Morphology of organized convection in tropics and subtropics Chuntao Liu

Table of content Differences between land and ocean in the organized convection. Where are the organized convection? Seasonal variation of the organized convection. Diurnal variation of the organized convection. Linear shaped organized convection and their orientations. Relationship between Wind shear and the shapes of the organized convection.

Examples of organized convection with different “shapes” The shape of the convective region is inferred by major and minor axis of fitting ellipse over the contiguous convective raining area identified by 2A23 algorithm

Precipitation regions and Convective regions land (contours) vs. ocean (color fill) Precipitation region: Size: Ocean > land Linear shape: more over ocean Convective region: Size: Land > Ocean Linear shape: more over ocean

Samples of the organized convection and precipitation region Convective regions (21 million > 80 km 2 ) Precipitation regions (28 million > 80 km 2 ) Ocean (83%)Land (17%)Ocean (80%)Land (20%) Regions > 1000 km 2 214, % 126, % 1,622, % 641, % Regions > 1000 km 2 & linear (R axis < 0.2) 0.18 %0.15 %0.49 %0.36 % Linear shape of regions > 1000 km 2 15 %5 %7 %3 % Regions > 1000 km 2 & round (R axis > 0.6) 0.18 % 0.71 %1.56 % 3.35 % Round shape of regions > 1000 km 2 14 %21 % 22 % 28 %

Where are they? More round systems over land. More convective lines over ocean. How about meridional change?

# of samples Sample bias is not removed.

Winter time frontal systems dominate the local organized convection Higher fraction of linear shape over ocean

For precipitation features

How about the seasonal variation? Large organized convection (> 1000 km 2 ) Linear shape organized convection (minor / major axis < 0.2)

After remove the sample bias, there are more organized convection over tropics than subtropics However, the fraction of the large convective regions is higher over subtropics, especially in winter time over ocean, and spring over land

Orientation of the convective lines

Color represents the orientation, deep red is from north- northeast to southwest deep blue is from north-northwest to southeast Size of the symbols represent the size of the convective lines Note the terrain impact to the orientation of the lines over south slope of Himalayas

Orientation transition from land to ocean Over subtropics, convective lines are more north-south oriented over ocean than over land East-westNortheast-SouthwestNorth-South Northwest-Southeast

Orientation of the precipitation regions are more complicated due to the complexity of the trailing stratiform region

Diurnal variation of shapes of organized convection

Convective lines tend to occur a little earlier in the day

Convective intensity differences land (contours) vs. ocean (colorfill) In addition to the general weaker convective intensity over ocean, there is a group of organized, but shallow convection over ocean (15% compare to 1.5% over land).

Shallow & large convective regions

Shallow & large convective lines

Fraction of shallow organized convection with linear shape

Why there are different shape of the convection? especially for those linear shape systems? Low level wind shear is shown to be important with the squall lines. The wind component along the line and cross line are believed to have some roles. CAPE? Mid level moisture.

Low level wind shear