scholarly journals The Interannual Stability of Cumulative Frequency Distributions for Convective System Size and Intensity

2009 ◽  
Vol 22 (19) ◽  
pp. 5218-5231 ◽  
Author(s):  
Karen I. Mohr ◽  
John Molinari ◽  
Chris D. Thorncroft
Keyword(s):  
West Africa ◽  
Brightness Temperature ◽  
Interannual Variability ◽  
Western Pacific ◽  
Convective System ◽  
Cumulative Frequency ◽  
Wet Season ◽  
Frequency Distributions ◽  
Convective Systems ◽  
The Western Pacific

Abstract The characteristics of convective system populations in West Africa and the western Pacific tropical cyclone basin were analyzed to investigate whether interannual variability in convective activity in tropical continental and oceanic environments is driven by variations in the number of events during the wet season or by favoring large and/or intense convective systems. Convective systems were defined from Tropical Rainfall Measuring Mission (TRMM) data as a cluster of pixels with an 85-GHz polarization-corrected brightness temperature below 255 K and with an area of at least 64 km2. The study database consisted of convective systems in West Africa from May to September 1998–2007, and in the western Pacific from May to November 1998–2007. Annual cumulative frequency distributions for system minimum brightness temperature and system area were constructed for both regions. For both regions, there were no statistically significant differences between the annual curves for system minimum brightness temperature. There were two groups of system area curves, split by the TRMM altitude boost in 2001. Within each set, there was no statistically significant interannual variability. Subsetting the database revealed some sensitivity in distribution shape to the size of the sampling area, the length of the sample period, and the climate zone. From a regional perspective, the stability of the cumulative frequency distributions implied that the probability that a convective system would attain a particular size or intensity does not change interannually. Variability in the number of convective events appeared to be more important in determining whether a year is either wetter or drier than normal.

scholarly journals Backward Adaptive Brightness Temperature Threshold Technique (BAB3T): A Methodology to Determine Extreme Convective Initiation Regions Using Satellite Infrared Imagery

2020 ◽  
Vol 12 (2) ◽  
pp. 337
Author(s):  
Maite Cancelada ◽  
Paola Salio ◽  
Daniel Vila ◽  
Stephen W. Nesbitt ◽  
Luciano Vidal
Keyword(s):  
Brightness Temperature ◽  
Deep Convection ◽  
Convective System ◽  
Temperature Threshold ◽  
Lightning Flash ◽  
Convective Initiation ◽  
Convective Storms ◽  
Convective Systems ◽  
Diurnal Cycles ◽  
Backward Tracking

Thunderstorms in southeastern South America (SESA) stand out in satellite observations as being among the strongest on Earth in terms of satellite-based convective proxies, such as lightning flash rate per storm, the prevalence for extremely tall, wide convective cores and broad stratiform regions. Accurately quantifying when and where strong convection is initiated presents great interest in operational forecasting and convective system process studies due to the relationship between convective storms and severe weather phenomena. This paper generates a novel methodology to determine convective initiation (CI) signatures associated with extreme convective systems, including extreme events. Based on the well-established area-overlapping technique, an adaptive brightness temperature threshold for identification and backward tracking with infrared data is introduced in order to better identify areas of deep convection associated with and embedded within larger cloud clusters. This is particularly important over SESA because ground-based weather radar observations are currently limited to particular areas. Extreme rain precipitation features (ERPFs) from Tropical Rainfall Measurement Mission are examined to quantify the full satellite-observed life cycle of extreme convective events, although this technique allows examination of other intense convection proxies such as the identification of overshooting tops. CI annual and diurnal cycles are analyzed and distinctive behaviors are observed for different regions over SESA. It is found that near principal mountain barriers, a bimodal diurnal CI distribution is observed denoting the existence of multiple CI triggers, while convective initiation over flat terrain has a maximum frequency in the afternoon.

scholarly journals Interannual Variability of Lower Equatorial Intermediate Current Response to ENSO in the Western Pacific

2020 ◽  
Vol 47 (16) ◽  
Author(s):  
Qiang Ma ◽  
Jianing Wang ◽  
Fan Wang ◽  
Dongxiao Zhang ◽  
Zhixiang Zhang ◽  
...  
Keyword(s):  
Interannual Variability ◽  
Western Pacific ◽  
Current Response ◽  
The Western Pacific ◽  
Equatorial Intermediate Current

