Possibility of stratospheric hydration by overshooting analyzed with space-borne sensorsSuginori Iwasaki (National Defense Academy, Japan)

T. Shibata (Nagoya University, Japan.), H. Ishimoto (Meteorological Research Institute, Japan), H. Kubota (Japan Agency for Marine-Earth Science and Technology, Japan)

To estimate the difference of occurrence frequency of overshooting among several definitions in the different researches. Because the occurrence frequencies retrieved by these thresholds below are not comparable. Threshold Sensors

Alcala and Dessler (2002, JGR)

HtopTRMM > 14 km TRMM

Schmetz et al. (1997, ASR) TBB(6.7μm) − TBB(11μm) > 0

METEOSAT

Iwasaki et al. (2010, JGR) HtopCloudSat > H380K

AIRS CloudSat, AIRS

HtopTRMM denotes a height of an echo top measured with the 14-GHz

radar of the tropical rainfall measuring mission (TRMM) and its noise level is about 15 dBZ. Htop

CloudSat denotes the same as HtopTRMM but the

94-GHz radar of the CloudSat, and its noise level is about −27dBZ. H380K

AIRS denotes a height of 380 K potential temperature estimated with AIRS.

Holton (1995, RG)

stratosphere380K

A height of 380 K is the boundary of the climatological stratosphere and it is the best threshold to consider water budget between the stratosphere and the troposphere.

Case 1 (#) Case 2 Case 3CloudSat-AIRS Htop

CloudSat > H380KAIRS Htop

CloudSat> HTminAIRS Htop

CloudSat > HTropoAIRS

Case 4 Case 5 Case 6CloudSat-ECMWF Htop

CloudSat > H380KECMWF Htop

CloudSat > HTminECMWF Htop

CloudSat> HTropoECMWF

Case 7TRMM Htop

CPR(15dBZ) > 14 km

Case 8Imager TBB(6.7μm) − TBB(11μm) > 0

We examine the difference of occurrence frequencies of overshooting defined by 8 thresholds as follows:

Htop denotes a height of a cloud top of a deep convection. Htop

CPR(15dBZ) denotes a height of an echo top of 15 dBZ measured with 95-GHz radar on CloudSat (not TRMM). HTropo denotes a height of WMO tropopause. TBB(6.7μm) and TBB(11μm) are averaged with the nearest 9 pixels to remove striping noise.

ground/sea

Htop

no echo

Htop

Case 1 Case 2 Case 3CloudSat-AIRS Htop

CloudSat > H380KAIRS Htop

CloudSat> HTminAIRS Htop

CloudSat > HTropoAIRS

Ratio 1 2.7 7.7 Case 4 Case 5 Case 6

CloudSat-ECMWF

HtopCloudSat > H380K

ECMWF HtopCloudSat > HTmin

ECMWF HtopCloudSat > HTropo

ECMWF

Ratio 2.1 7.5 9.7Case 7TRMM Htop

CPR(15dBZ) > 14 kmRatio 6.3

Case 8Imager TBB(6.7μm) − TBB(11μm) >

0Ratio 264.7

The occurrence frequency of overshooting defined by "Case X" in 20S-20N for one year:

the ratio of "Case 1" to "Case X"

overestimated

Objective 2We show the proof that the overshot air is mixed with that of stratosphere.# one of counter-examples against "overshot air is very cold due to adiabatic updraft; hence, the density of overshot air is much greater than that of ambient air. The overshot air falls very quickly and it is not mixed with stratospheric air."

We pick up overshooting below and one of samples is the right figures.

Latitude-Height sections of 532nm of CALIOP (upper left) and CloudSat (upper middle), respectively. Overlaps of CALIOP and CloudSat (upper right). White, yellow and red curves denote heights of 380K potential temperature, cold point temperature and MWO tropopause, and solid and dashed curves denotes AIRS and ECMWF data, respectively. Though it looks overshooting is separated from cirrus clouds, CloudSat detected it was one convection. Note: observed points of CALIOP are about 3km east of those of CloudSat in this case.

Example of overshooting

TBB measured by use of MODIS. The black solid line denotes observation points of CALIOP, and white line denotes area of overshooting. TBB of overshooting becomes 3 − 4 K higher than that of surrounding cloud clusters.

All data show air temperature below an overshot top are lower than TBB of overshooting (201 K).

Since CALIOP could not detect signals below 15.5 km due to attenuation of light, TBB warmer than 200K emitted below 15.5km was not detected by MODIS.

Cloud top of overshooting

Cloud top of cloud cluster

CALIOP cloud base

TBBCC = 193K 193K 193K

TBBover

= 201K

1 　 Pre-overshooting 2 　 Matured overshooting 3 　 Observed overshooting

Htopover > 19km?

