cloud drop effective radius

{{Short description|Average of size of cloud droplets}}

{{Use dmy dates|date=December 2023}}

The cloud drop effective radius (alternatively cloud effective radius or simply effective radius when in context) is a weighted mean of the size distribution of cloud droplets.{{cite web|url=http://disc.sci.gsfc.nasa.gov/PIP/shtml/cloud_effective_radius.shtml |title=Cloud Effective Radius |work=Goddard Earth Sciences Data and Information Services Center |accessdate=3 August 2009 |url-status=dead |archiveurl=https://web.archive.org/web/20090724155507/http://disc.sci.gsfc.nasa.gov/PIP/shtml/cloud_effective_radius.shtml |archivedate=24 July 2009 }} The term was defined in 1974 by James E. Hansen and Larry Travis as the ratio of the third to the second moment of a droplet size distribution to aid in the inversion of remotely sensed data.{{cite journal |author=Hansen., J.E. and L.D. Travis |title=Light scattering in planetary atmospheres |journal=Space Science Reviews |volume=16 |issue =4 |year=1974 |doi=10.1007/BF00168069 |pages=527–610 |bibcode=1974SSRv...16..527H|s2cid=122043532 }} Physically, it is an area weighted radius of the cloud drop particles.

Mathematically, this can be expressed as

$$r\_e\; =\; \backslash dfrac\{\backslash displaystyle\; \backslash int\_\{0\}^\{\backslash infty\}\; \backslash pi\; r^3\; \backslash cdot\; n(r)\backslash ,dr\}\{\backslash displaystyle\; \backslash int\_\{0\}^\{\backslash infty\}\; \backslash pi\; r^2\; \backslash cdot\; n(r)\backslash ,dr\}.$$

The global effective particle radius has different values for water and ice clouds: the former is around 14 μm, whereas for ice it is around 25 μm. Studies also indicate that the effective cloud droplet radius is larger over oceans than over ground by 15%–20%. By contrast, the difference in the ice particle size over land and oceans is much smaller (only 5%).

{{cite journal

| last1 = Stubenrauch | first1 = C. J.

| last2 = Rossow | first2 = W. B.

| last3 = Kinne | first3 = S.

| last4 = Ackerman | first4 = S.

| last5 = Cesana | first5 = G.

| last6 = Chepfer | first6 = H

| last7 = Di Girolamo | first7 = L.

| last8 = Getzewich | first8 = B.

| last9 = Guignard | first9 = A.

| last10 = Heidinger | first10 = A.

| last11 = Maddux | first11 = B. C.

| last12 = Menzel | first12 = W.P

| last13 = Minnis | first13 = P.

| last14 = Pearl | first14 = C.

| last15 = Platnick | first15 = S.

| last16 = Poulsen | first16 = C.

| last17 = Reidi | first17 = J.

| last18 = Sun-Mack | first18 = S

| last19 = Walther | first19 = A.

| last20 = Winker | first20 = D.

| last21 = Zeng | first21 = S.

| last22 = Zhao | first22 = G.

| title = Assessment of global cloud datasets from satellites: Project and Database initiated by GEWEX Radiation Panel

| journal = Bulletin of the American Meteorological Society

| date = 2013

| volume = 94 | issue = 7

| pages = 1031–1049

| bibcode = 2013BAMS...94.1031S

| doi = 10.1175/BAMS-D-12-00117.1

| url = https://hal.archives-ouvertes.fr/hal-01091218/document| doi-access = free

| hdl = 11858/00-001M-0000-0014-39DE-1

| hdl-access = free

}}