelvin Waves

2020 ◽  
Vol 77 (8) ◽  
pp. 2835-2846 ◽  
Author(s):  
Richard Newton ◽  
William Randel
Keyword(s):  
Indian Ocean ◽  
Large Scale ◽  
Indian Monsoon ◽  
Monsoon Season ◽  
Deep Convection ◽  
Equatorial Indian Ocean ◽  
Kelvin Waves ◽  
Tropospheric Temperature ◽  
Time Behavior ◽  
Temperature Inversions

Abstract High-vertical-resolution temperature measurements from GPS radio occultation data show frequent upper-tropospheric inversions over the equatorial Indian Ocean during the summer monsoon season. Each year, around 30% of profiles in this region have temperature inversions near 15 km during the monsoon season, peaking during July–September. This work describes the space–time behavior of these inversions, and their links to transient deep convection. The Indian Ocean inversions occur episodically several times each summer, with a time scale of 1–2 weeks, and are quasi stationary or slowly eastward moving. Strong inversions are characterized by cold anomalies in the upper-troposphere (12–15 km), warm anomalies in the tropopause layer (16–18 km), and strong zonal wind anomalies that are coherent with temperature anomalies. Temperature and wind anomalies are centered over the equator and show a characteristic eastward phase tilt with height with a vertical wavelength near 5 km, consistent with a Kelvin wave structure. Composites of outgoing longwave radiation (OLR) show that strong inversions are linked to enhanced deep convection over the equatorial Indian Ocean, preceding the inversions by ~2–6 days. These characteristics suggest that the inversions are linked to convectively forced Kelvin waves, which are Doppler shifted by the easterly monsoonal winds such that they remain quasi stationary in the equatorial Indian Ocean. These large-scale waves influence circulation on the equatorial side of the Indian monsoon anticyclone; they may provide a positive feedback to the underlying convection, and are possibly linked with regions of shear-induced turbulence.

scholarly journals Interannual variability of isotopic composition in water vapor over West Africa and its relation to ENSO

2014 ◽  
Vol 14 (17) ◽  
pp. 24441-24474
Author(s):  
A. Okazaki ◽  
Y. Satoh ◽  
G. Tremoy ◽  
F. Vimeux ◽  
R. Scheepmaker ◽  
...  
Keyword(s):  
West Africa ◽  
Isotopic Composition ◽  
Southern Oscillation ◽  
Monsoon Season ◽  
Precipitation Amount ◽  
West African Monsoon ◽  
Isotopic Signature ◽  
Atmospheric Environment ◽  
Global Spectral Model ◽  
Near Surface

Abstract. This study was performed to examine the relationship between isotopic composition in near-surface vapor (δ18Ov) over West Africa during the monsoon season and El Niño–Southern Oscillation (ENSO) activity using the Isotope-incorporated Global Spectral Model. The model was evaluated using a satellite and in situ observations at intraseasonal to interannual timescales. The model provided an accurate simulation of the spatial pattern and seasonal and interannual variations of isotopic composition in column and surface vapor and precipitation over West Africa. Encouraged by this result, a simulation stretching 34 years (1979–2012) was conducted to investigate the relation between atmospheric environment and isotopic signature at the interannual time scale. The simulation indicated that the depletion in the monsoon season does not appear every year at Niamey. The major difference between the composite fields with and without depletion was in the amount of precipitation in the upstream area of Niamey. As the interannual variation of the precipitation amount is influenced by the ENSO, we regressed the monsoon season averaged δ18Ov from the model and annually averaged NINO3 index, and found a statistically significant correlation (R = 0.56, P < 0.01) at Niamey. This relation suggests that there is a possibility of reconstructing past West African monsoon activity and ENSO using climate proxies.

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