Vertical cloud structures of the boreal summer intraseasonal variability based on CloudSat observations and ERA-interim reanalysis

Abstract

The boreal summer intraseasonal variability (BSISV), which is characterized by pronounced meridional propagation from the equatorial zone to the Indian Continent, exerts significant modulation of the active/break phases of the south Asian monsoon. This form of variability provides a primary source of subseasonal predictive skill of the Asian summer monsoon. Unfortunately, current general circulation models display large deficiencies in representing this variability. The new cloud observations made available by the CloudSat mission provide an unprecedented opportunity to advance our characterization of the BSISV. In this study, the vertical structures of cloud water content and cloud types associated with the BSISV over the Indian Ocean and subcontinent are analyzed based on CloudSat observations from 2006 to 2008. These cloud structures are also compared to their counterparts as derived from ERA-interim reanalysis. A marked vertical tilting structure in cloud water is illustrated during the northward propagation of the BSISV based on both datasets. Increased cloud liquid water content (LWC) tends to appear to the north of the rainfall maximum, while ice water content (IWC) in the upper troposphere slightly lags the convection. This northward shift of increased LWC, which is in accord with local enhanced moisture as previously documented, may play an important role in the northward propagation of the BSISV. The transition in cloud structures associated with BSISV convection is further demonstrated based on CloudSat, with shallow cumuli at the leading edge, followed by the deep convective clouds, and then upper anvil clouds. Some differences in cloud water structures between CloudSat and ERA-interim are also noted, particularly in the amplitudes of IWC and LWC fields.

Study of the microphysical properties associated with the Monsoon Intraseasonal Oscillation as seen from the TRMM observations

“…The transition from shallow to middle level cloud happens through the formation of mixed phase cloud or precipitable ice, and finally, the formation of anvil occurs subsequently. This is consistent with the results of Jiang et al (2010) based on Cloudsat and ERA40 data, where he showed that the high clouds with ice phases lag with respect to rainfall maxima followed by the mixed phase and by lower level clouds (predominantly cloud water). To see the associated dynamical parameters during the northward propagation, we analyzed vertical profile of temperature anomaly, vertical velocity, vorticity and anomaly of moist static energy (MSE) as a measure of convective instability.…”

“…cloud water distribution is reported by Jiang et al (2010). The cloud ice is found to be lagging with respect to convection centre and the stratiform rain maxima is collocated with the cloud ice maxima.…”

An evaluation of boreal summer intra-seasonal oscillation simulated by BCC_AGCM2.2

“…Some recent studies have suggested that interactions between different cloud regimes, circulation, and diabatic heating in the boundary layer may play a critical role for the evolution of the BSISO (Chattopadhyay et al 2009;Jiang et al 2011;Abhik et al 2013). The role of deficiencies in relation to background states in influencing the northward propagating BSISOs has also been suggested by many studies (Jiang and Li 2005;Ajayamohan and Goswami 2007;Seo et al 2007;Sabeerali et al 2013).…”

“…These biases may be associated with a strong and westward extension of WNPSH simulated in BCC_AGCM2.2, which will be detailed explored later. Figure 7 compares the vertical dynamic and thermodynamic structures following Jiang et al (2011) and Abhik et al (2013). This includes anomalous vorticity, specific humidity, equivalent potential temperature, cloud liquid water, vertical velocity and diabatic heating with observations on top and model simulations at the bottom.…”

Cloud vertical structure over a tropical station obtained using long-term high-resolution radiosonde measurements

“…Therefore, an accurate location of the cloud top and complete vertical structure information on the cloud can be obtained by the combined use of CPR and CALIOP, because of their unique complementary skills. Previous studies have shown that CloudSat-CALIPSO data have better accuracy compared with ISCCP and ground observation data (Sassen and Wang, 2008;Naud and Chen, 2010;Kim et al, 2011;Noh et al, 2011;Jiang et al, 2011). However, because the repeat time of these polar-orbiting satellites for any particular location is very large, the time resolution of such observations is low (L'Ecuyer and Jiang, 2010;Qian et al, 2012).…”