scholarly journals A study on summer monsoon season and rainfall characteristics in summer monsoon season over Southern Vietnam in 1981-2014 period

2017 ◽  
Vol 17 (4B) ◽  
pp. 44-50
Author(s):  
Huong Ngo-Thi-Thanh ◽  
Hang Vu-Thanh
Keyword(s):  
Summer Monsoon ◽  
Monsoon Season ◽  
Extreme Rainfall ◽  
Rain Gauge ◽  
Summer Monsoon Season ◽  
Monsoon Period ◽  
Rain Gauge Data ◽  
Rainfall Characteristics ◽  
Southern Vietnam ◽  
The Mean

This study determines the summer monsoon season over Southern Vietnam in 1981-2014 period by using observed daily rain-gauge data and reanalyzed daily 850 hPa wind data. The results show that the mean onset and retreat dates of summer monsoon over Southern Vietnam occur on May 15 and October 13, with standard deviations of 14.12 and 13.55 days, respectively. The results also show that the onset and retreat dates tend to precede in the recent years. In summer monsoon period, the values of RX1day and RX5day are high in Rach Gia and Ca Mau but low in Can Tho, CDD of all stations are low. In all stations, the values of extreme rainfall indices in 1998-2014 period are higher compared to those in 1981-1997 period.

scholarly journals Variations in O<sub>3</sub>, CO, and CH<sub>4</sub> over the Bay of Bengal during the summer monsoon season: Ship-borne measurements and model simulations

2016 ◽  
Author(s):  
Imran A. Girach ◽  
Narendra Ojha ◽  
Prabha R. Nair ◽  
Andrea Pozzer ◽  
Yogesh K. Tiwari ◽  
...  
Keyword(s):  
Summer Monsoon ◽  
Bay Of Bengal ◽  
Monsoon Season ◽  
Surface Ozone ◽  
Ozone Production ◽  
Spatial And Temporal Variability ◽  
Summer Monsoon Season ◽  
Rainfall Events ◽  
Model Simulations ◽  
Mixing Ratios

Abstract. We present ship-borne measurements of surface ozone, carbon monoxide and methane over the Bay of Bengal (BoB), the first time such measurements have been taken during the summer monsoon season, as a part of the Continental Tropical Convergence Zone (CTCZ) experiment during 2009. O3, CO, and CH4 mixing ratios exhibited significant spatial and temporal variability in the ranges of 8–54 nmol mol−1, 50–200 nmol mol−1, and 1.57–2.15 µmol mol−1, with means of 29.7 ± 6.8 nmol mol−1, 96 ± 25 nmol mol−1, and 1.83 ± 0.14 µmol mol−1, respectively. The average mixing ratios of trace gases over northern BoB (O3: 30 ± 7 nmol mol−1, CO: 95 ± 25 nmol mol−1, CH4: 1.86 ± 0.12 µmol mol−1), in airmasses from northern or central India, did not differ much from those over central BoB (O3: 27 ± 5 nmol mol−1, CO: 101 ± 27 nmol mol−1, CH4: 1.72 ± 0.14 µmol mol−1), in airmasses from southern India. Spatial variability is observed to be most significant for CH4. The ship-based observations, in conjunction with backward air trajectories and ground-based measurements over the Indian region, are analyzed to estimate a net ozone production of 1.5–4 nmol mol−1 day−1 in the outflow. Ozone mixing ratios over the BoB showed large reductions (by ~ 20 nmol mol−1) during four rainfall events. Temporal changes in the meteorological parameters, in conjunction with ozone vertical profiles, indicate that these low ozone events are associated with downdrafts of free-tropospheric ozone-poor airmasses. While the observed variations in O3 and CO are successfully reproduced using the Weather Research and Forecasting model with Chemistry (WRF-Chem), this model overestimates mean concentrations by about 20 %, generally overestimating O3 mixing ratios during the rainfall events. Analysis of the chemical tendencies from model simulations for a low-O3 event on August 10, 2009, captured successfully by the model, shows the key role of horizontal advection in rapidly transporting ozone-rich airmasses across the BoB. Our study fills a gap in the availability of trace gas measurements over the BoB, and when combined with data from previous campaigns, reveals large seasonal amplitude (~ 39 and ~ 207 nmol mol−1 for O3 and CO, respectively) over the northern BoB.