Relationship between prediction skill of surface winds in average of weeks 1 to 4 and interannual variability over the Western Pacific and Indian Ocean

2021 ◽  
Author(s):  
Ravi P. Shukla ◽  
J. L. Kinter
Keyword(s):  
Indian Ocean ◽  
Interannual Variability ◽  
Lead Time ◽  
Temporal Correlation ◽  
Western Pacific ◽  
Prediction Skill ◽  
Forecast System ◽  
Climate Forecast System ◽  
Region Model ◽  
The Western Pacific

AbstractThis study examines the possible relationship between predictions of weekly and biweekly averages of 10m winds at 3 weeks lead-time and interannual variability over Western Pacific and Indian Ocean (WP-IO) using Climate Forecast System version 2 (CFSv2) reforecasts for period 1979-2008. There is large temporal correlation between forecasts and reanalyses for zonal, meridional and total wind magnitudes at 10m over most of WP-IO for average of weeks 1 and 2 (W1 and W2) in reforecasts initialized in January (JIR) and May (MIR). The model has some correlations that exceed 95% confidence in some portions of WP-IO in week 3 (W3) but no skill in week 4 (W4) over most of the region. Model depicts prediction skill in 14-day average of weeks 3-4 (W3-4) over portions of WP-IO, similar to level of skill in W3. The amplitude of interannual variability (IAV) for 10m-winds in W1 of JIR and MIR is close to that in reanalyses. As lead-time increases, amplitude of IAV of 10m-winds gradually decreases over WP-IO in reforecasts; in contrast to behavior in reanalyses. The amplitude of IAV of predicted 10m-winds in W3-4 over WP-IO is equivalent to that in W3 and W4 in reforecasts. In contrast, the amplitude of IAV in W3-4 in January and May of reanalysis is much smaller than IAV of W3 and W4. Therefore, one of the possible causes for prediction skill in W3-4 over sub-regions of WP-IO is due to reduction of IAV bias in W3-4 in comparison to IAV bias in W3 and W4.

scholarly journals A 17 year climatology of the macrophysical properties of convection in Darwin

2018 ◽  
Vol 18 (23) ◽  
pp. 17687-17704 ◽  
Author(s):  
Robert C. Jackson ◽  
Scott M. Collis ◽  
Valentin Louf ◽  
Alain Protat ◽  
Leon Majewski
Keyword(s):  
Climate Models ◽  
Global Climate ◽  
Sea Breeze ◽  
Active Phase ◽  
Global Climate Models ◽  
Convective System ◽  
Wet Season ◽  
Australian Monsoon ◽  
Convective Systems ◽  
Mesoscale Convective

Abstract. The validation of convective processes in global climate models (GCMs) could benefit from the use of large datasets that provide long-term climatologies of the spatial statistics of convection. To that regard, echo top heights (ETHs), convective areas, and frequencies of mesoscale convective systems (MCSs) from 17 years of data from a C-band polarization (CPOL) radar are analyzed in varying phases of the Madden–Julian Oscillation (MJO) and northern Australian monsoon in order to provide ample validation statistics for GCM validation. The ETHs calculated using velocity texture and reflectivity provide similar results, showing that the ETHs are insensitive to various techniques that can be used. Retrieved ETHs are correlated with those from cloud top heights retrieved by Multifunctional Transport Satellites (MTSATs), showing that the ETHs capture the relative variability in cloud top heights over seasonal scales. Bimodal distributions of ETH, likely attributable to the cumulus congestus clouds and mature stages of convection, are more commonly observed when the active phase of the MJO is over Australia due to greater mid-level moisture during the active phase of the MJO. The presence of a convectively stable layer at around 5 km altitude over Darwin inhibiting convection past this level can explain the position of the modes at around 2–4 km and 7–9 km. Larger cells were observed during break conditions compared to monsoon conditions, but only during the inactive phase of the MJO. The spatial distributions show that Hector, a deep convective system that occurs almost daily during the wet season over the Tiwi Islands, and sea-breeze convergence lines are likely more common in break conditions. Oceanic MCSs are more common during the night over Darwin. Convective areas were generally smaller and MCSs more frequent during active monsoon conditions. In general, the MJO is a greater control on the ETHs in the deep convective mode observed over Darwin, with higher distributions of ETH when the MJO is active over Darwin.

scholarly journals Interannual Variability of the Mindanao Current/Undercurrent in Direct Observations and Numerical Simulations

