Seasonal variation of the diurnal cycle of rainfall in the eastern equatorial Indian Ocean

Abstract

The diurnal cycle of rainfall over the eastern equatorial Indian Ocean is studied for the period 23 rd October 2001 to 31 st October 2003 using the hourly data from the Triton buoy positioned at 1.5°S and 90°E. An analysis of the active and weak spells of the rainfall for different seasons showed that the rainfall peaked in the late evening hours in Winter, Summer and Fall seasons and in early morning hours (Spring) in 2002. The active spell of the rainfall peaked in the afternoon hours, during Winter, Spring and Summer seasons in 2003, which agrees with the previous results of Janowiak et al (1994). An analysis of the rainfall events showed that Fall 2002 had maximum rainfall events (90) and minimum (60) were observed in Spring 2003. Further it was seen that majority of the rain events (> 60%) were less than 3 hours duration throughout the study period. The longer duration rainfall events (i.e rain events greater than 6 hour duration) contributed significantly to Spring 2002 (20% of the total rainfall) and Winter 2003 (21% of the total rainfall) seasons respectively. Harmonic analysis of the hourly rainfall data for different seasons revealed that diurnal harmonic, explains more than 80% of the variance for all the seasons. Further, the diurnal harmonic has the maximum amplitude for all seasons except summer, where the semidiurnal and six hourly harmonics are significant.

How accurate are satellite estimates of precipitation over the north Indian Ocean?

“…As diurnal variation of precipitation is primarily associated with the underlying atmospheric dynamics and geographical features, reliable knowledge of the diurnal cycle is vital for a wide range of applications. Ramesh Kumar et al (2006) investigated the diurnal cycle of precipitation in the equatorial Indian Ocean using hourly TRITON buoy observations in 2002 and found that the precipitation peaked in the late evening during winter, summer and fall seasons and during early morning hours of spring season. Here, the diurnal cycle from hourly IMERG and buoy observations are investigated at two locations in the north Indian Ocean for the month of August 2014.…”

“…Precipitation also plays a key role in freshwater flux and sea surface salinity variations (Ramesh Kumar and Schulz 2002;Prakash et al 2012). However, in-situ observations of precipitation over the global oceans are essentially heterogeneous and sparse, limiting its applicability for global and regional scale applications (Ramesh Kumar and Prasad 1997;Ramesh Kumar et al 2006;Prakash et al 2013;. The Ocean Rain And Ice-phase precipitation measurement Network (OceanRAIN; Klepp 2015) project is aimed to better understand the global oceanic precipitation characteristics and for the validation of satellite, reanalysis and numerical model precipitation datasets.…”

“…In this study, precipitation estimates from IMERG final run version 4 product is first time extensively assessed over the north Indian Ocean using buoy measurements at hourly scale for the period of March 2014 to December 2015. It is to be noted that the precipitation over this oceanic region has paramount impact on the surrounding landmasses at distinct scales (Ramesh Kumar and Sreejith 2005;, 2006Pai et al 2016). For instance, the sea surface temperature, moisture and wind over the Arabian Sea is crucial for the onset and progress of the southwest monsoon over India.…”

Diurnal‐scale signatures of monsoon rainfall over the Indian region from TRMM satellite observations

“…Over the Arabian Sea, a spatially coherent pattern in the mode of diurnal rainfall peak over a region where it rains at least 30% of the time suggests well‐organized local convection as a probable cause behind the observed peak. Finally, while there appears to be organized convection over the western equatorial Indian Ocean (as seen from the homogeneity of the peak octet), the lack of spatial coherence over the eastern equatorial Indian Ocean suggests the dominance of locally triggered (unorganized) short‐duration events [e.g., see Ramesh Kumar et al , 2006].…”

Relation between rainfall duration and diurnal variation in the warm season precipitation over central eastern China

“…The problem is that in these studies the diurnal precipitation is generally presented by averaged hourly precipitation over the entire data record or over all of the rainy days, which could downplay the significance of diurnal cycle or misrepresent the mechanism behind different types of rainfall events. Multi‐phases of diurnal precipitation were seen in many regions, especially the semidiurnal harmonic variation of precipitation [ Dai , 2001; Ramesh Kumar et al , 2006; Yu et al , 2007]. The diurnal variations with multi‐phases usually present no significant diurnal cycle.…”