scholarly journals Tropospheric temperature variation over India and links with the Indian summer monsoon : 1971-2000

MAUSAM ◽  
2022 ◽  
Vol 53 (3) ◽  
pp. 289-308
Author(s):  
D. R. KOTHAWALE ◽  
K. RUPA KUMAR
Keyword(s):  
Summer Monsoon ◽  
Southern Oscillation ◽  
Monsoon Season ◽  
Temporal Variations ◽  
Mean Annual Temperature ◽  
Tropospheric Temperature ◽  
Temperature Variations ◽  
Annual Cycles ◽  
The Mean ◽  
Spatio Temporal

In the context of the ever increasing interest in the regional aspects of global warming, understanding the spatio-temporal variations of tropospheric temperature over India is of great importance. The present study, based on the data from 19 well distributed radiosonde stations for the period 1971-2000, examines the seasonal and annual mean temperature variations at the surface and five selected upper levels, viz., 850, 700, 500, 200 and 150 hPa. An attempt has also been made to bring out the association between tropospheric temperature variations over India and the summer monsoon variability, including the role of its major teleconnection parameter, the El Niño/Southern Oscillation (ENSO).   Seasonal and annual mean all-India temperature series are analyzed for surface and five tropospheric levels.  The mean annual cycles of temperature at different tropospheric levels indicate that the pre-monsoon season is slightly warmer than the monsoon season at the surface, 850 hPa and 150 hPa levels, while it is relatively cooler at all intermediate levels.  The mean annual temperature shows a warming of 0.18° C and 0.3° C per 10 years at the surface and 850 hPa, respectively.   Tropospheric temperature anomaly composites of excess (deficient) monsoon rainfall years show pronounced positive (negative) anomalies during the month of May, at all the levels.  The pre-monsoon pressure of Darwin has significant positive correlation with the monsoon temperature at the surface and 850 hPa.

Precipitation modes over the Western Ghats orography during the summer monsoon season

2021 ◽  
Author(s):  
Jayesh Phadtare ◽  
Jennifer Fletcher ◽  
Andrew Ross ◽  
Andy Turner ◽  
Thorwald Stein ◽  
...  
Keyword(s):  
Summer Monsoon ◽  
West Coast ◽  
Western Ghats ◽  
Monsoon Season ◽  
Radiosonde Data ◽  
Summer Monsoon Season ◽  
The West ◽  
Radiosonde Station ◽  
Westerly Flow ◽  
The Western Ghats

&lt;p&gt;Precipitation distribution around an orographic barrier is controlled by the Froude Number (Fr) of the impinging flow. Fr is essentially a ratio of kinetic energy and stratification of winds around the orography. For Fr &gt; 1 (Fr &lt;1), the flow is unblocked (blocked) and precipitation occurs over the mountain peaks and the lee region (upwind region). While idealized modelling studies have robustly established this relationship, its widespread real-world application is hampered by the dearth of relevant observations. Nevertheless, the data collected in the field campaigns give us an opportunity to explore this relationship and provide a testbed for numerical models. A realistic distribution of precipitation over a mountainous region in these models is necessary for flash-flood and landslide forecasting. The Western Ghats region is a classic example where the orographically induced precipitation leads to floods and landslides during the summer monsoon season. In the recent INCOMPASS field campaign, it was shown that the precipitation over the west coast of India occurred in alternate offshore and onshore phases. The Western Ghats received precipitation predominantly during the onshore phase which was characterized by a stronger westerly flow. Here, using the radiosonde data from a station over the Indian west coast and IMERG precipitation product, we show that climatologically, these phases can be mapped over an Fr-based classification of the monsoonal westerly flow. Classifying the flow as 'High Fr' (Fr &gt;1), 'Moderate Fr' ( 0.5 &lt; Fr &amp;#8804; 1) and 'Low Fr' ( Fr &amp;#8804; 0.5 ) gives three topographical modes of precipitation -- 'Orographic', 'Coastal' and 'Offshore', respectively. &amp;#160;Moreover, these modes are not sensitive to the choice of radiosonde station over the west coast.&lt;/p&gt;

scholarly journals Summer Monsoon Season Streamflow Variations in the Middle Yellow River since 1570 CE Inferred from Tree Rings of Pinus tabulaeformis

