# Presentation: 688034

## HIRDLS Observations of Subvisible Cirrus

_**HIRDLS Observations of Subvisible Cirrus**_

**Steven Massie, John Gille, John Barnett, **
**Rashid Koshravi, and Cheryl Craig**
**NCAR, University of Colorado, and Oxford University**

**AURA Science Team Meeting**
**Pasadena, California**
**October 1-5,  2007**

## Motivation

_**Motivation**_

_**Cirrus and dehydration **_
**Ice particles fall out of freezing air parcels,**
**which dehydrate the upper troposphere and**
**lower stratosphere**
**Cirrus is produced by**
** ****a)  blow-off from deep convection**
** ****b)  air parcels that freeze along vertical and**
**       ****horizontal trajectories**
**Jensen et al., A conceptual model of the dehydration**
**of air due to freeze-drying by optically thin, laminar**
**cirrus rising slowly across the tropical tropopause,**
**JGR, *****106*****, 17237-17252, 2001. **

## Motivation

_**Motivation**_

**Corti et al., The impact of cirrus clouds on tropical troposphere-to-stratosphere**
**transport, Atmos. Chem. Phys., 6, 2539-2547, 2006.**

## Outline

_**Outline**_

**Use HIRDLS and CALIPSO data to address the **
**following questions:**
**Where are cirrus layers located?**
**When are the layers most prevalent?**
**Are the layers related / unrelated to deep convection?**
**	**

## Data

_**HIRDLS**_**   February 2005 – March 2007****	****	****limb view**
**Cloud detection flags and preliminary extinction**
**	**
_**CALIPSO**_**   August 2006 – July 2007        ****	****nadir view**
**CAL_LID_L2_05kmCLay_Prov_V1_10 and V1_20 cloud files**
**Top and bottom altitude levels of the cloud layers**
_**MLS**_**	****	****	****	****	****	****	****limb view**
**RHI (relative humidity with respect to ice) data**
_**Climate Diagnostics Center**_**	****	****	****nadir view**
**OLR (Outgoing Longwave Radiation)**

**Notes:**
Note that HIRDLS is a limb viewing experiment, while the CALIPSO lidar is a nadir viewing experiment.

The HIRDLS cloud detection algorithms determine the radiance perturbation signatures of several cloud types. The altitude (pressure) levels of cirrus layers are determined by examination of preliminary extinction profiles, retrieved on a pressure grid.

## Tropical Cloud Radiance Profiles

_**Tropical Cloud Radiance Profiles**_

**Single 12 μm HIRDLS radiance profiles**

**Notes:**
The cirrus layer observation corresponds to 13.6 S and 314.78 E on May 18, 2006. 

The opaque cloud observation corresponds to 4.32 N and 220.00 E on January 27 2005.

The cloud detection algorithm assigns a cloud integer flag to different radiance profile signatures
0,1,2,3,4 corresponds to no clouds, unknown cloud type, cirrus layers, PSCs, and opaque clouds

Some “opaque clouds” correspond to deep convection, while others are not associated with deep convection.

## Cirrus Layer Extinction Profile 

_**Cirrus Layer Extinction Profile **_

**Single 12 μm HIRDLS extinction profile**

**Notes:**
This observation corresponds to 13.6 S and 314.78 E on May 18, 2006, the same profile as in
the previous slide.

## CALIPSO ObservationJanuary 9, 2007

**17 km**

**30 km **

**0**

**Latitude   7                 0              -8              -16            -24             -32        **

**Notes:**
The laminar cirrus layer at 17 km altitude spans 15 degrees of latitude (~1500 km). We look for cirrus layers that are isolated from deep convection (the cirrus layer has a clear sky region of at least 4 km below the layer).

## Where are clouds seen and expected? 

**All clouds**
**RHI**

**note scale**
**10 – 90%**

**Notes:**
HIRDLS frequency of occurrence for all cloud types are calculated using 
The cloud flags (which are based upon examination of radiance profiles)

## Seasonal Variation – All Clouds 

**Winter**
**Spring**
**Summer**
**Fall**

**Notes:**
Note that the frequency of occurrence of clouds is largest in winter, and that the frequencies of occurrence
are > 50% for much of the tropics at 100 hPa.

Frequencies were calculated by using the cloud flags (which are based upon an examination of
Radiance profiles).

## Seasonal Variations of Cirrus Layers – 121 hPa

**Winter**
**Spring**
**Summer**
**Fall**

**note scale: 0 – 18 %**

**Notes:**
Note that the frequency of occurrence of cirrus layers is mapped here on a smaller range ( 0 – 18 )
than that of the previous slide for all clouds (0 – 90).

## Seasonal Variations of Cirrus Layers – 100 hPa

_**Seasonal Variations of Cirrus Layers – 100 hPa**_

**Winter**
**Spring**
**Summer**
**Fall**

**Notes:**
Note that the frequency of occurrence of cirrus layers is mapped here on a smaller range ( 0 – 18 )
than that of the previous slide for all clouds (0 – 90).

## Cirrus Layers are Most Prevalent in Winter

_**Cirrus Layers are Most Prevalent in Winter**_

**Notes:**
The cirrus layers correspond to pressures between xx and xxd hPa.

## 100 hPa Temperatures are colder in Winter

_**100 hPa Temperatures are colder in Winter**_

**Notes:**
The cirrus layers correspond to pressures between xx and xxd hPa.

## The Thinnest Cirrus Layers are Located

_**The Thinnest Cirrus Layers are Located**_
_**Away from Deep Convection**_

**deep convection**

**Notes:**
The thinnest cirrus layers are located far away from deep convection

Vertical width is the average width over all cloud layers for a specified OLR bin
Latitudes are 30 S to 30 N

## Laminar Cirrus Origins

**What fraction of the time are the cirrus layers formed in-situ?**
**From previous work with HALOE cirrus and temperature observations**
**	****Ice frost point T****ice ****~ 191 K near 100 hPa**
**Used ECMWF wind and temperature fields in 2006 to calculate the**
**fraction of the time for which T > T****ice **** along back trajectories**
**at pressures < 121 hPa**
**5 day back trajectories**
**Used observations when the laminar cirrus > 200 km in horizontal extent**
**In situ formation fraction (T > 195 K): **
**	****~ 68%**
**Association with deep convection:**
**	****~ 14% of the trajectories have T < 195 K and OLR < 170 w m****-2**** **

## Conclusions

**Cirrus layers are most prevalent **
**	****Away from the maritime continent**
**	****Over the equatorial central Pacific**
**Cirrus layers are most prevalent during winter**
**Cirrus vertical widths decrease away from deep convection**
**Cirrus layers are produced by in-situ processes ~ 68%**
**of the time near 100 hPa when the horizontal scale **
**of the cirrus > 200 km**