2016 ◽  
Vol 46 (2) ◽  
pp. 483-499 ◽  
Author(s):  
Shijian Hu ◽  
Dunxin Hu ◽  
Cong Guan ◽  
Fan Wang ◽  
Linlin Zhang ◽  
...  
Keyword(s):  
Pacific Ocean ◽  
Interannual Variability ◽  
Western Pacific ◽  
Western Boundary ◽  
Western Pacific Ocean ◽  
Ekman Pumping ◽  
Wind Stress Curl ◽  
Boundary Currents ◽  
Mindanao Current ◽  
The Western Pacific

AbstractThe interannual variability of the boundary currents east of the Mindanao Island, including the Mindanao Current/Undercurrent (MC/MUC), is investigated using moored acoustic Doppler current profiler (ADCP) measurements combined with a series of numerical experiments. The ADCP mooring system was deployed east of the Mindanao Island at 7°59′N, 127°3′E during December 2010–August 2014. Depth-dependent interannual variability is detected in the two western boundary currents: strong and lower-frequency variability dominates the upper-layer MC, while weaker and higher-frequency fluctuation controls the subsurface MUC. Throughout the duration of mooring measurements, the weakest MC was observed in June 2012, in contrast to the maximum peaks in December 2010 and June 2014, while in the deeper layer the MUC shows speed peaks circa December 2010, January 2011, April 2013, and July 2014 and valleys circa June 2011, August 2012, and November 2013. Diagnostic analysis and numerical sensitivity experiments using a 2.5-layer reduced-gravity model indicate that wind forcing in the western Pacific Ocean is a driving agent in conditioning the interannual variability of MC and MUC. Results suggest that westward-propagating Rossby waves that generate in the western Pacific Ocean (roughly 150°–180°E) are of much significance in the interannual variability of the two boundary currents. Fluctuation of Ekman pumping due to local wind stress curl anomaly in the far western Pacific Ocean (roughly 120°–150°E) also plays a role in the interannual variability of the MC. The relationship between the MC/MUC and El Niño is discussed.

Interannual Variability of East Asian Summer Monsoon Simulated by CMIP3 and CMIP5 AGCMs: Skill Dependence on Indian Ocean–Western Pacific Anticyclone Teleconnection

2014 ◽  
Vol 27 (4) ◽  
pp. 1679-1697 ◽  
Author(s):  
Fengfei Song ◽  
Tianjun Zhou
Keyword(s):  
Indian Ocean ◽  
Interannual Variability ◽  
East Asian Summer Monsoon ◽  
Asian Summer Monsoon ◽  
East Asian ◽  
Western Pacific ◽  
Rainfall Pattern ◽  
Southward Shift ◽  
Asian Summer ◽  
The Western Pacific

Abstract The climatology and interannual variability of East Asian summer monsoon (EASM) are investigated by using 13 atmospheric general circulation models (AGCMs) from phase 3 of the Coupled Model Intercomparison Project (CMIP3) and 19 AGCMs from CMIP5. The mean low-level monsoon circulation is reasonably reproduced in the multimodel ensemble mean (MME) of CMIP3 and CMIP5 AGCMs, except for a northward shift of the western Pacific subtropical high. However, the monsoon rainband known as mei-yu/baiu/changma (28°–38°N, 105°–150°E) is poorly simulated, although a significant improvement is seen from CMIP3 to CMIP5. The interannual EASM pattern is obtained by regressing the precipitation and 850-hPa wind on the observed EASM index. The observed dipole rainfall pattern is partly reproduced in CMIP3 and CMIP5 MME but with two deficiencies: weaker magnitude and southward shift of the dipole rainfall pattern. These deficiencies are closely related to the weaker and southward shift of the western Pacific anticyclone (WPAC). The simulation skill of the interannual EASM pattern has been significantly improved from CMIP3 to CMIP5 MME accompanied by the enhanced dipole rainfall pattern and WPAC. Analyses demonstrate that the tropical eastern Indian Ocean (IO) rainfall response to local warm SST anomalies and the associated Kelvin wave response over the Indo–western Pacific region are important to maintain the WPAC. A successful reproduction of interannual EASM pattern depends highly on the IO–WPAC teleconnection. The significant improvement in the interannual EASM pattern from CMIP3 to CMIP5 MME is also due to a better reproduction of this teleconnection in CMIP5 models.

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