Atmosphere ◽  
2020 ◽  
Vol 11 (7) ◽  
pp. 717 ◽  
Author(s):  
Feng Chen ◽  
Magdalena Opała-Owczarek ◽  
Piotr Owczarek ◽  
Youping Chen
Keyword(s):  
Tree Rings ◽  
Summer Monsoon ◽  
Yellow River ◽  
Asian Summer Monsoon ◽  
Monsoon Season ◽  
Pinus Tabulaeformis ◽  
The Yellow River ◽  
Summer Monsoon Season ◽  
Streamflow Reconstruction ◽  
Asian Summer

This study investigates the potential reconstruction of summer monsoon season streamflow variations in the middle reaches of the Yellow River from tree rings in the Qinling Mountains. The regional chronology is significantly positively correlated with the July–October streamflow of the middle Yellow River from 1919 to 1949, and the derived reconstruction explains 36.4% of the actual streamflow variance during this period. High streamflows occurred during 1644–1757, 1795–1806, 1818–1833, 1882–1900, 1909–1920 and 1933–1963. Low streamflows occurred during 1570–1643, 1758–1794, 1807–1817, 1834–1868, 1921–1932 and 1964–2012. High and low streamflow intervals also correspond well to the East Asian summer monsoon (EASM) intensity. Some negative correlations of our streamflow reconstruction with Indo-Pacific sea surface temperature (SST) also suggest the linkage of regional streamflow changes to the Asian summer monsoon circulation. Although climate change has some important effects on the variation in streamflow, anthropogenic activities are the primary factors mediating the flow cessation of the Yellow River, based on streamflow reconstruction.

IMDAA Regional Reanalysis: Performance Evaluation During Indian Summer Monsoon Season

2020 ◽  
Vol 125 (2) ◽  
Author(s):  
Raghavendra Ashrit ◽  
S. Indira Rani ◽  
Sushant Kumar ◽  
S. Karunasagar ◽  
T. Arulalan ◽  
...  
Keyword(s):  
Performance Evaluation ◽  
Summer Monsoon ◽  
Indian Summer Monsoon ◽  
Monsoon Season ◽  
Summer Monsoon Season ◽  
Regional Reanalysis

Changes in TRMM Rainfall due to the Orbit Boost Estimated from Buoy Rain Gauge Data

2007 ◽  
Vol 24 (9) ◽  
pp. 1598-1607 ◽  
Author(s):  
Jeremy D. DeMoss ◽  
Kenneth P. Bowman
Keyword(s):  
Sampling Error ◽  
Tropical Rainfall Measuring Mission ◽  
Rain Gauge ◽  
Rain Gauge Data ◽  
Rain Gauges ◽  
Rate Dependent ◽  
Wide Range ◽  
The Mean ◽  
Microwave Imager ◽  
Trmm Microwave Imager

Abstract During the first three-and-a-half years of the Tropical Rainfall Measuring Mission (TRMM), the TRMM satellite operated at a nominal altitude of 350 km. To reduce drag, save maneuvering fuel, and prolong the mission lifetime, the orbit was boosted to 403 km in August 2001. The change in orbit altitude produced small changes in a wide range of observing parameters, including field-of-view size and viewing angles. Due to natural variability in rainfall and sampling error, it is not possible to evaluate possible changes in rainfall estimates from the satellite data alone. Changes in TRMM Microwave Imager (TMI) and the precipitation radar (PR) precipitation observations due to the orbit boost are estimated by comparing them with surface rain gauges on ocean buoys operated by the NOAA/Pacific Marine Environment Laboratory (PMEL). For each rain gauge, the bias between the satellite and the gauge for pre- and postboost time periods is computed. For the TMI, the satellite is biased ∼12% low relative to the gauges during the preboost period and ∼1% low during the postboost period. The mean change in bias relative to the gauges is approximately 0.4 mm day−1. The change in TMI bias is rain-rate-dependent, with larger changes in areas with higher mean precipitation rates. The PR is biased significantly low relative to the gauges during both boost periods, but the change in bias from the pre- to postboost period is not statistically significant.

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