Temperature above 19 km high is warmer than 201 K. Hover = 18km

16.9km16.9kmHCC = 16.9km

Note: Temperature at 18 km high is below 200 K

Result 2Schematic diagram of this overshooting

mixing

orwarm stratospheric air

mixingTout

air < 200K

Tad=178K 1K

m

It suggests that the overshooting once entered the warm lower stratosphere or warm stratospheric air fell and overshooting and stratospheric air were mixed, then the overshooting came down and A-train satellites measured the overshooting.

The occurrence frequency of this overshooting to Case 1 is 0.5; hence, the frequency is about 5 overshooting / min in 20S−20N.

TBBCC 193 K

TBBover 201 K

Tad 184 K(suppose −9K/km)

Toutair 198 K

Objective 1

Result 1

CALIOP and CloudSat readers in CCALIOP and CloudSat HDF readers in C are downloadable in http://www.nda.ac.jp/~iwasaki/CALIPSO_CLOUDSAT_PROGRAM/ which is linked from the "Resources" of the CloudSat data processing center (or just google "CloudSat reader")

down

Kuching (1.48N, 110.3E), MalaysiaSurabaja (7.37S, 112.8E), Indonesia

500km

500kmX Overshooting

X sonde

X sonde

Radiosondes

No lidar return = The warmer radiation emitted from clouds of the lower height is not detected by MODIS.

CALIOPObservations

sea sea sea

IntroductionOvershoot, a cloud intrusion through the level of neutral buoyancy above a deep convection, is believed as one of mechanisms to hydrate or dehydrate the lower stratosphere. Because there are a few observations of overshooting, its role in the Upper Troposphere / Lower Stratosphere is not well known. The A-train is one of the most promising satellite missions to measure vertical profiles and horizontal distributions of clouds, precipitation, and temperature; hence, they can clearly measure overshooting. Since thresholds to detect overshooting are different among researches, and the results, such as occurrence frequency of overshooting, are not comparable, we first summarize the dependence of occurrence frequency of overshooting on the thresholds. We then show one of counter-examples against "overshot air is very cold due to adiabatic updraft; hence, the density of overshot air is much greater than that of ambient air. The overshot air falls very quickly and it is not mixed with stratospheric air."

ResultsThe occurrence frequencies of overshooting defined with some thresholds are compared. The frequency with the threshold of "Htop

CloudSat > H380KAIRS" is the lowest because

H380KAIRS is the highest among the thresholds we considered.

The difference of occurrence frequencies retrieved with H380K

AIRS and H380KECMWF, and HTropo

AIRS and HTropoECMWF are agreed

within 3 times, respectively. The vertical resolutions of AIRS and ECMWF would cause retrieval error of the frequencies. The threshold of the14-GHz radar on TRMM retrieves overshooting whose cloud top height is from HTmin to HTropo or lower.The occurrence frequency retrieved with the difference of TBB is tens times more than the others; hence, it is overestimated.

We showed one example that overshooting was warmed by mixing of stratospheric air. The half of overshooting whose cloud top height is higher than that of 380 K potential temperature would be mixed with stratospheric air and warmed. Its occurrence frequency is about 5 /min in 20S-20N.

The threshold of the14-GHz radar on TRMM retrieves overshooting whose cloud top height is from HTmin to HTropo or lower height overshooting.

CloudSat

SymbolsHtop

CloudSat Echo top of CloudSat

HtopCPR(15dBZ) Echo top of 15dBZ measured with CloudSat

H380K, HTmin, HTmin Height of 380K potential temperature, cold point temperature, and WMO tropopause, respectively

TBB(6.7μm), TBB(11μm)

6.7μm and 11μm black body temperature, TBB, measured with MODIS

TBBCC, HCC TBB and height of cloud cluster

TBBover, Hover TBB and height of overshooting

Tad Temperature of air adiabatically risen from HCC

Toutair Temperature of surrounding air

HbaseCALIOP Height of cloud base measured with CALIOP.

Lidar returns below HbaseCALIOP are not detectable

due to attenuation.Suffixes AIRS and ECMWF denote values estimated with AIRS and ECMWF, respectively.

# The occurrence frequency of Case 1 is about 10 overshooting / min in Tropical area (Iwasaki et al. 2010JGR).

TBBover

CALIOP pseudo cloud base

ToutECMWF,air

CloudSat cloud top

H380KECMWF

ground/sea

HtopCloudSat

TBBover > Tout

ECMWF,air (ambient air temperature in TTL is cold)

A

HtopCloudSat > H380K

ECMWF (overshooting)Tbase

CALIOP < TBBover (TBB

over does not contain warmer TBB in troposphere)

Conditions

Ratio = num. of Case X / num. of Case 1