However, successive regularization programs3 have substantially reduced this irregularity rates: in Spain, from 60% in 2003 to 13% in 2008 (Cebolla & González-Ferrer, 2013), and in Italy, from 62% in 1990 to 7% in 2016 (Blangiardo, 2016).
For these reasons, the identification and analysis of irregular migrants is one of the most challenging aspects of migration studies, and their exclusion from the Anagrafe is a significant limitation, particularly in a context of with relatively high irregularity rates.
Italy and Spain, as countries of recent immigration and high irregularity rates, have struggled to adapt their statistical system, especially their population registers, to adequately reflect the presence of an increasing number of immigrants in their territory.
On the other hand, the positive correlation that appears in the Atlantic sector should not indicate a good correlation because the irregularity occurrence rate varies drastically from 4%to20%0% in June to December solstice, while the OLR occurrence rate stays flat at about 3 days/month (10%) year long.
The bar chart shows the number of days in a month for the OLR occurrence, and the red dotted line shows the irregularity occurrence rate.
In each panel (each season), the solid line represents the linear regression of the data, an empirical formula of the ESF occurrence probability as a function of the vertical drift is derived from the linear regression, and ρ is the correlation coefficient between the vertical drift velocity and the irregularity occurrence rate.
Therefore, we study the linear regression between the monthly total irregularity occurrence rates and the number of OLR observations between ±15° of the dip equator.
Figures 4 and 5 present distribution of density irregularities occurrence rate derived from the Swarm ROTI and RODI values for the different seasons.
Fig. 4 Linear regression analysis of the topside vertical ion drift velocities between 1800 and 1900 LT with the ESF irregularity occurrence rates measured by the ROCSAT-1 satellite.
An irregularly irregular heart rate has no real pattern of irregularity.
