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Analyzing Spatio-temporal Variability of Clouds over the Arabian Sea using ERA5 reanalysis dataset

Jaswant Moher (jaswant@cas.iitd.ac.in), Vimlesh Pant, Sagnik Dey

Data and Methodology

ERA5 hourly cloud cover data at 0.25°×0.25° at 37 pressure levels (1979-2018) Why ERA5 ?

ECCRA (Course resolution 10°×10°, Human observation bias) Eastman et al. (2011).

ISCCP (Systematic Artifacts, Use of geostationary and polar orbiting satellite data at Arabian Sea) Norris et al. (2015)

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Figure 2. (a) Diurnal variation of low-level clouds, (b) diurnal variation over the different sectors of the Arabian Sea (JJA)

Figure 3. Change in diurnal amplitude of high-level clouds over the AS, black dots represents statistically significance level above 95% .

Results

Figure 1. Seasonal trend of cloud cover over the Indian Ocean (1979-2018)

Results

Figure 4. (a) seasonal plots of local time of maximum Tmax for past (1979-1988) and present (2009-2018), (b) change in Tmax of a particular time bin as shown in legend

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Conclusions

1. Over last four decades low-level clouds have decreased while mid and high-level have increased.
2. The local time of maximum of low, mid and high-level clouds shows seasonal and spatial heterogeneity.
3. The diurnal amplitude of clouds have changed in last four decades.
4. At present clouds are peaking at later hours of the day than past.

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Acknowledgement

I thanks ECMWF for providing ERA5 data, I also acknowledge institute fellowship and research travel support by Indian Institute of Technology Delhi.

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References

1. Eastman, R., Warren, S. G., & Hahn, C. J. (2011). Variations in cloud cover and cloud types over the ocean from surface observations, 1954–2008. Journal of Climate, 24(22), 5914-5934.
2. Norris, J. R., & Evan, A. T. (2015). Empirical removal of artifacts from the ISCCP and PATMOS-x satellite cloud records. Journal of Atmospheric and Oceanic Technology, 32(4), 691-702.

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EGU23-1130 | CL2.1